印象採得したインプラント作業模型の精度：３種類の製作方法の比較

抄録

In recent years, zirconia copings produced by CAD/CAM have been used as the superstructures of implants. Since it is considered that the accuracy of fit of superstructures influences the long-term prognosis, it is necessary to maximize this accuracy of copings. Therefore, we produced zirconia copings from three types of working model which were made by clinically applicable methods, and investigated the accuracy of fit of the marginal area in order to compare the precision of the models.
We used a master model in which a lab analogue of seven Straumann implants was established. After taking an impression of the master model, three types of working model were produced. Each working model was produced according to each conventional method, in which a dowel pin model was produced using die casts, a straw model was produced by pouring dental plaster twice using straws, and a Zeiser model was produced using the Zeiser system. Thereafter, zirconia full-bridge copings were produced using CAD/CAM, and, after inserting them into the master model, the marginal discrepancy was measured. Furthermore, the marginal discrepancy was measured in the same way when scanning the master model.
The mean marginal discrepancy was 62 μm in the master model, 164 μm in the dowel pin model, 106 μm in the straw model, and 105 μm in the Zeiser model. The discrepancy was significantly higher in the dowel pin than in the other models. Furthermore, the discrepancy was lower in the master model than in the other models.
It was considered that the expansion of plaster most strongly influenced the dowel pin model. In the other two models in which the expansion of plaster was controlled, dimensional changes were suppressed. Since there were no differences between the straw and Zeiser models, it was revealed that the model production method using straws was simple, accurate, and clinically suitable. However, since differences were found between the master model and the three models produced in the present study, it was suggested that some technical measures to achieve a passive fit is necessary in clinical cases.