June 2006, Volume 2, Issue 5
Published by AEGIS Communications
Great White Ultra
Efficient and precise tooth preparation has been an integral component of restorative dental procedures since the conception of rotary instruments. Historically, carbide burs have been used for cavity preparations while diamonds have been used for crown and bridge preparations. Minimal preparation crossover has taken place for these 2 distinctly classified sets of rotary instruments, primarily because of the unique need for specific shapes, sizes, and grits necessary to complete each type of preparation. Carbide burs have been shown to cut more efficiently than diamonds when the substrate involves dentin1 because carbide burs cut with a shearing mechanism, whereas diamond instruments abrade the substrate. Another advantage of carbide burs over diamond instruments concerns clogging. Diamonds have been shown to clog at a much higher rate than carbide burs because the spaces between the diamond particles quickly fill with debris, and, as a consequence, their effectiveness in material reduction decreases rapidly.2
AN ALTERNATIVE TO DIAMONDS
SS White® has recently introduced a unique carbide bur that offers a fast and smooth cutting alternative to diamonds for crown and bridge preparations. Specifically designed for crown preparations, Great White Ultra operates differently from a diamond instrument because of its special blade design and carbide construction. Its unique dentated design cuts superbly, especially through mixed substrates, including existing amalgam, and composite restorations. Unlike many diamond instruments that can require multiple instruments to complete a crown preparation, the Great White Ultra bur allows the bulk reduction task to be completed as well as the placement of a smooth margin with a single instrument. It also clogs less because of its unique design. The Great White Ultra blade geometry results in a fast and smooth cutting instrument. Available in popular crown and bridge preparation shapes and sizes, Great White Ultra is the ultimate alternative to diamonds for crown preparation.
PARAMETERS FOR OPTIMAL SUCCESS
The requirement parameters for ceramic crown preparations should follow basic guidelines for achieving optimal success. Posterior crowns should incorporate a preparation, chamfer, or modified shoulder that eliminates all internal line angles. Occlusal depth requirements are generally a 2-mm reduction from the deepest fossa pits. Axial walls should ideally be reduced 1.5 mm.
Generally speaking, for anterior ceramic crown preparations, the chamfer or modified shoulder preparation remains ideal. Lingual surfaces should generally be reduced 1.5 mm at the area of centric contact and 0.8 mm to 1 mm along the remaining lingual surface. The degree of taper should be between 8 and 10 degrees, and the tooth preparation should include a 1.5-mm to 2-mm occlusal or incisal reduction.
References1. Roberson T, Heymann H, Swift E. Sturdevant’s Art & Science of Operative Dentistry. Elsevier/Mosby 4th ed. 2002; 340-341.
2. Siegel C, von Fraunhofer JA. Dental cutting with diamond burs: heavy-handed or light-touch? J Prosthodont. 1999;8(1):3-9.
The following case presents the appropriate reduction parameters for a ceramic crown preparation. (Figures provided by Dr. George Freedman, Toronto, Canada.)
Figure 1; Figure 2; Figure 3; Figure 4; Figure 5; Figure 6.
|The Great White™ Ultra Crown and Bridge Preparation Kit, designed for use with PFM as well as ceramic restorations.|
|Figure 1 Buccal preparation and chamfer margin placement is accomplished using the Great White Ultra 856-018.||Figure 2 The interproximal areas are easily prepared using the Great White Ultra 856- 016.|
|Figure 3 The Great White Ultra bur helps to provide precise, impression-ready margins.||Figure 4 The Great White Ultra 379-023 is ideal for occlusal/lingual reduction.|
|Figure 5 The 8-mm length of the 856 series Great White Ultra is ideal for preparing both anterior as well as posterior teeth.||Figure 6 The Great White Ultra 856-018 has a tip diameter of 1.45 mm, which meets the preparation requirements necessary for proper ceramic reduction.|