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 [email protected].
Question ...
On upper anterior teeth, which restoration has the greatest longevity potential - veneers on enamel, veneers primarily bonded to dentin, porcelain-fused-to-metal crowns, or the new zirconia-supported, all-ceramic crowns?
Answer from Dr. Christensen ...
To say I can answer this question scientifically would be an overstatement. However, I will attempt to answer it by extrapolating my experience with thousands of restorations of each type, except zirconium-oxide-based crowns, which are relatively new. PFM crowns have been used for nearly 50 years. Experienced dentists know that they have an esthetic life expectancy of at least five years and a functional longevity of 20 years or more. Superficial stains soon are removed by foods and drinks that contain acid, and gingival recession allows a chalky appearance and/or metal to show near the gum line, but the PFM crowns still serve functionally for many years.
In my experience, veneers bonded to enamel are as strong as virgin teeth if placed properly and with the incisal edge of the tooth properly covered with the ceramic. Since there is no metal line at the gingival margin, gingival recession does not cause a significant esthetic degeneration. They will serve much longer than PFM crowns. In more than 20 years, I have accomplished thousands of ceramic veneers cemented to enamel, and have replaced less than 10. How long will they serve? Only time will tell.
Veneers bonded to dentin are another story. As with veneers bonded to enamel, they do not have an esthetic degeneration when gingiva recedes. However, the threat of pulpal death on a small percentage and the reality of the veneers coming off during service make this type of veneer, in my opinion, less predictable and shorter-lived than PFM crowns or veneers cemented to enamel.
Where do thin veneers fit into the longevity picture? To date, their longevity is promising. Some dentists have reported success with them for many years. However, long-term observation by many dentists and comparative controlled studies are necessary for final conclusions. The only questionable characteristic for these minimally invasive restorations is the fragile, thin ceramic covering the incisal edge, the location of which must be planned carefully for optimum longevity potential.
The zirconium oxide-based, all-ceramic crowns and three-unit fixed prostheses, such as Lava™from 3M ESPE or Cercon® from DENTSPLY, are serving very well in clinical practice and Clinical Research Associates clinical investigations to date. Time is needed for final judgment.
To summarize, it is my opinion that veneers placed on enamel and PFM crowns are well-proven, long-lasting restorations. For the reasons discussed, it should be expected that veneers placed on dentin have less longevity potential. For my mouth, I would rather have a zirconium-oxide-based, all-ceramic crown than a veneer placed on dentin, if the destruction of the tooth requires such a deep preparation. It has been my observation that crowns are stronger than veneers placed on dentin. Only long-term, carefully controlled clinical studies would answer your question more adequately.
Question ...
Lately, I have seen much advertising for no-prep veneers, such as Lumineers™ from Den-Mat® and others. Is this type of ceramic veneer acceptable when compared to veneers placed on teeth that have significant tooth structure removed?
Answer from Dr. Christensen ...
No-prep veneers have been in the profession for many years. However, they have been popularized in recent months as Den-Mat reintroduced its original veneer concept. As a result of Lumineers’ functional and economic success for dentists and laboratory technicians, other companies are now emphasizing these noninvasive, minimal, or no-tooth-preparation veneers. As I see it, the interest in this type of veneer is almost a backlash against the highly promoted, deeply cut veneers seen by the public on various TV shows and promoted by some laboratories. In fact, some well-known commercial dental laboratories have influenced dentists to cut deep veneer preparations because the laboratory owners claim they are better veneers.
Are veneers placed deeply into dentin “better” veneers than the thin, superficially placed ones typified by Lumineers? What could possibly be better about the deeply prepared veneers? Let’s look at it from the technicians’ standpoint. Thick veneers have an inherent color that is the color the dentist prescribed. Usually, they are so thick that the color of the resin cement used to retain them or the color of the underlying tooth has little influence on the final veneer color. Additionally, when using thick veneers, the contour of teeth can be changed easily, creating any form the dentist, patient, or technician prefers. These apparent advantages are positive for both technicians and dentists, but ... are they advantages for our patients?
Deeply cut veneers almost always have transient or long-term postoperative tooth sensitivity. Some create pulpal death because total-etch bonding agents are unable to predictably eliminate ingress of the damaging constituents of resin cement into the dentinal canals. At this time, self-etch bonding agents aren’t indicated for veneer placement on enamel because of their slightly less-aggressive etch of enamel and dentin surfaces. However, self-etch resin cements are highly advantageous for crown cementation because they provide predictable tooth desensitization, and crowns don’t require the same extreme chemical/mechanical retention as veneers provided by total-etch systems.
No-prep ceramic veneers can be used for many patients. Obvious examples include patients with small teeth, lingually placed teeth, spaced teeth, and even some teeth of relatively normal anatomy. Obviously, over-contouring of normal or large teeth is a possibility with no-prep veneers, and this is their limitation. If teeth are large, are in a prognathic location, or even if some are normal in shape and size, minimal to moderate enamel removal is probably indicated to ensure that an over-contoured, “buck-tooth” look is not produced.
To answer your question, no-prep veneers appear to be viable, responsible restorations for many patients if the same care and precautions taken for more conventional veneer preps are observed.
Our newest release, V1512 “Veneers, the Most Beautiful of Restorations,” shows the complete veneer procedure, including making provisional restorations. For more information, contact Practical Clinical Courses at (800) 223-6569, or visit 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.
