Applied Osseointegration Research C/O Professor Tomas Albrektsson Department of Biomaterials P.O

APPLIED OSSEOINTEGRATIONOSSEOINTEGRATION RESEARCHRESEARCH

VolumeVolume 6: Clinical Performance and Enhanced StabilityStability FebruaryFebruary 2008 APPLIED OSSEOINTEGRATION RRESEARCHESEARCH

VolumeVolume 6: CClinicallinical PerformancePerformance andand EnhancedEnhanced StabilityStability FeFebruarybruary 2008

ISSN 1651-0070

Applied Osseointegration Research c/o Professor Tomas Albrektsson Department of Biomaterials P.O. Box 412 SE-405 30 Gothenburg Sweden Telephone +46 31-786-2945 Fax: +46 31-786-2941 email: [email protected] Applied Osseointegration Research - Volume 6, 2008

Editor-in-Chief TOMAS ALBREKTSSON Sweden

Associate Editors JAN GOTTLOW MAGNUS JACOBSSON LARS SENNERBY Sweden Sweden Sweden

ANN WENNERBERG WARREN MACDONALD LARS RASMUSSON Sweden UK Sweden Editorial Board Carlos Aparicio Burton Becker Sascha Jovanovic Spain USA USA

Hugo de Bruijn Georg Watzek George A Zarb Belgium Austria Canada

Young Taeg Sul Michael Norton Antonio Rocci Korea UK Italy

1 Applied Osseointegration Research - Volume 6, 2008

When are Implant Systems Really Safe for Clinical Use?

We are all concerned with the clinical safety of im- In the end, good clinical practice and good engineer- plant systems, be they dental implants, maxillofacial ing lead to the same conclusion – the ultimate test or systems or orthopaedic components. In particular, proof is in the real situation; the patient. Laboratory the means by which an implant system might be and computer testing and modelling may or may not proven safe before release for clinical use or even give conﬁdence that every risk has been accounted for marketing continues to attract debate or criticism. and every aspect of predicted service is accommodated in the system design and production. The real test Computer modelling and laboratory testing are two (the “gold standard”) is performance in the clinical well tried methods which can give useful indications setting. Good engineering and thorough pre-clinical in the search for safety of implants. Laboratory tests testing will reduce the risk to patients and the number under accurately known and measured conditions, of “clinical trial patients” required to be exposed to with carefully controlled variables and environments, unproven components or systems, but no amount can be helpful in comparing design solutions or com- of careful pre-clinical testing can remove the need petitive systems for similar applications. But systems for carefully designed and monitored clinical trials. which interface living bone and function within un- predictable human subjects can be subject to many So clinical results are the only complete and reli- factors for which we have little data and can provide able proof of a system’s suitability for clinical use. insufficient predictions. Under such constraints, laboratory tests may not be realistic, and may give unreliable indications of implant performance in Warren Macdonald clinical practice (unreliably pessimistic or unreliably Visiting Lecturer, Department of Biomaterials, optimistic). In all implant ﬁelds one can recall stories Institute of Clinical Sciences, of systems launched with claims of laboratory valida- University of Göteborg, tion, and complex and detailed test programmes in Göteborg support of their clinical performance, which neverthe- SWEDEN less demonstrated poor relevance to clinical realities and ultimately gave poor results in clinical practice.

Computer modelling is similarly reliant on the input information and accuracy of conditions modelled. Simplifying assumptions are nearly always required, but do they undermine any relevance of the modelling to the clinical situation? Marvellous complexity and incredible accuracy are possible with the com- puting power currently available, both for calculations and graphical displays or simulations, but the basic question still remains – how realistic is the model or how true are the assumptions being made? 2 Applied Osseointegration Research - Volume 6, 2008

The Neoss Implant System

Treatment with osseointegrated implants is an integral mediate or early loading protocols, the system is part of contemporary patient care. Many companies challenged by loading the bone simultaneously with provide the dental community with the necessary the healing process and development of stability. products. Quite frequently they also provide us unnecessary products! What should I use? Which The papers accepted for publication in this issue have implant system is the best? Naturally, there is no assessed the mechanical stability of Neoss implants single or easy answer to such a question. It’s a mat- at surgery by insertion torque values and ISQ values ter of preferences. These preferences will of course (resonance frequency analysis). The biological response vary from individual to individual, but also reflect during healing is documented using histological analy- different needs of the surgeon, the prosthodontist ses and biomechanical tests such as removal torque and and the dental technician. Not to forget the staff ISQ values. The clinical outcome of two-stage, one- member responsible for the inventory of the clinic! stage and immediate loading protocols has been evaluated at one-year follow-up by clinical and radiographic The founders of the Neoss company, Dr. Neil examinations. The biocompatibility of PEEK healing Meredith and Engineer Fredrik Engman, have cre- abutments is evaluated by means of bacterial coloniza- ated an implant system that should fulfil all needs tion and real-time PCR (polymerase chain reaction) of versatility, flexibility and ease-of-use, but through tests. The outcomes are, in my mind, excellent. Enjoy! a minimum of components and instruments.

I admit to finding the thinking and the design fea- Jan Gottlow, DDS, Ph D tures of the Neoss implant system attractive. But Guest-Editor-in-Chief of Volume 6 does it work? What’s the scientific evidence? In this Department of Biomaterials, issue of Applied Osseointegration Research you will Institute of Clinical Sciences, find a mix of clinical studies, animal experiments and University of Göteborg, laboratory tests evaluating the Neoss implant system. Göteborg SWEDEN The osseointegration process is influenced by the mechanical stability of the implant at surgery and the following biological response. The mechanical stability is related to the macro-design of the implant whereas the surface properties will influence the biological response. The modern moderately rough surfaces have demonstrated strong bone responses, allegedly shortening the healing time. However, the Neoss is a modern implant system that is, actually minimally rough (as demonstrated in surface topographical studies). Despite this the Neoss system obviously achieves quite positive results. Still, when using im- 3 Applied Osseointegration Research - Volume 6, 2008

4 Applied Osseointegration Research - Volume 6, 2008

Table of Contents

A REVIEW OF IMPLANT DESIGN, GEOMETRY AND PLACEMENT Neil Meredith 6

HISTOLOGICAL EVALUATION OF A BIMODAL TITANIUM IMPLANT SURFACE . A PILOT STUDY IN THE DOG MANDIBLE. Luiz A Salata1, Paulo EP Faria1, Marconi G Tavares1, Neil Meredith2,3 and Lars Sennerby4 13

HISTOLOGICAL AND BIOMECHANICAL ASPECTS OF SURFACE TOPOGRAPHY AND GEOMETRY OF NEOSS IMPLANTS. A STUDY IN RABBITS. Lars Sennerby1 , Jan Gottlow1, Fredrik Engman2 and Neil Meredith2,3 18

A ONEYEAR CLINICAL, RADIOGRAPHIC AND RFA STUDY OF NEOSS IMPLANTS USED IN TWOSTAGE PROCEDURES Peter Andersson1 , Damiano Verrocchi1, Rauno Viinamäki1, Lars Sennerby1,2 23

IMMEDIATE/EARLY LOADING OF NEOSS IMPLANTS. PRELIMINARY RESULTS FROM AN ONGOING STUDY Peter Andersson1 , Damiano Verrocchi1, Luca Pagliani2, Lars Sennerby3 27

A RETROSPECTIVE FOLLOWUP OF 50 CONSECUTIVE PATIENTS TREATED WITH NEOSS IMPLANTS WITH OR WITHOUT AN ADJUNCTIVE GBRPROCEDURE 1 2 Thomas Zumstein and Camilla Billström 31

INSERTION TORQUE MEASUREMENTS DURING PLACEMENT OF NEOSS IMPLANTS Luca Pagliani1, Lars Sennerby2, Peter Andersson3, Damiano Verrocchi3 , Neil Meredith4 36

STRESS EVALUATION OF DENTAL IMPLANT WALL THICKNESS USING NUMERICAL TECHNIQUES Rudi C. van Staden1, Hong Guan1, Yew-Chaye Loo1, Newell W. Johnson2, Neil Meredith3, 39

COMPARATIVE ANALYSIS OF TWO IMPLANTCROWN CONNECTION SYSTEMS  A FINITE ELEMENT STUDY Rudi C. van Staden1, Hong Guan1, Yew-Chaye Loo1, Newell W. Johnson2, Neil Meredith3, 48

COMPARISON OF EARLY BACTERIAL COLONIZATION OF PEEK AND TITANIUM HEALING ABUTMENTS USING REALTIME PCR Stefano Volpe1, Damiano Verrocchi2, Peter Andersson2, Jan Gottlow3, Lars Sennerby2,3 54

SURVIVAL RATE, FRACTURE RESISTANCE AND MODE OF FAILURE OF TITANIUM IMPLANTS IN CLINICAL FUNCTION AND DYNAMIC LOADING. Neil Meredith1,2 and Fredrik Engman2 57

5 Applied Osseointegration Research - Volume 6, 2008

A Review of Implant Design, Geometry and Placement

Neil Meredith University of Bristol, UK INTRODUCTION Biomechanics of implant placement and loading Bone is a unique structural material. Its physical and There are three main biomechanical parameters that mechanical properties mimic both natural materials influence the stress distribution and optimal stability such as wood and man-made materials including poly- of an implant in bone; these are the placement pro- mers. Its mechanical properties can be directly corre- cedures including the drilling of the osteotomy site lated to its complex structure and it should therefore be and the use of compression techniques to increase described as an anisotropic material (Carter & Beaupre, local stability (O’Sullivan et al. 2004a). Secondly, 2001). In contrast many man-made polymers have a the design features of the implant itself (O’Sullivan uniform structure in all directions and can thus be con- et al, 2000) and thirdly, the loading conditions to sidered homogenous materials. Bone’s unique property which the implant is subjected (Friberg et al, 1991). is its ability to form new bone and to remodel existing bone. This is especially important in its response Loading conditions may differ due to a single or two- to applied mechanical stresses (Carter et al, 1998). stage surgical placement technique (Sennerby L Roos J;1998). In a two-stage technique, the implant fixture Bone healing considerations is placed, typically level with the crest of the bone In the complete absence of stress bone can and will and submerged beneath the soft tissue, for a healing form and remodel; as with the bone formation occur- period which may vary but has historically been rec- ring during osseointegration in the submerged phase ommended as three months in the mandible and six of a two-stage implant (Lekholm & Zarb,1985). months in the maxilla. A two-stage protocol effectively There is also evidence to show that the application eliminates any dynamic functional loads during this of light mechanical loads can induce favourable healing and osseointegration period. A single-stage stresses within the bone, which may induce acceler- technique is different in that the implant is exposed to ated and enhanced bone formation (Pilliar & Ma- the oral environment at the time of initial surgery and niatopoulos, 1986) Much research has been carried placement. In this case, a number of options exist in out to analyse the influence of mechanical stress that the implant may be loaded (immediate loading) on bone formation, but it is extremely difficult to or may remain unloaded by the provision of a relieved model these parameters in a laboratory or even an prosthesis over the implant site for a healing period, animal model (Brunski, 1999, Brunski et al, 1993). which may typically vary from six to eight weeks.

It is clear that the application to bone of mechanical Loading protocols stresses in excess of a certain threshold level will not The alternative is early or immediate loading, in which induce bone formation but can lead to the formation a prosthesis or temporary restoration is placed directly of a fibrous tissue capsule and malunion, or in the at the time of surgery or a short period thereafter; case of dental implants a failure of osseointegration perhaps a week. Immediate loading and delayed (Szmukler-Moncler et al. 1998). This threshold is one-stage loading are very different. In delayed one- not clearly known or defined and is likely to vary in stage loading it is likely that the effectively unloaded individual cases and sites in relation to bone quality implant is subjected to small dynamic loads, applied and quantity, the loading conditions applied, and the through the soft tissue and through intermittent systemic and regenerative capacities of the patient contact with a prosthesis (Orenstein et al.; 1998). (Brunski et al, 2001). There is clearly a need to op- The clinical evidence for this protocol is that it is timise the factors associated with implant placement highly successful and that the dynamic loads if any and design which can optimise the conditions for are small enough and of appropriate frequency that bone remodelling or formation under immediate and they do not lead to a failure of osseointegration and early loading conditions (Sennerby & Roos, 1998) 6 Applied Osseointegration Research - Volume 6, 2008 formation of a fibrous tissue capsule. However, there is no strong evidence to suggest that this early loading one-stage technique will actually accelerate bone formation or enhance the quality of bone formed.

Immediate and early loading, attachment of a prosthesis at the time of implant placement or shortly, thereafter relies on the principal that the dynamic functional loading applied will be below the threshold which can induce failure of osseointegration and formation of a fibrous tissue capsule, and at a level whereby bone remodelling and formation may progress unhindered or even accelerated in the early Figure 1. illustrates the changes in implant stability at diferent clinical stages following implant placement. (After Andersson healing stage. The ranges of clinical, anatomical and et al. 2007) surgical parameters are very wide and therefore at present the selection, use and success of immediate in stability in bone qualities 3 and 4, more marked and early-loading techniques are generally founded than in bone quality 1 and 2 (Andersson et al. 2007) on the experience, knowledge and understanding of the clinician on an individual case by case basis. Clinical findings indicate that a large part of the healing and remodelling process, which is termed os- Primary Implant Stability seointegration, is probably completed within the first It is clear that one of the keys to successful osseointe- eight weeks of placement, under normal conditions. gration is the primary stability of an implant. It is Higher primary stability at placement is also measured considered highly desirable that this level of stability (Meredith N, Bok, K, Friberg, Sennerby ; 1997) in should be as high as possible. In experienced hands it is better quality and denser bone. O’Sullivan (2001) commonly measured by the insertion torque necessary measured implant stability as a function of the changes to place the implant. This is clearly a subjective feeling, in strain following implant placement for a period of but can give an experienced operator a level of confi- two hours following placement . He observed a sharp dence in the prospects of a successful outcome for a case. initial fall in stability and decrease in interfacial strain.

Electronic drill controllers displaying graphs of inser- This is interesting because it is not a biological or physi- tion torque are available, but the interpretation of such ological phenomenon, what is occurring is mechanical data is difficult (Friberg B, Sennerby L, Roos J; 1995). stress relaxation in the bone following placement. This An alternative technique is resonance frequency analy- suggests that although a high level of stability and sis (RFA)(Meredith N, Cawley P, Alleyne D; 1996), compression may occur at the time of insertion, this which has been available for some ten years. It utilises stability may decrease very rapidly thereby creating a a non-destructive test method to measure the local in- higher risk situation. This could be especially impor- terfacial stiffness of an implant and surrounding bone. tant where implants are placed in poor bone quality, or where the bone has been artificially compressed Secondary Implant Stability to a high level by the use of osteotomes for example. It is evident in the first six to eight weeks following placement that there is more new bone formation in It is clear therefore that there is a very complex poorer quality bone, typically in the anterior max- and subtle inter-relationship between bone qual- illa. Here the blood supply can be good but there is ity, stability, geometry and placement technique. an open trabecular network and primary stability is typically lower than in the mandible for example. In Implant Geometry the mandible, there are smaller changes in stability A range of geometries has been available for dental and these may be accompanied by local remodel- implants for a number of years and their variation and ling rather than new bone formation (Meredith et relation to success do warrant some observations. It al. 1997). This can result in a measurable increase is interesting to note that historically the cylindrical implant has been associated with a relatively high in- 7 Applied Osseointegration Research - Volume 6, 2008

Figure 2. Implant stability for different implant types and bone Implant geometries have not been routinely designed quality in the maxilla (After O’Sullivan, Sennerby, Meredith; for use in speciﬁc bone or quality types. However, 2000) implants having a slightly tapered geometry (approximately 4° from parallel) have been introduced to create compression in poorer bone qualities and optimise sta- cidence of implant failure (Albrektsson T, Sennerby L; bility (Brånemark MkIV; Nobelbiocare, Gothenburg, 1991). This has also born some relationship to speciﬁc Sweden) . Figure 2 Illustrates the stability at placement systems and it is important to be certain that the aeti- for a number of implant types in the human ca- ology of this failure is due to the geometry alone; the daver maxilla (O’Sullivan, Sennerby, Meredith; 2000) evidence suggests that this geometry could play a part.

However, by relatively small modifications in geom- Static and dynamic stresses What is apparent is that two separate issues need etry and placement technique it is possible to achieve to be considered in the successful placement and a highly successful implant system, the Straumann loading of a dental implant. These are the dynamic (Basle, Switzerland) systemwas essentially cylindri- stresses experienced by an implant in function and cal but with a small widely spaced thread super-im- the static stresses encountered during implant place- posed. The drilling protocol for this implant uses a ment. Dynamic stresses and applied loads can be small modification with the implant being 0.05mm considerable once an implant has reached an equilib- larger than the preparation site. The idea is that this rium position in bone and healing has taken place. creates localised compression around the implant. In general, this seems to be successful, although the Prior to this the nature, magnitude and direction of screw pattern used is that of a Thorpe screw, which applied dynamic loads can influence the treatment was designed for use in orthopaedic surgery to pull outcome (Goodman et al. 1993). Static loads at bone plates together (Ansell R, Scales J; 1968). the time of implant placement, however, are a con-

sequence of those techniques or geometry that are Threaded implants with a close pitch and a deep designed to contribute to the maximal stability of an profile (Brånemark; Nobelbiocare, Gothenburg, implant in bone. The use of slightly tapered threaded Sweden) are quite typical of another design of im- implants is one such way of seeking to increase plant which has been clinically highly successful. stability in poor bone qualities (O’Sullivan 2001). The variations in stress distribution between diﬀerent Is compression and the application of high levels of implant systems under applied loading would there- primary stress a clinical issue? The answer is potentially fore appear to be quite substantial. However, both yes, both at the time of placement in high initial bone these geometry types (the threaded cylinder and the qualities and at the time of abutment connection and threaded implant) are equally successful clinically. 8 Applied Osseointegration Research - Volume 6, 2008

Figure 3. Variation in insertion torque with drilling depth as a function of time for 3.75mm implants placed in final osteotomy diameters 2.85-3.7mm. (O’Sullivan, 2001) loading in two-stage implants (Misch C E,1990). A Figure 4. Bone relief chambers and cutting face number of implant systems use a drilling sequence that creates a preparation site that is only very slightly small- bility without over-compressing good bone and yet can er than the implant, being inserted. This will quite optimise the compression and stability for placement obviously create quite low levels of insertion stress. The in poor bone qualities. This would thereby optimise evidence is that these implants are highly successful in the success of implant placement in higher risk areas. average to good bone qualities where compression and stability are adequate and over-compression is avoided. Implant Design In systems inducing a high level of compression, pos- Such considerations have not been made hitherto sibly by use of a tapered implant or a drilling sequence in relation to implant design and placement tech- with a drill size much smaller than the implant diam- niques. This proposes a combination of geometry, eter there are occasions when the consequences of over- surface characteristics and placement procedures compression may be early failure of the implant itself which will optimise implant placement and stress (Hobkirk JA, Rusiniak K,1977) (Ivanoff C-J 1999). distribution in all bone qualities. To achieve this it Figure 3. illustrates the variation in insertion torque is evident that a tapered geometry will offer benefits for 3.75 mm implants placed in final osteotomies in bone compression and there is good evidence of differing diameter. This clearly demonstrates that only a small degree of taper achieves a substan- a relationship between compression of the oste- tial increase in stability (O’Sullivan et al., 2004b). otomy site and insertion torque. (O’Sullivan, 2001) It is therefore desirable to have an implant with a Most implant designs do not directly address the op- positive tolerance (taper) which will cause optimal timisation of stability in poor bone qualities. Some compression in poor bone qualities. In order to implants have become available with a slightly tapered address the seating, stability and compression levels geometry, which creates local compression and thereby within good bone qualities further consideration achieves good stability; these have been very successful. needs to be paid to the surface geometry. Many of today’s implant systems use a thread-cutting geom- The advantage of having a geometrical feature on the etry to tap a thread into the bone during insertion implant is that it does not rely on a complex placement into a cylindrical hole. This works very effectively or drilling protocol to create a level of compression, and creates a high level of bone-to-implant contact. which may be variable in relation to its outcome. The slightly tapered implant thus provides a simple way of A possible thread refinement from current implants repeatedly and consistently offering an increase in sta- is altering the implant to bone volume ratio within bility in poor bone qualities (O’Sullivan et al. 2004b). the threads by reducing the thickness of the implant The disadvantages of modified geometry implants of threads. An important feature of the geometry this type are that they can lead to over-compression of the thread cutting face is that there is adequate when used in good bone qualities and they may either volume in the relief chambers for bone clearance fail to seat or on some occasions may lead to failure. (Figure 4.). It is important that bone clearance What is needed therefore is an implant geometry and a chambers are designed to maximise the volume for placement method which can achieve a high level of sta- bone chip entrapment but also to provide maxi- 9 Applied Osseointegration Research - Volume 6, 2008 mal bone to implant contact on the threaded area. Historically some implant designs have been less successful because the bone collection chambers were very wide and very openly spaced (Friberg et al. 1997). It is also important that the cutting face of the self-tapping implant feature is sharp and without burrs. In order to optimise the placement of a threaded implant, having a positive tolerance in good bone qualities, a secondary cutting feature can be introduced along the side of the implant (Figure 4 and 5.). This secondary cutting face is much shallower than the apical cutting face and actually does not engage in soft bone qualities. In dense bone however, when the implant is inserted there will be elastic recovery during the insertion process such that the bone will engage the secondary cutting faces and a small amount will be removed. Figure 5. Implant design geometry for the Neoss implant

Figure 6 illustrates an insertion torque profile for the recommended on occasions where bone density is Neoss implant demonstrating a near linear increase extremely high and bone quality is very homogenous. in insertion torque with a modulated plot attribut- able to secondary cutting (Luca et al., 2007). This Insertion Torque will not impair the stability of the implant in the site Insertion torque is a commonly assessed qualitative but will create a different fits in dense bone quality or parameter during implant placement. Placements weak bone, thereby optimising stability in all bone and procedures vary considerably between systems qualities but without over compressing good bone. and between operators. Some clinicians favour a very The combination of features relating implant geometry high level of final insertion torque and other operators with forming and thread cutting in bone of different work with a very gentle insertion technique, rarely quality has been combined into a single implant design encountering an insertion torque greater than 30Ncm. ® and the concept is called TCF which represent a Thread Cutting and a thread Forming implant leading to cutting Historically, a high final peak insertion torque may be for optimal seating and forming for optimal stability. variously affected by three phenomena. The implant may bottom out in the site, so that the final tightening Screw taps work differently from the use of progres- torque is actually inducing very high levels of shear sively increasing drill sizes to match implant diam- stresses at the implant tissue interface, as the implant eters. They are available for use on rare occasions butts against the bottom of the preparation site. where there is uniformly dense cortical bone along A second cause of a high insertion torque may be the whole implant length. In such cases, the com- contact at the flange of the implant with the cre- pression occurring at the implant tissue interface is stal cortical plate, thereby achieving a high level of different from that under typical conditions where compression and static stresses. The third reason there is a combination of cortical and trabecular bone. is a very high level of interfacial stresses leading to a high level of implant stability. On occasion, this Under normal conditions the TCF feature of the may or may not accompany a level of over-compres- Neo implant is designed to create an optimal level of sion and very rarely it may lead to implant failure. compression, starting from the apex of the threads as the implant is inserted into a cylindrically prepared The Neoss implant system has been designed to achieve site. In uniformly dense bone, the use of a screw tap the optimal level of compression and stability, for to pre-tap the site will create a level of compression on implant placements of bone in all qualities. This does implant insertion that is uniformly applied to both the not rely on a very high level of final insertion torque. peaks and troughs of the thread, thereby achieving a Excellent results can be obtained using a gentle tech- comparable overall level of compression in a structur- nique where the insertion torque at any period dur- ally different quality of bone. Screw-taps are therefore 10 Applied Osseointegration Research - Volume 6, 2008

A third, but not commonly discussed reason may well be related to mechanical stresses. This is particularly prevalent with the earlier designs of implants using commercially pure, type I titanium, which is relatively soft. In such cases the combination of a static load at implant placement around the flange between the implants and the cortical bone and then the superimposed dynamic stresses at the time of implant loading will cause a high level of mechanical stress and bending within the implant body, around the Figure 6. Insertion torque plot for Neoss implant. neck, between the flange and the threaded body of the implant. The bone response to these localised stresses is likely to be resorption; the high levels of stress at ing placement does not exceed 30ncm. The optimal the implant neck can be visualised by a stress profile, tissue response can be expected to be achieved if an superimposed on an implant in bone in this region. insertion torque between 25 and 30Ncm is obtained. It is therefore highly desirable to have a flange and neck Historically, if implants fail to seat or encounter very design that minimises both the static stresses at place- high insertion torques, surgeons typically remove the ment and the dynamic stresses on the functional load- implant and use a screw-tap to aid the preparation. ing. The Neoss implant has been designed specifically In the case of a Neo implant, if the insertion torque dur- without a neck region, as in the external hex implant ing placement reaches high levels then the implant can designs, and the thread leads directly into the flange. simply be anti-rotated a few turns and then re-inserted. The relationship between the flange and the threaded This clears bone swarf from the cutting faces of the im- portion of the implant is slightly different for the 3.5, plant and reduces friction at the interface, thereby allow- 4 and 4.5mm diameters. This enables the use of one ing smooth insertion without any risk of over-heating. common abutment connection without impairing the fit of seating of the implant in the surrounding bone. A second feature that is important during implant placement is the static stresses obtained between the inter- In the flange region, it is therefore possible to assess face of the implant flange and the crestal, cortical bone. the level of compression occurring in the flange during implant insertion. The Neo system has great For Perifixtural bone loss a two-stage implant with a high level of surrounding A clear and well-recognised characteristic of the ex- bone a counter sink can be used to provide the opti- ternal hexed Brånemark implant is the loss of bone mal seating, minimising static stresses and optimising in the period following abutment connection and the interface between the flange and the surrounding early loading from the level of the abutment-implant bone, thereby providing optimal conditions for direct interface down to the first thread of the implant. The bone formation. The Neo implant system is there- aetiology of this is not clear, but a number of hypoth- fore designed with a number of features in geometry, eses have been put forward. It has been proposed preparation technique and material properties that for example that there is micro-leakage between the jointly result in the optimal biomechanical relationship abutment and the implant, of the implant abut- between a dental implant and the surrounding bone. ment interface, resulting in the release of bacterial toxins causing a local peri-implant reaction and bone REFERENCES loss within a localised zone around this interface. Albrektsson T, Sennerby L (1991). State of the art in oral implants. J. A second cause proposed is the surface characteristics Clin. Periodontol.; 18:474-81. of the implant; it has been suggested that one im- Andersson P ,Verrocchi D, Viinamäki R, Sennerby L. (2008) A One-Year plant system with micro grooves has a more favour- Clinical, Radiographic and RFA Study of Neoss Implants Used in Two- Stage Procedures. Appl. Oss. Res. 7;pp able coronal stress response and encourages bone formation by the presence of these micro grooves. Ansell R, Scales J (1968). A study of some factors which affect the 11 Applied Osseointegration Research - Volume 6, 2008

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IvanoﬀC-J(1999). On surgical and implant related factors inﬂuencing integration and function of titanium implants – expenmental and clinical aspects. Thesis. University of Goteborg, Sweden.

Johansson P, Strid KG. Assessment of bone quality from cutting resistance during implant surgery. Int J Oral Maxillofac Impl 1994;9:279-288

Lekholm U, Zarb GA. Patient selection and preparation. In: Brane- mark Pi , Zarb (iA, Albrektsson T (eds): Tissue-integrated prostheses: Osseointcgration in clinical dentistry. Quintessence, Chicago 1985, pp 199-209

Meredith N, Alleyne D, Cawley P. Quantitative determination of the stability of the implant-tissue interface using resonance frequency analysis. Clin Oral Impl Res 1996; 7: 261-267

Meredith N, Shagaldi F, Alleyne D, et al. The application of resonance frequency measurements to study the stability of titanium implants during healing in the rabbit tibia. Clin Oral Impl Res 1997; 8:234-243.

Meredith N, Book K, Friberg B, Jemt T, Sennerby L. Resonance frequency measurements of implant stability in vivo. A cross-sectional and longitudinal study of resonance frequency measurements on implants in the edentulous and partially dentate maxilla. Clin Oral Impl Res 12 Applied Osseointegration Research - Volume 6, 2008

Histological Evaluation of a Bimodal Titanium Implant surface . A Pilot Study in the Dog Mandible.

Luiz A Salata1, Paulo EP Faria1, Marconi G Tavares1, Neil Meredith2,3 and Lars Sennerby4

1Dept. Oral & Maxillofacial Surgery, Faculty of Dentistry of Ribeirao Preto, The University of Sao Paulo, Brasil 2University of Bristol, Bristol, UK 3Neoss Ltd, Harrogate, UK 4Dept Biomaterials, Institute of Clinical Sciences, Sahlgrenska Academy, Göteborg University, Sweden This histological pilot study revealed a favourable bone tissue response to a novel bimodal titanium implant surface after four months of healing, with no apparent differences from TiO-blasted and oxidized control implants.

INTRODUCTION The aim of the present pilot study was to analyse the bone tissue response to a novel implant surface (Bimo- New implant systems with different geometries and dal surface, Neo Implant System™) in comparison with surface topographies are continually being launched on two well-documented and commercially available im- the market. It is important to evaluate critically each plant surfaces (TioBlast™ surface and TiUnite™ surface). implant surface in both experimental models and in clinical follow-up studies. One prerequisite for a suc- MATERIALS AND METHODS cessful clinical outcome with osseointegrated titanium implants is secure bone integration immediately fol- Implants lowing surgery (Albrektsson et al. 1981). In essence, A total of eight test implants, 9 mm long and 3.5 the surgical trauma initiates a healing process which mm in diameter (Neo Implant System™, Neoss Ltd, includes the formation of a blood clot, migration and Harrogate, UK) (NE implants) were used in the study. differentiation of cells, formation of a granulation These implants had a bimodal surface created by blast- tissue and, finally, bone formation and remodelling. ing with 100 to 300 μm diameter ZrO spheres and In the presence of a titanium surface, healing results 2 subsequent blasting with irregularly shaped TiO-based in formation of direct bone-implant contacts (BICs) particles, 75 to 150 μm wide (Fig. 1a). Eight control and the number and extent of BICs increase with time implants were also used; four implants with a TiO - (Johansson et al. 1987, Sennerby et al. 1993). The peak 2 blasted surface, 9 mm long and 3.5 mm in diameter torque required to achieve implant removal increases (MicroThread™, AstraTech AB, Mölndal, Sweden) with time in parallel with increased BICs (Johansson (AT implants)(Fig. 1b), four implants with an oxi- et al. 1987). The first generation of osseointegrated dized surface, 10 mm long and 3.75 mm in diameter implants had either a minimally rough surface (ma- (Brånemark System™, MKIII, TiUnite, Nobel Biocare chined/turned surface) or a very rough surface pro- Ab, Gothenburg, Sweden) (NB implants)(Fig 1c). duced by titanium plasma spraying (TPS)(Brånemark et al. 1969, Schroeder et al. 1976). On the basis of further clinical and experimental research it is currently Animals and anaesthesia Four mongrel male dogs weighing between 20 and believed that moderately rough implant surfaces are 25 kg were used in the study. The animals were pre- preferable (Albrektsson & Wennerberg 2006); such as anaesthetized with xilazine (Ronpum®, Brazil, 20 surfaces produced by blasting, anodic oxidation, acid mg/Kg I.M.) and ketamine 1g (Dopalen®, Brazil, 0,8 etching or combinations of these techniques. Experi- g/Kg I.M.) and anaesthetized with thionembutal 1 mental research has generally demonstrated a stronger g (Tiopental®, Brazil, 20 mg/Kg I.V.). The animals bone tissue response to surface modified implants were kept on intravenous infusion of saline during than to smoother control surfaces, indicating more surgery, all of which was carried out under sterile rapid integration (Albrektsson & Wennerberg 2006).

13 Applied Osseointegration Research - Volume 6, 2008

Figure 1: Scanning electron micrography (SEM) of the three surfaces evaluated; a/ Bimodal surface, b/ TiO-blasted surface, c/ Oxidized surface

conditions. After surgery the animals received intra- venously vitamin compound (Potenay®, Brazil); an anti-inﬂammatory/analgesic (Banamine®, Brazil) and antibiotic (Pentabiótico®, Brazil). The antibiotic was administered in single doses immediately after surgery, and then 48 and 96 hours postoperatively. The study protocol had been approved by the University of Sao Paulo´s Animal Research Ethics committee.

Exprimental protocol The mandibular premolars were extracted five months prior to commencement of the experiment. At the time of implant placement, crestal incisions were made and mucoperiosteal flaps were raised bilaterally. Two implant cavities were prepared on each site, in accordance with the manufacturers guidelines. Two NE implants were placed on one side and one each of AT and NB implants on the contra lateral side (Figs. 2a and b). Cover screws were placed and the ﬂaps were closed and sutured.

After 4 months of healing, the dogs were sacrificed and the implants with their surrounding tissues were harvest- ed and fixed by immersion in buffered formaldehyde.

Histology The ﬁxed specimens were dehydrated in a graded series of ethanol and embedded in light curing methacrylate (Technovit® 7200 VCL, Kulzer, Friedrichsdorf, Germa- ny). Ground sections approximately 10 μm thick were prepared using a sawing and grinding technique (Exakt Apparatebau®, Norderstedt, Germany) and stained with toluidine blue. One central section was taken from each implant site in the bucco-lingual direction.

The sections were examined under a Leitz microscope equipped with a Microvid system for morphometrical measurements. The degree of bone-implant contact (BIC) was measured from the first bone contact and expressed as a percentage mean total BIC. The bone area (BA) within the implant threads was measured and expressed as a mean total BA.

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Figure 2. Clinical photographs showing a/ TiO-blasted (left) and oxidized (right) implants. b/ Bimodal surface implants.

RESULTS AND DISCUSSION

Healing was uneventful in all dogs. Some marginal bone resorption, especially on the buccal aspect, was seen for all implant types at the marginal portion which may be due to remodelling continuing after tooth extraction (Arajou et al. 2005).

Histology revealed close contact between mature bone and test implants (Figs 3). There were no apparent differences between test and control implants and new bone was observed to fill the threads of all three surfaces (Figs. 4a-c). In some areas, the presence of a thin layer of bone and an osteoblast seam facing the bone marrow indicated bone formation directly at the test implant surface (Fig. 5); as previously described for the control implant surfaces used in the study, i.e. blasted and oxidized surfaces (Ivanoff et al. 2001, Rocci Figure 3. Light micrograph showing overview of a test implant et al. 2003). It has been speculated that such direct (left) in contact with mature bone (B). The implant is covered bone formation seen at surface modified implants is the by oral mucosa (OM) lined by an epithelium (E). The arrow result of an adherent blood clot through which mes- points to the first bone contact. enchymal cells can migrate and differentiate to form bone directly on the implant surface (Davies 2003). CONCLUSION

The morphometric measurements showed no apparent The present pilot study revealed bone integration diﬀerences with regard to BIC or BA as similar mean of the novel bimodal implant surface, with no ap- values were obtained (Fig. 5). However, few animals parent diﬀerences from TiO-blasted and oxidized were used and statistics could not be applied. control implants after four months of healing.

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Figure 4. Light micrographs showing bone formation towards all three implant surfaces.: a/ Bimodal surface, b/ TiO-blasted surface, c/ Oxidized surface

REFERENCES

Albrektsson T, Brånemark PI, Hansson H, Lindström J. Osseointegrated implants. Requirements for ensuring a long-lasting direct bone-to-implant anchorage in man. Acta Orthop Scand 1981;52:155-170

Albrektsson T, Wennerberg A. Oral implant surfaces: Part 1--review focusing on topographic and chemical properties of diﬀerent surfaces and in vivo responses to them. Int J Prosthodont. 2004;17:536-43.

Araujo MG, Sukekava F, Wennstrom JL, Lindhe J. Ridge alterations following implant placement in fresh extraction sockets: an experimental study in the dog. J Clin Periodontol. 2005;32:645-52.

Branemark PI, Adell R, Breine U, Hansson BO, Lindstrom J, Ohlsson A. Intra-osseous anchorage of dental prostheses. I. Experimental studies. Scand J Plast Reconstr Surg. 1969;3(2):81-100.

Davies JE, Hosseini MM. Histodynamics of endosseous wound healing. In Davies, JE (ed) Bone engineering. Em squared incorporated, Toronto 2000, pp1-14

Davies JE. Understanding peri-implant endosseous healing. J Dent Educ 2003;67:932-949

Ivanoﬀ CJ, Hallgren C, Widmark G, Sennerby L, Wennerberg A. His- tologic evaluation of the bone integration of TiO(2) blasted and turned titanium microimplants in humans. Clin Oral Implants Res. 2001;12:128-34. 16 Applied Osseointegration Research - Volume 6, 2008

Johansson C, Albrektsson T. Integration of screw implants in the rabbit: a 1-year follow-up of removal torque of titanium implants. Int J Oral Maxillofac Implants. 1987;2:69-75.

Rocci A, Martignoni M, Burgos PM, Gottlow J, Sennerby L. Histol- ogy of retrieved immediately and early loaded oxidized implants: light microscopic observations after 5 to 9 months of loading in the posterior mandible. Clin Implant Dent Relat Res. 2003;5 Suppl 1:88-98.

Schroeder A, Pohler O, Sutter F. [Tissue reaction to an implant of a titanium hollow cylinder with a titanium surface spray layer] SSO Schweiz Monatsschr Zahnheilkd. 1976;86:713-27.

Sennerby, L., Thomsen, P. and Ericson, L.E. Early bone tissue response to titanium implants inserted in rabbit cortical bone. I. Light microscopic observations. J Mat Sci: Mat Med 1993; 4:240-250

Figure 5. Light micrograph of a bimodal implant surface (I). Bone (B) is formed from the surface and towards the bone marrow (BM). Os = osteoid, V= vessel

Figure 6. Results from morphometrical measurements of BIC and BA.

100

60 Astra 50 Nobel (%) Neoss 40

0 Bone area BIC 17 Applied Osseointegration Research - Volume 6, 2008

Histological and Biomechanical Aspects of Surface Topography and Geometry of Neoss Implants. A Study in Rabbits.

Lars Sennerby1 , Jan Gottlow1, Fredrik Engman2 and Neil Meredith2,3

1Department of Biomaterials, Institute of Clinical Sciences, Sahlgrenska Academy, Göteborg University, Sweden 2Neoss Ltd, Harrogate, UK 3University of Bristol, Bristol, UK

This experimental study showed evidence of surface mediated bone formation on the bimodal titanium surface as previously described for other commercially available surface modified implants. Removal torque tests showed increased stability by adding a modified surface and vertical flutes as compared to turned control implants without flutes.

INTRODUCTION integration and stability, as shown in numerous experi- Osseointegrated implants are clinically successful if a mental studies (Albrektsson & Wennerberg 2004). It direct bone-implant contact can be established and is believed that the surface irregularities ensure a firm maintained (Albrektsson et al. 1981). The bone-im- contact with the blood clot allowing primitive cells to plant interface is biomechanically challenged in rota- migrate to the interface, differentiate to osteoblasts tional, axial and lateral directions during healing, the and form bone directly on the surface (Davies 2003). prosthetic phase and clinical function. The ability to For a smooth surface, shrinkage of the blood clot will withstand loading is decisive for the clinical outcome create a gap at the interface and cells cannot reach the and factors of importance are (i) type and magnitude of surface (Miranda-Burgos et al. 2007). Thus, implants loading, (ii) the quality of the bone-implant integration with a moderately rough surface integrate more rapidly and (iii) the mechanical properties of the surrounding and with more bone contacts than smooth surfaced bone. Implant integration is time dependent and the implants (Ivanoff et al. 2001, Zechner et al. 2003). biomechanical properties of the bone-implant interface improve with time (Johansson et al. 1987, Sennerby et A second means of improving implant integration is by al. 1993, Friberg et al. 1999). Therefore, the use of a geometric features. Most dental implants are self-tap- two-stage procedure with three to six months of heal- ping and have an apical configuration including cutting ing usually ensures a mature bone-implant interface edges and bone chambers. Bone ingrowth into such and good clinical results. However, the trend today voids is most likely to increase the rotational stability of is to use immediate/early loading protocols, which the implant. Recent research has indicated that grooves make great demands on the bone-implant interface at the thread flank may lead to improved healing by since the implants will be loaded during initial healing. guided bone formation as well as to an improved inter- lock with bone (Hall et al, 2005). The Neoss implant The first generation of osseointegrated implants is a self-tapping implant with apical bone chambers had a relatively smooth (machined, turned) surface and vertical flutes. It has a bimodal surface topogra- (Brånemark et al. 1969). Good long-term clini- phy which is produced by blasting with two different cal outcomes have been reported on all indications sizes of ZrO and Ti-based particles. The influence of when used in good bone qualities and using a two- the surface topography and geometry on the bone stage procedure (Albrektsson & Sennerby, 1991). tissue response and stability is presently not known. However, in more challenging situations such as low bone densities, bone grafting and immediate loading, The present study was conducted to examine the early increased failure rates have been reported (Friberg et tissue responses to the bimodal titanium surface. The al. 1991, Becktor et al. 2004, Glauser et al. 2001). aim was also to evaluate the effect of surface topography and geometrical features on rotational stability. Surface modification is one way of improving implant 18 Applied Osseointegration Research - Volume 6, 2008

MATERIALS AND METHODS

Implants A total of 96 implants, 7 mm long and 4.0 mm in diameter were implanted in the study. These were both original and modified Neoss implants (Neoss Ltd, Harrogate, UK) as follows (fig. 1); v 48 implants with a bimodal surface created by

blasting with 100 to 300 μm wide ZrO2 spheres followed by irregularly shaped Ti-based particles, 75 to 150 μm wide (Fig 2). - 36 with vertical flutes (original surface and geometry)(B+)(Fig 3a) - 12 without flutes (B-)(Fig 3b) v 24 implants with turned surfaces - 12 with two vertical flutes (original geometry) (T+) - 12 without flutes (T-) FIgure 2. Three-dimensional view of the bimodal surface topography at a thread flank. v 24 other implants used for another investigation.

FIgure 1. The four types of implants used in the study; (L to R) bimodal surfaced fluted and non-fluted and two with turned surfaces. Animals, anaesthesia and experimental protocol A total of 12 female New Zealand white rabbits were used in the study, after the protocol had been approved Figure 3a. Close up of an implant with bimodal surface and by the animal ethics committee of the Gothenburg vertical flutes (B+). 3b. Non-fluted bimodal implant (B-) University.. General anesthesia was induced by intra- each of T+, T-, B+ and B-implants were placed in muscular injections of fluanisone-fentanyl (0.7 mL, the femora of each animal. Two B+ and two B- im- Hypnorm™, Helsingborg, Sweden) and intraperitoneal plants were placed in the tibiae of each animal. Cover injection of diazepam (0.25 mg/kg, Apozepam™, Al- screws were placed and the flaps were closed with pharma AB, Stockholm, Sweden). Local anesthesia was resorbable sutures. The animals were allowed to heal induced at both proximal tibial metaphyses and distal for three (n=4) and six (n= 8) weeks after surgery. femoral condyles by injections of lidocaine (about 2 mL, Xylocaine®,Astra Zeneca AB, Södertälje, Sweden). Removal torque After six weeks of healing, the femoral implants The distal femoral condyles and proximal tibial in eight animals were subjected to removal torque metaphyses were used as experimental sites. The bone (RTQ) test. The tests were performed in a specially was exposed via incisions through skin and fascia. designed rig using a motor-driven device. A linearly Two implant sites were prepared in each femur and increasing torque was applied until failure of integra- tibia; each animal receiving 8 implants. Implants tion occurred; the peak value in Newton-centimeters were selected by a rotational scheme, so that one (Ncm) was recorded. A mean value was calculated 19 Applied Osseointegration Research - Volume 6, 2008 for each of the four implant types. The percentage difference from that of turned implants without vertical flutes was calculated for each of the other groups. The Wilcoxon Signed Rank test was used for statistics and a difference was considered if p < 0.05.

Histology All implants and surrounding bone tissues were retrieved and ﬁxed by immersion in a 4% buﬀered formaldehyde solution. The specimens were then dehydrated in a graded series of ethanol and embedded in light curing methacrylate (Technovit® 7200 VCL, Kulzer, Friedrichsdorf, Germany). Ground sections, approximately 10 μm thick, were prepared using a sawing and grinding technique (Exakt Apparatebau®, Norderstedt, Germany). One central section was taken from each implant site, stained with Toluidine Blue and examined in a Nikon light microscope.

RESULTS

Light microscopy of the three-week specimens of FIgure 4. Light micrographs showing Neoss implants after the bimodal implant surface revealed bone forma- three weeks of healing. tion directly onto the implant surface (Fig. 4a). This a/ Overview showing thin rims of bone following the contour of the threads (Arrows), I = implant, LCT = loose connective could be seen as thin rims of bone following the tissue. contour of the implant threads (Figs. 4a and b) and b/ Close up of a. Bone (B) has been formed directly on the as solitary islets with no obvious connection to exist- implant (I) surface. Osteoblasts (Os) and osteoid can be observed on the surface of the bone facing a loose connective ing bone surfaces (Fig. 5). Osteoblastic seams were tissue (LCT). often seen on the bone rims, facing the adjacent soft tissues (Figs. 4b and 6). Non-bone areas consisted of a loose connective tissue rich in cells and vessels and devoid of signs of inﬂammation (Figs. 4a-b, 5 and 6). A more mature bone-implant interface was seen in the six-week specimens and a larger proportion of the implant surface was in contact with bone (Fig. 7).

The removal torques were found to be correlated with surface topography and the absence or presence of vertical ﬂutes (Fig. 8); the lowest torques were recorded for machined implants without flutes and the highest for bimodal surface implants with vertical flutes (p<0.05)(TABLE 1).

DISCUSSION

The present study indicated that the bimodal topography induced bone formation directly at the implant surface as previously described for other commercially available surface modiﬁed implants (Piattelli et al. 1996, Ivanoﬀ et al. 2001, Rocci et al. 2003, Berglundh 20 Applied Osseointegration Research - Volume 6, 2008

Turned Turned Bimodal Bimodal The removal torque tests revealed an improved resist- with flute with flute ance to torque with modified topography and a verti- (T-) (T+ (B-) (B+) cal flute added. This is best explained by ingrowth of 42.4 44.4 46.9 58.5 bone into micro- and macroscopic undercuts at the (15.4) (15.0) (13.2) (13.2)* surface. Hall et al (2005) showed that a macroscopic * P<0.05 compared with T- implants groove added to the thread flank can stimulate bone formation over the implant surface. The relatively Table 1. Results from removal toruqe measurements. Figure 6. Light micrograph showing bone formation at the bottom of a thread after three weeks of healing. New bone et al. 2003). This was seen as seen thin rims or solitary (NB) is formed by osteoblasts (Os) on previously formed bone islets of bone at the surface with osteoblastic seams fac- (PB) and separated by a cement line (white arrow). LCT = loose connective tissue ing the adjacent bone marrow. Previous descriptions of the healing of smooth, turned implants have reported bone formation from the adjacent tissues and towards the implant surface (Sennerby et al 1992, Palma et al. 2006, Miranda-Burgos et al. 2007). The mechanisms behind the different integration pathways are probably related to the integrity of the blood clot-implant interface during the early events of bone healing (Davies 2003). With a rough surface, the clot can maintain a firm contact in spite of shrinkage, whereas a gap may be formed at a smooth implant surface. In the former case mesenchymal cells can migrate to the implant surface, differentiate and start to produce bone matrix. The influence of surface modification on the clinical outcome is not clear. For instance, clinical studies comparing titanium-plasma sprayed and turned surfaces or FIgure 7. Light micrographs after 6 weeks of healing showing almost complete bone filling of a thread with mature bone. TiO2 blasted and turned surfaces could not find any Arrows point at newly formed secondary osteons indicative of statistically significant differences with regard to sur- remodelling. vival rate and marginal bone loss (Åstrand et al. 2004a, 2004 b). However, other non-comparative studies have indicated better survival rates for surface modified than for turned implants in challenging clinical situations such as bone grafting (Brechter et al. 2005) and in immediate loading (Glauser et al 2001, 2003). Since the trend today is to use immediate/early loading, the use of surface modified implants is preferable.

Figure 5. Light micrograph after three weeks showing solitary bone formation (B) at the apical part of the implant (I) facing a loose connective tissue (LCT) rich of cells.

21 Applied Osseointegration Research - Volume 6, 2008

Berglundh T, Abrahamsson I, Lang NP, Lindhe J. De novo alveolar bone formation adjacent to endosseous implants. A model study in the dog. Clin Oral Implants Res 2003;14:251-262

Branemark PI, Adell R, Breine U, Hansson BO, Lindstrom J, Ohlsson A. Intra-osseous anchorage of dental prostheses. I. Experimental studies. Scand J Plast Reconstr Surg. 1969;3(2):81-100.

Brechter M, Nilson H, Lundgren S. Oxidized titanium implants in reconstructive jaw surgery. Clin Implant Dent Relat Res. 2005;7 Suppl 1:S83-7.

Davies JE. Understanding peri-implant endosseous healing. J Dent Educ 2003;67:932-949

Friberg B, Jemt T, Lekholm U. Early failures in 4,641 consecutively placed Branemark dental implants: a study from stage 1 surgery to the connection of completed prostheses. Int J Oral Maxillofac Implants. 1991 Summer; 6(2):142-6.

Figure 8. Graph showing the percentage change of removal Friberg B. (1999) On bone quality and implant stability measurements. torque in comparison with turned implants without vertical Thesis. Dept of Biomaterials/Handicap Research, Göteborg University, flutes (T-). * p< 0.05 Sweden.

Glauser R, Ree A, Lundgren A, Gottlow J, Hammerle CH, Scharer P. Immediate occlusal loading of Branemark implants applied in various small effect of surface topography may be explained jawbone regions: a prospective, 1-year clinical study. Clin Implant Dent by the design of the test implants, since they all had Relat Res. 2001;3(4):204-13. apical undercuts, i.e. cutting edges and bone chambers. Glauser R, Lundgren AK, Gottlow J, Sennerby L, Portmann M, Ruhstaller P, Hammerle CH. Immediate occlusal loading of Branemark TiUnite implants placed predominantly in soft bone: 1-year results of a CONCLUSION prospective clinical study. Clin Implant Dent Relat Res. 2003;5 Suppl 1:47-56. The present experimental study showed evidence Ivanoff CJ, Hallgren C, Widmark G, Sennerby L, Wennerberg A. His- of surface mediated bone formation at the bimodal tologic evaluation of the bone integration of TiO(2) blasted and turned surface as previously described for other commer- titanium microimplants in humans. Clin Oral Implants Res. 2001; cially available surface modified implants. Removal 12:128-34. torque tests showed increased stability with the Johansson C, Albrektsson T. Integration of screw implants in the rabbit: modified surface and adding vertical flutes when a 1-year follow-up of removal torque of titanium implants. Int J Oral compared to turned control implants without flutes. Maxillofac Implants. 1987;2:69-75. Miranda-Burgos P, Rasmusson L, Meirelles L, Sennerby L. Early bone tissue responses to oxidized and machined titanium implants in the rab- REFERENCES bit tibia. Clin Implant Dent Relat Res, Accepted for publication

Albrektsson T, Brånemark PI, Hansson H, Lindström J. Osseointegrated Palma VC, Magro-Filho O, de Oliveria JA, Lundgren S, Salata LA, Sen- implants. Requirements for ensuring a long-lasting direct bone-to-im- nerby L. Bone reformation and implant integration following maxillary plant anchorage in man. Acta Orthop Scand 1981;52:155-170 sinus membrane elevation: an experimental study in primates. Clin Implant Dent Relat Res. 2006;8:11-24. Albrektsson T & Sennerby L.State of the art in oral implants. J Clin Peri- odontol. 1991;18:474-81. Piattelli A, Scarano A, PIattelli M, Calabrese L. Direct bone formation on sand-blasted titanium implants: an experimental study. Biomaterials Albrektsson T & Wennerberg A. Oral implant surfaces: Part 1--review 1996;17:1015-8 focusing on topographic and chemical properties of diﬀerent surfaces and in vivo responses to them. Int J Prosthodont. 2004;17:536-43. Rocci A, Martignoni M, Burgos PM, Gottlow J, Sennerby L. Histol- ogy of retrieved immediately and early loaded oxidized implants: light Åstrand P, Engquist B, Anzen B, Bergendal T, Hallman M, Karlsson U, microscopic observations after 5 to 9 months of loading in the posterior Kvint S, Lysell L, Rundcranz T. A three-year follow-up report of a com- mandible. Clin Implant Dent Relat Res. 2003;5 Suppl 1:88-98. parative study of ITI Dental Implants and Branemark System implants in the treatment of the partially edentulous maxilla. Sennerby, L., Thomsen, P. and Ericson, L.E. Early bone tissue response Clin Implant Dent Relat Res. 2004a;:130-41. to titanium implants inserted in rabbit cortical bone. I. Light microscopic observations. J Mat Sci: Mat Med 1993;4:240-250 Åstrand P, Engquist B, Dahlgren S, Grondahl K, Engquist E, Feldmann H. Astra Tech and Branemark system implants: a 5-year prospective Zechner W, Tangl S, Furst G, Tepper G, Thams U, Mailath G, Watzek study of marginal bone reactions. G. Osseous healing characteristics of three diﬀerent implant types. Clin Clin Oral Implants Res. 2004b Aug;15:413-20. Oral Implants Res. 2003a Apr;14(2):150-7.

22 Applied Osseointegration Research - Volume 6, 2008

A One-Year Clinical, Radiographic and RFA Study of Neoss Implants Used in Two-Stage Procedures

Peter Andersson1 , Damiano Verrocchi1, Rauno Viinamäki1, Lars Sennerby1,2

1Private Practice, Fiera di Primiero and Feltre, Italy 2Dept Biomaterials, Inst Clinical Sciences, Sahlgrenska Academy, Gothenburg University, Sweden

This study reports a survival rate of 98.1% for 102 Neoss implants in 44 patients with a mean bone loss of 0.7 mm after one year. The reduced component inventory and innovative designs enhancing primary stability and facilitating laboratory technology/prosthetics offer practical advantages whilst the clinical results with the implant system tested compare favourably with existing systems

INTRODUCTION tients should be over 18 years old and present no con- The use of implant-supported bridges is a routine traindications for oral surgery under local anaesthesia. treatment modality for the edentulous patient with documented good long-term results (Albrektsson & Clinical techniques Patients were administered 2 gr of amoxicillin (Aug- Sennerby 1991, Esposito et al. 1998). From initially a ® rather complicated and restricted procedure, the tech- mentin , Roche, Milan, Italy) and sedation if required niques of implant-supported dentistry have improved (Valium®, Roche, Milan, Italy, 5 mg) prior to surgery. and simplified, at least from a surgical point of view. Anaesthesia was induced by infiltration with articain/ The introduction of self-tapping and surface modified epinephrine (Septocain™, Specialites Septodont, Saint- implants, surgical guides, shortened healing periods Maur-Des-Fosses, France). Crestal incisions were used and immediate loading are some examples. However, for flap elevation. Implant sites were prepared with a improvements could still be made in dental laboratory 2.2 mm twist drill followed by a 3 mm (3.5 mm wide and prosthetic techniques in order to reduce further implant), 3.4 mm (4.0 mm wide implant) and 3.9 mm treatment times and the overall cost of the treatment. drills (4.5 mm wide implant) (Neoss ltd, Harrogate, UK). Full countersink preparation was made for all The aim of the present study was to evaluate a new implants. Implants were inserted with the torque driver implant system (Neoss) for one year using clinical set to 40 Ncm and final seating was performed with a and radiographic examinations and implant stability hand wrench. Cover screws were applied and the flaps measurements by resonance frequency analysis (RFA). were replaced and sutured. Bone quality and quantity according to Lekholm and Zarb (1985) were registered. MATERIALS AND METHODS Abutment connection was performed 3 months Patient inclusion later, usually with a punch technique and no sutures. Consecutive patients requiring implant treatment for Bite registration and impressions were taken with total or partial loss of teeth were included in the study closed tray and then healing abutments were con- until at least 100 implants had been inserted. Only nected. Neolink™ abutments (Neoss ltd, Harrogate, two-stage procedures with 3 months of healing from UK) of gold or titanium (to match the metal of the placement to abutment connection were performed. framework) were used. Abutments were either cast or welded into the metal frameworks. Porcelain Preoperative examinations included intraoral and and acrylic veneers were used. Constructions were panoramic radiographs. Computerized tomography screw-retained if implant angulation permitted; was used if required. The implant sites should have otherwise, individual abutments (Neo Matrix, Ne- sufficient bone for at least 7 mm long implants. Pa- oss ltd, Harrogate, UK) were used for cementation. 23 Applied Osseointegration Research - Volume 6, 2008

Follow-up Implant stability was assessed by RFA (Mentor®, Integration Diagnostics AB, Gothenburg, Sweden) at implant surgery, abutment connection and after one year of loading (after unscrewing the constructions ). Cemented constructions were not removed.

Digital or conventional intraoral radiographs were taken at abutment connection and after one-year of service. Conventional radiographs were pho- tographed with a digital camera on a light desk. Measurements were made using a personal computer (Image J 1.34S, National Institutes of Health, USA) at mesial and distal aspects. Each radiograph was calibrated using the known width of the coronal cyl- inders of the implants. The upper platform was used as a reference point for measurements (Figure 1) .

RESULTS

Forty-four (44) patients (16 male and 28 female, mean age 54 years) were treated according to the protocol. Forty-eight (48) prosthetic constructions were delivered including ﬁve full cross-arch bridges, 28 partial bridges and 17 single crowns. A total of 102 implants were placed, 34 in the maxilla and 68 in the mandible, in bone quality and Figure 1. Clinical photographs showing quantity as presented in Table 1. Implant lengths a/ two implants in the posterior mandible after insertion, and diameters are presented in Tables 2 and 3. b/ healing of soft tissues at the time of bridge delivery, c/ final bridge.

At writing all patients have completed one year Quantity Number Quality Number in function. All constructions except one pa- A 3 1 3 tient with a cemented bridge on five implants were removed for stability checking. B 47 2 68

All patients maintained a ﬁxed bridge or crown during C 52 3 26 the one year study. Two failures were experienced, giving a survival rate of 98.1% after one year. One 13 mm D - 4 5 long by 4.0 mm wide implant placed in a defect in a Table 1. Bone Quality and Quanitity encountered mandible was removed at impression due to mobility. In this case, a new implant was placed and a temporary bridge was made on the remaining three implants whilst Table 2. Implant Sizes placed Table 3. Implant lengths placed awaiting healing. One 7 mm long by 4.5 mm wide im- Diameter Number Diameter Number plant in Q4 bone in the1st molar region in a maxilla was lost after one year. The implant was removed and 7 9 3.5 mm. the three-unit bridge was supported on the remain- 17 9 30 ing two implants. No other prosthetic complications such as fractures or screw-loosening were experienced. 4.0 mm. 57 11 23 13 19 4.5 mm. A total of 92 implants with readable radiographs at 28 15 21 24 Applied Osseointegration Research - Volume 6, 2008 baseline and follow-up have been evaluated to date. On average, the marginal bone level was located 0.6 mm (SD 0.7) below the platform at baseline and 1.3 mm (SD 1.0) below after one year; giving an average bone loss of 0.7 mm (SD 1.0) at one year. X implants showed more than 3 mm bone loss.

Stability measures by RFA gave a mean of 75.0 (SD 6.5) ISQ at placement, 74.4 (SD 6.8) at abutment connection and 76.2 (SD 6.6) after one-year. There seems to be a relation between bone quality and ISQ at implant placement (Fig. 4). Implant stability increased with time for implants in Q4 bone whilst stability decreased for implants in very dense bone, resulting in a similar stability for all implants after one year.

DISCUSSION

Early experience with the Neoss implant system used in a two-stage procedure with 3 months of healing in the present study shows satisfactory results. Two of 102 implants were lost during one year which compares well with the results reported from other implant systems (Albrektsson & Wennerberg 2004). From a surgical point of view, the implant was stable during insertion and good primary stability was generally Figure 2. Radiographs from a single tooth case at a/ baseline achieved. When poor primary stability was encoun- and b/ after one year tered, a wider implant was used to enhance stability. Since the different implant diameters have the same advances twice as far with one turn as for a single-helix prosthetic platform, an implant could be replaced thread. This feature reduces the insertion time and with a wider diameter without requiring changes to counteracts wobbling during insertion. Secondly, the the other prosthetic components, as is commonly implant has a positive tolerance, meaning that the necessary with other implant systems. Abutment implant is slightly conical in the coronal direction connection was easier with this implant than previ- and as the implant screws home its diameter increases ously experienced with external connection implants, slightly and there is a slight tendency to tighten the which often require a flap procedure and removal thread base against the bone. Previous research has of bone tissue in order to fit an abutment. A punch shown higher stability for slightly tapered implants technique without suturing could frequently be used in soft bone than for parallel-sided implants, without in the present study and in most cases impressions jeopardizing the integration process (O’Sullivan et were taken in conjunction with abutment connection. al 2000, O´Sullivan et al 2004a, 2004b). Decreased The use of integrated abutments with the framework primary stability was seen with decreased bone den- facilitated prosthetics and reduced the overall costs . sity, which is in line with the findings of Östman et al (2006). Implant stability increased slightly with time The RFA measurements revealed a high average pri- and was similar for all bone qualities after one year mary stability of these implants which is most probably of function, which indicates a favourable bone tissue due to the geometric features of the implant. Firstly, it response to the implants. The greatest increase of stabil- has a two-start thread, a twin helix, with two threads ity was seen for implants in Q4 bone which is in line running parallel but on diametrically opposite sides of with the findings of Friberg et al. (1999).. This can be the cylindrical substrate. Thus, the actual thread pitch explained by stiffening of the bone-implant interface is double the “apparent” thread spacing, so the implant with time due to bone formation and remodelling. 25 Applied Osseointegration Research - Volume 6, 2008

In contrast, decreased stability was observed in dense bone, which may be explained by mechanical relaxation and/or bone remodelling as a response to the pre- sumably high stresses induced by implant placement.

The radiographic analysis revealed that about 0.7 mm of bone was lost during the ﬁrst year of loading, which is in the range of previously reported results with other systems (Oh et al. 2002). X implants showed more than 3 mm bone loss during one year. The fact that the bone level was located 0.6 mm below the platform at abutment connection indicates some remodelling during healing as generally the implants were placed flush with the surrounding bone. This accords with the ﬁndings of Engquist et al. (2001) who compared the marginal bone tissue response at Astra Tech and Brånemark system implants.

It is concluded that prosthetic rehabilitation of the edentulous patient with the Neoss implant system results in good short-term clinical and radiographic outcomes. The innovative design solutions do seem to enhance primary stability and facilitate laboratory technology/prosthetics, and with the reduced component inventory this system oﬀers advantages over our experiences with other implant systems. Figure 3. Radiographs from a partial edentulous mandible at a/ REFERENCES baseline and b/ after one year

Albrektsson T & Sennerby L.State of the art in oral implants. J Clin Peri- odontol. 1991;18:474-81. 100 95 Albrektsson T, Wennerberg A.Oral implant surfaces: Part 2--review focusing on clinical knowledge of diﬀerent surfaces. Int J Prosthodont. 90 2004;17:544-64. 85 80 Q 1 Engquist B, Astrand P, Dahlgren S, Engquist E, Feldmann H, Grondahl Q2 K. Marginal bone reaction to oral implants: a prospective comparative 75 Q3 study of Astra Tech and Branemark System implants. Clin Oral Implants 70 Q4 Res. 2002;13:30-7. 65

Esposito M, Hirsch JM, Lekholm U, Thomsen P. Biological factors con- Implant stability (ISQ) _ 60 tributing to failures of osseointegrated oral implants. (I). Success criteria 55 and epidemiology. Eur J Oral Sci. 1998;106):527-51. 50 Friberg B, Sennerby L, Meredith N, Lekholm U. A comparison between Placement Abutment One year cutting torque and resonance frequency measurements of maxillary Figure 4. Results from RFA measurements in relation to bone implants. A 20-month clinical study. quality and time. Int J Oral Maxillofac Surg. 1999;28:297-303.

Lekholm U, Zarb GA. Patient selection. In: Brånemark P.-I, Zarb GA, Relat Res. 2004a;6:48-57. Albrektsson T, eds. Tissue integrated prostheses. Osseointegration in clinical dentistry. Chicago: Quintessence, 1985:199–209. O’Sullivan D, Sennerby L, Meredith N. Inﬂuence of implant taper on the primary and secondary stability of osseointegrated titanium implants. O’Sullivan D, Sennerby L, Meredith N. Measurements comparing the Clin Oral Implants Res. 2004b;15:474-80. initial stability of ﬁve designs of dental implants: a human cadaver study. Clin Implant Dent Relat Res. 2000;2(2):85-92. Ostman PO, Hellman M, Wendelhag I, Sennerby L. Resonance frequency analysis measurements of implants at placement surgery. O’Sullivan D, Sennerby L, Jagger D, Meredith N.A comparison of two Int J Prosthodont. 2006;19:77-83; methods of enhancing implant primary stability. Clin Implant Dent 26 Applied Osseointegration Research - Volume 6, 2008

Immediate/Early loading of Neoss Implants. Preliminary Results from an Ongoing Study

Peter Andersson1 , Damiano Verrocchi1, Luca Pagliani2, Lars Sennerby3

1Private Practice, Fiera di Primiero and Feltre, Italy 2Private Practice, Milano and Legnano, Italy 3Dept Biomaterials, Inst Clinical Sciences, Sahlgrenska Academy, Gothenburg University, Sweden

This interim report of an ongoing study on immediate/early loading of Neoss implants reports a survival rate of 96.5 % for 141 Neoss implants in 33 patients after 6 months to three years of loading. All patients received and maintained a ﬁxed bridge in spite of ﬁve failures in three patients

INTRODUCTION MATERIALS AND METHODS

The use of immediate/ early loading protocols for Patient group implant-supported crowns and bridges has obvious The study group consisted of 33 patients (18 female advantages for the patients since only one surgical and 15 male) from three clinics, representing consecu- procedure and no healing periods are needed. Both tive treatments with immediately/early loaded implant- function and aesthetics can be immediately restored supported provisional bridges or crowns. The patients with a temporary crown or bridge. Concerns have been were totally edentulous (n= 18), partially edentulous raised about increased failure rates, since the original (n=12) or treated for single tooth loss (n=3) (Table concept of osseointegration prescribed a submerged 1). The possibility of placing long implants with good and unloaded healing period of 3 to 6 months before primary stability was assessed in each patient on the loading (Brånemark et al. 1969, Albrektsson et al. basis of radiography and clinical examinations. A final 1981). Today, histology from experimental and clinical decision was taken after discussions with the patient. studies has demonstrated that implants can integrate under the influence of functional loads (Piattelli et al. Implant surgery was performed under local anaes- 1998, Rocci et al. 2003). Moreover, clinical follow-up thesia and a total of 141 implants were inserted, 79 studies have reported similar good clinical outcomes in the maxilla and 62 in the mandible (Neoss Ltd, as for two-stage procedures (Attard & Zarb 2003). In fact, immediate/early loading is now a clinical reality Quantity Number Quality Number and a commonly used procedure. In many studies, of of authors have identified primary implant stability sites sites as a critical factor for success (Östman et al 2006). A 10 1 3 Inclusion criteria based on insertion torque values and RFA measurements have been used (Calandriello B 104 2 81 et al, 2003, Rocci et al 2003, Vanden Bogaerde et al 2004, Östman et al 2005). It has been shown that C 26348 the use of self-tapping implants, reduced final drill diameters and tapered implants may improve pri- D 149 mary stability (O’Sullivan et al 2001, 2004). E- The aim of the present study was to report on the early experiences of an immediate/early loading protocol using a new implant designed to give firm primary stability. Table 1. Bone quantity and quality of implant sites according to Lekholm and Zarb (1985).

27 Applied Osseointegration Research - Volume 6, 2008

Table 2. Implant diameters Table 3. Implant lengths placed in this study placed in this study Diameter Number Diameter Number

3.5 18 7 2 4.0 111 9 7 11 13 4.5 12 13 33 Total 141 15 83 17 3 Total 141

Harrogate, UK) using an insertion torque of at least 40 Ncm. Primary stability was ensured by reducing the ﬁnal drill diameter in soft bone qualities. The majority of implants were 4 mm in diameter and 13-15 mm long (Table 2 and 3). Most implants had been placed in bone quantity b and quality 2 according the Lekholm & Zarb index (Table 4 and 5).

Sterile impression copings were attached directly to the implants (n=75) or to straight or angulated abutments (n=66) (Southern Implants™, Protera AB, Gothenburg, Sweden). Impressions and bite registration were taken after suturing. Healing abutments were then connected to the implants. A screw-retained laboratory-made crown (n=3) or metal-reinforced bridge (n=31) was delivered one to three days after surgery. In two patients treated in the posterior mandible, a provisional bridge was made in the mouth the same day. Altogether, 34 provisional prosthetic constructions were delivered to the 33 patients. Single and partial constructions were not in occlusion. Total cross-arch bridges were carefully adjusted with regard to occlusion, striving towards group function and contacts over implant sites. Figure 1. Immediate loading in a mandible after extraction of After a period of 3 to 6 months, the provisional construc- three teeth. a. Six implants have been placed tions were replaced with permanent crowns or bridges b. Provisional bridge from the laboratory. made of gold or titanium with acrylic or porcelain veneers. c. Showing the connected bridge

Follow-up Digital or conventional intraoral radiographs were The patients were monitored with clinical exami- taken at baseline and after one-year of service. nations controlling the occlusion during the first weeks and months. The protocol includes RFA RESULTS AND DISCUSSION measurements (Mentor®, Integration Diagnostics AB, Gothenburg, Sweden) at implant surgery, on delivery All 33 patients have passed 6 months of loading and of the final prosthesis and after one year of loading. 13 have exceeded one year. A total of five failures were experienced, giving a survival rate of 96.5% after 6 28 Applied Osseointegration Research - Volume 6, 2008 months to 3 years. All patients received and maintained a fixed prosthesis during the follow-up period. The failures all occurred in the maxilla within three months of surgery (Table 4). Implant stability was 73.5 (SD 7.0) ISQ at placement and 74.4 (SD9.2) ISQ at final prosthesis delivery after 4 months on average.

DISCUSSION

The use of immediate/early loading protocols conveys obvious advantages for the patient since only one surgery and no healing periods are needed. Moreo- ver, there is no need for removable appliances; which can be difficult and uncomfortable to wear. In the present study, a fixed provisional bridge or crown was fabricated chair-side or delivered within a few days. In this interim report of an ongoing study, five of 141 implants failed after a follow-up of at least 6 months. All patients received and maintained a fixed construction throughout the study period in spite of five failed implants. The 3.5 % failure rate of this study is similar to those reported by other authors in studies on immediate loading. For instance, Glauser et al lost about 3 % of implants when used on all indications as in the present study. All failures in the present study occurred in the maxilla; a failure rate of Figure 2. Immediate loading in a maxilla. 6.3 % which corroborates the findings of Olsson et al a. Six implants have been installed in an arch-form (2003). Consequently, the results were better in man- b. The laboratory-made provisional bridge has been connected to the implants dibular bone as no implant failures were experienced; which is also in line with the findings in the literature faster and with more bone contacts than implants with (Attard & Zarb 2005). It can be speculated that dif- a smooth surface. It is also possible that this contrib- ferences in bone density may explain this finding as uted to the good outcome of the present study. The implants get better primary stability in mandibular RFA measurements revealed firm primary stability bone (Östman et al 2006). However, all but one implant showed high stability values and other factors This interim report of an ongoing study on im- such as unfavourable loading need to be considered. mediate/early loading of Neoss implants reports a survival rate of 96.5 % for 141 Neoss implants in The implants used in the present study have a surface 33 patients after 6 months to three years of load- topography modified by blasting. It is known from ing. All patients received and maintained a fixed animal experiments that such surfaces seem to integrate bridge in spite of five failures in three patients. Table 4. Characteristics of implant failures.

Diameter Quantity Primary stability Patient Position Case Time of failure /Length /Quality (ISQ)

1 16 Partial 4/15 C/3 44 3 months

2 13 Total 4/13 B/3 75 3 months

3 14 Total 4/13 B/2 75 3 months

3 11 Total 4/13 B/2 66 3 months

3 26 Total 4/15 B/3 77 3 months

29 Applied Osseointegration Research - Volume 6, 2008

REFERENCES

Albrektsson T, Brånemark PI, Hansson H, Lindström J. Osseointegrated implants. Requirements for ensuring a long-lasting direct bone-to-implant anchorage in man. Acta Orthop Scand 1981;52:155-170

Attard NJ, Zarb GA.Immediate and early implant loading protocols: a literature review of clinicalstudies. J Prosthet Dent. 2005 Sep;94(3):242- 58.

Branemark PI, Adell R, Breine U, Hansson BO, Lindstrom J, Ohlsson A. Intra-osseous anchorage of dental prostheses. I. Experimental studies. Scand J Plast Reconstr Surg. 1969;3(2):81-100.

Calandriello R, Tomatis M, Rangert B. Immediate functional loading of Branemark System implants with enhanced initial stability: a prospective 1- to 2-year clinical and radiographic study. Clin Implant Dent Relat Res. 2003;5 Suppl 1:10-20.

Glauser R, Lundgren AK, Gottlow J, Sennerby L, Portmann M, Ruhstaller P, Hammerle CH. Immediate occlusal loading of Branemark TiUnite implants placed predominantly in soft bone: 1-year results of a prospective clinical study. Clin Implant Dent Relat Res. 2003;5 Suppl 1:47-56.

Lekholm U, Zarb GA. Patient selection. In: Brånemark P.-I, Zarb GA, Albrektsson T, eds. Tissue integrated prostheses. Osseointegration in clinical dentistry. Chicago: Quintessence, 1985:199–209.

Olsson M, Urde G, Andersen JB, Sennerby L.Early loading of maxillary ﬁxed cross-arch dental prostheses supported by six or eight oxidized titanium implants: results after 1 year of loading, case series. Clin Implant Dent Relat Res. 2003;5 Suppl 1:81-7.

Ostman PO, Hellman M, Sennerby L. Direct implant loading in the edentulous maxilla using a bone density-adapted surgical protocol and primary implant stability criteria for inclusion. Clin Implant Dent Relat Res. 2005;7 Suppl 1:S60-9.

Figure 3. Immediate loading in a posterior mandible using a Ostman PO, Hellman M, Wendelhag I, Sennerby L. Resonance fre- chair-side made bridge quency analysis measurements of implants at placement surgery. a. Three implants have been placed Int J Prosthodont. 2006;19:77-83; b. Temorary PEK abutments connected to the implants O’Sullivan D, Sennerby L, Meredith N. Measurements comparing the c. The pre-fabricated bridge is tried on the abutments and initial stability of ﬁve designs of dental implants: a human cadaver study. adjusted. Clin Implant Dent Relat Res. 2000;2(2):85-92. d. The bridge after setting of the resin. e. The finalized provisional bridge O’Sullivan D, Sennerby L, Jagger D, Meredith N.A comparison of two f. The bridge in position. methods of enhancing implant primary stability. Clin Implant Dent Relat Res. 2004a;6:48-57.

O’Sullivan D, Sennerby L, Meredith N. Inﬂuence of implant taper on the primary and secondary stability of osseointegrated titanium implants. Clin Oral Implants Res. 2004b;15:474-80.

Piattelli A, Corigliano M, Scarano A, Costigliola G, Paolantonio M. Immediate loading of titanium plasma-sprayed implants: an histologic analysis in monkeys. J Periodontol. 1998 Mar;69(3):321-7.

Vanden Bogaerde L, Pedretti G, Dellacasa P, Mozzati M, Rangert B, Wendelhag I. Early function of splinted implants in maxillas and posterior mandibles, using Branemark System Tiunite implants: an 18-month prospective clinical multicenter study. Clin Implant Dent Relat Res. 2004;6(3):121-9.

30 Applied Osseointegration Research - Volume 6, 2008

A Retrospective Follow-up of 50 consecutive patients treated with Neoss Implants with or without an Adjunctive GBR-Procedure

1 2 Thomas Zumstein and Camilla Billström 1 Dr. med. dent., Private practice, Luzern, Switzerland 2 Neoss AB, Mölnlycke, Sweden This retrospective study of 50 patients and 183 Neoss implants showed a survival rate of 98.2% for routine cases and 94.4 % for GBR cases after a follow-up of 1 to 2 years. The marginal bone loss was 0.3 mm the ﬁrst and 0.1 mm the second year. GBR procedures involving short implants and soft bone seemed to increase the risk of implant failure.

INTRODUCTION MATERIALS AND METHODS

The use of osseointegrated implants has been proven Patients and surgery to result in good clinical outcomes in the prosthetic Fifty consecutive patients (20 males, 30 females, mean rehabilitation of the edentulous patient, whether used age 57 years) needing implant treatment were enrolled in totally or partially edentulous jaws, including single in the study. Three patients were treated in both maxilla tooth replacements (Esposito et al. 1998). Since the and mandible resulting in 53 treatment areas (jaws) introduction some 40 years ago, the osseointegration included in the study. Intraoral and panoramic radio- technique has been continuously developed and refined graphs as well as CT scans were used for presurgical in order to simplify and shorten implant treatment. evaluations. Nine patients were totally edentulous (two For instance, the introduction of self-tapping implants, in both jaws), 21 were partially edentulous (one in two surface modifications and immediate/early loading areas) and 20 patients were treated for single tooth loss. protocols has markedly facilitated implant treatment. The presence of sufficient bone volumes was originally The patients were administered antibiotics prior to an absolute criterion for using implants. Today, num- surgery (Dalacin® C 300mg, Pfizer). Surgery was per- bers of reconstructive techniques including the use of formed under sterile conditions and local anaesthesia bone grafts, bone substitutes, osteodistraction devices with Ultracain® DS Forte. Crestal incisions were used and membranes are available to increase the load-bear- and implant sites were drilled in accordance with the ing volume of the jaw bone. A localized defect such guidelines given by the manufacturer for the appro- as that due to incomplete healing after extraction may priate implant diameter. Implants were inserted into complicate the placement of an implant by exposure position with a drilling unit. A total of 183 Neoss of parts of the implant. In such cases, the use of a implants (Neoss Ltd, Harrogate, UK) were placed; bovine bone substitute and a resorbable membrane 116 in the maxilla and 67 in the mandible (Table 1). is commonly used to achieve complete bone cover- Implant lengths and diameters are shown in Table 2 age (Hurzeler et al. 1998, Hammerle & Lang 2001). and 3. Bone quality and quantity according to the Lekholm and Zarb index (1985) were registered (Ta- The Neoss implant system (Neoss Ltd, Harrogate, bles 4 and 5). The implant collar was either fully sub- UK) is a novel design which according to the manu- merged in bone (n=1087) or to half its length (n=75). facturer was developed to provide simple and effective solutions for all kinds of cases with minimal Thirty of the treatment areas with 126 implants components. Special attention has been paid to the underwent GBR using BioOss™ and a resorb- technical/prosthetic phase and only one prosthetic able BioGide™ membrane (Geistlich, Switzer- platform is used irrespective of implant diameter. land) simultaneously with implant placement.

The aim of this retrospective study was to report on Healing abutments were connected after a healing the experiences with Neoss implants from the ﬁrst period of 3 to 6 months in 32 treatment areas (89 consecutive 50 patients treated in one private oﬃce. implants). In 21 areas (94 implants) healing abut- 31 Applied Osseointegration Research - Volume 6, 2008

MAXILLA 28 27 26 25 24 23 22 21 11 12 13 14 15 16 17 18 TOTAL 011116179644791212710116 0395345126556112067 MANDIBLE 38 37 36 35 34 33 32 31 41 42 43 44 45 46 47 48 TOTAL

Table 1. Distribution of implants in relation to position ments were placed in conjunction with implant surgery and 8 of these (57 implants) were loaded with a crown/bridge for immediate function.

Table 2. Placed and failed implants in relation to length Prosthetics Impressions were taken on implant level for screw- retained prosthetics using Neolink abutments (Neoss Ltd, Harrogate, UK) and gold-ceramic or gold- acrylic frameworks. All crowns and partial bridges TOTAL FAILED FAILED FAILED FAILED PLACED LENGTH IMPLANT IMPLANT IMPLANTS IMPLANTS IN NON-GBR

IMPLANTS IN were gold-ceramic reconstructions and all but one of IMPLANTS IN GBR PATIENTS the full jaw bridges were gold-acrylic reconstructions. 7 mm 7 2 2 0 The crowns/bridges were attached with gold screws 9 mm 51 4 3 1 using a preload of 32 Ncm. 11 mm 75 2 2 0 13 mm 44 0 0 0 Follow-up 15 mm 6 0 0 0 The patients were scheduled for annual check-ups with 17 mm 0 0 0 0 clinical and radiographic examinations using intraoral Total 183 8 7 1 or panoramic radiographs. Marginal bone level measurements were performed by an independent radiolo- gist in one baseline and one follow-up radiograph. Table 3. Placed and failed implants in relation to diameter

RESULTS

Forty-nine of the patients attended the ﬁrst annual TOTAL FAILED FAILED FAILED FAILED FAILED check up and 26 the second. A total of eight implant PLACED IMPLANT IMPLANT NON-GBR PATIENTS IMPLANTS DIAMETER IMPLANTS IN IMPLANTS IN IMPLANTS IN

GBR PATIENTS failures were registered, all during the ﬁrst year in service, giving an overall Cumulative Success Rate 3,5 mm 58 5 4 1 (CSR) of 95.6% (Table 6). All but one failure oc- 4,0 mm 112 2 2 0 curred in the GBR group, giving a CSR of 94.4% for 4,5 mm 13 1 1 0 the GBR-group and 98.2 % for the non-GBR group 5,5 mm 0000 after 1 year (Table 6). The characteristics of failed Total 183 8 7 1 implants are shown in Table 7. Failures occurred

Table 5. Placed and failed implants in relation to bone quantity Table 4. Placed and failed implants in relation to bone quality GBR BONE FAILED FAILED IN GBR FAILED FAILED FAILED IN NON- PLACED IN TOTAL PATIENTS IMPLANTS IMPLANTS IMPLANTS IMPLANTS QUANTITY GBR BONE FAILED FAILED IN GBR FAILED FAILED FAILED IN NON- PLACED QUALITY IN TOTAL PATIENTS IMPLANTS IMPLANTS IMPLANTS IMPLANTS A44000 1 0000 B 103 4 4 0 247220 C26431 3115440 D10000 421211 E0000 Total 183 8 7 1 Total 183 8 7 1 32 Applied Osseointegration Research - Volume 6, 2008 more often for short implants and in soft bone. In Table 6. Life-tables spite of the failures, all patients received and maintained a ﬁxed crown/ bridge during the follow-up. TOTAL FAILED FAILED A total of 270 radiographs could be used for meas- CSR (%) IMPLANTS IMPLANTS urements of marginal bone levels. On average, the SURVIVING Implant placement bone was situated 1.6 (S.D. 0.75) mm below the 183 2 0 98.9% – Prosthesis delivery top of the collar at baseline and 1.9 (S.D. 0.73) Prosthesis delivery – 181 6 0 95.6% mm at the follow-up one year later. Thus, the total 1 year bone loss amounted to 0.3 (S.D. 0.88) mm (Table 1 year – 2 years 175 0 14 95.6% 8) during this year. There were only small diﬀer- ences between the GBR and non-GBR groups. 2 years – 3 years 93 0 6 95.6% 3 years 13 - - - DISCUSSION

The experiences with the Neoss implant system from GBR GROUP

the ﬁrst 50 patients treated in one clinic are reported. FAILED CSR (%) IMPLANTS IMPLANTS IMPLANTS SURVIVING SURVIVING

A survival rate of 98.2 % was achieved after one to WITHDRAWN two years in routine cases with no need for bone Implant placement 126 2 0 98.4% augmentation procedures. This is in accordance with – Prosthesis delivery recent studies on other implant systems (Albrektsson Prosthesis delivery 124 5 0 94.4% & Wennerberg, 2004). The implant that failed in this – 1 year group was of 3.5 mm diameter with length 9 mm 1 year – 2 years 119 0 8 94.4% placed in quality type 4 bone in the maxilla. It was 2 years – 3 years 60 0 8 94.4% one of 8 implants placed with an immediate loading protocol for a full bridge reconstruction. A higher 3 years 11 - - - failure rate was seen when implants were placed with a simultaneous GBR procedure using bovine bone and a resorbable membrane, as 7 of 126 implants were lost NON-GBR GROUP FAILED FAILED (5.6%). The results indicate that osseointegration of CSR (%) IMPLANTS IMPLANTS IMPLANTS SURVIVING SURVIVING the exposed parts of the implants was not achieved WITHDRAWN Implant placement for these implants during healing prior to loading, 57 0 0 100% resulting in an unfavourable biomechanical situation. – Prosthesis delivery Prosthesis delivery 57 1 0 98.2% This notion is further supported by the fact that short – 1 year implants (7 and 9 mm) and implants in soft bone qual- 1 year – 2 years 56 0 6 98.2% ity failed more often. It is possible that a prolonged healing period is needed, as also suggested for sinus lift 2 years – 3 years 33 0 0 98.2% procedures with bovine bone (Hallman et al. 2005). 3 years 2 - - -

Table 7. Characteristics of failed implants PATIENT BONE BONE TIME OF POSITION LENGTH DIAMETER GBR NUMBER QUALITY QUANTITY FAILURE 2865 22 9 3.5 3 C Yes Prosthesis 1896 23 9 3.5 3 C Yes Prosthesis 47 15 11 4.5 4 C Yes 1 year 154 36 7 3.5 2 B Yes 1 year 154 44 7 3.5 3 B Yes 1 year 1454 35 11 4.0 2 B Yes 1 year 1454 25 9 4.0 3 B Yes 1 year 2782 26 9 3.5 4 C No 1 year 33 Applied Osseointegration Research - Volume 6, 2008

BONE LEVEL 1 BONE LEVEL 2 BONE LOSS BONE LEVEL BONE LOSS 1 YEAR FOLLOW- YEAR FOLLOW- BASELINE TO 1 BASELINE YEAR TO 2 YEAR UP VISIT UP VISIT YEAR Mean 1.60 1.90 2.28 0.30 0.09 S.D. 0.75 0.73 0.70 0.88 0.74 N 8076605622 Table 8. Marginal bone level measurements

Due to the retrospective character of the present study, radiographs could not be provided for all implants. Prospective studies with radiographs of consecutive implants are needed to properly evaluate marginal bone levels. Nevertheless, the marginal bone measurements indicated an acceptable degree of bone loss during follow-up. The average marginal bone level at follow-up was still situated at the implant collar. For the Brånemark implant design, the marginal bone level usually ends up at the ﬁrst thread some 1.5 to 2 mm below the platform (Oh et al, 2002). Other implant designs have shown only minor bone loss which may be due to micro threads on the collar (Shin et al. 2006) Too few radiographs were available to evaluate the inﬂuence of countersink depth of the implant collar on marginal bone loss.

The clinical experiences with the present implant system from a surgical, prosthetic and laboratory technician point of view were positive. The implant design resulted in ﬁrm primary stability in all bone qualities. This is probably due to the geometry of the implant, which has a positive tolerance and is thereby slightly tapered. During insertion the bone is compressed Figure 1. Periapical radiographs taken after delivery of a two- in a lateral direction which increases the stability of unit bridge and after one year of loading. the implant. Internal connection is an advantage as it makes abutment connection easy. Impressions are taken on implant level and the technician chooses the type of abutment, which in case of screw-re- REFERENCES tained prosthetics is integrated with the framework. Albrektsson T, Wennerberg A.Oral implant surfaces: Part 2--review focusing on clinical knowledge of diﬀerent surfaces. Int J Prosthodont. CONCLUSIONS 2004 Sep-Oct;17(5):544-64.

Esposito M, Hirsch JM, Lekholm U, Thomsen P. Biological factors con- Within the limitations of the present retrospective tributing to failures of osseointegrated oral implants. (I). Success criteria study, it is concluded that the Neoss implant system and epidemiology. Eur J Oral Sci. 1998 Feb;106(1):527-51. results in good clinical outcomes in routine cases as Hallman M, Hedin M, Sennerby L, Lundgren S.A prospective 1-year evidenced by survival rate and marginal bone loss. clinical and radiographic study of implants placed after maxillary sinus GBR procedures involving short implants and soft ﬂoor augmentation with bovine hydroxyapatite and autogenous bone. bone seem to increase the risk of implant failure. J Oral Maxillofac Surg. 2002 Mar;60(3):277-84; Hammerle CH, Lang NP.Single stage surgery combining transmucosal implant placement with guided bone regeneration and bioresorbable materials. Clin Oral Implants Res. 2001 Feb;12(1):9-18.

34 Applied Osseointegration Research - Volume 6, 2008

Figure 2. Periapical radiographs of a single tooth restoration at impression taking and after one year of loading

Hurzeler MB, Kohal RJ, Naghshbandi J, Mota LF, Conradt J, Hut- macher D, Caﬀesse RG. Evaluation of a new bioresorbable barrier to facilitate guided bone regeneration around exposed implant threads. An experimental study in the monkey. Int J Oral Maxillofac Surg. 1998 Aug;27(4):315-20.

Lekholm U, Zarb GA. Patient selection. In: Brånemark P.-I, Zarb GA, Albrektsson T, eds. Tissue integrated prostheses. Osseointegration in clinical dentistry. Chicago: Quintessence, 1985:199–209.

Oh TJ, Yoon J, Misch CE, Wang HL. The causes of early implant bone loss: myth or science? J Periodontol. 2002 Mar;73(3):322-33.

Shin YK, Han CH, Heo SJ, Kim S, Chun HJ. Ra- diographic evaluation of marginal bone level around implants with diﬀerent neck designs after 1 year.

35 Applied Osseointegration Research - Volume 6, 2008

Insertion Torque Measurements During Placement of Neoss Implants

Luca Pagliani1, Lars Sennerby2, Peter Andersson3, Damiano Verrocchi3 , Neil Meredith4 1Private Practice, Milano and Legnano, Italy 2Dept Biomaterials, Inst Clinical Sciences, Sahlgrenska Academy, Gothenburg University, Sweden 3Private Practice, Fiera di Primiero and Feltre, Italy 4 Bristol Dental Hospital and University, Bristol, UK

This clinical study demonstrates that the Neoss implant design develops continuously increasing insertion torque (IT) during placement; as expected for a tapered implant design. This indicates that the total implant length laterally compresses the adjacent bone, providing ﬁrm primary stability of the implant. Moreover, the study demonstrates a correlation between insertion torque and resonance frequency analysis measurements.

INTRODUCTION According to the manufacturer, the Neoss implant has a positive tolerance, meaning that it is slightly coni- Primary stability is considered a key factor for the cal in the coronal direction, like a tapered implant. clinical success of dental implants. It is determined However, the insertion torque characteristics of that by the density of the bone at the site, the surgical implant design are not known at present. The objec- technique and the design of the implant (Sennerby tive of this clinical study was to evaluate the primary & Meredith 1998). Historically, increased failure stability of the Neoss implant using IT and RFA meas- rates have been reported in sites of low bone den- urements. The aim was also to look for correlations sity (Jaffin & Berman 1991, Friberg et al 1991). between IT and factors such as bone quality and RFA. Modified drilling protocols have been proposed with the final drill diameter reduced in an attempt MATERIALS AND METHODS to increase compression and thereby the stability of the implant during insertion (Friberg et al 1999). A total of 118 implants (Neoss ltd, Harrogate, UK) of different lengths and diameters (Table 1) placed Tapered implant designs have been introduced on the in both jaws (59 mandibular, 59 maxillary) of 38 pa- market in order to improve primary stability. Experi- tients were evaluated at placement surgery. Insertion mental and clinical studies with insertion torque (IT) torque in Ncm was measured at 20 rpm and 8 Hz to a measurements and/or resonance frequency analysis maximum of 50 Ncm using a drilling unit specially de- (RFA)have demonstrated higher primary stability for signed for implant surgery (Elcomed, W&H, Milano, tapered implants compared with parallel-walled im- Italy)(Figure 1). A torque/time curve was obtained, plants (O’Sullivan et al 2000, O´Sullivan et al 2004a, saved and extracted. The final drill diameter and the 2004b). Parallel-sided implants may show a high peak degree of countersinking were noted. After final seat- insertion torque which indicates a high degree of stabil- ing, the stability of each implant was measured with ity. However, this is mainly due to the clamping effect resonance frequency analysis in ISQ units (Mentor, when the implant head reaches the marginal bone, Osstell AB, Gothenburg, Sweden). Bone density and whilst the threaded part of the implant shows little quantity were assessed by the Lekholm & Zarb index. resistance during insertion. Tapered implants demon- strate continuously increasing insertion torque due to The torque/time curves were examined for mean inser- lateral compression of the bone from the whole im- tion torque over the total curve and for the apical (E1), plant length during insertion (O’Sullivan et al (2000)). mid (E2) and coronal thirds (E3). The E1 and E3 parts Then stresses would be distributed along the tapered always included 40 measurements (corresponding to 5 implant surface and not concentrated to a few spots. seconds). The registration time for the E2 part varied due to the different implant lengths accounted for. 36 Applied Osseointegration Research - Volume 6, 2008

2. Showing a typical torque/time curve for a 4 x 13 mm implant placed in the second premolar region in the maxilla. This implant showed an ISQ value of 76.

Figure 1. The Elcomed drilling unit used in the study. The handpiece was calibrated before each use (right).

tion between total mean IT and bone density as as- Spearman’s rho test was used to test for pos- sessed using the Lekholm and Zarb index (1985). This sible correlations. A statistically signifi- may reﬂect the subjective nature of the latter method cant correlation was considered if p<0.05. which is purely based on the surgeon’s perception of bone density during drilling of the implant site. RESULTS It is concluded that the Neoss implant design de- The torque/time curves displayed continuously increas- velops a continuously increasing insertion torque ing torque during insertion (Figure 2). Thus, the im- during placement as expected for a tapered implant plants behaved as expected for a tapered implant design design. This indicates that the total implant length as previously described by O’Sullivan et al (2000). The is involved in lateral compression, providing ﬁrm total mean insertion torque was 15.1 Ncm (SD 7.2) primary stability for the implant. Moreover, there is and for regions was 4.8 Ncm (SD 6.5) in the E1, 13.3 a correlation between IT and RFA measurements. Ncm (SD 6.5) during E2 and 26.9 Ncm (SD 11.9) in E3 (Figure 3). Except for the E1 region, these torques REFERENCES are higher than those previously reported by Friberg et al (1999a) in 523 self-tapping parallel-sided implants; Friberg B, Jemt T, Lekholm U.Early failures in 4,641 consecutively placed Brånemark dental implants: a study from stage 1 surgery to the used in both jaws of 105 patients. The data indicate connection of completed prostheses. Int J Oral Maxillofac Implants. higher primary stability for the present implant design 1991;6:142-6. as described by IT measurements. This accords with Friberg B, Sennerby L, Gröndahl K, Bergström C, Bäck T, Lekholm U. previous experimental research which showed higher On cutting torque measurements during implant placement: a 3-year stability for tapered implants than for parallel-sided clinical prospective study. Clin Implant Dent Relat Res. 1999a;1:75-83. ones, without jeopardizing the integration process (O’Sullivan et al 2000, O´Sullivan et al 2004a, 2004b).

A statistically signiﬁcant correlation between IT and RFA was demonstrated for the total implant lengths as well as for the E1-E3 regions individually (Table 2). The same correlation was reported by Friberg et al (1999b) in measurements of 47 parallel-sided implants placed in maxillary bone of nine patients. Since RFA measures stability as a function of stiﬀness, the results indicate that the insertion torque technique can be used to measure bone density and to predict primary 3. Graphic presentation of the total mean insertion torque and stability as measured with RFA. There was no correla- for E1-E3 regions 37 Applied Osseointegration Research - Volume 6, 2008

Friberg B, Sennerby L, Meredith N, Lekholm U. A comparison between cutting torque and resonance frequency measurements of maxillary implants. A 20-month clinical study. Int J Oral Maxillofac Surg. 1999b;28:297-303.

Jaﬃn RA, Berman CL. The excessive loss of Branemark ﬁxtures in type IV bone: a 5-year analysis. J Periodontol. 1991;62:2-4.

Lekholm U, Zarb GA. Patient selection. In: Brånemark P.-I, Zarb GA, Albrektsson T, eds. Tissue integrated prostheses. Osseointegration in clinical dentistry. Chicago: Quintessence, 1985:199–209.

O’Sullivan D, Sennerby L, Meredith N. Measurements comparing the initial stability of ﬁve designs of dental implants: a human cadaver study. Clin Implant Dent Relat Res. 2000;2(2):85-92.

O’Sullivan D, Sennerby L, Jagger D, Meredith N.A comparison of two methods of enhancing implant primary stability. Clin Implant Dent Relat Res. 2004a;6:48-57.

O’Sullivan D, Sennerby L, Meredith N. Inﬂuence of implant taper on the primary and secondary stability of osseointegrated titanium implants. Clin Oral Implants Res. 2004b;15:474-80.

Sennerby L, Meredith N. Resonance frequency analysis: measuring implant stability and osseointegration. Compend Contin Educ Dent. 1998;19:493-8.

38 Applied Osseointegration Research - Volume 6, 2008

Stress Evaluation of Dental Implant Wall Thickness using Numerical Techniques

Rudi C. van Staden1, Hong Guan1, Yew-Chaye Loo1, Newell W. Johnson2, Neil Meredith3,

1Griffith School of Engineering, Griffith University Gold Coast Campus, Australia; 2School of Dentistry and Oral Health, Griffith University Gold Coast Campus, Australia; 3Neoss Ltd, Harrogate, United Kingdom

Using the Finite Element Method, four implant diameters were evaluated for their effect on the stress distribution at the implant wall. A two-dimensional model of the implant and mandibular bone used triangular and quadrilateral plane strain elements to compute the von Mises stress in the bone with varied masticatory forces and abutment screw preloads. The masticatory force is found to be more influential than abutment screw preload, and implant wall thickness significantly influences the stress magnitude within the implant.

INTRODUCTION

Development of an ideal substitute for missing teeth The distribution and magnitude of stresses within the has been a major aim of dental practitioners for mil- implant are influenced by the implant dimensions, lennia (Irish 2004). Dental implants are biocompat- as documented by (Huang et al. 2005, Capodiferro ible threaded titanium ‘fixtures’ surgically inserted et al. 2006, Winklere et al. 2003, Naert et al. 1992, into the mandible or maxilla to replace missing teeth. Tolman and Laney 1992). Catastrophic mechanical The establishment of a good biomechanical link failure of the implant may occur by implant fatigue between implant and jawbone is called osseointegra- (Huang et al. 2005, Capodiferro et al. 2006), implant tion (Branemark et al. 1969, 1977). The success of fractures, veneering resin/ceramic fractures or other osseointegration depends on many factors including: mechanical retention failures (Winklere et al. 2003, medical status of the patient, smoking habits, bone Naert et al. 1992, Tolman and Laney 1992). From quality, bone grafting, disturbance, sensation or its an engineering perspective, an important criterion in disruption, haematoma, haemorrhage, tooth necrosis, designing an implant is to have a geometry that can irradiation therapy, parafunctions, operator experience, minimize mechanical failure caused by an extensive degree of surgical trauma, bacterial contamination, range of loading. As part of the implantation process, lack of preoperative antibiotics, immediate loading, the torque is applied to the abutment screw causing nonsubmerged procedure and implant surface char- an equivalent preload or clamping force between the acteristics (Esposito et al. 1998). Excessive surgical abutment and implant. This is to ensure that the trauma and impaired healing ability, premature loading various implant components are perfectly attached to and infection are likely to be the most common causes each other. However, to date no published research for early implant losses, whereas progressive chronic appears to have investigated the influence of mastica- marginal infection (peri-implantitis) and overload in tory forces and abutment screw preloading on stresses conjunction with host characteristics are the major in implants of various diameters. Therefore, the aim reasons for delayed failures (Esposito et al. 1998). of this study is to evaluate the stress within an imme- For both early and late implant failures, loading is diately loaded implant under a range of masticatory considered an important factor (Geng et al. 2001). forces, abutment preloads and implant diameters,.

39 Applied Osseointegration Research - Volume 6, 2008

Masticatory force, FM = 200, 500, 1000N VV1 o y F 45 Crown M F P Abutment x VV1-2 VV2 Abutment screw torque, T = 110, 320, 550Nmm (Equivalent abutment screw preload, VV3 FP = 201.93, 587.44, 1009.67N) VV2-3 Implant (Diameter, D = 3.5, 4.0, 4.5, 5.5) (Length, L = 11mm) FP VV3-4 Cancellous bone (Young’s modulus = 1GPa)

Cortical bone (Young’s modulus = 13.7GPa) (Thickness = 1.2mm) Fixed constraints VV4

Figure 1. Finite element model of implant, components, implant/bone interface and bone

MATERIALS AND METHODS The effect on stress in the implant wall under different mastication forces (FM) and abutment preload (FP) Modelling and simulation were performed using the was evaluated. For all the possible parametric combi- Strand7 (2004) Finite Element Analysis (FEA) System. nations, the von Mises stress along the line VV in the First the implant and bone geometry were defined, implant wall was investigated and is believed to play then material properties for the implant and various a crucial role in the probability of implant fracture. bone components were assigned in terms of Young’s modulus, Poisson’s ratio and density. The loading and As indicated in Figure 1 the von Mises stresses along restraint conditions were applied and the effect on the lines VV1-2, VV2-3 and VV3-4 are reported for the stress profile within the implant was evaluated. all possible combinations of loading and diameters. The relative locations of these lines are also detailed Modelling in the figure. Each line is identified by its start and A two-dimensional (2D) representation of the implant end points, so, for example, line VV1-2 begins at and mandibular bone was analysed because this was VV1 and ends at VV2. These locations were sug- considered to be equally accurate and more efficient in gested by clinicians to be prone to micro fractures. computation time, as three-dimensional (3D) modelling. Data were acquired for the bone dimensions by The range of implant diameters (3.5, 4.0, 4.5 CT scanning. Two different types of bone, cancellous and 5.5mm) is shown in Figure 2. Note that and cortical, were distinguished and the boundaries the cortical bone is constrained distally were identified in order to assign different material to represent normal function of the mandible. properties within the finite element model. Figure 1 shows an implant and mandible section with the Figure 2 . Finite element model showing different implant loading and restraint conditions. Also shown in the diameters figure are the parameters investigated in this study.

The implant is based on that used by Neoss (2006), it is conical with 2 degrees of taper and a helical thread. For the ﬁnite element model with D = 4.5mm, L = 11mm, Tcor = 1.2mm, 3314 plate elements and 3665 nodal points were used for the implant, 3804 elements and 4079 nodes for cancellous bone, and 3.5mm 4.0mm 4.5mm 5.5mm 1216 elements and 1453 nodes for cortical bone. 40 Applied Osseointegration Research - Volume 6, 2008

x Mandible 2D Slice

FM z y

o 45 x FM

z -x 2D Slice

Figure 3. Location of 2D slice in a mandible a) Top view b) Isometric view

Plane strain elements Loading conditions The model represents a cross-sectional slice from the Loading conditions included the masticatory force, mandible (Figure 3). The “arc length” of the mandible FM, applied to the occlusal surface of the crown is comparable to the width and depth of the slice. set at 200, 500 and 1000N, as shown in Figure 1, When the slice is subjected to in-plane (x-y) masti- and applied at 45o inclination in the x y plane (re- catory forces (FM), it is restrained from deforming fer to Figure 1). A preload, FP, was applied to the out-of-plane (in the z-axis) and it was assumed that abutment screw of magnitude 201.93, 587.44 or all strains are conﬁned in the z-axis. To accurately 1009.67 N through the use of temperature sensi- represent the mechanical behaviour of the bone and tive elements. The technique for applying the implant, 3-node triangular (Tri3) and 4-node quadri- masticatory forces to the crown, and the preload lateral (Quad4) plane strain elements were therefore applied to the abutment screw, are discussed below. used for the construction of the ﬁnite element models. Note that for plane strain elements each node has a Masticatory force, FM complete set of spatial degrees of freedom includ- During normal function the crown is subjected to ing u and v. The constraints meant that nodes could oblique loads applied to the occlusal surface of the only translate in the x- (u) and y- (v) directions. crown. These loads are a result of normal masticatory function. The theoretical study by Choi et al. Material properties (2005) suggests that this loading condition can be The material properties adopted were specified considered to represent all applied loads. The implant in terms of Young’s modulus, Poisson’s ratio and was restrained in the x, y and z directions within density for the implant and all associated com- the jawbone, assuming complete osseointegration ponents (Table 1). All materials were assumed to at the bone and implant interface. Figure 1 shows exhibit linear, homogeneous elastic behaviour. the positions of the applied loading and restraints.

Table 1. Material properties

Component Description Young’s Modulus, E (GPa) Poissons ratio, v Density, ρ (g/cm3) Implant, abutment, washer Titanium (grade 4) 105.00 0.37 4.51 Abutment screw Gold (precision alloy) 93.00 0.30 16.30 Crown Zirconia (Y-TZP) 172.00 0.33 6.05 Cancellous bone 1.00 0.30 0.74 Cortical bone Cortical thickness = 1.2mm 13.70 0.30 2.19 41 Applied Osseointegration Research - Volume 6, 2008

Implant Abutment Abutment screw Manual screwdriver

y Torque applied to top of abutment screw z x Fig. 4. Implant system The relationship between the torque applied to the abutment screw and the preload achieved was expressed by Dekker (1995) as: Preload, FP ¥ i M r ´ The torque applied to the abutment screw causes T F ¦ t t M r µ the preload or clamping forces between the im- in P ¦ 2 cos n n µ § P B ¶ …..(1) plant and abutment. The procedure for calculating FP and applying a temperature sensitive element, using the conditions listed in Table 2; functioning throughout the abutment screw devel- oping the preload (or torque), is described below. Note that the effective radius (rt and rn) is the Note that for the purpose of this article only the distance between the geometric centre of the part Neoss system calculations for FP and tempera- (implant, abutment or abutment screw) and the ture sensitive elements are shown as an example. circle of points through which the resultant contact forces between mating parts (implant, abut- A dental implant system typically consists of a ment or abutment screw) pass (refer to Figure 4). crown, abutment and abutment screw. The abutment screw is screwed with a manual screwdriver Calculations of the preload are shown in equation (Figure 4) into the internal thread of the implant. 2 below, using information derived in equation 1. Finally, the crown is placed on to the abutment using cement at the crown and abutment interface. ¥ 0.4 (0.26 s 0.8725) ´ 320 FP ¦ (0.20 s1.1125)µ The nature of the forces clamping implant com- § 2P cos(28 .72 ) ¶ ponents together, and how they are generated and ...... ………………..(2) sustained, are not comprehensively covered in the literature. Preload was considered in ﬁnite element Rearranging for FP; modelling by Haack et al. 1995, Lang et al. 2003 and 320 Byrne et al. 2006. These studies were either based FP ¥ 0.4 (0.26 s 0.8725) ´ on complicated 3D modelling or did not specify ¦ (0.20 s1.1125)µ the techniques used for replicating FP. For the pur- ¦ 2 cos(28 .72 ) µ § P ¶ pose of this study the calculation used to determine the preload is based on ﬁndings by Dekker (1995). FP = 587.44N

Table 2. Conditions applied in equation 1 Abbreviation Description Magnitude Reference

Tin = torque applied to the abutment screw (Nmm) = 320 Neoss (2006)

FP = preload created in the abutment screw (N) = Unknown factor i = the pitch of the abutment screw threads (mm) = 0.40 Neoss (2006) = the coefficient of friction between abutment screw thread Lang et al. miu surfaces and internal implant screw thread surfaces = 0.26 t (2003) (dimensionless) r = the effective contact radius between the inner implant = (r + r )/2 = (0.99 + 0.755)/2 t 3 4 Neoss (2006) thread and the abutment screw threads. (mm) = 1.745 / 2 = 0.87 = the half-angle of the threads (degree) (Neoss (2006 28.72ْ = = the coefficient of friction between the face of the abutment Lang et al. miu = 0.20 n screw and the upper surface of the abutment (dimensionless) (2003) = the effective radius of contact between the abutment and = (r + r )/2 = (1.275 + 0.95)/2 r 1 2 Neoss (2006) n implant surface (mm) = 2.225 / 2 = 1.11 42 Applied Osseointegration Research - Volume 6, 2008

Figure 5. Effective radius of abutment and abutment screw

a) Abutment

The preload clamping the abutment to the implant y is transferred through two interfaces. The ﬁrst interface (SA1) is between the abutment and abutment screw and the second (SA2), between the abutment screw threads and the inner threads of the implant x

(Figure 5). The calculated preload, PF , is assumed to act equally, as a pressure, q, across the ﬁrst and second interfaces. Due to equilibrium, only the z pressure q, acting on SA1 is considered in this study.

2 2 SA1 = (π × r1 ) - (π × r2 ) = (π × 1.2752) - (π × 0.952) 2 Abutment SA1 = 2.27mm SA The pressure acting on SA1 , when FP 1 = 587.77N, was calculated as follows: x F 587.4 q P SA 1 2.2748984 .....…….……(3) z r q = 258.22 N/mm2 1 r2 The clamping pressure, q, is a result of the applied torque and is a means of replicating the 3D torque in a 2D man- b) Abutment screw ner. For the present study, q, is calculated as above for the applied torques of 110, 320 and 550Nmm (Table 3).

In the analysis a negative temperature (-10 Kelvin, CL K) is applied to all the nodal points within the abutment screw, causing each element to shrink. A trial and error process is applied to determine the tem- SA2 y perature coeﬃcient, C, that can yield an equivalent q. The corresponding C is also presented in Table 3. x Abutment screw

Table 3. Abutment screw torque (T), preload FP, and surface pressure q

2 -12 -12 -12 -12 T (Nmm) FP (N) q (N/mm ) C3.5mm (×10 ) C4.0mm (×10 ) C4.5mm (×10 ) C5.5mm (×10 )

110.00 201.93 88.76 -2.62 -2.54 -3.52 -4.14

320.00 587.44 258.22 -7.61 -7.39 -10.20 -12.71

550.00 1009.67 443.83 -13.08 -12.67 -17.64 -20.78

43 Applied Osseointegration Research - Volume 6, 2008

RESULTS DISCUSSION

The distribution of von Mises stresses in the implant FEA has been used extensively to predict the bio- is discussed for all combinations of masticatory and mechanical and mechanical performance of implant preload forces. Each parameter is discussed in a sepa- designs as well as the eﬀect of clinical factors on rate section for all four implant diameters. The von the success of implantation (DeTolla et al. 2000,

Mises stresses are reported between locations VV1-2 Geng et al. 2001). The principal diﬃculty in simu-

(0 - 1.51mm in length), VV2-3 (1.51 - 2.24mm) lating the mechanical behaviour of implants is the and NN3-4 (2.24 - 3.77mm), as shown in Figure 1. modelling of the living human bone tissue and its response to applied mechanical forces (van Staden

Masticatory Force, FM et al. 2006). A few studies have considered the inﬂu- The distributions of von Mises stresses along ence of such factors as the torque (Lang et al.2003) the lines VV1-2, VV2-3 and VV3-4 for all values with which the abutment is connected, and the of FM are shown in Figure 6. Note that the pre- effect of masticatory forces on the probability of load, FP, is set at its medium value, i.e. 587.44N. implant failure or loosening (Byrne et al. 2006).

In general, when the applied masticatory force, FM, is This paper considers various combinations of loading increased, the von Mises stresses also increase propor- parameters and their inﬂuence on the stress produced tionally, because the system being analysed is linear within implants of diameters 3.5, 4.0, 4.5 and 5.5mm. elastic. As expected the 3.5mm implant shows higher As expected, increased masticatory forces lead to great- stresses than all other diameters (refer to Figures 6 a er stresses within the implant. The preload applied to and b). The 3.5mm also indicates stress peaks along the abutment has less inﬂuence on the stresses than the the lines VV1-2 and VV2-3 where all other parameters masticatory forces. The 3.5mm implant shows higher only have elevated stress peaks along the line VV1-2 stresses than all other diameters and indicates stress

(Figures 6 a, c, e and g). This is because the implant peaks along the lines VV1-2 and VV2-3 where all other wall thickness for the 3.5mm implant is significantly parameters only have elevated stress peaks along the reduced in the region corresponding to VV2-3, hence line VV1-2. The 4.0 and 4.5mm diameter implants have causing stress concentration. The 4.0 and 4.5mm similar stress distribution characteristics and the 5.5mm diameter implants have similar stress distribution implant displays greatly reduced stresses at all loca- characteristics but the stresses are lower in magnitude tions, with peak stresses occurring close to point VV1. at VV1-2, VV2-3 and VV3-4 than with the 3.5mm implant because of the greater wall thickness (Figures 6 CONCLUSION d and f). The 5.5mm implant displays greatly reduced stresses at all locations (Figures 6 g and h), with peak Overall, it was found that the masticatory force is stresses occurring close to point VV1 (see Figure 1). more influential on implant stresses than the abutment screw preload. As expected the implant wall Preload Force, FP thickness significantly influences the stress magnitude within the implant. Note also that when the wall

To investigate the effect of different preload FP, FM is thickness is decreased (especially for the 3.5mm) kept as a constant and its medium value, i.e. 500N stress concentration occurs at the internal and external is considered herein. The distributions of von Mises threads as well as at sharp corners of the implant wall. stresses along the lines VV1-2, VV2-3 and VV3-4 for all values of FP are shown in Figure 7. Similar stress Characteristically the stress showed an increase at the distribution characteristics were found when varying top of the implant thread and the top of the implant F as with F . Note that when F increases, the von P M P (line VV1-2). It should be noted that this research was Mises stresses also increase. However, the increase is a pilot study aimed at offering an initial understanding not proportional to the increase of FP. . This is because of the complicated stress distribution characteristics

FP, as an internal force, is a function of the abutment due to the various parameters. Other parameters which screw and implant diameters. This suggests that fail- may be evaluated for their inﬂuence on implant stress ure of the crown is more likely to be caused by FM. proﬁles include the implant taper, pitch and design of 44 Applied Osseointegration Research - Volume 6, 2008

VV1-2

VV2-3

VV3-4

FM = 200N, FM = 500N, FM = 1000N, a) Stress profile b) Stress contour

VV1-2

VV2-3

VV3-4

FM = 200N, FM = 500N, FM = 1000N, c) Stress profile d) Stress contour

VV Figure 6. Stress characteristics 1-2

when varying FM.

VV2-3

VV3-4

FM = 200N, FM = 500N, FM = 1000N, e) Stress profile f) Stress contour

VV1-2

VV2-3

VV3-4

FM = 200N, FM = 500N, FM = 1000N,

g) Stress profile h) Stress contour

Figure 6. Stress characteristics when varying FM. 45 Applied Osseointegration Research - Volume 6, 2008

VV1-2

VV2-3

VV3-4

FP = 201.93N, FP = 587.44N, FP = 1009.67N, a) Stress profile b) Stress contour

VV1-2

VV2-3

VV3-4

FP = 201.93N, FP = 587.44N, FP = 1009.67N, c) Stress profile d) Stress contour

VV1-2

VV2-3

VV3-4

FP = 201.93N, FP = 587.44N, FP = 1009.67N, e) Stress profile f) Stress contour

VV1-2

VV2-3

VV3-4

FP = 201.93N, FP = 587.44N, FP = 1009.67N, g) Stress profile h) Stress contour

Figure 7. Stress characteristics when varying FP 46 Applied Osseointegration Research - Volume 6, 2008 implant thread, implant neck offset, different stages of 859. bone remodelling and implant orientation within the Irish JD. A 5,500 year old artificial human tooth from Egypt: a his- bone. It is important that clinicians understand the torical note. International Journal of Oral & Maxillofacial Implants. methodology, applications, and limitations of FEA in 2004;19(5):645-647. implant dentistry, and become more confident in inter- Lang LA, Kang B, Wang RF, Lang BR. Finite element analysis to preting results from FEA studies to clinical situations. determine implant preload. The Journal of Prosthetic Dentistry. 2003;90(6):539-546. ACKNOWLEDGEMENTS Naert I, Quirynen M, van Steenberghe D, Darius P. A study of 589 consecutive implants supporting complete fixture prostheses. Part II: prosthetic aspects. Journal of Prosthetic Dentistry. 1992;68:949-956. This work was made possible by the collaborative support from Griffith’s School of Engineering and Neoss Limited (2006), Neoss Implant System Surgical Guidelines, UK. School of Dentistry and Oral Health. A special thank Strand7 Pty Ltd (2004) Strand7 Theoretical Manual, Sydney, Australia. you goes to Messer John Divitini and Fredrik Engman from Neoss Limited for their continual contribution. Tolman DE, Laney WR. Tissue integrated prosthesis complications. International Journal of Oral & Maxillofacial Implants 1992;7:477-484.

van Staden RC, Guan H, Loo YC. Application of the ﬁnite element REFERENCES method in dental implant research. Computer Methods in Biomechani- cal and Biomedical Engineering. 2006;9(4):257-270. Branemark PI, Adell R, Breine U, Hansson BO, Lindstrom J, Ohls- son A. Intra-osseous anchorage of dental prostheses. I. Experimental Winkler S, Ring K, Ring JD, Boberick KG. Implant screw mechan- studies. Scandinavian Journal of Plastic and Reconstructive Surgery. ics and the settling eﬀect: overview. Journal of Oral Implantology. 1969;3(2):81-100. 2003;29(5):242-245.

Branemark PI, Hansson BO, Adell R, Breine U, Lindstrom J, Hallen O, Ohman A. Osseointegrated implants in the treatment of the edentulous jaw. Experience from a 10-year period. Scandinavian Journal of Plastic and Reconstructive Surgery. 1977;16:1-132.

Byrne D, Jacobs S, O’Connell B, Houston F, Claﬀey N. Preloads generated with repeated tightening in three types of screws used in dental implant assemblies. The Journal of Prosthetic Dentistry. 2006;15(3):164- 171.

Capodiferro S, Favia G, Scivetti M, De Frenza G, Grassi R. Clinical management and microscopic characterisation of fatique-induced failure of a dental implant. Case report. Head & Face Medicine. 2006;22(2):18.

Choi AH, Ben-Nissan B, Conway RC. Three-dimensional modelling and ﬁnite element analysis of the human mandible during clenching. Austral- ian Dental Journal. 2005;50(1):42-48.

Dekker M. An introduction to the design and behavior of bolted joints / John H. Bickford. 1995;3rd ed.

DeTolla DH, Andreana S, Patra A, Buhite R, Comella B. Role of the ﬁnite element model in dental implants. Journal of Oral Implantology. 2000;26(2):77-81.

Esposito M, Hirsch JM, Lekholm U, Thomsen P. Biological factors contributing to failures of osseointegrated oral implants. (II). Etiopatho- genesis. European Journal of Oral Sciences. 1998;106(3):721-764.

Geng JP, Tan KB, Liu GR. Application of ﬁnite element analysis in implant dentistry: a review of the literature. Journal of Prosthetic Dentistry. 2001;85:585-598.

Haack JE, Sakaguchi RL, Sun T, Coﬀey JP. Elongation and preload stress in dental implant abutment screws. International Journal of Oral & Maxillofacial Implants. 1995;10(5):529-536.

Huang HM, Tsai CM, Chang CC, Lin CT, Lee SY. Evaluation of loading conditions on fatigue-failed implants by fracture surface analysis. International Journal of Oral & Maxillofacial Implants. 2005;20(6):854- 47 Applied Osseointegration Research - Volume 6, 2008

Comparative Analysis of Two Implant-Crown Connection Systems - A Finite Element Study

Rudi C. van Staden1, Hong Guan1, Yew-Chaye Loo1, Newell W. Johnson2, Neil Meredith3,

The internal and external-hex connections of the Neoss and 3i implant systems, were compared in a three-dimensional Finite Element Analysis. Chewing forces of 200, 500 and 1000N and abutment screw preloads of 110, 320 and 550Nmm were studied. The connection type strongly inﬂuences the stress proﬁle within the crown, with the external-hex connection exhibiting greater stresses than the internal-hex.

INTRODUCTION Studies by Maeda et al. (2006), Khraisat et al. (2002) Dental implants are a well accepted treatment for and Merz et al. (2000) have all considered the stress partially or totally edentulous subjects. Innovations within the abutment screw but disregarded the stress through research have led to advancements in sur- within the crown. To date no published research gical and restorative techniques, improved surface appears to have investigated the stress profile in features and restorative components. Dental implants the crown due to an internal-hex or external-hex typically use either internal-hex or external-hex connection. Ultimately, the outcome of this study will connections with the crown (Figure 1 a). Although help dental practitioners to identify locations within both connections are extensively used clinically, the implant system susceptible to stress concentrations. distinctly different stress distributions are produced within the crown. Clinicians have reported implant MATERIALS AND METHODS components linked to mechanical failure of crown and implant (Maeda et al. 2006, Merz et al. 2000, The modelling and simulation herein are performed Khraisat et al. 2002). Two major factors may be using the Strand7 FEA System (2004). The first step of implicated in crown and implant failure. These are; the modelling is to define the geometry of the implant system. Then the material behaviour of the model is - over tightening of the abutment screw lead- specified in terms of Young’s modulus, Poisson’s ratio ing to failure of the crown for internal-hex and and density for all components. The appropriate load- external-hex connection type implant systems. ing and restraint conditions are applied and the indi- - excessive masticatory loads transferred from the oc- vidual parameters and their contribution to the stress clusal plane of the crown to a stress concentration at profile within the crown and implant is evaluated. the interface between the abutment and implant body. Modelling Theoretical techniques such as the Finite Element Geometry for the implant systems were obtained Method (FEM) can be used to evaluate mechanical from the manufacturers (Figure 1a). Section AA factors that could affect implant performance is set at a location where maximum compres- and success (Capodiferro et al. 2006, Gehrke sive stresses occur within the crown, positioned et al. 2006, Huang et al. 2005, Khraisat et al. at 30o from the x-axis towards the negative z-axis. 2005). This study was undertaken using Finite Element Analysis (FEA) to aid understanding of The parameters investigated are shown in Figure 1b. the stresses in both internal-hex and external-hex The implant is conical with 2 degrees of taper, a heli- implant systems under different loading conditions. cal thread, outside diameter of 4.5mm and length of 48 Applied Osseointegration Research - Volume 6, 2008

Neoss Internal connection External connection 3i

Crown

Abutment

Abutment screw

Implant Section AA Section AA

Fig. 1. Finite element model of external and internal-hex system a) Implant system

b) Loading and restraint conditions (with detailed parameters) c) Locations for measuring stress profile and contour

y-axis Masticatory force, Section AA FM = 200, 500, 1000N II x-axis 2-3 y NN1 II1 o F 90 M x NN1-2 NN2 II1-2 o 45 NN3 II2 z II3 NN3-4 II II4 II 3-4 NN4 5-6 Abutment screw torque, T = 110, 320, II5 550Nmm (Equivalent abutment screw II6 II6-7 II7 preload, FP = 201.93, 587.44, 1009.67N)

Fixed restraint, Rz, Dx and Dy NN II Fixed restraint, Rxyz 2-3 4-5 Internal connection External connection and Dxyz

11mm. Half the implant is modelled and symmetrical constraints are applied along the plane of symmetry The main focus of this study is to examine the as indicated (Figure 1b). For the Neoss (2006) and 3i stress characteristics within the crown and next to (2006) ﬁnite element models, the total numbers of the crown-abutment interface. Therefore an as- elements are respectively 13464 and 30420 for the sumption is made to restrain the outer edge of the implant, 3564 and 9108 for the abutment, 17424 and implant (Figure 1b) when the mandibular bone 25956 for the abutment screw, and 38484 and 47052 is not included in the ﬁnite element model. Note for the crown. The total number of nodal points for the that these loading and restraint conditions are the entire Neoss model are 122688 and 82547 for the 3i. same for both internal and external-hex systems.

49 Applied Osseointegration Research - Volume 6, 2008

Stress reporting Kelvin, K) was applied to all the nodal points within

The von Mises stresses along the lines NN (NN1-2, the abutment screw, causing each element to shrink.

NN2-3 and NN3-4) and II (II1-2, II2-3, II3-4, II4-5, II5-6 A trial and error process was applied to determine and II6-7) for both systems are reported for all possible the temperature coefficient, C, for the Neoss and combinations of loading (Figure 1 c). The relative 3i systems (i.e. CNeoss and C3i) that can yield an locations of these lines are also detailed in the figure, equivalent q. It was found that when FP = 201.93, -4 which are identified by their start and end points. 587.44 and 1009.67N then CNeoss = -3.51×10 , -4 -4 - So, for example, the line II1-2 begins at II1 and ends -9.28×10 and -15.60×10 /K, and C3i = -0.98×10 4 -4 -4 at II2. The von Mises stresses along the lines NN and , -1.80×10 and -2.68×10 /K, respectively. II, in the crown, are believed to play a crucial role in the probability of crown fracture. On Section AA RESULTS lines NN and II were chosen because the greatest stresses due to the masticatory loading (compres- Zirconia, typically used as a dielectric material, has sive is prominent over tensile) occur on this plane. proven adequate for application in dentistry. With its white appearance and high Young’s modulus it is ideal Material properties for use in sub frames for dental restorations such as The material properties in the model are specified crowns and bridges, which can then be veneered with in terms of Young’s modulus, Poisson’s ratio and conventional feldspathic porcelain. Zirconia has a frac- density for the implant and all associated com- ture strength greater than titanium; therefore it may ponents (Table 1). All materials are assumed to be considered as a high strength material. However exhibit linear, elastic and homogeneous behaviour. with masticatory and preload forces the compressive strength of 2.1 GPa (Curtis et al. (2005)) can easily Loading conditions be exceeded; especially for implant systems with exter-

Masticatory force, FM, was applied to the occlusal nal-hex connections, as conﬁrmed during this study. surface of the crown at 100, 250 or 500N, inclined at o 45 to the x and y-axes (Figure 1 b). The preload, FP, of The distribution of von Mises stresses in the crown is 100.97, 293.72 or 504.84N is applied to the abutment discussed for all parametric combinations of mastica- screw through the use of temperature sensitive ele- tory and preload forces. Each parameter is discussed ments (Figure 1 b). Note that FM and FP are set to half in a separate section. For the Neoss system, the von of the total magnitude because only half of the implant Mises stresses are reported between locations NN1- system is modelled. Therefore the total FM modelled is 2 (0-1.76mm in length), NN2-3 (1.76-1.87mm)

200, 500, 1000N and FP is 201.93, 587.44, 1009.67N. and NN3-4 (1.87-3.96mm). For the 3i system the The manner of modelling the masticatory forces and von Mises stresses are reported between locations the preload applied to the abutment screw was de- II1-2 (0-2.38mm), II2-3 (2.38-2.78mm), II3-4 (2.78- scribed by van Staden et al. (2008). For the purposes 3.67mm), II4-5 (3.67-4.06mm), II5-6 (4.06-4.65mm) of this study both the abutment screw preload, FP, and II6-7 (4.65-5.27mm), as shown in Figure 1c. and the surface area between abutment and abutment screw, SA , are halved when compared to those 1 Masticatory Force, FM used by van Staden et al. (2008) due to the modelling assumption (half model). Calculations for the abut- The distributions of von Mises stresses along the lines NN ment screw surface pressure, q, confer identical and II for all values of FM are shown in Figure 2. Note that results to those found by van Staden et al. (2008). the preload, Fp, is set at its medium value, i.e. 587.44N.

For the present study a negative temperature (-10 In general, when the applied masticatory force, FM, is increased, the von Mises stresses also increase propor- Table 1. Material properties

Young’s Modulus, E Poissons Density, ρ Component Description (GPa) ratio, v (g/cm3) Implant, abutment, washer Titanium (grade 4) 105.00 0.37 4.51 Abutment screw Gold (precision alloy) 93.00 0.30 16.30 50 Applied Osseointegration Research - Volume 6, 2008

FM = 200N FM = 1000N Crown

NN1

NN1-2 NN2 NN3

NN3-4

NN4 NN2-3 a) Stress profile b) Stress contour

FM = 200N FM = 1000N Crown

II2-3

II1

II1-2

II2

II3 II II 3-4 II5-6 4 II5 II6 II6-7 II7 II4-5 c) Stress profile d) Stress contour

Figure2. Stress characteristics when varying FM

tionally, because the system being analysed is linear higher stresses in the 3i system when FM is increased. elastic. When FM increases the stress along the line NN increases showing two peaks along the line NN3-4 (refer Preload Force, F to Figure 2a). The larger of these two peaks occurs at P a distance of ±3.8mm in length from NN1. This stress To investigate the effect of different preload F , peak (as can be identified in Figure 2 b) is caused by a P FM is kept as a constant and its medium value, sharp corner and sudden change in section at this point. i.e. 500N is considered herein. The distributions of von Mises stresses along the lines NN and Elevated stress concentrations are identified at the be- II for all values of FP are shown in Figure 3. ginning of the line II3-4 (Figures 2 c and d). This stress peak, as can be identified in Figure 2 c, is caused by a As found in Section 3.1 for FM, when FP increases the sharp corner at this point. For the 3i system the volume stresses calculated along the line NN increase, showing of the crown exceeds that of the Neoss system, thereby two peaks along the line NN (refer to Figures 3 a suggesting that the 3i crown may show greater resis- 3-4 and b). Also, as found for FM, elevated stress peaks are tance to the applied masticatory forces. However, even identified at the beginning of the line II (Figures 3 though the Neoss crown has a thinner wall along the 3-4 c and d). Overall, all values of FM cause greater stresses line NN3-4, reduced stresses are still evident due to the along lines NN and II, than do varying values of F . abutment’s high Young’s modulus. Overall, the design P differences between the Neoss and 3i systems result in 51 Applied Osseointegration Research - Volume 6, 2008

FP = 201.93N FP = 1009.67N Crown

NN1

NN1-2 NN2 NN3

NN3-4

NN4 NN2-3 a) Stress profile b) Stress contour

FP = 201.93N FP = 1009.67N Crown

II2-3

II1

II1-2

II2

II3 II II 3-4 II5-6 4 II5 II6 II6-7 II7 II4-5 c) Stress profile d) Stress contour

Figure3. Stress characteristics when varying FP

DISCUSSION loading parameters of FM and FP. As shown in Table 2, two stress peaks were revealed along the lines NN and II at locations 3.76 and 2.89mm from the top. The stress FEA has been used extensively to predict the biome- values shown were calculated with the other parameter chanical performance of the jawbone surrounding (i.e. F or F ) set to its average. The mastication force a dental implant (DeTolla et al. 2000, Geng et al. M P F is applied on the occlusal surface of the crown, 2001). Previous research considered the inﬂuence of M evenly distributed along 378 nodal locations (Figure 1 the implant dimensions and the bone-implant bond b), and orientated at 45o in the x-y plane. This induces on the stress in the surrounding bone. However, compressive stresses in the right hand side of the crown to date no research has been conducted to evaluate and tensile in the left. Varying F from 200 to 1000N the stress produced by diﬀerent implant to crown M for the internal-hex and external-hex systems results connections (ie. internal-hex and external-hex). in a change in von Mises stress of 545.64 (818.47- 272.82MPa) and 698.09MPa (1047.14-349.05MPa) The analysis completed in this paper uses the FEM to respectively. The geometrical design of the external-hex replicate internal-hex and external-hex connections for system tends to induce stress concentrations, located

Table 2. von Mises stress (MPa) in the crown (location of stress reporting in brackets)

Parameter ------FM (N)------FP (N)------

Line 200 500 1000 201.93 587.44 1009.67 NN (3.76mm) 272.82 545.64 818.47 231.55 545.64 891.83 II (2.89mm) 349.05 698.09 1047.14 466.21 698.09 951.67 52 Applied Osseointegration Research - Volume 6, 2008

2.89mm from the apex in this study. For this system, a REFERENCES stress concentration at this point is also induced by F , P Capodiferro S, Favia G, Scivetti M, De Frenza G, Grassi R. Clini- increasing the compressive stresses on the right hand cal management and microscopic characterisation of fatique-induced failure of a dental implant. Case report. Head and Face Medicine. side of the crown. Increasing FP from its minimum to maximum values, for the external-hex system, increases 2006;22(2):18. the stress by 485.46MPa (951.67-466.21MPa). Curtis AR, Wright AJ, Fleming GJ. The influence of simulated masticatory loading regimes on the bi-axial flexure strength and reliability of a The internal-hex system has reduced stress Y-TZP dental ceramic. Journal of Dentistry. 2006;34(5):317-325. concentrations, demonstrating that this design is DeTolla DH, Andreana S, Patra A, Buhite R, Comella B. Role of the less susceptible to stress concentrations within the finite element model in dental implants. Journal of Oral Implantology. crown. However, because of the transfer of the preload 2000;26(2):77-81. through the abutment screw to abutment contact, Gehrke P, Dhom G, Brunner J, Wolf D, Degidi M, Piattelli A. Zir- changing F is more influential on this hex system conium implant abutments: fracture strength and influence of cyclic P loading on retaining-screw loosening. Quintessence International. than FM. Overall FM is more influential on the stress 2006;37(1):19-26. within the crown for the external-hex system and Geng JP, Tan KB, Liu GR. Application of finite element analysis in im- F is more influential on the internal-hex system. plant dentistry: a review of the literature. Journal of Prosthetic Dentistry. P 2001;85(6):585-598. CONCLUSION http://www.3i-online.com.htm (accessed 12th July 2006). Huang HM, Tsai CM, Chang CC, Lin CT, Lee SY. Evaluation of load- This research is a pilot study aimed at offering an initial ing conditions on fatigue-failed implants by fracture surface analysis. International Journal of Oral & Maxillofacial Implants. 2005;20(6):854- understanding of the stress distribution characteristics 859. in the crown under different loading conditions. Realistic geometries, material properties, loading and Khraisat A, Stegaroiu R, Nomura S, Miyakawa O. Fatigue resistance of two implant/abutment joint designs. Journal of Prosthetic Dentistry. support conditions for the implant system were used. 2002;88:604-610.

Khraisat A. Stability of implant-abutment interface with a hexagon-me- The geometrical design of the external-hex system diated butt joint: failure mode and bending resistance. Clinical Implant tends to induce stress concentrations in the crown at a Dentistry Related Research. 2005;7(4):221-228. distance of 2.89mm from the apex. At this location F P Maeda Y, Satoh T, Sogo M. In vitro differences of stress concentrations also affects the stresses, so that the compressive stresses for internal and external hex implant-abutment connections: a short on the right hand side of the crown are increased. The communication. Journal of Oral Rehabilitation. 2006;33:75-78. internal-hex system has reduced stress concentrations in Merz BR, Hunenbart S, Belser UC. Mechanics of the implant-abutment the crown. However, because the preload is transferred connection: an 8-degree taper compared to a butt joint connection. In- through the abutment screw to the abutment contact, ternational Journal of Oral & Maxillofacial Implants. 2000;15:519-526. changing FP has greater effect on this hex system Neoss Limited (2006) Neoss Implant System Surgical Guidelines, UK. than FM. Overall FM is more influential on the stress within the crown for the external-hex system and Strand7 Pty Ltd (2004) Strand7 Theoretical Manual, Sydney, Australia.

FP is more inﬂuential on the internal-hex system. van Staden RC, Guan H, Loo YC, Johnson NW, Meredith N. Stress Evaluation of Dental Implant Wall Thickness using Numerical Tech- Future recommendations include the evaluation of other niques. Applied Osseointegration Research. 2008 (In Press). implant parameters such as the implant wall thickness and thread design. Ultimately, all implant components can be understood in terms of their influence on the stress produced within the implant itself.

ACKNOWLEDGEMENTS This work was made possible by the collaborative support from Griﬃth’s School of Engineering and School of Dentistry and Oral Health. A special thank you goes to Messires John Divitini and Ian Kitchingham from Neoss Limited for their continual contribution. 53 Applied Osseointegration Research - Volume 6, 2008

Comparison of early bacterial colonization of PEEK and titanium healing abutments using real-time PCR

Stefano Volpe1, Damiano Verrocchi2, Peter Andersson2, Jan Gottlow3, Lars Sennerby2,3

1Private Practice, Rome, Italy 2Private Practice, Fiera di Primiero and Feltre, Italy 3Dept Biomaterials, Inst Clinical Sciences, Sahlgrenska Academy, Gothenburg University, Sweden Thise study found no differences in total bacterial load at PEEK or titanium Neoss healing abutment surfaces or their adjacent peri-implant pockets/sulci. The number of periodontal pathogens was low and there was no signiﬁcant difference between the abutment materials. The ﬁndings support the use of PEEK as abutment material in dental implant care.

INTRODUCTION

PEEK (polyetheretherketone) is a synthetic polymer with high biomechanical strength and inert chemical properties, which make it attractive for use in industrial and medical applications (for review see Kurtz & De- vine 2007). Healing abutments made of commercially pure titanium have been the “gold standard” in dental implant care for many years. Wound healing studies have documented the formation of a healthy mucosal barrier adhering to the titanium abutment surface after abutment connection (e.g. Berglundh et al 1991). Yet, it has been shown that peri-implant pockets are colonized FIgure 1. Clinical photograph showing the PEEK (left) and by bacteria, including periodontal pathogens, already titanium (right) healing abutments within 2 weeks after abutment connection (Koka et al 1993, Quirynen et al 2006). The Neoss implant system titanium and one PEEK healing abutment. A chlo- offers both titanium and PEEK healing abutments. rhexidine rinse regimen was instituted during the first postoperative week. Sutures were removed after 7 days. The aim of the present study was to evaluate the biocompatibility of PEEK abutments to that of titanium Bacterial sampling was performed two weeks after abutments by comparing the bacterial coloniza- abutment connection using a commercial test system ® tion of the abutment surfaces and the surrounding (Meridol Perio Diagnostics, GABA International, peri-implant pocket/sulcus using real-time PCR. Münchenstein, Switzerland). Each test kit contains 4 paperpoints for sampling. All samples were taken at the distal surface of the abutments in order to stay as MATERIALS AND METHODS far as possible away from the neighbouring anterior teeth. Two paperpoints were used at each titanium Patient and sampling sites and PEEK abutment site. The first paperpoint was Fourteen (14) partially edentulous patients (9 women positioned in close contact with the abutment surface and 5 men with a mean age of 58 years) with need of im- at the mucosal margin. The second paperpoint was plant treatment volunteered for the study. All patients placed in the peri-abutment sulcus/pocket area after were of good general health and had not received any removal of the abutment. Each paperpoint was held antibiotic therapy within the previous 3 months. Every in position for 10 seconds and immediately thereafter patient received 2 submerged Neoss implants in one placed in a test tube (accompanying the test kit). The edentulous area. Second stage surgery was performed samples were sent to a specialized microbiological after 3-6 months of healing. Each patient received one laboratory (Carpagen GmbH, Münster, Germany). 54 Applied Osseointegration Research - Volume 6, 2008

Real-time PCR Real-time polymerase chain reaction (PCR) by the Meridol® Perio Diagnostics (GABA International, Münchenstein, Switzerland) detects and quantiﬁes six periodontal pathogens (A. actinomycetemcomitans, F. nucleatum ssp., P. gingivalis, P. intermedia, T. forsythensis and T. denticola) and the total bacterial load.

Statistical analysis The Wilcoxon signed rank test was used to calculate the significance of the differences found between Figure 2. Clinical photograph of the peri-implant mucosa after numbers of bacteria at titanium and PEEK abutment removal of the healing abutments sites. Hultin and coworkers (2002) described microbio- RESULTS logical findings and host response in partially edentulous patients with peri-implantitis. DNA-probe The study involved 28 healing abutments (14 analysis sensitive for A. actinomycetemcomitans, P. PEEK and 14 titanium abutments) in 14 patients. gingivalis, P. intermedia, T. forsythensis and T. den- At the day of bacterial sampling all sites showed ticola found presence of periodontal pathogens at clinically healthy tissue conditions (Fig. 1 and 2). healthy as well as at diseased implant sites. However, only around implants with peri-implantitis were all The total bacterial load at the mucosal margin 5 species recovered in amounts ≥106 of the target 6 6 was on the average 13*10 (median 5*10 ) at ti- bacterial cells in each sample. No sample in the 6 6 tanium abutments and 14*10 (median 7*10 ) present study showed ≥106 of periodontal pathogens at PEEK abutments (table 1). The correspond- indicating healthy conditions at the tested sites. ing value for the peri-implant pocket/sulcus was 9*106 (median 2*106) at titanium abutments and Table 1. Total bacterial load - surface 3*106 (median 1*106) at PEEK abutments (table 2). The differences were not statistically significant. Patient Titanium PEEK 1 470 000 2 000 000 The total number of the 6 periodontal pathogens 2 21 000 000 720 000 3 detectable by the PCR test was on the average 18*10 3 56 000 000 60 000 000 3 3 (median 1*10 ) at titanium abutments and 14*10 4 2 100 000 47 000 000 3 (median 2*10 ) at PEEK abutments (table 3). The 5 50 000 000 16 000 000 corresponding value for the peri-implant pocket/sulcus 6 180 000 190 000 was 23*103 (median 2*103) at titanium abutments 7 12 000 000 3 000 000 and 75*103 (median 8*103) at PEEK abutments 8 6 000 000 24 000 000 (table 4). No sample showed ≥106 of periodontal pathogens. The differences between titanium and 9 4 600 000 12 000 000 PEEK abutments were not statistically significant. 10 2 300 000 790 000 11 6 300 000 9 800 000 DISCUSSION 12 4 200 000 5 000 000 13 12 000 000 12 000 000 14 1 500 000 2 200 000 The Neoss PEEK abutments showed similar amounts of bacterial adhesion as the Neoss titanium abutments Mean 12 760 714 13907 143 when evaluated using real-time PCR. This method is Median 5 300 000 7 400 000 very sensitive since both living and dead bacteria are Min 180 000 190 000 detected, which makes it more accurate than cultiva- Max 56 000 000 60 000 000 tion. The detection limit for each periodontal pathogen Sum 178 650 000 194 700 000 is as low as 100 bacteria (Jervøe-Storm et al 2005). p = 0,507 55 Applied Osseointegration Research - Volume 6, 2008

Table 2. Total bacterial load - sulcus The findings of the present study sup- Patient Titanium PEEK port continued investigation of PEEK as 1 4 400 000 220 000 an abutment material in dental implant care. 2 27 000 000 7 800 000 3 1 500 000 16 000 000 ACKNOWLEDGEMENT 4 10 000 000 3 000 000 The authors want to thank Dr. Emanuele 5 39 000 000 550 000 Leoncini, Medical Faculty, University La 6 370 000 1 300 000 Sapienza, Rome, Italy, for the statistical analyses. 7 650 000 310 000 8 1 600 000 430 000 REFERENCES 9 1 400 000 2 600 000 Berglundh T, Lindhe J, Ericsson I, Marinello CP, Liljenberg B, Thomsen 10 1 700 000 170 000 P. The soft tissue barrier at implants and teeth. Clin Oral Implants Res 11 1 000 000 6 700 000 1991;2:81-90. 12 1 600 000 190 000 Hultin M, Gustafsson A, Hallström H, Johansson LA, Ekfeldt A, Klinge B. Microbiological findings and host response in patients with peri- 13 150 000 1 200 000 implantitis. Clin Oral Implants Res. 2002;13:349-58. 14 31 000 000 4 300 000 Jervøe-Storm P-M, Koltzscher M, Falk W, Dörfler A, Jepsen S. Compari- Mean 8669286 3 197 857 son of culture and real-time PCR for detection and quantification of five Median 1 600 000 1 250 000 putative periodontopathogenic bacteria in subginvial plaque samples. J Clin Periodontol 2005;32:778-783. Min 150 000 170 000 Koka S, Razzoog M, Bloem T, Syed S. Microbial colonization of Max 39 000 000 16 000 000 dental implants in partially edentulous subjects. J Prosthetic Dentistry Sum 121 370 000 44 770 000 1993;70:141-144. p=0,158 Kurtz S, Devine J. PEEK biomaterials in trauma, orthopedic, and spinal implants. A review. Biomaterials 2007;28:4845-4869. Table 3. Total amount of periodontal pathogens - surface Quirynen, M; Vogels, R; Peeters, W; van Steenberghe, D; Naert, I; Haffajee, A. Dynamics of initial subgingival colonization of ‘pristine’ Patient Titanium PEEK peri-implant pockets. Clin Oral Implants Res. 2006;17:25-37. 1 1 300 1 490 2 1 450 1 310 Table 4. Total amount of periodontal pathogens - sulcus 3 177 040 145 600 Patient Titanium PEEK 4 2 710 7 400 1 6 960 6 350 5 750 750 2 2 000 8 700 6 600 600 3 15 400 895 550 7 1 380 900 4 20 760 25 530 8 920 5 590 5 1 340 13 950 9 600 1 050 6 600 850 10 750 3 330 7 600 600 11 1 800 11 790 8 900 750 12 1 170 1 700 9 4 350 67 750 13 2 100 6 500 10 5 210 600 14 53 630 2 410 11 900 750 Mean 17 586 13 601 12 1 100 10 220 Median 1 340 2 055 13 750 14 130 Min 600 600 14 261 390 1 950 Max 177 040 145 600 Mean 23 019 74 834 Sum 246 200 190 420 Median 1 670 7 525 p=0,388 Min 600 600 Max 261 390 895 550 Sum 322 260 1 047 680 p = 0,133 56 Applied Osseointegration Research - Volume 6, 2008

Survival rate, fracture resistance and mode of failure of titanium implants in clinical function and dynamic loading.

Neil Meredith1,2 and Fredrik Engman2

1University of Bristol, Bristol, UK 2Neoss Ltd, Harrogate, UK

The possible causes of implant fracture under dynamic loading conditions are discussed with regard to the in-vivo clinical behaviour and in-vitro testing.

INTRODUCTION ing possible contributory factors. An international Fracture of endosseous dental implants during place- standard (ISO 14801:2003(E)) exists for fatigue test- ment or function will have serious implications for pa- ing of endosseous dental implants. It is most useful tients. Fracture of implants during insertion may occur for comparing implants of different designs or sizes. as the insertion load exceeds the fracture strength of the implant. Such a failure is most unlikely to be the result The published standard carries an important caveat of clinical misuse and is most probably due to an error not included in the similar standard for the testing in design or material selection. Errors in manufacturing of orthopaedic prostheses: ‘ Whilst it simulates the and flaws in materials may also contribute to failure. A functional loading of an endosseous dental implant design error is likely to involve a number of components body and its premanufactured prosthetic compo- whereas manufacturing and material errors may be lim- nents under ‘worst case’ conditions, the standard is ited to a single component or batch of raw material. not applicable for predicting the in-vivo performance of an endosseous dental implant or prosthesis.’ Failures at placement are generally noticed clinically at the time. However, should the clinician fail to notice a A number of workers have identified the potential risks crack or flaw and the component was then incorporat- of fatigue failure, particularly in single tooth restorations ed in a structure then potentially serious bone loss and (Marinello et al. 1997; Schmitt and Zarb 1993). Henry clinical complications may arise which may not be ap- et al. (1996), however, reported a very low incidence parent for some months or even years post restoration. of fatigue fracture in a prospective five year study. Ac- curate seating of the abutment on an implant is critical The other mechanism of failure for implant compo- (Binon, 2000a). A loss of preload in the abutment screw nents; fixtures, abutments and screws is fatigue failure. can result in loosening with wear and fracture (Binon This occurs as a result of cyclic functional loading; the 2000b)(Haak et al. 1995) in the flat-on-flat systems. magnitude of which may be well below the ultimate strengths of the components. Good clinical practice If failure of an implant component occurs as a result and adherence to sound biomechanical principles of of fatigue it is essential to understand the mode of prosthesis design should minimise the risks of fatigue failure. The loss of preload in an abutment screw (pos- failure, although component design may play a role. sibly due to an incorrect torque at placement) may result in loosening of the implant abutment connec- Catastrophic failure can be modelled in-vitro with tion and the subsequent development of unexpected some confidence by the application of a single load bending loads causing fracture of the implant. Clear cycle applied by a calibrated testing system until fail- interpretation of the steps leading to failure by making ure occurs. Fatigue loading is much more complex to a thorough examination of fractured components is model in-vivo and it can be difficult to extrapolate the only way to correct diagnosis. It therefore becomes to clinical behaviour from such findings. Clinical clear that simulation and modelling in-vitro of multi- study of failure specimens may be helpful in identify- factorial dynamic fracture modes is a great challenge. 57 Applied Osseointegration Research - Volume 6, 2008

A number of workers have developed sophisticated METHOD and elegant loading machines designed specifically to model masticatory function (Sakaguchi et al. 1986; Twenty four implants (Neoss Limited; Harrogate UK) Bates, Stafford and Harrison, 1975) for the study of in two groups of diameter 3.5mm and 4.0mm were wear and less frequently fracture. However, a simple embedded in a specimen holder with a heat curing uniaxial loading regimen can be useful in compar- resin (Epotek 353ND, CA, Modulus 4.0GN/m2) ing implant performance (ISO 14801:2003(E)). and at a depth in accordancewith ISO14801. Abut- ments (identification number 10547) were attached This investigation was prompted by the only reported to each implant with a gold abutment screw (iden- clinical failure of a specific implant (Neoss system; Neoss tification number E8140) and torqued to 32Ncm-1 Limited, Harrogate, England). The fracture of the im- using a calibrated torque wrench. A hemispherical plant flange occurred and was identified some 3.5 years loading member was attached to each abutment. after placement. The implant was one of three com- The fatigue tests were performed in a servo hy- prising a bar retained overdenture with electroformed draulic test machine (Instron 1341; Instron Ltd, denture. Figure 1 illustrates the fractured implant in- Uxbridge, England) as constant load amplitude situ. The fractured element was removed and examined tests with R=0.1 at 15 Hz. R is defined as Fmin under scanning electron microscopy (SEM; Figure 2). divided by Fmax. Fracture was defined as a visible As a result of these investigations it was deduced that the most likely aetiology of failure was fatigue Figure 2. Fractured part of implant flange.. fracture . In order to better understand the events contributing to this single failure an in-vitro investigation was carried out according to the international standard test method ISO14801. The National Swed- ish Test House (Sveriges Tekniska Forskningsin- stitut) was commissioned to undertake this study.

Figure 1. a.) fractured implant in-situ and b.) overdenture bar construction

Figure 2b. SEM of fracture surface in implant flange..

58 Applied Osseointegration Research - Volume 6, 2008 unrecovered deformation, i.e. when a deflection of approximately five millimetres of the loading point occurred. The initial position of the deflection is measured at Fmax. The test set-up is shown in figure 3.

The aluminium cylinder of the test specimen was mounted in a holder of stainless steel so that the force was applied at 30° to the centre axis of the specimen top. The force was applied to the polished loading point of the specimen top using a flat ended cylindrical rod with a concave recess mounted onto the load cell. The holder was mounted on the base plate of a cylindrical stainless steel test reservoir and positioned to ensure vertical load application. The horizontal position of the specimen holder was adjusted at the start of the test to ensure the load application was in a vertical line beneath the load cell The loading parameters are listed in Tables 1 and 2. Load cycling was carried out on each specimen for 5million cycles (‘run out’) or until fracture occurred. Fracture was classified as A – of the abutment screw, B – of the abutment screw and crack on the fixture or C- fracture on the fixture and epoxy (Epotek 353ND; Epotek Corp. Ca). Figure 3. Schematic of Test Set Up 1. Loading Device 2. Nominal Bone Level RESULTS 3. Abutment 4. Hemispherical Loading Member 5. Dental Implant Body 6. Specimen Holder The results from the fatigue tests are tabulated in Table 1 for 3.5mm implants and Table 2 for 4.0mm implants. fracture. The constants A and B are calculated as a least square fit in a log-log plot where Fmax is the controlled Results from fatigue tests are plotted as a Wohler graph (Fmax vs. Numbers of cycles in logarithmic scale) for the 3.5mm variable and N (the numbers of cycles to fracture) is the implants (Figure 4) and 4.0mm implants (Figure 5). obtained variable. The results are tabulated in Table 3. B In the Wohler graph the formula N = A x Fmax describes the relation between Fmax and the numbers of cycles to

Table 1. Test results from fatigue fracture of 3.5mm diameter Table 2. Test results from fatigue fracture of 4.0mm diameter implants implants Specimen F F No. of Fracture max min Specimen Fmax Fmin No. of Fracture location/ No. (N) (N) cycles location/ No. (N) (N) cycles remarks remarks 1 350 35 4744655 Fracture A 1 240 24 5000000 Runout 2 420 42 97422 Fracture A 2 420 42 66832 FractureB 3 380 13 1712227 Fracture A 3 380 38 45705 FractureC 4 330 33 5000000 Runout 4 330 33 925828 FractureA 5 330 33 2106541 Fracture A 5 280 28 5000000 Runout 6 330 33 5000000 Runout 6 280 28 5000000 Runout 7 330 33 5000000 Runout 7 280 28 5000000 Runout 8 350 35 2653842 Fracture A 8 420 42 39477 FractureB 9 420 42 47775 Fracture B 9 380 38 190138 FractureB 10 380 38 106771 Fracture B 10 330 33 2369670 FractureA 11 380 38 725278 Fracture A 11 330 33 847538 FractureB 12 420 42 90652 Fracture A 59 Applied Osseointegration Research - Volume 6, 2008

Figure 4. Wohler graph for the fatigue test on fixture 3.5 mm diameter

Figure 5. Wohler graph for the fatigue test on fixture 4.0 mm diameter

Table 3. Linear regression parameters for fractured specimens

Fixture Constant A Constant B R2 3.5mm dia. 1.433 x 1043 -14.72 -0.75924 4.0mm dia. 1.524 x 1050 -17.25 -0.76404 60 Applied Osseointegration Research - Volume 6, 2008

DISCUSSION

Fatigue testing is the repeated application of cyclic mechanical loading to a specimen with the intention of simulating accelerated function leading to possible fracture. The complex loading conditions and variables in occlusal function make accurate simulation of such loading extremely diﬃcult(De Boever, 1978; Kraus, Jordan and Abrams, 1969; Haraldson, Carls- son and Ingervall, 1979). Indeed the ISO standard (14801:2003(E)) states that whilst the standard is designed to simulate the functional loading of an endosseous dental implant body and its premanufactured prosthetic components under worst case conditions the standard is not applicable for predicting Figure 7. Overdenture supported by fractured implant in clinical the in-vivo performance of an endosseous implant. case illustrating biomechanical overload

The purpose and value of such testing may therefore be open to question. However such testing is useful in giving indicators of possible weaknesses in design and production and for comparison between prod- Figure 7 illustrates the over denture which was be- ucts and implant systems (Strub & Gerds, 2003). ing supported by the fractured implant. There were originally four implants placed, two each in the The most useful parameter in the results is the lowest premolar regions. One implant was lost shortly after value of Fmax at which an implant abutment complex prosthetic reconstruction and not replaced. Three ceases to fail and performs a repeatable runout be- and a half years later the remaining implant was the tween specimens. In this study the value was 280N for one that fractured on the left side. This illustrates 3.5mm diameter implants Published data is relatively significant mesial and distal cantilevers and the scarce, however Straumann (2007) have published clinician described the aetiology as biomechanical data comparable data for 3.5mm implants obtained overload. Furthermore examination of the fractured by the ISO 14801 standard ( Figure 6). It is also implant margin (Figure 8.) indicates burnishing of important to understand the mode and pattern of the top face (Cibirka et al. 2001). This would only failure that occurs. Clinically, for example, abutment occur if the abutment screw had loosened allowing screw fracture may have less serious implications in unnoticed movement of the implant and abutment screw retained system than in cemented restorations at the interface resulting in high loads being applied (Drago 1995). Fracture of an implant will nearly al- to the implant margin leading to the failure (Gratton, ways have serious consequences. Clinical examination Aquilino and Stanford, 2001; Khraisat et al. 2004). of the case described previously with the one and only fractured Neoss illustrates a number of useful points. In conclusion fatigue testing of dental implants and components alone is of limited value. In com-

Figure 6. Comparison of fixture fatigue strengths bination with clinical data and an understanding of the aetiology of failure useful data can be obtained to predict implant performance. The fatigue data for 3.5 and 4.0mm diameter Neoss implant compare favourably with other industry standard implant systems of unspecified size or function.

61 Applied Osseointegration Research - Volume 6, 2008

the implant-abutment interface after fatigue testing. J Prosthet Dent. 2001;85:26&-275.

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INTERNATIONAL STANDARD; Dentistry — Fatigue test for endosseous dental implants ISO 14801:2003(E)

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Kraus BS, Jordan EJ, Abrams LA. The dentition: its alignment and articulation. In: Kraus BS, Jordan EJ, Abrams LA, eds. A study of the masticatory system. Dental anatomy and occlusion. Baltimore: Williams & Wilkins; 1969:223-237 Figure 8. SEM fractured implant face (a) of burnished implant/ abutment interface (b) Marinello CP, Meyenberg KH, Zitzmann N, Luthy H, Soom U, Im- oberdorf M. Single-tooth replacement: some clinical aspects. ,J Prosthet Dent. 1997;9:169-178.

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Cibirka RM, Nelson SK, Lang BR, Rueggeberg FA. Examination of 62

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