Ask Dr. Christensen

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 email to info@pccdental.com.

by Gordon J. Christensen, DDS, MSD, PhD

Question ...

Every current dental journal has advertisements for nonmetal crowns and bridges. The ads are confusing, because some of the products are advertised as though they can be used in any location for single crowns or fixed prostheses, and others do not emphasize multiple-tooth, fixed-prosthesis applications. Which brand can I use for a three-unit bridge?

Answer from Dr. Christensen ...

There are numerous all-ceramic products that can be used successfully for most patients for single crowns in any part of the mouth, and other products that are strong enough for use in the posterior or for three or more units of a fixed prosthesis. Among the most popular brands of all-ceramic restorations are Procera Aluminous from Nobel Biocare, and IPS Empress from Ivoclar Vivadent. Millions of single units of both Procera and Empress have been serving this need successfully for years, and dentists are relatively pleased with their service record. When these two brands of all-ceramic restorations are used as single crowns, fractures have been observed only infrequently. However, neither brand is indicated for use as a three-unit fixed prosthesis.

One of the most significant advancements of the last few years has been the introduction of zirconia crowns and bridges. The two most popular brands are Cercon from Dentsply Ceramco and Lava from 3M ESPE. Both brands use zirconia substructures, with fired ceramic as a veneering material. After several years of clinical and basic-science research — and a few years of clinical use — these types of crowns and fixed prostheses have demonstrated that they are the strongest all-ceramic restorations used in dentistry to date. Neither brand of zirconia restorations has been available long enough to be well-known among practitioners, and each brand still is establishing itself in the thousands of laboratories throughout the United States.

As you know, some patients demand — on the basis of personal preference — restorations that do not contain metal frameworks. Others have soft-tissue sensitivities to metal used in tooth restorations, and the gingiva around metal restorations in those mouths becomes inflamed, unsightly, and potentially pathologic. Still other patients, without significant scientific justification, feel that metal in the mouth can be associated with systemic disease conditions. All three categories of patients should receive informed consent about all-ceramic alternatives available for crowns or fixed prostheses, before initiating treatment.

For single crowns, inlays, and onlays, IPS Empress or many other similar brands of pressed ceramic provide unprecedented aesthetic acceptability. This type of restoration is my personal choice for single crowns in the anterior portion of the mouth when I am trying to match the color of adjacent teeth. Many clinicians suggest IPS Empress should be cemented with resin cement instead of conventional cements for additional strength. A stronger modification of IPS Empress, called IPS Eris, has been formulated for use for not only crowns, but also for three-unit fixed prostheses in the anterior part of the mouth. Both products are beautiful and well-accepted. IPS Eris is strong enough to be cemented with conventional cement, such as resin-modified glass ionomer instead of resin cement. Numerous similar pressed ceramic products are available from other companies.

Procera also is well-proven for single-unit, all-ceramic crowns. The aluminous ceramic understructure provides enough strength for routine use as single crowns and for cementation with standard cements. The recent introduction of zirconia understructure for Procera restorations improves its strength, and further developments are coming with this product for multiple-unit restorations.

To answer your question very specifically, selection of all-ceramic restorative material for a three-unit fixed prosthesis in the posterior part of the mouth is relatively limited. Cercon or Lava probably are the most popular and well-proven choices, but several other lesser-known brands could be considered as well.

For further information on all-ceramic restorations, see our video, V19-99, "Successful All-Ceramic Crowns and Fixed Prostheses." It shows all of the types and their indications, as well as new clinical techniques. For more information, contact Practical Clinical Courses at (800) 223-6569 or go to www.pccdental.com.

Question ...

I like the resin-modified glass ionomer cements for routine cementation of my crowns and bridges, but I still have occasional postoperative tooth sensitivity. It has not been as severe as it was with other cements I've used in the past, but I would like to reduce the incidence of this disagreeable problem.

Answer from Dr. Christensen ...

I have personally cemented thousands of restorations with resin-modified glass ionomer. I agree that this category of cement is excellent, since it bonds to tooth structure, is easy to use, has high strength and low solubility, and releases fluoride during service. The most popular brand is RelyX Luting Cement from 3M ESPE, and the same cement formulation is in its newer packaging and dispensing version, RelyX Luting Cement Plus. In my opinion, the self-measuring form, RelyX Luting Cement Plus, is desirable for most practices, since it eliminates the frustrating variable of too much or too little powder or liquid and the subsequent poor quality mixture.

The GC brand, Fuji Cem, also is a self-measuring form of resin-modified glass ionomer. It has captured a significant part of the cement market, because of its ease of use, fast set, and the ability to calibrate the dispensing device to release variable amounts of cement in relation to the quantity required for specific clinical situations.

Both of these brands of cements may help you to reduce the postoperative tooth sensitivity you have described, because you will have a correct mix almost every time.

There are other factors that may be contributing to your postoperative tooth-sensitivity challenge. Among them is potentially overdrying the tooth preparation prior to the cementation step.

The resin-modified glass ionomer cements require slight moisture to complete the chemical reaction and the bond to tooth structure. I suggest that when using this type of cement, you use the following technique:

1) Clean the prepared tooth with a slurry of flour of pumice and water on a rotating soft rubber cup. Do not allow saliva or blood to get on the tooth preparation after you have cleaned it.

2) Keep the tooth wet with water while you prepare the cement. At the exact moment you bring the crown or prosthesis to the mouth to cement it, aim the air syringe directly down the long axis of the tooth and blow for one second, while you rotate the air syringe around the periphery of the tooth preparation.

3) Cement the restoration immediately.

Contamination of the tooth preparation with blood, saliva, or other debris should be avoided during cementation, because these contaminants negatively influence the success of the cementation procedure in several ways.

If the tooth has been sensitive during the provisional restoration period, I advise using GLUMA from Heraeus Kulzer before cementation. Two 30-second applications of GLUMA after cleaning the preparation — immediately before cementation — will reduce or eliminate postoperative tooth sensitivity. Avoid getting GLUMA on the soft tissues.

When more cement strength is necessary, the resin cement, RelyX Unicem from 3M ESPE, has been shown to provide additional strength with almost no reported postoperative tooth sensitivity. This problem is avoided because of the incorporation of a self-etching primer in the formulation of the resin cement, thus sealing the dentinal canals during cementation.

If the described precautions and techniques have been carried out carefully, and the tooth pulp is not hyperemic or traumatized, there is little reason to expect any postoperative tooth sensitivity with the cements I have described.

For more information on the best cementation techniques, please see our recent videos, C504A, "RelyX Unicem — A Unique Self-Etching Cement" and C102A, "Cement — A Critical Choice." They are great staff-training aids! For more information, contact Practical Clinical Courses at (800) 223-6569 or go to www.pccdental.com.

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 to the dental profession in the well-known CRA Newsletter. He is an adjunct professor at Brigham Young University and the University of Utah. 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.

Dr. Christensen's views do not necessarily reflect the opinions of the editorial staff at Dental Economics.

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