CONTINUING EDUCATION

Challenging aspects of implant restoration

Drs. Brenda Baker and David Reaney explain various methods to restore function and esthetics to patients in need of implant restoration

mplant has revolutionized the Iway we restore function and esthetics Educational aims and objectives to patients who, historically, would have This article aims to explain the various methods to restore function and esthetics to needed removable prosthetics or less patients in need of implant restoration. mechanically favorable fixed prosthetics. However, it is not always smooth sailing, Expected outcomes Implant Practice US subscribers can answer the CE questions on page 34 to and we need to be aware of some of the earn 2 hours of CE from reading this article. Correctly answering the questions will possible pitfalls and issues. demonstrate the reader can: • Recognize the pitfalls and issues to restoring function and esthetics in certain Try-in and torquing of implants types of patients. • Be able to monitor peri-implant tissues. There is confusion between the torque • Identify the maintenance protocols after restoration has taken place. load delivered to the implant complex, the initial force transformation and stress devel- oped within the system during the implant implant complex. The insertion torque should favoring the formation of cartilage and complex assembly, and how the clamping not exceed 30Ncm, especially for immediate connective tissue. forces at the interfaces and the preload load implants, as higher insertion torques stress impact the implant prior to external above 50Ncm can generate high-compressive Common complications loading. The application of any external load stresses to the peri-implant tissues, causing (Goodacre, et al., 2003) to the implant complex must be preceded blood supply deficiency and bone necrosis by the assembly of the abutment onto the during the osseointegration phase, as well Screw loosening implant, achieved by tightening the abut- as early implant failure (usually within the first There are two main reasons why screw ment screw to create a stable screw joint month after placement) (Trisi, et al., 2009). loosening occurs: and, thus, form the implant complex. It is the A high insertion torque may occur during first step in preparing the assembled implant implant placement in high-density bone Incorrect torque complex to transfer loads. tissue. Under high stresses, significant Torque drivers should always be used to Accuracy, with respect to the applied changes impair the formation of new blood tighten screws. The correct preload must be load, is critical in the determination of load vessels, causing hypoxia in the peri-implant applied to the screw. The material of the screw transfer to and through the complex to the tissues, thus inhibiting bone formation and must be stretched to 80% of its elastic limit, bone. The dynamic nature of the implant complex assembly generated by a certain magnitude of torque loading is essential for understanding the response of any implant system to external loading. The contact forces, including the preload, are the first response to the torque experienced by the

Brenda Baker, BDS (Hons), MSc, graduated from Sydney University with honors and completed a master’s degree in conservative dentistry from Eastman Dental College. She has taught in the prosthetic faculty at Sydney University and pursued a preventively oriented career in private practice. Throughout her career, Dr. Baker has had a commitment to continuing education in a variety of disciplines, including , periodontics, and pain management and is currently director of clinical education for Southern Cross Dental.

David Reaney, BDS (Edin), DGDP(UK), MClinDent (Prosthodontics), graduated with distinction from the University of Edinburgh. He has held the position of clinical lecturer at the School of Dentistry, Royal Victoria Hospital in Belfast and is currently in private practice in Moy, Northern Ireland. Dr. Reaney is general manager of Southern Cross Dental. Figure 1: Anterior tooth esthetics are critical. Color data with shade tabs against various teeth will help guide the laboratory

Volume 8 Number 1 Implant practice 35 CONTINUING EDUCATION

Figure 2: Minimal space is evident anteriorly for esthetic functional reconstruction Figure 3: The irregularity of the occlusal plane is clearly illustrated when the patient’s mouth is partially open

which means that the screw will return to its There is always a small mismatch in Then, a cemented post and abutment can original length as the torque is released, and fit between the top of the implant and the be made with an impression of the internal the two components are clamped together. undersurface of the abutment due to the surface of the implant, and a new super- If the screw is tightened by hand, adequate tolerance during manufacturing. Forces structure fabricated. preload will not be achieved, which means are applied that cause a small amount of that the screw will not be stretched to its movement between the component parts Fracture of the superstructure full potential, and repeated screw loosening during function. If applied forces fall outside This can occur in either porcelain or resin, will occur. If the screw is over-tightened and the diameter of the implant, the movement as found by Molin and Karlsson (2008) and exceeds the elastic limit, it will become plastic between the component parts is magnified, Larsson and colleagues (2006). If the occlu- and not return to its original length. There will and the screw is more likely to become loose. sion has not been designed properly, or the also be no tension placed into the system. The diameter of the implant should match the interface between the veneering material and Thus, loosening of the screw will occur and diameter of the tooth that is being replaced as the underlying metal framework is placed may cause eventual fracture. The design of closely as possible. When considering multi- under stress, then material fracture can the screw head has an impact on the ability unit cases, the correct number of implants occur. The framework must be made rigid to apply the preload. Slotted screws do not should be chosen to allow even distribution enough to support the veneering material. allow enough preload to be applied. However, of the forces. Components should be chosen Extensive cantilevering can increase the square and hexagonal screws allow the from the same manufacturer, or the use of risk of fractures, as can parafunction. The preload to be transmitted through the screw, customized abutments specifically tailored occlusion should be checked in lateral excur- and either can be used. for each clinical scenario may prove to be sions to ensure that there are no interfer- A screw can loosen where the abut- even more accurate. ences. If a needs to be removed, then ment underlying the crown becomes loose, it is possible to either unscrew the compo- yet the crown remains cemented. Always Screw fracture nent — if it is screw-retained — or ease it replace abutment screws that have loosened Kim and colleagues found that screw off if it is cement-retained after having used repeatedly or are damaged. The crown may fracture occurs as a result of overloading an a temporary cement. not detach from the abutment easily. If the implant by occlusal forces (2005). The abut- If acrylic resin is too thin, it too will fracture crown will not separate, it may be possible to ment screws become loose and eventually when loaded, and the alignment of the screw cut a hole in the crown to expose the screw fracture. Incorrect preload may also create access hole, when using a screw-retained access hole underneath. The access hole ultimate screw fracture. Over-tightening of restoration, should be in the central fossa of may not be in the center of the abutment the screw may eventually cause fracture, the restoration to allow adequate thickness and can be difficult to locate. Considerable and occlusal overload caused by exces- of porcelain or acrylic. cutting of the crown can damage the under- sive cantilever design should be avoided. lying abutment and possibly lead to eventual The forces applied to the prosthesis should Inflammation and peri-implantitis replacement of the entire assembly. be controlled, and it is important to avoid Cochran reported that during main- It is also possible to cut through the damaging the internal thread of the implant. tenance, gingival inflammation can be interproximal contacts and unscrew the The worst case scenario is that the detected. It may either be mucositis, which whole assembly. Then, the abutment can implant would have to be removed surgically, is reversible without evidence of bone loss be relocated onto the implant and the screw the site be allowed to heal, and then a new or peri-implantitis (2002). Most frequently, torqued down. A new impression can be implant placed and restored once osseo- mucositis is caused by abutment loosening. fabricated to construct a new restoration. integration has occurred. The design of the The loosening of the abutment enables superstructure should be carefully planned bacterial infiltration. Mismatch between the diameter of the as this could cause fracture of the screw. If Lindhe and Meyle found that if the muco- implant and the width of the crown that the screw cannot be removed, it may have to sitis caused by abutment loosening goes the final prosthesis replaces be drilled out in order to salvage the implant. undetected, it can result in peri-implantitis

36 Implant practice Volume 8 Number 1 CONTINUING EDUCATION

(2008). Mucositis lesions can show apical progression after 3 months of plaque build- up around implants. In order to detect abutment loosening, look for abutment separation on the radio- graph — seen as a dark line between the components and prosthesis mobility. Abut- ment loosening can result in uncomfortable pressure on the prosthesis if gingival tissue has overgrown into the opened junction. The excess soft tissue must be removed before the abutment or prosthesis can be tightened back into place. Treatment of peri-implantitis involves inflammation control and modifying the exposed implant surface.

Occlusal evaluation The occlusal status of the implant and its prosthesis must be assessed routinely at Figure 4: These implants show excellent tissue health around the abutments every maintenance appointment. Occlusal overload can cause a variety of problems, including loosening of abutment screws, The patient’s motivation and skill in • Possible need for antimicrobials implant and prosthetic failure (Zarb and undertaking measures may • Re-evaluation of present mainte- Schmitt, 1990). Occlusal contact patterns influence prosthetic design. Importantly, if nance intervals that may be altered should be assessed, as well as the mobility the patient is unable to achieve adequate depending on the clinical situation of the implant and opposing dentition. oral hygiene, then this should be a possible • Mobility Successful implants should not be contraindication to implant placement. It is Any movement would indicate possible clearly mobile. A failing implant is not mobile essential to monitor peri-implant tissues at lack of osseointegration of the fixture, until all or most of the bone has been lost. regular intervals so that disease can be noted possible failure of the cement bond between Abnormal occlusal loading will negatively early in treatment if possible. the superstructure and the retainer, or screw affect the various parts of the implant- The maintenance appointment should failure by fracture or loosening. supported prosthesis. Hence, premature include evaluation of: If an abutment is loose, then the microgap contacts or interferences should be iden- • Presence of plaque and calculus and widens, which can result in the formation of tified and corrected to prevent occlusal oral hygiene a fistula. overload. There should be light centric • Clinical appearance of peri-implant By using the recommended torque contact with no contacts in lateral excur- tissue and deposit removal from settings, biologic considerations of the sions (Engleman, 1996). implant/prosthesis surface peri-implant areas, and adhering to certain Lundgren and Laurell believe that • Occlusal status and stability of pros- biomechanical principles governing abut- shim stock should be able to be held only theses and implants ment and restoration shapes and sizes, we with hard-clenched teeth (1994). Possible • Probing depths and presence of can avoid much heartache through careful bruxism and parafunctional activities must be exudates or bleeding on probing planning so that we have content patients evaluated as excessive concentrated forces • Patient comfort and function with favorable lifelong outcomes. can result in rapid and significant peri-implant bone loss. REFERENCES If a failed implant is connected to a 1. Cochran DL. Tampa and convenient diseases. [newsletter]. Academy of Osseointegration News. 2012;23(4):1, 13. 2. Engelman MJ. Chicago: Quintessence;1996. multi-unit prosthesis, it may mask evidence Occlusion in: Clinical decision making and treatment planning in osseointegration. 3. Goodacre CJ, Bernal G, Rungcharassaeng K, Kan JY. Clinical complications with implants and implant prostheses. J Prosthet of mobility. Dent. 2003;90(2):121-132. 4. Kim Y, Oh TJ, Misch CE, Wang HL. Occlusal considerations in implant therapy: clinical guidelines with biomechanical rationale. Maintenance protocols Clin Oral Implants Res. 2005;16(1):26-35. 5. Lang NP, Wilson TG, Corbet EF. Biological complications with dental implants: their prevention, diagnosis and treatment. (Lang, Wilson, and Corbet, 2000) Clinical Oral Implants Res. 2000;11(Suppl 1):146-155. These should be customized for the 6. Larsson C, Vult von Steyern P, Sunzel B, Nilner K. All-ceramic two- to five-unit implant-supported reconstructions. A random- ized, prospective clinical trial. 2006;30(2):45-53. individual patient. There is insufficient data Swed Dent J. 7. Lindhe J, Meyle J, Group of European Workshop on . Peri-implant diseases: Consensus Report of the on exact recall intervals, methods of plaque Sixth European Workshop on Periodontology. J Clin Periodontol. 2008;35(8 Suppl):282-285. and calculus removal, and appropriate anti- 8. Lundgren D, Laurell L. Biomechanical aspects of fixed bridgework supported by natural teeth and endosseous implants. 1994;4:23-40. microbials for maintenance around implants. Periodontol 2000. 9. Molin MK, Karlsson SL (2008) Five-year clinical prospective evaluation of zirconia-based Denzir 3-unit FPDs. Int J Prosthodont. Before implant placement, the patient’s 2008;21(3):223-227. ability for home care and motivation must be 10. Trisi P, Perfetti G, Baldoni E, Berardi D, Colagiovanni M, Scogna G. Implant micromotion is related to peak insertion torque and bone density. Clinical Oral Implants Res. 2009;20(5):467-471. assessed, and the patient must understand 11. Zarb GA, Schmitt A. The longitudinal clinical significance of ossseointegrated dental implants: the Toronto study. Part III: his/her role in caring for the implant. Problems and complications encountered. J Prosthet Dent. 1990;64(2):185-194.

Volume 8 Number 1 Implant practice 37