RestorativeDentistry

Jasneet Singh Gulati Sara Tabiat-Pour, Sophie Watkins and Avijit Banerjee Resin-Bonded Bridges − the Problem or the Solution? Part 1: Assessment and Design

Abstract: Resin-bonded bridges (RBBs) have an important role to play in the minimally invasive prosthodontic replacement of missing teeth. This treatment modality is perceived to have a high clinical failure rate by some practitioners, which may be associated with poorly planned and executed designs and adhesive techniques. This paper, the first part of a two-part series, discusses the important planning stages in the successful provision of RBBs, including assessment, appropriate abutment selection and design considerations. The second part of this series will focus on the clinical stages of RBB provision. CPD/Clinical Relevance: This paper aims to provide the general dental practitioner with a guide to appropriate case selection and an overview of the planning stages involved for the provision of RBBs. Dent Update 2016; 43: 506–521

How long can RBBs last? of 87.7% at 5 years,2 deeming them an When can RBBs be used? Resin-bonded bridges (RBBs) acceptable and minimally invasive (MI) RBBs have an important role have been used to replace teeth in short method of restoring modest-sized spaces to play in restorative , with edentulous spans with increasing success in the dental arch. It has often been their indications extending beyond the since the 1970s.1 A systematic review by considered that they are an under-utilized replacement of lateral incisors. They restoration modality in general dental Pjetursson et al reported a survival rate are a MI way of replacing missing teeth practice due to a perceived high rate of compared to conventional bridgework10 clinical failure, which may be associated or implants, usually not requiring local with incorrect design and execution.3 anaesthetic, making the procedure suitable Jasneet Singh Gulati, BDS, A recent prospective study of for patients who are needle phobic or do PgCert(DentEd), MFDS RCPS(Glas), 771 adhesive bridges by King et al found not wish to go through lengthy surgical Dental Core Trainee 1 (gulatij@gmail. that most failures of RBBs occurred within com), Sara Tabiat-Pour, BDS, MSc, treatment. RBBs are an option where there the first four years, and that very few failed MFDS RCS(Eng) FDS(Rest Dent) RCS, thereafter, with an estimated survival rate may be a lack of 3-dimensional space or Consultant in Restorative Dentistry, of 80.4% at 10 years.4 In this single-centre bone for implant placement. The benefits of Sophie Watkins, BDS, MSc, FDS(Rest shorter appointments and associated cost, Dent), RCPS FDS RCS(Eng), Consultant study, because the point of failure was compared to conventional bridgework and in Restorative Dentistry, Guy’s and St recorded as the first de-bond, the overall Thomas’ NHS Foundation Trust, King’s survival in clinical service may have been implant-supported restorations, are also Health Partners and Avijit Banerjee, greater where bridges had been re-bonded favoured by patients. BDS, MSc, PhD(Lond), LDS FDS(Rest successfully. An evidence-informed However, as with any form of Dent), FDS RCS(Eng) FHEA, Professor summary of key papers assessing RBBs has treatment, the use of RBBs is not without of Cariology and Operative Dentistry/ been given in Table 1.4-9 limitations and success is associated with Honorary Consultant and Clinical Careful case selection, appropriate appropriate case selection and planning. As Lead, Restorative Dentistry, KCL Dental design and attention to operative detail are with the provision of any restoration, the Institute at Guy’s Hospital, King’s Health key factors for the clinical longevity of RBBs patient must be well motivated with good Partners, London, UK. and will therefore be covered in this paper. oral hygiene and primary dental disease 506 DentalUpdate July/August 2016 RestorativeDentistry

4 6 Authors (Year King et al (2015) – Botelho et al Djemal et al (1999) – Pröbster and Henrich Hussey and Linden Berekally and Smales of publication) University of Bristol (2014)5 – Faculty Eastman Dental Institute for (1997)7 – Johannes (1996)8 – The Queen’s (1993)9 – Adelaide Dental Hospital and of Dentistry, The Oral Healthcare Sciences, Gutenberg University, University of Belfast, Dental Hospital, School, United Kingdom University of Hong University of London, United Mainz, Germany Northern Ireland, United Australia Kong Kingdom Kingdom

Design of Prospective Retrospective Retrospective Prospective Retrospective Prospective study

Number of 771 211 832 325 142 262 RBBs (including 38 hybrids/ (including 205 movable connector and 199 ‘Maryland’ bridges splint type bridges) 34 ‘Rochette’ bridges of various designs)

Definition of - First de-bond - First de-bond - First de-bond - First de-bond - Second de-bond - First de-bond RBB failure - Fractured porcelain or - Extraction of the - Fractured porcelain or - Loose retainer - Fractured porcelain metal abutment tooth metal - CARS or metal - Diagnosis of caries - Diagnosis of CARS - Diagnosis of CARS associated with - Others including aesthetic - Others including restorations and sealants failure and periodontal loss abutment tooth (CARS) of abutment fracture and - Others including periodontal loss of aesthetic failure abutment

Survival 80.8% at 5 years 84.4% with a mean Median survival of 61% at 5 years 88% at 3 years Median survival (excluding life service of 9.4 7.83 years of 2.60 years for re-bond data) 80.4% at 10 years years ‘Maryland’ bridges 70% at 3 years when pontic failures are excluded from failure definition

Survival No re-bonding data 97% at 5 years No re-bonding data 76% at 5 years, 60% 94% at 3 years No re-bonding data (including 91% at 10 years after 10 years re-bond data) 84% at 15 years

Anterior vs Anteriors (552) Anteriors (111) Anteriors (604) Anterior (279) Anterior (131) Anterior (150) Posterior RBBs Posteriors (219) Posteriors (100) Posterior (228) Posterior (46) Posterior (11) Posterior (78) (n) Posterior RBBs are Posterior RBBS are more likely to fail by an twice as likely to No significant difference in No significant No comparison made No difference in odds ratio of 1.79 de-bond compared survival difference in survival – results to anterior RBBs survival were not statistically significant

Cantilever vs Cantilever (476) All RBBs were Cantilever (171) All RBBs were Fixed- All RBBs were cantilever. Most 'Maryland' Fixed-fixed Fixed-fixed (295) cantilever Fixed-fixed (424) fixed. bridges were Fixed- RBBs (n) Fixed-fixed RBBs are Fixed-fixed RBBs are more fixed (93%). more likely to fail by an likely to fail by an odds odds ratio of 2.23 ratio of 1.94

Unrestored Unrestored or new No comparisons No comparisons possible Unrestored (236) No comparisons No comparisons vs Restored restoration (706) possible Restored (89) possible possible Abutments Old restorations (65) The presence of an No influence old restoration is of presence of associated with higher restoration failure by an odds ratio of 3.21 

Table 1. A table summarizing the seminal papers studying RBBs over the last 22 years. Significant points have been highlighted.

July/August 2016 DentalUpdate 507 RestorativeDentistry

Preparation Minimal preparation (357) No comparisons No comparisons possible No preparation (65) No comparisons Non-retentive vs Non- Intermediate or maximal possible Slice-cut, grooves and possible preparation (58) preparation preparation (414) pinholes, or extensive Retentive preparation Intermediate or preparation (260) (170) maximal preparation No significant Non-retentive RBBs are more likely difference in survival preparation RBBs are to fail by an odds ratio more likely to fail by of 2.85 an odds ratio of 1.82 However, this was not significant when pontic failures were excluded from failure definition

Perforated vs All retainers were All retainers were Perforated (105) All retainers were All retainers were Perforated (34) Unperforated unperforated unperforated Unperforated (727) unperforated unperforated Unperforated (228) Retainer Perforated retainers are Perforated retainers more likely to fail by an odds are more likely to ratio of 1.38 fail by an odds ratio of 1.88

Critique The protocol suggested in Abutment teeth were The period of study (1978 The period of study All abutment teeth were This study used two of this paper is in agreement prepared, where – 1993) covered many (1984 – 1995) covered minimally prepared different alloys for construction with our suggested necessary, to lower developments of resin- many developments within enamel with a casting, of which both protocol protocol: the survey line to retained cast restorations. of resin-retained wraparound design and contained beryllium. - Nickel-chromium increase wraparound Therefore there are many cast restorations. cingulum rests. Beryllium containing alloy of at least 0.7 mm of the retainer. This variables in their bridge Therefore there are Nickel chromium alloy alloys are no longer thickness was achieved by axial construction protocol many variables in their used, air abraded with 50 used due to concerns - Unperforated retainers, preparation of the including the choice of bridge construction microns alumina prior to about their safety, air abraded with 50 interproximal surfaces. resin cement, casting alloy protocol including the fitting. and the availability microns alumina Anterior abutment and techniques for metal choice of resin cement, Rubber dam isolation was of alternative metal - Chemically adhesive teeth were prepared preparation casting alloy and mandatory. surface conditioning resin cement Panavia 21 with opposing techniques for metal All RBBs luted with techniques that do (Kuraray Co Ltd, Osaka, interproximal grooves, preparation. Panavia 21. not rely on etching. Japan) however the authors A 2-mm distance Planned for pontic All bridge retainer - Maximal coverage of (Botelho et al) suggest between framework in light contact in surfaces were air enamel this is not currently and marginal gingiva centric , and abraded with 50 recommended and was attempted to be protected from loading in microns alumina, not a required tooth maintained ‘to avoid excursions followed by preparation feature. an adverse periodontal electrochemical Occlusal clearance reaction’. Therefore the etching, which is why was created when RBBs in this study did they are referred to as necessary by not utilize all available ‘Maryland’ bridges in preparation of enamel this study. The term abutment tooth, 'Maryland' bridge is opposing dentition or therefore historic. both to accommodate Various resin cements a 0.8 mm thick retainer. were used for They used nickel bonding, and two chromium alloy different types of retainers, unperforated, pontic; porcelain and and air abraded with 50 light-cured hybrid microns alumina. resin All RBBs were bonded with Panavia EX (Kuraray Co. Ltd, Osaka, Japan) or Panavia 21

508 DentalUpdate July/August 2016 RestorativeDentistry

well controlled. The indications and contra- and sufficient connector height, not only Post-orthodontic fixed retention indications are summarized in Table 2. considering the one arch in isolation, but in can also be incorporated into adhesive The loss of a tooth can have both static and dynamic occlusion. A lack bridge design with some success.4 Since unwanted changes and effects in the of vertical space may require an increase the use of RBBs lends itself particularly to mouth that may complicate the provision in the occlusal vertical dimension (OVD), the restoration of missing teeth in mild or of a prosthetic replacement, such as tilting which will be discussed in this paper. In moderate hypodontia, this is frequently of adjacent teeth or over-eruption of cases where the mesio-distal dimension of useful in the management of cases where the opposing dentition.11 Therefore, the an edentulous space is smaller than ideal, a pre-restorative orthodontics has been edentulous space should be assessed for RBB may be feasible if aesthetics allow, but carried out to create appropriate spaces for adequate space for an aesthetic pontic implant placement may not be practical. replacement of the missing teeth. In Figure 1, the central incisor teeth have been used as abutments with the framework a c linked to prevent orthodontic relapse. Similarly, where canines have been de-rotated, these may be incorporated in a fixed-fixed design to replace lateral incisors, which would control the position of the canines and prevent orthodontic relapse. An alternative would be to use a cantilever design of an adhesive bridge and provide a separate form of orthodontic retention, such as a vacuum-formed Essix retainer, but b d this is reliant on patient compliance with regards to retainer wear and is therefore arguably less predictable. Consideration of parafunctional habits is important, as fixed prosthodontic work may be more likely to fail where heavy loads are placed on the teeth. The provision Figure 1. The use of RBBs for post-orthodontic permanent retention. (a) Post-orthodontic labial view of RBBs in bruxists, therefore, requires of a patient with missing upper lateral incisors. (b) Pre-operative occlusal view, showing electrosurgery careful occlusal assessment and planning, preparation of the pontic sites to accommodate a larger pontic and improve aesthetics. (c) Post- as described later in this paper, and operative occlusal view. The metal framework across the upper central incisors is linked to provide consideration may be given to protecting permanent post-orthodontic retention. Note the extension of the framework on to the incisal edges of restorative work through the use of an the central incisors. (d) Post-operative labial view. occlusal splint.12,13

Indications Contra-indications Selecting suitable abutment teeth Where abutment teeth are minimally Heavily restored abutment teeth with There are multiple factors to or unrestored, with sufficient enamel reduced enamel available for adhesion consider in the selection of appropriate present for adhesion abutment teeth for RBBs. These are outlined Patients unwilling or unsuitable for Small abutment teeth, eg peg laterals, below and also summarized in a flowchart surgical treatment including implants, microdont teeth with a reduced surface area (Figure 2). bone augmentation for adhesion Fixed retention after orthodontic Mal-aligned abutment teeth which will Size treatment result in a poor path of insertion and poor RBBs are ideally suited to the aesthetics replacement of single units where the adjacent abutment tooth is minimally or Splinting periodontally compromised Significant differential mobility of abutment unrestored, with sufficient enamel available teeth to improve comfort, although teeth where more than one abutment is for adhesion. A large area of enamel allows significant differential mobility may be a incorporated in the design, as this frequently for a predictable bond to the abutment contra-indication leads to de-bond and is a crucial indicator of success.6 It is Needle-phobic patients Allergy to base metal alloys, eg nickel therefore desirable that the abutment tooth (although nickel-free alloys exist) has sufficient height and width to ensure that a sufficient surface area of enamel is Table 2. Indications and relative contra-indications to the provision of RBBs. available for bonding and that the retainer 510 DentalUpdate July/August 2016 RestorativeDentistry

Figure 2. A flowchart of various factors to consider in the selection of suitable abutment teeth. design is such that it incorporates the associated with a three-fold increase in risk Angulation and position maximum available enamel. of failure, whereas a new restoration was An unfavourably tilted or bulbous abutment not significantly more likely to fail than an tooth anatomy may reduce the 4 Restorative status unrestored abutment. Traditional opinion height of the connector between the pontic Where potential abutment has suggested that old restorations should and retainer wing, causing an increase teeth have existing restorations, it must be replaced with a new resin composite in flexibility of the framework. In such restoration prior to the impression stage.15,16 be borne in mind that the bond strength cases, consideration should be given to a A more contemporary MI solution is to will be limited by the weakest adherent, minimal proximal surface preparation of the resurface old resin composite restorations, with the hierarchy being enamel > resin abutment to reduce the bulbosity, thereby rather than completely replace them, to composite > glass ionomer cement (GIC) maximizing connector height to increase ensure conservation of tooth structure. A > dentine = amalgam.14 It is therefore not rigidity, and allowing the maximum protocol is outlined in Table 3. ideal to select heavily restored abutments surface area to be incorporated into the (as these might be better crowned), or Clinical Tip design (Figure 3). This also limits the path teeth where significant amounts of dentine Replace any small GIC or amalgam restorations of insertion, which assists in retention may be exposed, such as in erosive wear with resin composite. Re-surface old resin by reducing forces on the cement lute. cases. However, it may be acceptable to composite restorations that are otherwise As well as all these advantages, proximal consider a less than ideal abutment tooth sound. Remember that healthy enamel is the surface preparation can also reduce the where MI conservative treatment and best bonding surface and is critical for the size of embrasure spaces to eliminate cost-effectiveness are paramount. King et successful provision of RBBs. If there is limited black triangles in anterior regions. As with al found that the presence of one or more enamel, reconsider the choice of abutment or all forms of cantilever bridges, mesial old restorations on the abutment tooth was avoid restoring with a RBB altogether. cantilever designs are preferred over July/August 2016 DentalUpdate 511 RestorativeDentistry

successfully.19 As a practical guide, careful consideration should be given if there is greater than 50% bone loss around the roots. Where bone loss is more than 50% and, especially if there are mobile teeth, the use of a fixed-fixed design to splint the mobile teeth may be considered to improve patient comfort, and ensure that occlusal Figure 3. A diagrammatic illustration of proximal surface preparation to reduce bulbosity, thereby forces are shared across multiple abutment increasing the connector height and rigidity and allowing a suitable path of insertion. teeth. To minimize the risk of partial de-bond due to differential mobility of abutment teeth, the RBB must be designed carefully to include abutment teeth that  Ensure adequate moisture control. Rubber dam isolation is advised have a similar mobility, both in direction  Use rotary instrumentation to remove uniformly at least 1.0 mm depth of old and magnitude. This is especially true for restoration from the abutment surface teeth that exhibit more mobility due to a  Ensure that a fresh cavity margin of enamel is exposed; ensure removal of residual loss of periodontal bone support. It is also resin composite, and expose a favourable substrate for better micromechanical/ worth noting that the use of this technique chemical adhesion is particularly technique sensitive, especially  Roughen the surface of the resin composite substrate with intra-oral air-abrasion at the impression stage, where mobile (Microetcher, Danville Engineering Company, IA, USA), or lightly with a fine grit abutment teeth may be displaced by the diamond bur if this is not available impression material, resulting in a poor fit of  Acid-etch the newly prepared enamel margins with 37% orthophosphoric acid (K the framework. Etchant Gel, Kuraray Co Ltd, Osaka, Japan) – 20 seconds for enamel (10 seconds for dentine if unavoidably exposed) Preparing abutment teeth  Apply primer (Clearfil SE Bond Primer, Kuraray Co Ltd, Osaka, Japan) to the margins Over the years, some literature where there is freshly cut tooth tissue, wait 20 seconds and gently air dry has suggested that a degree of coronal  Mix primer and silane (Clearfil SE Porcelain Bond Activator, Kuraray Co Ltd, Osaka, preparation (such as vertical grooves and Japan) in 1:1 ratio, and apply over old resin composite substrate, wait 5 seconds preparation of rest seats) of abutment and gently air dry* teeth can increase resistance form and  Apply adhesive agent (Clearfil SE Bond Adhesive, Kuraray Co Ltd, Osaka, Japan) thereby longevity of RBBs.9,20,21 However, onto all cavity surfaces, then dry gently and light cure for 20 seconds there is conflicting evidence in relation to  Add resin composite incrementally, light cure and finish this as some studies suggest no benefit *Clinically, it is difficult to separate the silanation procedure with the adhesive protocol, and it is of abutment preparation on the overall often omitted for this reason. success of RBBs, and that significant preparation is associated with an increased Table 3. A clinical protocol for re-surfacing old resin composite restorations17 (the precise use of risk of failure.4,5, 6,22 The biological cost adhesive will depend on the manufacturer and type). of tooth preparation, however minimal, is significant enough to negate the requirement for preparation as there are distal cantilever bridges. This is due to the is not necessarily a contra-indication for undeniable advantages of the MI approach, increased biomechanical levering forces adhesive bridgework, providing there is no whilst the preservation of enamel for around the abutment, which acts as a evidence of active periodontal disease and adhesion is important for RBB success. The fulcrum. lost periodontal support does not result in non-operative approach avoids the risk excessive mobility. Results of a systematic of exposing dentine,23 which is less ideal review by Lulic et al indicated that the as an adhesive substrate and more prone Periodontal status long-term prognosis of bridgework using to Caries Associated with Restorations/ The presence of an adhesive abutments that have severely reduced Sealants (CARS, previously known as bridge in itself does not have an adverse periodontal support depends on the secondary or recurrent caries) if the bond effect on the periodontium when compared maintenance of a healthy periodontium.19 fails. There are also complications associated to other types of restoration.18 The careful control of occlusal force with tooth preparation, such as the need for It is difficult to define an absolute distribution in this cohort of patients is the preparation to be sufficiently accurate threshold of periodontal support below advised. with parallel retention slots/grooves in which bridgework is contra-indicated, In well-motivated patients, order for them to be usable or confer any as there is no clinical evidence relating with plaque control compatible with good advantage with respect to limiting the path to this. A reduced level of bone support periodontal health, RBBs can be used of insertion. The preparation must then be 512 DentalUpdate July/August 2016 RestorativeDentistry

recorded accurately and transferred to the wings during function and increases dental laboratory via the master impression rigidity of the framework, protecting it from and working cast, and for the laboratory to dislodging forces. conform the retainer manufacture exactly In anterior cases, extending the to the preparation. The loss of detail at each retainer onto the incisal edge is advocated stage may adversely affect the final fit of the as this can assist with location of the RBB and negate any perceived advantage. retainer, provides a degree of resistance One suggested advantage against axial shear forces, and increases of tooth preparation is that it can create the area of bonding further (Figure 5).6 space for the retainer, removing the need The effect on aesthetics is minimal as for occlusal adjustment of the opposing when the patient smiles with his/her teeth dentition. However, preparation for this apart, the retainer extension becomes less purpose is not advised at the impression visible against the dark background of Figure 4. Factoring in the connector height of stage as it is difficult to provisionalize the oral cavity (Figure 5a). The aesthetic RBBs. The UR2 has been restored with a RBB predictably, risking loss of the created requirements of the patient should also using the UR1 as a cantilever abutment. Note space in the interim between impression be assessed and good communication the difference between the prosthetic UR2 and and fit appointments due to dento-alveolar maintained throughout the planning and the natural UL2. The connector height on UR2 is compensation and over-eruption. consent stages to ensure that the patient necessary for the framework to maintain rigidity. However, minimal preparation of has understood the potential impact that Note also how this improves aesthetics, however, by eliminating the embrasure space, which might the abutment teeth to create a guide plane a visible metal wing retainer may have otherwise result in a ‘black triangle’. Note also within enamel by removing the natural on his/her smile against the perceived how the use of opaque cement has eliminated bulbosity of the clinical crown can assist advantages associated with this approach. incisal greying of UR1, but that it no longer positive seating of the RBB and increase The rationale for maximum palatal coverage exhibits the natural incisal translucency that resistance form by limiting the path of and wrapping on to the incisal edge should UL1 does. insertion as well as providing the room for be made clear to the patient, but in the an increased connector height (Figures 3 authors’ experience this is often not a a and 4). This is particularly suited for fixed- problem for the patient. Potential aesthetic fixed RBB designs, where the terminal guide failure of RBBs is sometimes described, planes must be parallel. due to the grey shine through of the metal retainer at the translucent incisal edge, but Clinical Tip this can be eliminated predictably by using Use a long parallel-sided microfine diamond opaque luting cement. bur to prepare guide planes where necessary The use of an incisal locating to increase connector height and reduce tag has been described in cases where ‘black triangle’ formation. Be careful not to retainer location may be difficult, but this b sink the tip of the bur into the tooth, as this can result in inaccurate seating of the would create a margin, which is not necessary retainer, resulting in an increased thickness and requires precise adaptation of the metal of luting cement.25 In addition to this, the retainer wing in this area, which is more locating tag must be removed at the fit technically demanding. (Figure 3) appointment, which theoretically may compromise the cement lute owing to Figure 5. A case where the RBB retainer has been Designing the RBB framework vibration and heating of the immature material immediately after polymerization. extended on to the incisal edge. (a) Labial view with the teeth apart, showing the acceptable Degree of coverage The authors’ preference lies with extension aesthetic implications of wrapping the retainer The literature suggests that the of the retainer on to the incisal edge, for the on to the incisal surface of maxillary right and left best outcome for adhesive bridges can be advantages already described. canines. (b) Occlusal view showing the extent of achieved where maximum enamel coverage In addition to the coverage of the retainers. In this case, the patient is incorporated in the retainer design, and aforementioned advantages of maximum was unconcerned about the small amount a 180-degree wraparound of the abutment coverage of the framework in RBB designs, of metal showing and therefore maximum teeth is often recommended.6,24 there is an additional benefit of full extension was maintained. Incorporating the palatal/lingual cusps and coverage in fixed-fixed RBBs. Stopping occlusal surfaces of posterior teeth within short of the incisal edge is contra-indicated the retainer wing coverage increases the in fixed-fixed cases where protrusive and retainers are used. Therefore, the retainer surface area of enamel for bonding. This excursive forces beyond the retainer may should be full coverage to prevent such a also offers some protection against shear result in differential movement of the mode of failure in fixed-fixed cases where forces that would be applied to the cement abutment tooth, in effect pushing the the excursive guidance may otherwise drive lute in the axial portions of the retainer tooth away from the framework when two the teeth away from the framework. July/August 2016 DentalUpdate 515 RestorativeDentistry

a Clinical Tip fixed-fixed design retained on the lateral Incorporate the maximum available enamel incisor teeth has frequently been used. for bonding within the framework design. For This makes bonding more straightforward, anterior teeth, this should include the entire and the similar mobility of these two palatal/lingual surface, as well as extending on abutment teeth both in direction and in to the incisal edge. For posterior abutments, magnitude reduces the risk of de-bond extend the framework on to the occlusal compared to the previous scenario. surface. This also increases the rigidity of the Due to the differential mobility framework. of abutment teeth in fixed-fixed designs, there is an increased risk of partial de-bond with the bridge remaining in situ, rather than the complete detached failure 26 Number of abutments seen with cantilever adhesive bridges. b The design of choice when Classically, the fixed-fixed design may fail replacing a single unit is to cantilever the silently, going unnoticed by the patient. pontic from a single abutment tooth.15 Plaque biofilm stagnation and the ensuing Fixed-fixed adhesive bridgework has a lower development of caries can occur under survival rate and there is evidence that the de-bonded wing, especially in cases 27 they are twice as likely to fail compared to where dentine is exposed. Therefore, cantilever designs.4,6 in all cases where a fixed-fixed design is Although RBBs are ideally suited used for adhesive bridgework, the patient for shorter spans, they have also been used should be given appropriate advice to be successfully for larger spans using a fixed- alert to partial de-bond of the framework Figure 6. A posterior cantilever RBB to replace fixed design.6 Using adhesive bridgework and caries progression. Patients should UL5. (a) Post-operative occlusal view showing to replace multiple units requires the be advised to be aware of mobility of maximal coverage of the UL6 abutment tooth. consideration of additional factors and will the framework, feeling a sharp surface (b) Post-operative buccal view of the posterior therefore require more careful planning. at the margin, food trapping around RBB. Note the extension of the framework over the entire occlusal surface of UL6. No preparation The development of dental implants and the framework and a bad taste coming was carried out. The bridge was cemented high in their increasing use in routine dental from the bridge as potential signs of a occlusion and occlusal contacts are expected to partial bridge de-bond, and should be practice means that this treatment option re-establish in 6–12 months using the principles may be selected in preference to adhesive encouraged to seek prompt dental care. of the . bridgework where multiple teeth are Similarly, it is important that absent. However, MI adhesive bridgework fixed-fixed adhesive bridges are checked can offer a more cost-effective solution that carefully at review as a de-bond is not by extending the frameworks over both does not rely on bone availability, and does always obvious on examination. palatal/lingual and occlusal surfaces. not involve surgery. It is acceptable to use a fixed- Framework rigidity Using RBBs to replace missing fixed design to replace teeth in cases The thickness of the nickel- posterior teeth where it would be inappropriate to use a chromium retainer should be at least Due to an ageing population cantilever design due to factors such as 0.7 mm to achieve adequate rigidity within and a change in the pattern of tooth loss, increased span, occlusal demands and 28,29 the framework in anterior RBBs. The there is likely to be an increase in the where stability of abutment tooth position longer the span of bridge, the greater the number of partially dentate patients in the is unpredictable. In post-orthodontic need for rigidity in the framework, as its population. Although accepting a gap is treatment cases described above, and flexure may lead to bond failure. Rigidity sometimes appropriate, this may lead to in periodontal splinting, it is also more of the framework is therefore paramount unwanted complications such as tilting acceptable to use a fixed-fixed design for posterior RBBs where the sustained of adjacent teeth and over-eruption of to replace a single unit. However, the loads are likely to be higher. It is important unopposed teeth, which has been reported differential mobility of a lower canine and that this is communicated to the dental to occur in up to 83.9% of cases.11 This lower incisor tooth is such that, as a general technician, as anecdotal evidence may complicate the future restoration of rule, the authors avoid incorporating these suggests that adhesive metal framework the edentulous space, and may introduce two teeth in combination as abutments in is often cast or milled to a thickness of occlusal interferences. Therefore there a fixed-fixed design as, in our experience, less than 0.5 mm where the thickness may be an increasingly significant role this frequently results in de-bond, often has not been specified in the laboratory that adhesive bridges can play in the at the incisor retainer, and is felt to be too prescription. Increased rigidity is also replacement of posterior teeth in a MI way unpredictable. In contrast, in cases where achieved by increasing the connector in order to maintain tooth position. two lower central incisors are absent, a height(s) via proximal preparation and There is sometimes cause for 516 DentalUpdate July/August 2016 RestorativeDentistry

a a is advised because this incorporates more enamel for bonding and increases the rigidity of the framework. Furthermore, the cement lute is protected from shear forces that could dislodge a bridge that is retained by a retainer wing limited to the axial walls only because the occlusal load is directed onto the occlusal extension, and therefore the cement is loaded in compression. b b Occlusion and RBBs Pre-operative assessment should include examination of the patient’s occlusion in the inter-cuspal position (ICP) and in dynamic excursions to ensure that there is enough room for a functional and aesthetic replacement. Ideally, the occlusion should be organized so that the pontic is in light contact in ICP to control the axial position of the opposing tooth, but not c Figure 8. Large span RBB replacing four incisor involved in guidance, where possible. If teeth with careful planning of the occlusal scheme. guidance on the pontic cannot be avoided, (a) Labial view showing the incisal wrapover of the guidance should be shared with the natural canine abutment teeth to increase enamel surface teeth, especially where a cantilever design is area for adhesion and to assist correct seating of the bridge. The upper central and lateral incisors used. The ICP contact should be kept away have been replaced. (b) Occlusal view to show the from the margin of the retainer. This may framework has been contoured to provide occlusal be achieved by minimal adjustment of the contacts directed axially in ICP. opposing dentition. It is prudent to warn Figure 7. A fixed-fixed posterior RBB demonstrating the patient about this prior to bonding, to the principles of full coverage design. (a) Pre- reassure the patient that the adjustment operative labial view. The upper lateral incisors, is planned rather than a necessity to upper second premolars and lower second more favourable stress distribution through compensate for a poorly fitting bridge. The premolars are developmentally absent. The the framework and a greater surface area maxillary canines occupy the space of the lateral of the combined two abutment teeth can use of a facebow transfer to allow casts to incisors. Note the inter-occlusal space which can be utilized. The alternative option is to be mounted on an articulator, although not accommodate the framework thickness of the cantilever mesially from the second molar always essential for RBB provision, may aid RBB. (b) Post-operative labial view after restorative tooth, with generous occlusal and lingual/ in planning a predictable occlusal scheme camouflage of the upper canines using resin palatal coverage (Figure 6). In most cases in larger span or multiple bridges (Figure 8). composite, and the replacement of all second the authors prefer a cantilever design in If pre-operative assessment premolar teeth using fixed-fixed RBBs. (c) Post- this situation, however, a fixed-fixed design reveals limited space available for the metal operative upper occlusal view. The framework may be accepted to match the increased framework, an increase in the OVD can be has been designed to be full coverage, including occlusal demands posteriorly or where planned. The bridge can be bonded at an the palatal and occlusal surfaces, which increases there is concern regarding the risk of tilting increased vertical dimension, to achieve surface area of bonding and rigidity of the what is commonly referred to as the framework whilst increasing posterior inter occlusal of the molar abutment (Figure 7). contact for improved masticatory efficiency. The use of RBBs to replace ‘Dahl effect’. This should result in relative posterior teeth is less predictable than axial movement as a result of alveolar anterior teeth due to increased occlusal compensation of the teeth brought out of concern with using RBBs in the first molar demands.4,5 There is little published contact in this way, such that the occlusal region with regards to design and success evidence assessing the factors associated contacts re-establish in the weeks or associated with the large mesio-distal with success for the replacement of molar months following bridge placement.30 dimensions of the edentulous space. One teeth with RBBs. However, applying the The technique was initially described option is to replace a first molar with two general principles described previously, using an anterior bite plane to create space premolar-sized pontics on cantilevered the rigidity of the framework, degree of anteriorly after a number of months. The bridges, using the second molar and the coverage and the occlusion are likely to be mechanism described for the creation second premolar as abutment teeth. By important factors for consideration. The of space in an anterior ‘Dahl appliance’ using two smaller adhesive cantilever extension of the retainer onto the occlusal was found to be through a combination bridges to replace one large unit, there is surface of posterior teeth (Figures 6 and 7) of intrusion of anterior teeth (40%), July/August 2016 DentalUpdate 517 RestorativeDentistry

and eruption of unopposed posterior and is therefore preferred by the authors. 7. Pröbster B, Henrich GM. 11-year teeth (60%).31 The use of this technique follow-up study of resin-bonded fixed specifically for RBBs has also been described Clinical Tip partial . Int J Prosthodont by Briggs et al and is part of the standard Consider soft tissue modification using 1997; 10: 259−268. protocol for achieving interocclusal space electrosurgery to improve the aesthetics and 8. Hussey DL, Linden GJ. The clinical for RBB restorations in our secondary care emergence profile of the pontic. performance of cantilevered resin- unit.32 bonded bridgework. J Dent 1996; 24: 251−256. The patient should be pre-warned Summary 9. Berekally TL, Smales RJ. A retrospective about occlusal changes and the possibility As with all aspects of clinical evaluation of resin-bonded of transient lisping, and how chewing restorative dentistry, careful case selection bridges inserted at the Adelaide may feel awkward at first. A review of the and attention to detail are critical for the Dental Hospital. Aus Dent J 1993; 38: literature suggests that the Dahl technique successful provision of RBBs. This paper 85–96. has a high predictability of success has covered common challenges that 10. Edelhoff D, Sorensen JA. Tooth (94−100%) and is generally well tolerated practitioners face during planning and structure removal associated with by patients. designing of RBBs, and hopes to have various preparation designs for The average amount of time emphasized the key, evidence-based anterior teeth. J Prosthet Dent 2002; for contacts to re-establish is 6 months, principles of design that are important for 87: 503−509. therefore a longer period of follow-up is their longevity. The operative techniques 11. Craddock HL, Youngson CC. A study advised where this technique is used.33 involved in RBB provision, including of the incidence of and occlusal interferences in unopposed Clinical Tip effective laboratory communication, will be covered in Part 2. posterior teeth. Br Dent J 2004; 196: RBBs are frequently bonded high in occlusion. 341−348. Avoid high static and dynamic contacts that 12. Porter RJ, Poyser NE, Briggs PF, are on the pontic only. The contact should References Kelleher M. Demolition experts: instead be on the retainer wing or shared 1. Howe DF, Denehy GE. Anterior fixed management of the parafunctional between the natural teeth and pontic, as partial dentures utilizing the acid- patient: 1. Diagnosis and prevention. should guidance in excursions. Minimal etch technique and a cast metal Dent Update 2007; 34: 198−207. adjustment of the pontic and opposing teeth framework. J Prosthet Dent 1977; 37: 13. St George G, Hemmings K, Patel K. can achieve this. Warn the patient that this 28–31. Resin-retained bridges re-visited. Part is a planned adjustment and of the potential 2. Pjetursson BE, Tan WC, Tan K, 1. Prim Dent Care 2002; 9: 87−91. effects of any short-term disclusion. Brägger U, Zwahlen M, Lang NP. A 14. Aboush YE, Jenkins CB. The bonding systematic review of the survival and of an adhesive resin cement to complication rates of resin-bonded single and combined adherends RBB pontic design bridges after an observation period of encountered in resin-bonded bridge The pontic should achieve at least 5 years. Clin Oral Implants Res work: an in vitro study. Br Dent J 1991; a passive contact with the tissues and 2008; 19: 131−141. 171: 166−169. allow adequate hygiene by the patient. 3. Patsiatzi E, Grey NJ. An investigation 15. Walls AW, Nohl FS, Wassell RW. Crowns The two most common pontic designs of aspects of design of resin-bonded and other extra-coronal restorations: for bridgework are the modified ridge-lap bridges in general dental practice and resin bonded metal restorations. and the ovate pontic. The potential benefit hospital services. Prim Dent Care 2004; Br Dent J 2002; 193: 135−142. of ovate over the modified ridge lap is its 11: 87−89. 16. Hemmings K, Harrington Z. potentially improved emergence profile 4. King PA, Foster LV, Yates RJ, Replacement of missing teeth with and aesthetics. However, the use of an Newcombe RG, Garrett MJ. Survival fixed prostheses. Dent Update 2004; ovate pontic is more technically demanding characteristics of 771 resin-retained 31: 137−141. as it requires planning and possibly the bridges provided at a UK dental 17. Jafarzadeh Kashi TS, Erfan M, creation of room for the convex portion teaching hospital. Br Dent J 2015; 218: Rakhshan V, Aghabaigi N, Tabatabaei of the pontic. Where the soft tissue in the 423-428. FS. An in vitro assessment of the 5. Botelho MG, Ma X, Cheung GJ, Law pontic bearing area is thick, convex and effects of three surface treatments RK, Tai MT, Lam WY. Long-term not compressible, this may be achieved on repair bond strength of aged clinical evaluation of 211 two-unit with the use of electrosurgery or, where composites. Oper Dent 2011; 36: cantilevered resin-bonded fixed partial this is not available, the use of an oval- 608−617. dentures. J Dent 2014; 42: 778−784. 18. Freilich MA, Niekrash CE, Katz RV, shaped, diamond bur in a high-speed air 6. Djemal S, Setchell D, King P, Wickens J. Simonsen RJ. The effects of resin turbine handpiece has been described.34 Long-term survival characteristics of bonded and conventional fixed Electrosurgery has distinct advantages 832 resin-retained bridges and splints partial dentures on the periodontium: for this as it also arrests haemorrhage and provided in a post-graduate teaching restoration type evaluated. allows the master impression to be taken hospital between 1978 and 1993. J Am Dent Assoc 1990; 121: 265−269. immediately after soft tissue re-contouring J Oral Rehabil 1999; 26: 302−320. 19. Lulic M, Brägger U, Lang NP, Zwahlen 518 DentalUpdate July/August 2016 RestorativeDentistry DELIVER COMFORTABLE

M, Salvi GE. Ante’s (1926) law revisited: a systematic INJECTIONS review on survival rates and complications of fixed dental prostheses (FDPs) on severely reduced periodontal tissue support. Clin Oral Implants Res 2007; 18(Suppl 3): 63−72. 20. Simon JF, Gartrell RG, Grogono A. Improved retention of NOW acid-etched fixed partial dentures: a longitudinal study. takes 2.2ml J Prosthet Dent 1992; 68: 611−615. & 1.8ml cartridges 21. Emara RZ, Byrne D, Hussey DL, Claffey N. Effect of groove placement on the retention/resistance of resin-bonded retainers for maxillary and mandibular second molars. J Prosthet Dent 2001; 85: 472−478. 22. Verzidjen CW, Creugers NH, Van’t Hof MA. A meta-analysis of two different trials on posterior resin-bonded bridges. J Dent 1994; 22: 29−32. 23. Bassi GS, Youngson CC. An in vitro study of dentin exposure during resin-bonded fixed partial denture preparation. Quintessence Int 2004; 35: 541–548. Position your practice as a calm and friendly environment 24. Ibbetson R. Clinical considerations for adhesive with CALAJECT, a great practice-builder that helps you to bridgework. Dent Update 2004; 31: 254−265. deliver comfortable injections. CALAJECT automatically 25. Chana HS, Ibbetson RJ, Pearson GJ, Eder A. The influence controls the fl ow rate for each programme setting to prevent the pain often caused by the speed of the injection and the of cement thickness on the tensile strength of two resin resultant pressure in the tissue. cements. Int J Prosthodont 1997; 10: 340–344. 26. Wong TL, Botelho MG. The fatigue bond strength of fixed- • User-friendly and simple to use fixed versus cantilever resin-bonded partial fixed dental • Can be used for all types of local anaesthesia prostheses. J Prosthet Dent 2014; 3: 136−141. • Cost-effective as used with standard needles and 27. Gilmour AS. Resin-bonded bridges: a note of caution. cartridges. No other consumables are needed Br Dent J 1989; 167: 140−141. • IPC (Intelligent Pressure Control) to control injection pressure 28. Ibrahim AA, Byrne D, Hussey DL, Claffey N. Bond strengths • Automatic aspiration when pressure on the foot control of maxillary anterior base metal resin-bonded retainers is released with different thicknesses. J Prosthet Dent 1997; 78: 281– • Acoustic signal indicates actual fl ow rate 285. • Optional safe-sheathing system 29. Sato Y, Yuasa Y, Abe Y, Akagawa Y. Finite element and Weibull analysis to estimate failure risk in resin-bonded “CALAJECT gives me the confi dence of knowing my retainers. Int J Prosthodont 1995; 8: 73−78. injections will always be delivered at a constant rate 30. Dahl BL, Krogstad O, Karlsen K. An alternative treatment and at a speed appropriate for the procedure. This in cases with advanced localised attrition. J Oral Rehabil greatly enhances patient satisfaction. As many people 1975; 2: 209−214. reject treatment they need because of fear of the 31. Dahl BL, Krogstad O. The effect of a partial bite raising dental injection, taking away this concern is not only splint on the occlusal face height. An x-ray cephalometric a relief for them but also improves my number of accepted treatment plans.“ study in human adults. Acta Odontol Scand 1982; 40: 17–24. Philip Lewis BDS, Avenue Road Dental Practice 32. Briggs P, Dunne S, Bishop K. The single unit, single retainer, cantilever resin-bonded bridge. Br Dent J 1996; For more information Freephone 181(10): 373−379. 0500 321111 or visit calaject.co.uk 33. Poyser NJ, Porter RW, Briggs PF, Chana HS, Kelleher MG. The Dahl Concept: past, present and future. Br Dent J 2005; 198: 669−676. 34. Gahan MJ, Nixon PJ, Robinson S, Chan MFW-Y. The ovate pontic for fixed bridgework. Dent Update 2012; 39: 407−415. July/August 2016 DentalUpdate 521