Ask Dr. Christensen

In this monthly feature, Dr. Gordon Christensen addresses the most frequently asked questions from Dental Economics® readers.

In this monthly feature, Dr. Gordon Christensen addresses the most frequently asked questions from Dental Economics® readers. If you would like to submit a question to Dr. Christensen, please send an e-mail to info@pccdental.com.

Ask Dr. Christensen | Gordon J. Christensen, DDS, MSD, PhD

Q: I just treatment planned for a three-unit fixed-prosthesis to be attached to two relatively broken down, but built-up vital abutment teeth. Is there some way I can give these teeth more support and retention to potentially provide longer-term service for the patient?

A: I assume that the teeth have been built up using bonding agents, composite resin, and maybe pins for retention of the build-up material. Further, I assume that you will be able to preserve at least 1.5 to 2 mm of solid tooth structure around the gingival portions of the tooth preparations to provide a collar of tooth for retention of the prosthesis. If these characteristics are present - and strong resin or resin-modified glass ionomer cement is used - the chance for adequate fixed-partial denture longevity is good. However, occasionally, the previously described characteristics cannot be obtained.

The following technique is under study and patients should be told this, but I have had excellent success with this procedure in solving the problem you described:

  1. On the day of the tooth preparation, place a “mini” implant in the center of the pontic area through the soft tissue without a flap procedure. Make the “mini” implant parallel to the “draw” of the tooth preparations. These small implants are minimal in diameter, as narrow as 1.8 mm. Most pontic areas have at least 4 mm of bone in a facial-lingual direction, which is necessary for placement of a “mini” implant. I prefer 13 mm of bone in a crestal-apical direction. Many pontic areas do not have 13 mm of bone in a crestal-apical direction, and although they are not my choice, “mini” implants as short as 10 mm can be used. The most popular “mini” implant company is IMTEC MDI Sendax [(800) 879-9799 or www.imtec.com].
  2. Place an abutment on the “mini” implant. Abutments are available from the manufacturer. Make an impression of the tooth preparations as usual, which includes an impression of the cemented pre-made abutment. There are various techniques to attach the fixed prosthesis to the “mini” implant, including use of the manufacturer-made abutment. Consult with the manufacturer concerning the best technique for your specific situation.
  3. Make the fixed prosthesis to fit the two tooth abutments and the “mini” abutment.
  4. On the second appointment, cement the fixed prosthesis over the two teeth and the “mini” implant with strong resin cement to avoid the mesial or distal tooth abutment coming loose from the tooth preparations and causing intrusion of the affected tooth. For extra retention of the fixed prosthesis, use diamond rotary instrument roughening of the internal of the crowns fitting the tooth abutments and the tooth preparations themselves. “Mini” implants can be loaded immediately for many situations, including the one described.

Although this technique is a last resort for atypical low-strength, low-retention cases, it has been successful in such situations, as well as for salvaging prostheses that have come loose during service. More clinical research is l needed, and positive reports continue to come forth on the success of “mini” implants for many uses.

Our new PCC video, V2317 “Mini Implants for Your Practice,” shows in close-up, live clinical procedures the most up-to-date selection and use of small diameter implants for fixed and removable prostheses. Live clinical cases are demonstrated. For more information, contact Practical Clinical Courses at (800) 223-6569, or visit our Web site at www.pccdental.com.

Q: I was taught in dental school that glazed ceramic was the most appropriate material to place adjacent to gingival tissues or to have occluding with opposing teeth. When I have to change the contour of ceramic contacting gingival surfaces or on an occlusal surface, how should the altered ceramic surface be smoothed for the best gingival acceptance or the lowest occlusal wear of opposing teeth and smoothness?

A: There are many past beliefs that have been disproved by research. The old adage that fired ceramic was the best material to place adjacent to gingival tissues has been refuted scientifically. It has been found that the smoothness of the material is more important relative to gingival health than the composition of the material. With the exception of people who have actual sensitivities to certain dental materials, gingival tissues do not react differently to polished gold alloy or other alloys than they do to glazed, polished-fired, or pressed ceramic.

What should a clinician do when adjustment of the occlusion is necessary before or after cementation of a ceramic restoration? Occasionally, all clinicians are required to adjust ceramic restorations before cementing them in the mouth. Additionally, the more complex and multi-unit the ceramic restorations are, the more likely the necessity to adjust the ceramic restorations after cementation.

What should be done to the altered restorations before cementation, and what should be expected as the patient abrades the opposing teeth with the altered ceramic restorations? Obviously, the best technique is to have the crowns or fixed prostheses fabricated accurately so that occlusal adjustment is not necessary. Since that is impossible to accomplish much of the time, what can be done with a crown or prosthesis that is too high? I suggest several techniques:

  • Before trying the crown or prosthesis into the mouth, advise the patient that you may want to smooth and polish the teeth on the opposing arch after trying the new prosthesis into the mouth. You accomplish two purposes by telling the patient about the potential need to smooth the opposing teeth - you will make the opposing teeth smooth, and you will adjust restorations or enamel on the opposing arch without upsetting the patient about “grinding” on the opposing teeth.
  • Adjust and smooth the altered surfaces of the ceramic restoration before cementation. For single ceramic crowns or short-span prostheses, this is usually possible before cementation. This adjustment can be made with long-shank, straight-handpiece, large polishing wheels, such as Brasseler prepolishing wheels and Brasseler Ceramic Pro™ Dialite polishing wheels [(800) 841-4522, www.brasselerusa.com]. Following the Dialite polishing technique, further polish the adjusted ceramic surfaces with a stiff polishing brush and VH Technologies’ Diashine [(800) 628-8300, www.vhtechnologies.com].
  • If the restorations have been cemented and more adjustment of the ceramic is needed, perform the aforementioned technique with short-shank Dialite intraoral wheels in a low-speed contrangle handpiece, followed by VH Technologies Polish on a stiff short-shank brush.

If the ceramic used in the adjusted restorations contains small particles of low-wear ceramic, the polished ceramic surfaces will retain the polish nearly indefinitely. If the adjusted ceramic material contains large particles, the rough surface will reappear, along with the aggressive wear of teeth.

The best adjustment of ceramic restorations is no adjustment at all, but judicious adjustment and polishing of the ceramic surfaces is occasionally necessary.

Dr. Christensen is a practicing prosthodontist in Provo, Utah. He is the founder and director of Practical Clinical Courses, an international continuing-education organization for dental professionals initiated in 1981. Dr. Christensen is a co-founder (with his wife, Rella) and senior consultant of Clinical Research Associates which, since 1976, has conducted research in all areas of dentistry and publishes its findings in the well-known “CRA Newsletter.” Dr. Christensen has educational videos and hands-on courses on the above topics available through Practical Clinical Courses. Call (800) 223-6569 or (801) 226-6569.

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