[A fundamental study on measurement of study cast]

The dental study cast has a complicated shape. Therefore, many dead angles are recognized during three-dimensional (3-D) measurement using a light source. To overcome this problem, several divisional measurement methods have been developed. However, in these methods, inadequate accuracy and the discontinuity of data were observed on the reconstructed image. In this study, a new divisional measurement method was developed and the overall accuracy was evaluated. The standardized stone model, which has three spheres, was kept by the specifically designed high precision jig. The distances between the reference points of each sphere were measured by using a 3-D curved shape measurement apparatus with a laser source. Then the values were compared with those obtained by using a contact type 3-D measurement apparatus. There were slight differences between the two methods, but they were not statistically significant. In addition, when the individual data were combined, the distances between the reference points of each sphere were not significantly different. These results suggested that the shape of the study cast can be accurately measured by the divisional measurement method.