The purpose of this study was to develop a three-dimensional measurement system and to investigate the influence of tray design upon alginate impressions.
This measuring system was made up of a measuring microscope and a personal computer.
A metallic model of a simplified maxillary dentition was prepared. Two types of trays were selected to make the impressions. One was a perforated stock tray and the other was an original occlusal tray which does not cover the undercut area of the teeth.
The coordinates of 19 points on the stone cast were compared.
The results were as follows:
1) This measuring system appears to be appropriate for measuring dimensional change and distortion of stone casts. This system could be applied to various uses.
2) The merit of this model is that part of dentition could be removed from the base. Therefore, both the master model and the stone cast were measured with the same three standard points.
3) Under the conditions of this study, all the stone casts had a tendency to be oversized.
4) The anterior teeth distorted toward the buccal direction, but the posterior teeth distorted toward the distal direction.
5) The cast made from the occlusal tray seemed to be more accurate than the cast made from the stock tray.