The Influence of the Dentist's Positions on the Abutment Preparation of Full Cast Crowns
With Special Reference to the Home Positions
1983 Volume 27 Issue 2 Pages 292-307
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1983 Volume 27 Issue 2 Pages 292-307
The introduction of air-turbines has resulted in improved dental treatment and, consequently, the sitting dentistry has been designed and recommended in view of work simplification and the dentists' health. Studies and observations, however, are rare as to the influence of dentists' sitting positions on the external prepared abutment in crown and bridge procedures. The present paper was intended to evaluate the influence of the dentists' sitting positions on the abutment preparation of full cast crowns and then the author classified the sitting positions into two categories as follow:
1. Home Position (abbreviated as H. P.)
This dental treatment system arranges the dentist in a sitting position and the patient in a supine position and all the basic postures of a dentist is regulated exactly.
2. Random Position (abbreviated as R. P.)
This position allows the various sitting positions up to the maximum range and most dentists usually practise in this posture.
The author here studied the tendency of the upper left first molar prepared at H.P. of five dentists with clinical experiences of one to four years.
1) At occlusal surface, distobuccal and mesiolingual cusps were reduced deeper than the direction (1.3mm) of occlusal preparation, on the contrary the central pit had less reduction.
2) In four axial walls, particularly in the buccal and lingual grooves were reduced much shallower than the direction (0.6mm) in axial walls and the errors in depth were from half to one third of the direction.
3) In spite of the direction for the subgingival reduction (1.0mm), almost all the points were less than 1.0mm in depth. And clear outlines of the lingual margin became scarecely observable.
4) The convergence angles of each axial wall were larger than 3°, that indicated the cutting instrument's angle. And the lingual and distal walls on any abutment showed more inclination (15-20°).
5) In view of the regular depths of preparation, abutment preparation at H.P. attained its object except the convergence angles.
6) The increase of the number of the abutment preparations did not indicate morphological difference. While the total time to finish preparations decreased, the time to confirm the preparation tended to increase.
7) H. P. system, therefore, should be given more credits and popularity as one of the efficient methods to assure constant tooth preparation.
