Abstract
The right lower first molar is prepared for the outside abutment for a full cast crown in the random position (R. P.). In order to clarify the possible effect on the abutment form, the amount of reduction of the abutment was measured. In comparison with the results obtained in the home position (H. P.) by Koizumi, the following results were obtained.
1. A significant difference in the effect on the abutment, resulting from a difference in position between R. P. and H. P. was noticed in the taper degrees, especially on the axial surface; the imaginary crown axis was inclined to the distal proximal side, in the opposite direction from that in H. P.
2. In comparison with the time required for the preparation of the abutment between R.P.and H.P., no significant difference was noticed in the time of operation or in the non-operatingtime of the air turbine.
