Abstract
Lately many researchers are advocating the dentist's posture known as the Home Position, claiming the need for reappraisal of the sitting posture from the standpoint of the systematization of work and the health of the dentist. In fact, theeffectiveness of the Home Position on cavity preparation has been observed from the standpoint of restorative dentistry, but there are many unclear points on the abutment tooth preparation of fixed prosthodontics. The author undertook a study of the effect that will be exerted on the prepared abutment tooth contour, when an abutment tooth was prepared for full cast crown of the mandibular right first molar. As the result of this study the author reached the conclusions as follows.
1. The distinctive features of the contours of the abutment prepared under the Home Position system were observed on the reduced extent of occlusal surface, the reduced extent on subgingiva and the axial tapers, but not on the reduced extent on axial surface.
2. The reduced extent of occlusal surface in excess of the directed extent was found on the mesiolingual cusp, the lingual groove and the mesiolingual cusp.
3. Subgingival reduction close to the directed extent was found on the lingual and distal surface; in the other parts, reduction had not reached the directed values.
4. Axial taper in excess of the directed degree was found on the distal surface, distolingual lineangle, lingual surface and mesiolingual lineangle. As the result the abutment teeth on the whole inclined in the direction of the mesiobuccal side.
5. While abutment tooth preparation for the full cast crown of the mandibular right first molar under the Home Position system gives rise to problems in the detailes of work, which constitute one of the most important clinical procedures like the continuity of margin, the present system has been found to be the clinically effective abutment teeth preparing method on the point of allowing work in conformity with directions.
