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.

Question ...

Most of the dentin bonding agents I have are the light-cure type. I don’t have a dual-cure bonding material. When seating ceramic veneers, Empress crowns, or tooth-colored inlays and onlays, I don’t know when to cure the bonding agent. Should it be cured before seating the restorations or after they are seated?

Answer from Dr. Christensen ...

I have heard your question many times. But, apparently, the majority of dental-manufacturing companies have yet to recognize the problem, and they do not include this subject in their instructions.

Bonding agents have varying film thicknesses. As an example, Parkell Brush&Bond has a film thickness so thin that it does not interfere when seating an indirect restoration. However, most two-bottle, light-curing bonding agents have a film thickness that varies from 40 to 100 microns. The thickness may be more if the material is not blown very thin before curing. If you cured a thin bonding agent before seating a restoration, such as Brush&Bond, you would have no difficulty seating the restoration after it was cured. If you cured one of the thick light-curing bonding agents before seating the restoration, it is possible that you would not be able to seat the restoration completely.

Two excellent bonding products that have dual-cure chemistry - and eliminate the frustrating challenge just discussed - are OptiBond® Solo Plus SE (Kerr) and Prelude (Danville Materials). Both of these products, and a few others, allow you to seat the indirect restoration without curing the dual-cure bonding material. Place the cement on the restoration, seat the restoration over the uncured bonding agent, cure the cement and the bonding agent, and expect the cement and most of the bonding agent to cure. Any portion of the bonding agent not reached by the light cures by itself due to the dual-cure nature of the bonding material. Check the film thickness of the bonding material you are using and determine if you can cure before or after seating the restoration.

As you know, the most important reason for using a bonding material before seating restorations - such as ceramic veneers, Empress crowns, and tooth-colored inlays and onlays with resin cement - is to reduce or eliminate the potential for postoperative tooth sensitivity. Another option also is available. If the restorations can be seated with resin cement containing a self-etch primer component, you eliminate the problem you described. The most popular self-etching cements are RelyXUnicem (3M ESPE) and Maxcem (Kerr). The products’ only major limitation is that they are not indicated for veneer cementation.

Our new one-hour video, V1512 “Veneers, The Most Beautiful of Restorations,” shows use of bonding agents when veneer preps have both enamel and dentin exposed. For more information, contact Practical Clinical Courses at (800) 223-6569, or visit our Web site at www.pccdental.com.

Question ...

I am seeing both fired and pressed ceramic veneers advertised by laboratories. I am confused about which method is the best to fabricate ceramic veneers. Is one type better?

Answer from Dr. Christensen ...

Either fabrication method for ceramic veneers can produce excellent results. Some technicians tend to favor one type or the other. The fired-ceramic veneers are built and fired either on refractory dies (that can be heated to the fusion temperature of the ceramic being used) or on standard stone dies (that have platinum foil adapted to them). Different colors can be fired into the internal ceramic of the veneer, thus characterizing them to the desired esthetic appearance. If the anatomy of the veneer needs to be changed, the ceramic can be shaped and later smoothed and polished in the office, thus allowing cementation on that appointment. The most commonly used instruments to smooth the ceramic are the Brasseler Dialite ceramic polishing wheels that are available in various shapes and sizes.

Pressed-ceramic veneers are fabricated quite differently. A stone die is used to make a wax pattern representing the desired anatomy of the veneer. The wax is then invested and burned out. Molten ceramic is pressed into the void, just as a cast gold alloy restoration is made. These veneers are pressed from a molten ingot of ceramic that is all one color. Therefore, the desired color characterization for the veneer must be placed on the veneer in the laboratory using superficial, lower-fusing ceramic staining material. If the anatomy of these pressed restorations needs to be changed, the superficial color is removed in the area being altered. This contour change requires the veneer to be fired again to replace the color that was removed.

I have a personal preference for ceramic veneers fired on platinum matrices, because the color can be built into the ceramic internally. If necessary, these veneers can be altered. However, I feel confident that competent laboratory technicians can fabricate excellent veneers using either technique. The choice is yours - veneers are indeed the most beautiful of all restorations.

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.

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