March 2008, Volume 4, Issue 3
Published by AEGIS Communications
Question: Discuss the pros and cons of no-preparation,minimal-preparation, and full-preparation veneers
Ronald Goldstein, DDS; Wynn Okuda, DMD; Thomas Trinkner, DDS
Open up almost any consumer magazine today and you will find an ad for “no-preparation veneers that can magically change your smile.” I wish that was always the case, but the sad truth is that such cases are in the minority. In my practice, only about 10% of patients’ needs would be met with no preparation at all.
The majority of cases where no-preparation veneers are possible include: teeth that are lingually inclined that need more labial prominence; teeth that could use building out to give a more rounded arch, and partial or full laminate veneers to close unwanted spaces.
In my experience, the great majority of patients who choose porcelain laminates do so to brighten their smiles. However, because brightly shaded laminates tend to make the teeth appear more protrusive, patients may object to building out the teeth. The combination of a lighter shade and the surface position of the thicker anterior laminates may make the patient feel like the teeth are “sticking out” even more than they actually are.
The major problem with no-preparation or minimal-preparation laminates is the challenge of obtaining sufficient porcelain to mask discoloration in the underlying tooth structure. If the underlying tooth structure is very dark, it is usually a problem to use minimal- or no-prep-aration veneers unless sufficient tooth reduction is accomplished or the ability to build out the tooth with sufficient porcelain is esthetically possible.
A further challenge occurs with extremely dark teeth. Too many times, the underlying tooth discoloration tends to “bleed through” the laminates and creates a gray shadow either immediately after cementation or after a period of time. So the dark understructure must be masked with opaque porcelain, which often makes the laminates look fake or unnatural, compromising a successful esthetic result. In these types of cases, full crowns or aggressive tooth preparation may be necessary.
Preservation of dentition through minimally invasive care is essential in the evolution of dentistry. Whenever possible, min-imal intervention treatment should be first considered. In cosmetic/restorative treatment it is important to keep the end in mind. Through a proper esthetic diagnosis and treatment planning, we are able to understand how the final result should look before starting any tooth preparations. This is essential in determining what restorative procedures will be needed to accomplish the esthetic goals of the patient. Procedures such as “no-preparation” veneers, minimal-preparation veneers, and full-preparation veneers are all viable treatment options if used in the correct situation.
The advantage of no-preparation veneers and minimal-preparation veneers is minimal sacrifice of dental enamel. With the preservation of enamel, long-term success can be attained as a result of a strong adhesive bond to enamel. Moreover, bonding to enamel gives an exceptional overall strength to the final restoration. The disadvantages are that it takes more technical skill on behalf of both the dentist and the ceramist. Creating natural depth of shade in a thin veneer as well as neutralizing internal color problems are challenging issues. In addition, the emergence profile can be bulky and over-contoured if the porcelain margins are not finished properly.
With full-preparation veneers, the issue of over-contoured margins and problems resulting from irregular internal color are not readily seen if the procedure is performed correctly. However, the more invasive preparation depth that is necessary for a full-preparation veneer removes a significant amount of enamel, thereby relying heavily on dentinal adhesion. Depending on the circumstances, this can play a role in the long-term success of the final restoration.
Certainly, the chief argument for no-preparation veneer cases is the conservative nature of the preservation of tooth, but we have to be able to accomplish this with some sort of goal in mind—whether that be a clinical goal or the goal established by the patient. The cons for this technique include a very high technical difficulty in diagnosing each individual tooth appropriately as it relates to the patient’s goals. Also, we must keep in mind the fact that, although this is a noninvasive procedure, it is also an irreversible procedure. A conservative no-preparation case can become a poor clinical case when used the wrong way and the patient's goals are not reached.
As we looked at conservative no-preparation cases and worked through our diagnosis of appropriate areas for no reduction, we also tended to learn which specific tooth or multiple teeth may need to have slight modification or enamel-plasty. This leads us to the minimal-preparation decision-making process. We are actually defining minimal-preparation as an area where the no-preparation design will not work and not be achievable with material choices.
With more invasive preparations, the pros are that we have a more predictable result, especially esthetically, but the cons would certainly be more loss of tooth structure. When we have very conservative treatment where few teeth are prepped, it re-quires greater attention to shape, form, and color matching in post-bleaching shades, which can be quite challenging. Additionally, with more invasive preparations, we have to develop a strategy for treatment based on the underlying color and the degree of color change desired, and the clinician must also have determined the thickness of the ceramic material to modify underlying color and produce the desired optical result. The greater deviation between the existing preparation color and the final desired restoration color, the more aggressive the preparation will need to be to achieve a successful color match. With a more invasive preparation design, we have more control over changes in anterior function, which may be a driving force in design criteria.
|About the Authors|
|Ronald Goldstein, DDS |
Clinical Professor of Oral Rehabilitation
Medical College of Georgia School of Dentistry
|Wynn Okuda, DMD |
|Thomas Trinkner, DDS |
Columbia, South Carolina