Analysis of dental preparation scanning data

Abstract

When a tooth has been wounded, there are several methods to repair it. One way is to remove the wounded part by grinding the tooth and replace it by a dental crown. In the manufacturing process one of the steps is to scan the cast model of the grinded tooth. Assume now that a mechanical probe scanner has registered a set of discrete points from the cast model. With the help of these points, a triangulated surface that represents the surface of the grinded tooth is constructed. In this paper an analysis of the scanned data has been done to see how well the triangulated surface represents the original preparation. This is done by constructing two surfaces between which both the triangulated surface and the surface of the cast model sit. Then the distance between the two surfaces is studied. In my calculations I have assumed that the hit between the probe and the surface of the preparation occurs at the top of the probe in the direction of the probe axis. I have also approximated the volume, see page 17, this is done since the programming is otherwise very time consuming. The calculations in this paper has been done on an upper premolar which was represented by 39 747 triangles. When the volume between the triangles and the lower surface was divided with the area of the triangles, , 92% of the triangles were approved, by this I mean that the average distance between the surfaces is not greater than the glue padding between the preparation and the crown. When the volume between the triangles and the upper surface was divided with the area of the triangles, , 99% of the triangles was approved. In the last case the volume between the two surfaces, was divided with the area of the triangles, , 95% of the triangles were approved. This indicates that the volume between the triangles and the upper surfaces contributes to a greater volume than the volume between the triangles and the lower surfaces. By visual analysis of Figure 21, convex surfaces gives a smaller tolerance which means better fitting than the concave surfaces with a larger tolerance.