Inside Dental Technology
October 2010, Volume 1, Issue 1
Published by AEGIS Communications
MasterClass: Hands On
No Grind Occlusion
Technique allows precise occlusion without high-speed occlusal carving.
Richard Pavlak CDT, MDT, FNGS
The No Grind Occlusion technique, since its introduction by this author in the mid-1990s, has greatly helped technicians fabricate natural-looking posterior crowns and bridges with precise occlusion without the need for high-speed occlusal carving. Using this technique, occlusal anatomy was created by careful manipulation of the ceramic material using the brush tip as opposed to post-fired grinding and carving. When a ceramist became proficient at using the no-grind technique, the total labor time to create the desired occlusal effect proved to be no greater than the time it took a ceramist specialized in the traditional overbuild–grind-in technique. However, the final results using the no-grind technique were infinitely better (Figure 1 and Figure 2).
The biggest obstacle for any ceramist who wanted to master no-grind occlusion was the length of the learning curve. One would have to be disciplined enough to not waiver from the technique for at least a month in order to master it. In a production situation this was difficult at best.
Today, flexible occlusal molds such as the Gnathoflex Premium molds (Bredent, www.xpdent.com) (Figure 3 and Figure 4) have taken the place of the no-grind technique, making the learning curve a thing of the past and increasing production capabilities. A ceramist with even the most basic knowledge of occlusal principles can become a no-grind occlusion expert in a very short period of time.
The crown presented in this article is an inVizion crown (Vident, www.vident.com), created using a flexible occlusal mold. The crown substructure was milled from shaded and sintered VITA YZ (yttria stabilized zirconia) and veneered with VITA VM9 ceramic material (Vident).
Occlusal Mold Technique
The milled zirconia coping (Figure 5) is coated with an ultra-thin layer of effect liner material. The effect liner layer is applied using VITA’s Akzent stain liquid (Figure 6) to ensure the thinness of the layer. When fired to its appropriate temperature (Figure 7), this layer serves several purposes. Not only does the effect liner establish an optimal bond for the porcelain layer and add fluorescence to the coping, but also creatively shades the coping with the addition of shade-appropriate stains (Figure 8).
Next, an appropriate occlusal mold is selected and coated with a ceramic separator (Figure 9). The mold is then filled with the proper shade of dentin porcelain (Figure 10). The filled mold is placed on the coping (Figure 11) and the articulator is completely closed into the maximum intercuspation position (Figure 12). The mold is slightly tapped and blotted to ensure a homogeneous ceramic mass (Figure 13), then carefully removed. Now there is an exact duplicate of the occlusal surface of the mold that is, at this point, in infra-occlusion (Figure 14). The remaining contours are quickly completed (Figure 15) with dentin material and the crown is removed from the model. A slight cut-back is performed and any voids are filled (Figure 16 and Figure 17). The crown is ready to be fired (Figure 18).
The post-fired crown is now checked on the articulated model. The contacts should be open with ample clearance for enamel porcelain (Figure 19). A thin layer of gray enamel is placed incisally and wrapped onto the mesial and distal marginal ridges (Figure 20). Some occlusal characterizations are applied with Akzent stains (Figure 21) and the crown is fired (Figure 22 and Figure 23). Note: The addition of gray-effect enamel could have been incorporated into the dentin bake and the staining done at the glaze stage to further increase production capabilities.
The fired crown is now ready for the enamel layer. The same flexible occlusal mold is again lubricated and filled with the selected enamel porcelain (Figure 24). The filled mold is now carefully seated (Figure 25), articulated (Figure 26), and vibrated and blotted just as in the first bake stage. The mold is carefully removed (Figure 27 and Figure 28). The proper effect enamel shade is selected (Figure 29) and blended to complete the contour (Figure 30). A predetermined effect enamel is used to complete the gingival to middle one-third contours (Figure 31). The crown is then carefully removed, contacts added (always add half the amount that is thought to be needed) and fired (Figure 32).
After firing, the crown appears close to final contour (Figure 33). All that remains is touching in the contacts and achieving the proper surface texture, which should take minutes if the crown was not overbuilt. The crown is now wetted with Akzent stain liquid (Figure 34) and subtle shade characterizations are carried out using the appropriate stain mixed with Akzent Finishing Agent in a 50/50 ratio (Figure 35). The occlusal mold thickness creates a space that causes slight deficiencies in the occlusion with the complete closure of the articulator upon each build-up. These discrepancies are corrected at the time of the glaze by using a mixture of correction material with effect opal in a mix of equal proportion and applying the mass to the appropriate occlusal areas (Figure 36). Note: The correction material fires at a much lower temperature than the enamel porcelain.
The glaze bake is carried out under vacuum because of the addition of correction material (Figure 37 and Figure 38). Using articulation tape, the case is checked on the solid cast for accuracy of contacts, contour, and occlusion (Figure 39). The occlusion in this case is slightly heavy on the mesial marginal ridge (Figure 40). This is carefully adjusted with a rubber point (Figure 41). When proper function is achieved, the entire crown is polished using diamond polishing paste (Figure 42). The finished crown is fit to the solid model and checked (Figure 43 and Figure 44).
The esthetic advantages of the inVizion crown are quite apparent when light is placed inside the restoration (Figure 45). The use of occlusal molds allows technicians to create highly esthetic posterior crowns and bridges at a production level that is competitive in the marketplace (Figure 46).
About the Author
CDT, MDT, FNGS
Porcelain-Plus Dental Systems Inc
Cranford, New Jersey