Figure 4

Process of defining tooth preparation margin based on geometric algorithm. When the shortest distance to the tooth model was smaller than the error bound, each search point was updated with the vertex located on the crown area (blue vertices). When the shortest distance was bigger than the threshold (orange vertex and dark blue arrow), it was assumed to be around the preparation margin (A,B). Among the neighborhood vertices (yellow and green), the vertex with the biggest Laplacian value (red) was determined as the vertex on the preparation margin (C,D). By connecting the intentionally distorted distance field, the preparation margin can be mathematically detected (E,F).