Ｈｏｍｅ Ｐｏｓｉｔｉｏｎ診療姿勢が全部鋳造冠支台形態へ及ぼす影響について 上がく右側第１大きゅう歯

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The introduction of air-turbines has resulted in improved dental treatment and, consequently, the sitting dentistry has been designed and recommended in view ofwork simplification and the dentists' health. Studies and observations, however, are rare as to the influence of dentists' sitting positions on the external contour of prepared abutment.The present paper was, therefore, intended to evaluate the influence of the dentists' sitting positions on the abutment preparation of full cast crowns. The author studied Home Position, one of the following two categories reported by Kakehashi:1. Home Position (abbreviated as HT.)This dental treatment system arranges the dentist in a sitting position and the patient in a supine position. All the basic postures of a dentist during treatment is regulated exactly.2. Random Position (abbreviated as R. P.)This position allows various sitting positions up to the maximum range and most dentists usually treat the patients in this posture.The author here studied the tendency of the maxillary right first molar prepared at H.P. of five dentists with clinical experiences from two to five years.As a result of this study, the author arrived at the following conclusions:1. At occlusal surface, distobuccal and mesiolingual cusps were reduced deeper than the direction of 1.3mm of occlusal preparation ; on the contrary the central pit had less reduction.2. As to the four axial surfaces, the mesial surface were particularly reduced deeper than the direction of 0.6 mm in axial surfaces and the other surfaces were of same depth as direction.3. In spite of the direction for the subgingival reduction of 1.0 mm, lingual, mesio-buccal and distobuccal line angles were less than the direction of 1.0 mm in depth. The outlines of the lingual margin became scarecely observable.4. With regard to the taper angles of distal and distobuccal lines and buccal surfaces to the vertical axes all exceeded 3 degrees, which indicated the cutting instrument's angle. The buccal and distal surfaces on anyabutment showed more inclination (10 to 15 degrees). As a result, therefore, most abutment teeth appeared to incline in the direction of mesial from supposed crown axes.5. In view of the regular depths of preparation, abutment preparation at H.P. attained its objective except the taper angles. The author suggest that H.P. system could be given more credits and popularity as one of the efficient methods.