Considerations in Abutment Selection

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1 Volume 36 No. 3 Page 74 Considerations in Abutment Selection Authored by Jack Piermatti, DMD Upon successful completion of this CE activity, 2 CE credit hours may be awarded. Opinions expressed by CE authors are their own and may not reflect those of Dentistry Today. Mention of specific product names does not infer endorsement by Dentistry Today. Information contained in CE articles and courses is not a substitute for sound clinical judgment and accepted standards of care. Participants are urged to contact their state dental boards for continuing education requirements.

2 Considerations in Abutment Selection Effective Date: 3/01/17 Expiration Date: 3/01/20 About the Author Disclosure: Dr. Piermatti reports no disclosures. Dr. Piermatti, a Diplomate of the American Board of Prosthodontics and a Fellow of the American College of Prosthodontics, is a former president (2015) of the American Board of Oral Implantology. He maintains a private practice limited to prosthodontics and implant dentistry in Voorhees, NJ, and is an associate professor of graduate prosthodontics and the director of the dental implant maxicourse at Rutgers University School of Dental Medicine in Newark, NJ. He can be reached via at jpiermatti@ yahoo.com, via phone at (856) , or visit dentalartsofsouthjersey.com. INTRODUCTION Dental implants have had a profound effect on prosthodontic treatment plans and have changed the way clinicians consider the mutilated dentition. Certainly, there has been a paradigm shift in the way we handle teeth that are periodontally compromised, grossly carious, or failing endodontically. Procedures such as periodontal flap surgery with ostectomy/ osteoplasty, mandibular molar hemisections, and maxillary molar root resections are used much less frequently in favor of extraction and implant placement. In general, furcated molars are not easy to maintain long-term, due to a propensity for early loss because of periodontal disease. 1 Undoubtedly, patients and doctors alike are much more likely to consider a case to be a terminal dentition and plan an implant-supported reconstruction rather than restore highly questionable natural teeth, since implants have become such a predictable solution. Because most clinicians consider an implant to be a better alternative than a marginally restorable tooth, it is critical for restorative dentists to be able to deliver a functional, aesthetic, and comfortable restoration that remains healthy throughout time. This often becomes challenging with the single-tooth restoration that must exist in an environment where adjacent teeth contribute to a harsh microbiological milieu. When considering the single-tooth implant restoration, proper placement of the implant fixture is only half of the challenge. After surgical placement, if healing has resulted in an osseointegrated implant surrounded by adequate keratinized epithelium and a dense and thick connective tissue complex, the implant is ready for the restorative phase of treatment. Attention must be paid to every detail of the case, from the initial impressions to the seating of the final crown. One often overlooked element of the restoration is the implant abutment. This one component often contributes to the success or failure with respect to aesthetics, comfort, and function of the cement-retained crown. Implant abutments designed for cement-retained crowns can be classified as either stock or custom and each has its advantages and disadvantages. This article will highlight the intricacies of material composition, design, fabrication, and delivery of the implant abutment for the cement-retained crown restoration. MATERIAL CHOICES Since the implant abutment emerges from the implant platform, this restorative component typically rests deep within the connective tissue complex. Obviously, the material composition of the abutment must be biocompatible with the surrounding tissues, and consequently, abutments are made of titanium, gold alloy, zirconium, and lithium disilicate. Some researchers have suggested that gold alloy is a poor choice for abutments. This is because inflammation and bone resorption have been reported in cases restored with this material due to a lack of mucosal surface attachment to the abutment. Conversely, abutments made of titanium or zirconium formed a mucosal surface attachment to the abutment. 2,3 These studies would suggest that use of titanium or zirconium abutments would be the material of choice. However, other studies have concluded that higher bone levels were not influenced by choice of titanium, gold alloy, or zirconium in abutment composition. 4 Due to the variable results achieved in the literature regarding abutment material composition, it is fair to say that additional study is indicated into implant abutment material compatibility and its effect on stability of peri-implant tissues. Generally, abutments composed of zirconium and lithium disilicate are reserved for anterior crown restorations since aesthetics is improved when the white color of these materials emerges through the permucosal tissues (Figure 1). Lithium disilicate satisfies aesthetic demands similar to zirconia, and when made as a 2-part component with a titanium base, provides adequate strength for a predictable restoration. Titanium can also be used for the anterior restoration, but anodization is advised in order to give the titanium material a warm, rich, yellow color, preventing gray shine-through of the permucosal tissues (Figure 2). 1

ABUTMENT DESIGN When considering the implant abutment, first and foremost, the component interface must be strong, secure, and resist screw loosening under function.

When reviewing the current literature, it is reasonable to conclude that prevention of component misfit and applying adequate torque to retaining screws are the most predictable methods for keeping

5,6 The importance of the implant abutment design for the cement-retained crown cannot be overemphasized.

Just as underprepared or malposed natural teeth result in unacceptable crown restoration contours, the same is true with respect to the crown cemented on a poorly designed implant abutment.

3 ABUTMENT DESIGN When considering the implant abutment, first and foremost, the component interface must be strong, secure, and resist screw loosening under function. Much has been written regarding screw-joint stability and maintenance of clamping force. When reviewing the current literature, it is reasonable to conclude that prevention of component misfit and applying adequate torque to retaining screws are the most predictable methods for keeping implant-abutment joints secure. These principles apply to all implants regardless of the nature of the implant-abutment interface morphology. 5,6 The importance of the implant abutment design for the cement-retained crown cannot be overemphasized. When abutments are designed poorly, it is often extremely difficult if not impossible to compensate for this and create a perfect crown restoration. Just as underprepared or malposed natural teeth result in unacceptable crown restoration contours, the same is true with respect to the crown cemented on a poorly designed implant abutment. As stated above, implant abutments can be either stock or custom-made and patient specific. Stock abutments are manufactured with both the profile and the finishing margin of the crown placed arbitrarily without regard to individual morphology (Figure 3). Stock abutments typically are circular rather than scalloped, and require modification either intraorally or at the laboratory bench. If the stock abutment has a premade scalloped margin, the gingival contour will not necessarily match the gingival contour of the patient. An additional complication of the stock abutment lies in the preparation of the abutment body. When an implant is angled off the direct axis plane, it may require excessive reduction to allow full seating of the crown. This reduction may compromise the retention and resistance form of the abutment body, leading to subsequent crown dislodgement under function. Lastly, stock abutments have a predetermined emergence profile. This is another significant disadvantage, since most cases require increased or decreased profile dimensions due to clinical conditions. Eliminating the ability to alter the emergence profile of the abutment makes creation of ideal contours of the final crown restoration much more difficult. Gingival embrasure form, crown contact areas, and aesthetics all are compromised when the abutment emergence profile is predetermined. If there is any advantage of the stock abutment, it is cost and availability. Custom abutments, on the other hand, are patientspecific that is, made specially for the individual case being restored (Figure 4). When accurate elastomeric impressions are taken of the healed implant fixture, a master cast with a silicone gingival simulation will provide an exact replica of Figure 1. Custom-milled zirconium abutment for a cement-retained crown. Figure 2. Custom-milled titanium abutments anodized to a yellow color. Figure 3. Stock abutments for NobelActive (Nobel Biocare) implants. Figure 4. Custom abutments for NobelActive implants. Abutment on left milled in zirconium, abutment on right milled in titanium. the patient s case on the laboratory bench. From the master cast, an ideally shaped implant abutment can be fabricated, satisfying all the parameters with which each individual case presents (Figure 5). The finishing line for the subsequent crown restoration can be placed 2.0 mm subgingivally on the buccal aspect and at or slightly below the gingival margin on the lingual. Easy access to the finishing line facilitates cement removal, thus ensuring a clean margin post-insertion. Emergence profile, which is the angle of the abutment as it projects from the implant platform, can also be idealized to properly manage the gingival embrasures (Figure 6). If the implant fixture is placed between 2 teeth and placement is too close to one of the teeth, emergence can be significantly reduced on one side of the abutment and increased on the other side, preventing the large black triangle often seen in 2

healthy bone/ gingival complex. Preparation of the body of the abutment can be designed with adequate bulk for retention of the final crown restoration.

The most common method of custom abutment fabrication in contemporary implant dentistry is CAD/CAM milling in either titanium or zirconium composition.

Alternatively, abutments can be waxed to proposed design characteristics and then contact-scanned with data sent for the same milling procedure.

4 implant restorations (Figures 6 and 7). If 2 implants have been placed too close together, the approximating surfaces of the 2 abutments can be made with zero or even negative emergence profile to create the space necessary to have a healthy bone/ gingival complex. Preparation of the body of the abutment can be designed with adequate bulk for retention of the final crown restoration. In the case of multiple abutments with splinted crowns, custom abutments can easily be fabricated with ideal tapering walls for proper path of draw of the restorative units (Figure 8). The most common method of custom abutment fabrication in contemporary implant dentistry is CAD/CAM milling in either titanium or zirconium composition. The abutments are designed virtually on a computer and, after approval, the data is sent to a milling machine that creates the abutments with extreme precision. Alternatively, abutments can be waxed to proposed design characteristics and then contact-scanned with data sent for the same milling procedure. Either way, the resultant abutment is smooth, strong, and free of fabrication defects. Abutments fabricated in lithium disilicate are made as a 2-part component. The body of the abutment is either milled in the CAD/CAM method or waxed on a titanium base. The body is then removed from the base, invested, and ceramic is pressed from a molten ingot. This part is then cemented to a premanufactured titanium base for a strong and durable component. Proper abutment design is critical for the cementable implant-supported crown restoration. Emergence profile of the abutment from the implant platform must permit support of the soft-tissue complex, and at the same time avoid impingement of the connective tissue. The intrasulcular morphology of the abutment must aid in development of an ideal gingival embrasure of the crown restoration, preventing food collection and contributing to papilla health. The abutment must have a well-defined crown finishing margin allowing complete cement removal, yet keeping the margin hidden within the sulcus for uncompromised aesthetics. CLOSING COMMENTS The author has concluded the only way to satisfy all the required parameters for a satisfactory restoration is by using custom, patient-specific, implant abutments for the cementretained crown.f References 1. Kinsel RP, Lamb RE, Ho D. The treatment dilemma of the furcated molar: root resection versus single-tooth implant restoration. A literature review. Int J Oral Maxillofac Implants. 1998;13: Figure 5. Custom-milled titanium abutments on maxillary master cast. Figure 6. Note mesial position of the implant. Figure 7. Mesial position of the implant corrected with a custom titanium abutment. Figure 8. Multiple units, custom-milled with ideal tapering walls and adequate bulk for crown retention. 2. Abrahamsson I, Berglundh T, Glantz PO, et al. The mucosal attachment at different abutments. An experimental study in dogs. J Clin Periodontol. 1998;25: Welander M, Abrahamsson I, Berglundh T. The mucosal barrier at implant abutments of different materials. Clin Oral Implants Res. 2008;19: Linkevicius T, Apse P. Influence of abutment material on stability of peri-implant tissues: a systematic review. Int J Oral Maxillofac Implants. 2008;23: Piermatti J, Yousef H, Luke A, et al. An in vitro analysis of implant screw torque loss with external hex and internal connection implant systems. Implant Dent. 2006;15: Theoharidou A, Petridis HP, Tzannas K, et al. Abutment screw loosening in single-implant restorations: a systematic review. Int J Oral Maxillofac Implants. 2008;23:

5 POST EXAMINATION INFORMATION To receive continuing education credit for participation in this educational activity you must complete the program post examination and receive a score of 70% or better. Traditional Completion Option: You may fax or mail your answers with payment to Dentistry Today (see Traditional Completion Information on following page). All information requested must be provided in order to process the program for credit. Be sure to complete your Payment, Personal Certification Information, Answers, and Evaluation forms. Your exam will be graded within 72 hours of receipt. Upon successful completion of the post-exam (70% or higher), a letter of completion will be mailed to the address provided. Online Completion Option: Use this page to review the questions and mark your answers. Return to dentalcetoday.com and sign in. If you have not previously purchased the program, select it from the Online Courses listing and complete the online purchase process. Once purchased, the program will be added to your User History page where a Take Exam link will be provided directly across from the program title. Select the Take Exam link, complete all the program questions and Submit your answers. An immediate grade report will be provided. Upon receiving a passing grade, complete the online evaluation form. Upon submitting the form, your Letter of Completion will be provided immediately for printing. General Program Information: Online users may log in to dentalcetoday.com any time in the future to access previously purchased programs and view or print letters of completion and results. POST EXAMINATION QUESTIONS 1. The author states that furcated molars are not easy to maintain long-term, due to a propensity for early loss due to caries. 2. The implant abutment often contributes to success or failure with respect to aesthetics, comfort, and function of the cement-retained crown. 3. Some researchers have suggested that gold alloy is one of the best choices for abutments. 4. Generally, abutments composed of zirconium are reserved for posterior crown restorations due to their superior strength. 5. When abutments are designed poorly, it is often extremely difficult if not impossible to compensate for this and create a perfect crown restoration. 6. When an implant is angled off the direct axis plane, it may require excessive reduction to allow full seating of the crown. 7. Eliminating the ability to alter the emergence profile of the abutment makes creation of ideal contours of the final crown restoration much easier to accomplish. 8. In the case of multiple abutments with splinted crowns, custom abutments can easily be fabricated with ideal tapering walls for proper path of draw of the restorative units. 4

6 PROGRAM COMPLETION INFORMATION If you wish to purchase and complete this activity traditionally (mail or fax) rather than online, you must provide the information requested below. Please be sure to select your answers carefully and complete the evaluation information. To receive credit you must answer at least 6 of the 8 questions correctly. Complete online at: dentalcetoday.com TRADITIONAL COMPLETION INFORMATION: Mail or fax this completed form with payment to: Dentistry Today Department of Continuing Education 100 Passaic Avenue Fairfield, NJ Fax: PAYMENT & CREDIT INFORMATION: Examination Fee: $40.00 Credit Hours: 2 Note: There is a $10 surcharge to process a check drawn on any bank other than a US bank. Should you have additional questions, please contact us at (973) o I have enclosed a check or money order. PERSONAL CERTIFICATION INFORMATION: Last Name (PLEASE PRINT CLEARLY OR TYPE) First Name Profession / Credentials License Number Street Address Suite or Apartment Number City State Zip Code Daytime Telephone Number With Area Code Fax Number With Area Code Address ANSWER FORM: VOLUME 36 NO. 3 PAGE 74 Please check the correct box for each question below. 1. o a. True o b. False 5. o a. True o b. False o I am using a credit card. My credit card information is provided below. o American Express o Visa o MC o Discover Please provide the following (please print clearly): 2. o a. True o b. False 3. o a. True o b. False 4. o a. True o b. False 6. o a. True o b. False 7. o a. True o b. False 8. o a. True o b. False Exact Name on Credit Card Credit Card # Signature Expiration Date This CE activity was not developed in accordance with AGD PACE or ADA CERP standards. CEUs for this activity will not be accepted by the AGD for MAGD/FAGD credit. PROGRAM EVAUATION FORM Please complete the following activity evaluation questions. Rating Scale: Excellent = 5 and Poor = 0 Course objectives were achieved. Content was useful and benefited your clinical practice. Review questions were clear and relevant to the editorial. Illustrations and photographs were clear and relevant. Written presentation was informative and concise. How much time did you spend reading the activity and completing the test? What aspect of this course was most helpful and why? What topics interest you for future Dentistry Today CE courses? 5

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