October 2010, Volume 6, Issue 9
Published by AEGIS Communications
Brasseler USA Bur System
Depth-cutting burs designed based on average enamel thickness.
The primary goal of restorative dentistry is to preserve natural tooth structure while achieving the desired esthetic outcome. The extent of the reduction when preparing teeth for ceramic veneers is dependent on the color and value of the underlying tooth structure, and the amount of space needed for the restorative materials to accomplish the established goals. If the underlying tooth structure is of normal color and value, a conservative preparation can be considered. If it is discolored or of low value, enough space must be created for the ceramist to correct the problem and eliminate the "show through" transition line of the preparation. Ceramic veneers have the highest success rate when the restoration is bonded to enamel rather than dentin. Relying on the cementation and bonding material to create the desired changes is highly variable and unpredictable, and should only be used if needed to enhance the outcome.
The Bob Winter Restorative Design Prep Kit #K0197 (Brasseler USA, http://www.brasselerusa.com) contains all five depth-cutting burs (Figure 1 and Figure 2). The two incisal depth-cutting burs are designed to create adequate space for the ceramist to develop natural internal characteristics and translucency in the incisal edge of the veneer restoration. This reduction is determined based on the definitive length of the final restoration. In addition, a series of three depth-cutting burs was developed so that the label reduction is tapered and corresponds to the average enamel thickness of anterior teeth. They are used in two planes to follow the labial morphology (Figure 3). The average enamel thicknesses of anterior teeth are: 1.2 mm to 1.3 mm in the incisal one third; 0.8 mm to 1 mm in the middle third; and 0.3 mm to 0.5 mm in the gingival third.
- The RW 2.0 is a 2-mm reduction bur to be used as an anterior incisal-edge depth guide for ceramic veneers when no core is required, and as a posterior occlusal depth guide for posterior ceramic restorations.
- The RW 2.5 is a 2.5-mm reduction bur for use as an anterior incisal-edge depth guide for extensive veneers and for full-crown restorations, and provides a 2-mm space for layering ceramic and a 0.5-mm space for the core material (metal, zirconia, etc)
- The RW Mand is a labial depth-cutting bur that provides 0.7-mm reduction in the incisal one third, 0.5-mm reduction in the mid tooth, and 0.3-mm reduction in the gingival one third.
- The RW Max is a labial depth-cutting bur that provides 0.9-mm reduction in the incisal one third, 0.7-mm reduction in the mid tooth, and 0.5-mm reduction in the gingival one third.
- The RW Press is a labial depth-cutting bur that provides 1.2-mm reduction in the incisal one third, 1-mm reduction in the mid tooth, and 0.8-mm reduction in the gingival one third.
If the underlying tooth structure is of normal color and value and there is minimal change in esthetics required, a conservative tooth preparation can be considered. The RW 2.0 and RW Mand burs would be used.
If there is moderate change desired in the ultimate color and value, a conventional reduction is recommended. The RW 2.0 and RW Max burs would be used.
If there are significant color/value changes, or if there is a combination of veneers and crowns, a greater reduction is required to allow the restorative material to be similar between the two types of restorations. To create natural depth and translucency in the final restoration, whether it is a crown or veneer, 0.5 mm of enamel ceramic is recommended. The RW 2.5 and RW Press burs would be used.
By following the guidelines as suggested, you can produce a highly predictable result (Figure 4). While dentists strive to do only minimally invasive procedures, in some cases a more significant reduction is in the best long-term interest of the patient, if the goal is to create a natural-looking restoration.
This article was written by Robert R. Winter, DDS.
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