Abstract
An abutment-tooth preparation with a full cast crown was done on the upper left second Premolar using Home position (H. P.) which, among the seating-posture during treatments, strictly specifies the relative relations of the dentist and patient. And measurement and examination of the prepared tooth form were made and the following conclusion was obtained:
1. The reduced extent of occlusal surface was excessively large at the buccal and lingual cusps while the minimum value was obtained at the central fossa area.
2. As for the reduced extent of axial surface, that at the buccal surface was half the value at other positions.
3. The reduced extent of subgingiva was excessively small at the buccal and lingual surfaces and at distobuccal line angle, with the value at the buccal surface, in particular, being about half as much.
4. The taper of axial surface showed high intensity at the distal surface in a treatment by any dentists. Consequently, a tooth which was given an abutment-tooth preparation tended to be reduced in such a way as to lean toward the mesio-buccal and distal-surface directions.
5. The time needed for the abutment-tooth preparation was about 11 minutes, 70% of which, or about 8 minutes, was accounted for by the operation of air-turbine. The most time-consuming work was the alteration and polishing.
6. The abutment-tooth preparation by the Home position system has almost achieved its goal in that it enabled even reduction of abutment-tooth. So, clinically, the H. P. system seems to be a method that can be highly evaluated.
