Abstract
In the random position (R. P.) where the patient lies on a dental chair and the operator sits on a chair for treatment, the left upper first molar is prepared for the abutment for a full cast crown. The author compared the measurement of the form of the abutment in R.P. and the date of home position (H. P.) conducted by Kakehashi. This study has led to the following results:
1. A significant difference in the amount of reduction for the preparation of the abutment between R. P. and H. P. was noticed as to the amount of the axial reduction and subgingival reduction on the buccal surface, and the taper degrees on both axial surfaces at the center of the buccal-lingual surfaces.
2. In comparison with the time required for the preparation of the abutment between R. P. and H. P., no large difference was noticed in the time of operation of the air turbine, while the time of non-operation in R. P. was about 1/3 of that in H. P., The total time required in R. P. was about 1/2 of that in H. P.
3. R. P. was superior to H. P. in a clinically important point of the continuance of the finish line as well as in the efficiency of operation; i. e. the total time reqired.
