[Utility of the impression technique with the individual tray for cast crown]

This study was executed at an opportunity for taking the impressions of a full crown abutment tooth by the five different methods with the four different impression materials; the copper ring tray on the abutment method with the polysulfide rubber, the resin ring tray on the abutment method with silicone rubber, the wash technique with silicone rubber, the hydrocolloid impression technique and the hydrocolloid-alginate impression technique. The reproducibility of the preparation margin on the ten stone dies was photographically measured and the following results were obtained. 1. The reproducibility of the preparation margin was affected considerably by the following conditions. 1) The character of the impression materials, 2) the position of the preparation margin in the gingiva sulcus and 3 the undercut degree beneath the preparation margin. 2. The impression technique with the individual ring tray on the abutment showed great utility under any condition of the preparation margin on the abutment. 3. The impression method should be selected clinically according to the condition of the abutment.