Occlusal reduction is a challenge I face daily in my practice. I want to make sure that there has been adequate tooth reduction and at the same time not taking away more tooth structure then necessary. This is also a common place that I realize I have under reduced when fabricating the provisional or worse yet when the lab calls or sends the restoration back thin. There are many ways to ensure I have created the right amount of reduction, but before i can do this, I need a goal in mind, so how much space to I need to create.
Having adequate occlusal reduction creates predictability of the final restoration, both esthetically and structurally. The evidence is clear when I look at the literature to see the success rates of all porcelain restorations in the posterior relative to occlusal reduction. Inadequate reduction increases the risk of fracture and failure of the restoration prematurely when placing all porcelain restorations. Due to the inherent physical properties of the porcelain, there are minimal thicknesses for success, and we need to prepare teeth to meet these parameters.
There is a magic number
The number is 2.0 mm of occlusal reduction, the applies to ALL occlusal surfaces. Although there are differences in the fracture resistance of the different types of ceramic materials currently being used for all porcelain posterior restorations, they all do well under these minimal thickness parameters.
To some this number may seem high which may bring up questions about conservative preparation. Predictably creating a minimum of 2mm of occlusal reduction in all of the load bearing areas is a key to predictable success. Now you have the magic number, create the reduction and verify it before taking final impressions.