A simplified approach to restoring implants
It seems everywhere you turn, Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) are involved in the designing and manufacturing of things we use every day, from cabinets and furniture to automobiles. Even in our profession of dentistry, we have been exposed to restorations like CEREC Chairside CAD/CAM from Sirona or copings like Lava from 3M ESPE that utilize CAD/CAM technology. Well, now it seems this knowledge and information have been applied to implant abutments in a universal system that can be used in conjunction with the many implant systems called Atlantis Abutment in Zirconia.
The next step
Computer-designed and -generated implant abutments will fundamentally change the present restorative protocols for implant dentistry. Standard implant prosthetic techniques rely on implant-level impressions and costly casting technology for component fabrication. Many dentists are uncomfortable making implant-level impressions and resort to time-consuming conventional techniques of intraoral abutment preparation, or they simply do not offer implants as a treatment option.
Implant abutments generated by computer-aided design and computer-aided manufacturing (CAD/CAM) are, in my view, more precise than those created using traditional casting technology. This increased accuracy has specific application to implant dentistry, where precision of components may affect implant longevity, prosthetic success, and ease of restoration. After reading this article, the reader should be able to recognize and understand the CAD/CAM application in the dental field when restoring implants.
A dental implant has three main components; the fixture, which anchors the implant to the jawbone; the abutment, the part that screws into the fixture and holds the crown in; and the crown, which replaces the coronal portion of the tooth (Figure 1). Perhaps the most challenging stage of the procedure for the restorative dentist is fitting the abutment.
Figure 1: Diagram of fixture, abutment, and crown
Figure 2: Atlantis abutments of teeth #12, 13, 14, 15
Figure 3: Crown restorations of teeth #12, 13, 14, 15
Figure 4: X-Ray of fixture, abutment crown complex
In the past there have been two main types of abutments available for restoring implants. These types include stock or prefabricated abutments and custom cast abutments.1 Stock titanium abutments are available from many major implant manufacturers in a variety of shapes, sizes, and angulations. They are adjusted or modified manually, either at the laboratory or in the office, to adapt the shape according to the position of the implant and the patient’s individual anatomy. When there is an inadequate volume of metal for proper reduction in order to establish margin definition, anti-rotation, and emergence profile necessitated by patient differences in tissue height and width, stock abutments offer few options.
Stock abutments
Although many successful restorations have been fabricated on stock abutments, severe limitations exist because of the size and shape of the stock abutments. Custom Cast Abutments (CCA) or UCLA abutments, which are fabricated from a plastic waxing sleeve, offered another type of abutment for the restorative dentist. This sleeve was modified by the technician to establish proper contours and emergence profile to compensate for any misaligned implants. Using the lost wax technique, the plastic sleeve is invested and cast into the alloy of choice. A CCA can be labor intensive, costly, and may contain porosities in the casting. Its success is directly related to the skill of the laboratory technician. However, CCA and UCLA abutments have also been wonderful restorative alternatives that have enabled clinicians to deliver excellent results.
Computer Milled Abutments
Computer Milled Abutments (CMAs) are the next evolution in abutment fabrication. Some of these systems currently on the market include; Encode from BIOMET 3i, Procera from Nobel Biocare, and Atlantis Abutment in Zirconia from DENTSPLY Implants. These abutments are milled from a block of titanium or zirconium, making them extremely strong, compatible with a specific implant, and without porosity inherent with the lost wax method.1,2 Unlike the other CAD/CAM systems mentioned that are implant specific, the Atlantis abutment system can be utilized with almost any implant company’s products.
As with other techniques, a fixture level transfer impression is required to locate the spatial and rotational position of the implant intraorally. Once a working cast is fabricated with a soft tissue model, and the lab analogs are in place, the cast is scanned optically to generate exact 3D images of the region. This includes the location of the analog and its anti-rotational feature. Through a patented process developed by Atlantis Components, Inc., one of the most current implant systems, a computer system views the adjacent and opposing dentition, surrounding tissue levels, and implant location to design an ideal, anatomically correct virtual abutment for the edentulous space accounting for all alignment and size requirements. The restorative dentist and lab technician can then design the abutment with certain guidelines that make the seating process easier and insure the long-term success of the implant-abutment crown complex.
The software program for Atlantis Abutments suggests setting the margins in relation to the free gingival margin with the following defaults: (1) facial/ buccal-1 mm subgingival (2) interproximal-0.75 mm subgingival (3) lingual/palatal-0.5 mm subgingival. After rigorous inspection on the computer screen, the virtual abutment designs are sent to a CNC milling machine to manufacture the morphologically correct abutment from a block of titanium alloy (Figure 2). The move from stock and custom abutments to computer aided design abutments has had a positive impact on both dentists and labs, and may represent the future of abutment fabrication. As seen in this photo the final crown restorations were easily fabricated due to the parallelism of the Atlantis abutments (Figure 3). Reviewing the x-Ray of the final fixture, abutment, and restoration clearly designates the effectiveness of this system (Figure 4).
More complex, multiple abutment implant restorations require a high degree of accuracy and parallelism to achieve a passive fit.7 These worrisome issues of parallelism and passivity are overcome by the Computer Milled Abutment process of the Atlantis system, adding a new level of confidence for dentist, surgeon and patient.1,2 Using this system, the virtual abutment created through computer aided design can be evaluated for proper morphology prior to the milling process. Once accepted by the restoring dentist, the final abutment has proper emergence, gingival contours, and contact points to promote healthy papilla formation. In other words, Atlantis Abutments provide the restorative dentist simplicity, precision, and time savings.
Advantages of the Atlantis Abutment:
- Compensate for offset or angled fixture placement
- Have an anatomical shape
- Increase crown retention
- Provide the ideal coronal preparation
- Create parallelism in complex, multiple-unit cases
- Are compatible with most implant systems
Conclusion
Computer-milled abutments have been shown to have significant advantages as compared to stock and custom cast abutments. These advantages include overall simplicity; reduction in the number of impressions; accuracy of fabrication; ability to create duplicate abutments; ability for accelerated treatment protocols; superior fit of copings to the abutment; significant reduction in chair time associated with the restoration phase; and a decrease in cost, especially with multiple abutments.
References
- Ganz S. How to Profit from Implants. Dental Economics. May 2005.
- Adams M. Computer-Designed and Milled Patient Specific Implant Abutments. Dentistry Today. June 2005. Volume 24 No. 6, pages 1-4.
- Misch C, Dietsch-Misch F. Diagnostic Cast Pre-implant Prosthodontics Treatment Prosthesis and Surgical Templates. 2nd ed. St. Louis, Mosby: 1999
- Sullivan P. Guidelines for Optimal Fixture Placement. In Parel SM, Sullivan DY, eds. Esthetic and Osseointegration. Dallas, Texas. Osseointegration Seminars Inc. 1989.
- Tarnow D, Elian N, Fletcher P, et al. Vertical distance from the crest of bone to the height of interproximal papilla between adjacent implants. J Periodontal. 2003; 74(12): 1785-1788.
- Miyasaki M. No Laser? Here’s what you’re missing. Dental Economics. February 2002; 70-74.
- Shillingburg HT, Hobo S, Whitsett LD. Fundamentals of Fixed Prosthodontics. Chicago, Ill: Quintessence Publishing; 1981:79, chapter 3.