PubMed · 802199
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T Jung. 1975. [Planning errors in cast model prostheses].. https://pubmed.ncbi.nlm.nih.gov/802199/
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This article describes a procedure for making an indicator to be used in fitting a casting to a die. It also describes how to use the indicator in the laboratory. The materials for making the indicator are inexpensive, present no health hazard, and are readily available at any arts and crafts store.
The self-glazing technique provides an esthetic and hygienic surface for crowns and fixed partial dentures that use porcelain veneers. A study of the biaxial flexure strengths of polished vs. glazed specimens is needed to verify that current laboratory methods are appropriate for planned fatigue studies. Four groups of 50 porcelain disk specimens each were subjected to the following polishing and firing procedures: group one was fired, glazed-no hold, and polished; group two was fired, polished, and glazed-no hold; group three was fired, polished and glazed-1 min. hold; group four was fired, polished, and not glazed. The piston-on-three-ball method was used for testing biaxial flexure strengths. Significantly lower differences in biaxial flexure strengths were noted when group two values were compared with values from groups one, three and four. The results show that the Weibull distribution is an appropriate model for our studies. Differences in glaze thickness among the groups were noted in SEM examination; however, bulk (interior) microcrack density differences were absent. The specimens that were fired, polished to a 1 micron surface finish, and not glazed (group four) were significantly higher in flexure strength than groups one and three at the p less than 0.001 level. The hypothesis that glazing of porcelain surfaces improves the biaxial flexure strength of test specimens was rejected.
The purpose of this research was to evaluate the clinical acceptability of various impression techniques by comparing the dimensional accuracy of their working casts. An original metallic model was designed for this experiment. It has reference points to overlap and compare the master model and the working casts for measuring their dimensional accuracy under the same condition. The amount of distortion in each area of the working casts was examined by the measuring points within the model. The master model simulated an abutment for a full veneer crown with undercuts between the adjacent teeth. It was planned so that the amount of undercuts and distances between the adjacent teeth could be changed. As a result, a small distortion of the working casts due to the undercuts was observed by the technique using an individual tooth tray and polysulfide rubber base impression material. There was no significant dimensional change in the working casts made with silicone rubber base material. For the working casts made by hydrocolloid-alginate combination technique, the dimensional change was greater and distortion was observed in the abutment cast when the undercuts of the adjacent teeth were great. However, the distortion was less when the undercuts were small.