Diagnostico Salud Bucal

76

INSIDE DENTISTRY—MAY 2006

taLk
Edward A. McLaren, DDS, MDC

LAB

Laboratory perspectives from the inside out.

Porcelain Veneer Preparations: To Prep or Not to Prep
Edward A. McLaren, DDS, MDC

In recent years, bonded porcelain
restorations have geometrically expanded in their clinical use. Increased patient demands for esthetics coupled with the desire by the profession forconservative treatments have fueled this expansion. Early concerns about the fragile nature of the thin shells of ceramic have been allayed as multiple clinical reports have documented good to excellent clinical success. Because of this documented success, porcelain veneers have been used for more restorative situations and not for just esthetic enhancement. One exhaustive study that followedveneers for up to 15 years reported total failures of only 7%, equaling approximately a 1% chance of failure per year.1 Of the reported failures, more than half were fractures. Several other reports documenting the success or failure of porcelain veneers cite margin placement and

whether or not the margins were placed in enamel as the primary causes of failure. Bonding mechanisms and materials haveimproved over the years with bonding failure minimized because of these improvements. The main mode of failure with bonded porcelain is fracture and bond failure, which are interrelated. Many different causes can contribute to ceramic failure, including preparation design and proper tooth reduction. Confusion exists over the many different preparation designs, specifically whether or not to removetooth structure, how much tooth structure to remove, and margin design and placement. This article is intended to give rational guidelines on preparation parameters for porcelain veneers, particularly the issue of “to prep or not to prep” and, if prepping, “how much.” The ultimate goal in any dental treatment should be to be as conservative as

possible to obtain the desired result. The same istrue for bonded porcelain (porcelain veneers). Ideally, none or only a minimal amount of tooth structure should be removed. One decision that always needs to be considered is whether adjunctive orthodontics should be completed to place the teeth in the ideal position so that there is minimal or no reduction for bonded porcelain. In the authors’ experience, if the teeth require bonded porcelainanyway for reasons of form correction, color alteration, or replacement of failed restorations, and the amount of healthy tooth structure removal will be similar even if orthodontics is done, then bonded porcelain without adjunctive orthodontics should be accomplished. But if orthodontics significantly reduces the need for healthy tooth structure removal, specifically, if the preparation has tocross the dentinoenamel junction, then orthodontics should be completed.

Director, Center for Esthetic Dentistry Founder and Director Master Dental Ceramist Residency Program Adjunct Associate Professor The University of California, Los Angeles School of Dentistry Private Practice limited to Prosthodontics and Esthetic Dentistry Los Angeles, California

PREPARATION GUIDELINES FOR PORCELAINVENEERS
Preparations are always dictated 3dimensionally by how the final restoration is placed within the frame of the face, lips, and gingiva. This is determined by smile design with patient input and needs to be verified functionally. The clinician should work backward and remove tooth structure based on the specific material requirements for space (ie, thickness of the restorative material).Figure 1 Preoperative condition in which tooth No. 10 is in slight lingual version and the patient desires a fuller contour.

Figure 2 Postoperative view of a veneer which was fabricated with no preparation to alter contour.

In the case of a translucent material such as a porcelain veneer, the desired color or shade change needs to be considered. Generally speaking, a veneer requires a minimum...