In the early days of veneers, either a no-preparation or minimal tooth preparation, not extending into the dentin, was suggested.2,4,5 This is once again gaining popularity with certain companies. Dentists routinely remove at least 0.5 mm-0.8 mm of enamel. Removal of some enamel aids in achieving better bond strength,6,7 but care must be taken not to remove more than 0.5 mm-0.8 mm, especially in the proximal and cervical areas. Even though dentin adhesives have improved dramatically, porcelain bonding to enamel is better than porcelain bonding to dentin.8Depth Guide Cuts – Prior to preparation always examine study models in order to avoid over-reducing areas of the tooth that may be rotated or lingually inclined. Hence, the use of a reduction guide is recommended.
A diamond depth cut bur can be used to scribe horizontal depth cut grooves on the labial surface of any anterior tooth. Extend these grooves from mesial to distal, taking care not to damage the adjacent teeth that are not being prepared. It may be necessary to angle the bur in relation to the contour of the labial surface to achieve the appropriate depth for these guide cuts. The finish line of the preparation could end gingivally or supragingivally, approximately 0.5 mm incisal to cemento-enamel junction (CEJ). Do not place your gingival depth cut so as to cut into the CEJ area.
Labial Reduction – Using a tapered diamond, reduce the remaining labial tooth structure between the depth cuts. Simultaneously create a chamfer ending 0.5 mm incisal to the CEJ. This reduction should also extend interproximally. Opening the interproximal contact with the adjacent tooth is often preferable to better approximate the veneer and have a clear finish line in the master impression. In cases with mobile teeth and those having recently having completed orthodontics it may be advisable to not pass through the contact areas to prevent tooth movement during temporization.
Types of Veneer Preparation
The incisal edge is not reduced in length. This type of preparation is often used on cuspids and is done in order to preserve the natural guiding palatal surface of the tooth, which is important functionally. Add an additional space for the incisal porcelain by creating a chamfer along the facial incisal margin using the tip of a tapered diamond (Figure 3).
Laboratory InstructionsA detailed prescription is written to the laboratory technicians. The prescription should include: