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How to: Design Veneers

Dental Products ReportDental Products Report-2012-01-01
Issue 1

The proper use of laminate veneers facilitates esthetic outcomes while honoring biology and preserving hard tissue. Factors that affect the success of these restorations include appropriate preparation design, adequate reduction, marginal adaptation, stress management and distribution of occlusal forces.

The proper use of laminate veneers facilitates esthetic outcomes while honoring biology and preserving hard tissue. Factors that affect the success of these restorations include appropriate preparation design, adequate reduction, marginal adaptation, stress management and distribution of occlusal forces. The following technique honors these factors.

Appropriate reduction
The adhesive properties of bonding allow significant stresses to be applied to the tooth-restoration interface. A tooth preparation maintained in mineralized enamel ensures optimal bond strength while preserving tooth structure. However, if a final restoration contour is within the confines of the pre-existing tooth, irreversible tooth reduction is necessary.

Case presentation
Prior to anterior preparation, the amount of required tooth reduction should be evaluated via a pre-operative diagnostic wax-up. A silicone stint is placed over the unprepared tooth, and reduction requirements are determined (Fig. 1).

When the pre-existing tooth position is acceptable, depth orientation grooves may be the simplest, most accurate reduction guide. In the majority of clinical situations, however, changes in position and contour of the original tooth are desirable. When changes are needed in the original labial surface, the silicone reduction guide indicates where reduction is required based upon the desired final restoration position. Tooth reduction and depth-orientation grooves are increased or decreased so the final restoration has a consistent thickness.

Note: The minimum reduction amounts for veneer preparations are: gingival – 0.5 mm; mid-facial – 0.7 mm; and incisal – 1.5 mm. Typically, pressed ceramics require more thickness than feldspathic restorations.

Two depth-orientation grooves are placed so the final restorative incisal thickness is a minimum of 1.5 mm deep. This is completed with a 018 KOMET S6947KR round-end tapered diamond bur, which also is used for incisal reduction (Figs. 2 and 3).

Appropriate reduction is imperative at the gingival and interproximal marginal extent of the restoration. Inadequate reduction in these areas may result in either an over-contoured restoration or a thin, fragile margin that may affect the restoration’s structural integrity. Axial outline reduction addresses these aspects by initially “outlining” the desired interproximal and gingival perimeter of the preparation.

Appropriate reduction transitioning from the facial to the interproximal is best accomplished with a 012 KOMET 801 round-ball diamond, which ensures that prepping halfway into the round-ball depth in any direction results in 0.6 mm of reduction. This facilitates optimum esthetics and structural integrity by providing adequate reduction in the interproximal area.

The round-ball diamond is taken to one-half its depth, starting on the midfacial surface (Fig. 4) and carefully following the FGM. Note: Keep in mind that the height of contour, or “zenith,” is often slightly offset to the distal.

Midfacial outline reduction is then continued along the free gingival margin into the interproximal area. It’s continued from the interproximal into the previously completed incisal reduction.

The silicone index is placed to verify appropriate reduction. Note a reverse curve or “wing” of tooth structure remaining interproximally (Fig. 5). This will be eliminated later in the preparation sequence.

The 012 round-ball diamond is now used for placing facial depth-orientation grooves (Fig. 6). Assuming the pre-existing facial surface is the desired final restoration position, the bur is sunk to ½ its depth, resulting in 0.6-mm deep grooves. These groove depths are slightly lessened toward the gingival, and slightly deepened at the incisal. Note: Depth amounts vary depending on the type of restoration. More reduction is indicated for a pressed leucite-reinforced restoration as compared to amounts needed for either a pressed lithium disilicate veneer or a feldspathic restoration.

A 018 round-end tapered KOMET S6947KR diamond is used to complete facial reduction. Viewing this reduction to ensure it follows the contours of the adjacent teeth is critical. Note: This is NOT a “biplanar” reduction, which suggests that the facial reduction is in two planes. Instead, facial reduction is an “infinite planar” reduction, suggesting multiple planes with the resultant labial reduction being a gentle curve; it mimics the desired final contour and often mirrors the contour of adjacent unprepared teeth.

A cord is placed into the gingival sulcus to slightly displace the tissue. The cord occupies the space while creating minor apical displacement of soft tissue. This displacement results in maximal tooth structure exposure. The gingival margin is extended with the 012 round-ball diamond just to the FGM. The cord remains in place during scanning or impressions. When the cord is removed, the gingiva falls to cover the margin.

The wings that result from the interproximal reduction with the round-ball diamond now need to be addressed. A 012 flame-shaped KOMET 863 diamond is placed onto the interproximal margin and angled to flatten the wing, resulting in the extension of the margin moving slightly lingual (Fig. 7).

A diamond strip is used to further open the interproximal. The goal should be to open the interproximal area enough to pass a saw blade through. The use of the flame-shaped diamond eliminates the concavity of this proximal margin, which is desired for adequate structural integrity and optimum esthetics. For this reason, it is mandatory to re-establish this definition in the interproximal area with the round-ball diamond (Fig. 8).

The final proximal extension of the preparation varies depending on the clinical situation. Options include leaving the contact intact, minimally opening the contact, or extending the preparation lingually to open the contact. In this example, we demonstrate the technique for achieving minimal extension to achieve a slight separation with the adjacent teeth.

Wrapping the margin slightly into the proximal adds several esthetic advantages to veneer cases: It hides the margin, thereby improving esthetics as well as access for finishing, and it assists the ceramist with emergence contours. This is an area that often needs a thickness of material for translucency, thus the need for this space.

When attempting to close proximal spaces or hide unsightly tooth structure, cervical extensions may require minimal extension into the gingival crevice and slightly to the lingual.

The axial reduction and outline form should continue from the interproximal onto the initial incisal reduction. Suggestions have been made to extend the lingual margin, wrapping it over the lingual. The majority of marginal stresses occur at the palatal concavity area.1 For this reason, an incisal shoulder margin is suggested, protecting the margin from harmful tensile stresses in the palatal concavity. Note: The use of a long chamfer that extends into the palatal concavity is not recommended because it creates a thin extension of ceramic in an area of maximum tensile stresses. The incisal preparation design and extension is another area that may be modified in response to particular clinical situations.

Often, it’s the junction of interproximal to the incisal line angle that’s sharp or under-reduced. Many times, this is an area that’s high in translucency, requiring more space for the ceramist to be successful. Additionally, this can be an area that carries a heavier functional load, requiring structural integrity. For that reason, it is critical to subtly extend the proximal round-ball finish line onto the incisal shoulder to create a “Corner Cushion” (Fig. 9). This is a subtle reduction from the proximal onto the lingual shoulder that softens any sharp line angles, creates additional space for esthetics, increases space for structural integrity, and creates a positive seating area for bonding.

A 018 KOMET 8979K finishing diamond is used for refinement, eliminating any sharp internal line angles. Reduction and contours are verified prior to scanning or impressions. Figure 10 shows the completed preparation.

About the authors
Dr. Fling maintains a private practice in Oklahoma City. He has served as course director and clinical assistant Professor at the OU College of Dentistry. He currently serves as a guest lecturer at the College’s Department of Fixed Prosthodontics and as associate faculty at the L.D. Pankey Institute. Dr. Fling is the founder and president of Fling Seminars, and he lectures internationally on the principles of restorative dentistry and achieving technical excellence.

Dr. Kessler is the chairman of education at the Pankey Institute for Advanced Dental Education. After 20 years in private practice, he is now in his 14th year in dental education. In January 2007, Dr. Kessler became the Herbert T. Shillingburg professor and chair of the Division of Restorative Dentistry at the University

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