Study On The Cervical Definition Of Impression And Accuracy Of Model With Individual Tray

Abstract:Objective:To compare the cervical definition of impressions with the individual resin tray impression technique, traditional alginate(ALG) impression technique and silicon rubber impression technique, and to appraise the three-dimensional(3D) accuracy of plaster models with the individual resin tray impression technique, one-step,two-step technique of silicon rubber and ALG impression technique. Methods:The abutment A1 and B1 were prepared on the master model, with 90°and 1mm shoulder in the dental cervix and 2°-5°incisal convergence angle. Then to prepared the artificial gingiva,with the shoulder of A1 equalizing the gingival margin and the shoulder of B1 0.5mm under the gingival margin. Obtained the impressions of A1 and B1 by the individual resin tray with ALG, ready-made tray with ALG and silicon rubber respectively when their gingiva have not been retracted and have been mechanically retracted. Rank-sum test was used to compare the cervical accuracy among the impressions. One-step technique, two-step technique of putty/wash polyvinyl silicone impression materials, individual resin tray impression technique and alginat etechnique were used to make impressions with different length of fixed bridge. Plaster models were made of all impressions.Vertical and horizontal dimensions between landmarks on the master and plaster models were measured with electronic caliper(precision is 5μm). LSD-test was used to compare the mean differences between the master model and plaster models. Results:There was no significant difference between individual resin tray with ALG group and silicon rubber group in the cervical accuracy, and there was significant difference between ready-made tray with ALG group and the traditional ALG groups.On three- unit fixed bridge model, there was significant difference between the test groups(one-step technique group and alginat etechnique group in vertical dimension (OG)) and master model group (P<0.05).There was no significant difference in other measurements. On five- unit fixed- bridge model, there was significant difference between the test groups(one-step technique group in occlusal midpoint dimension (IP) and alginat etechnique group in mesial-distal dimension (MD)) and master model group (P<0.05). On eight- unit fixed-bridge model, there was significant difference between the test groups(two-step technique group and alginat etechnique group) and master model group, and there was significant difference between the test groups(two-step technique group in OG and the individual resin tray with ALG in MD) and master model group (P<0.05). Conclusions:The indication of the impression technique with individual resin tray is better than the alginate impression technique, and it is similar to the silicone impression technique. The impression technique with individual resin tray was easy to make. Accurate impressions of each prepared tooth with the subgingival contour were smoothly obtained. It deserves to be extensively popularized.