Impression taking is essential step in prosthetic clinical work and a tray of an appropriate size and form must be selected to obtain accurate impressions. In taking impressions of edentulous jaws, in particular, the morphology of the alveolar ridge must be grasped precisely. Length and width of the alveolar crest therefore were measured and their correlation was examined.1. The coefficients of correlation of the maximal length of the alveolar crest with width between the posterior margins of the alveolar crest, with the width between the alveolar crest at the first molars, and with the width between alveolar crest at the canines were r=0.20, 0.43, 0.38, respectively, for the upper jaws, and r=0.14, 0.01, 0.02, respectively, for the lower jaws. No significant correlation was found.2. Significant correlation was found between the posterior margins of the alveolar crest and the width between the alveolar crest at the first molars and the width between the alveolar crest at the canines (r=0.66, 0.70) for the upper jaws.3. Significant correlation was found between the posterior margins of the alveolar crest with the width between the alveolar crest at the first molars (r=0.76) for the lower jaws.
Astudy was made on the effect of cooling methods on deformation occurring immedi − ately after molding of polyethersulfone resin (PES),adenture base materiaL The results were as follows : 1. In comparison with heat curing acrylic resin , considerable deformation was pro − duced in PES molded by routin methods . 2 . Gradual cooling of PES starting from the temperature for softening after com − pression molding restrained deformatiQn . 3. Keeping PES for about 30 minutes at the temperature for softening after com − pression molding restrained deformation . 4 . Keeping PES for about 30 minutes at the temperature for softening and gradual cooling thereafter restrained deformation most effectively , Key word8 : PE3 / Denture base material / D
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