歯科鋳造過程における表面あらさの変化
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概要
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Surface roughness of the cast restorations may sometimes affect their fit or retention on the prepared teeth. It has been reported that the abutment teeth generally have the roughness of 2 to 40μm on their surfaces after preparation. The roughness will be unexpectedly changed in the various succeeding processes from taking impression to casting and finishing. The present study was scheduled to find out the changing aspects of the roughness in the series of the process, by comparing the surface roughness of the original, the stone model and the casting with one another. Metal blocks having uniform V-shaped grooves on the tapered axial surface were made to simulate the abutment teeth. The grooves on block A, B and C were 16.80, 28.00 and 38.10μm in depth respectively. These values were treated as the roughness of the blocks. A glass plate was also employed as the control surface having no grooves. When a silicone rubber or a polysulfide rubber impression material was used, the smooth surface of the glass plate and the grooved surface of block A were reproduced with a few micrometer larger roughness on the stone model. Judging from the fairly well duplicated details of the grooves on the model, setting expansion of the stone might be regarded as one of the main factors to cause such an increased roughness value. For blocks B and C having deeper grooves, on the contrary, the reproduced stone model exhibited a general tendency to decrease in roughness value, owing to the slight distortion of the convexes toward the removal direction of the impression as well as the dull convexes and concaves resulting from the incomplete flow of the impression material and/or the stone slurry into the detail of deep grooves. Hydrocolloid impression materials seemed to intensify this tendency by an additional effect of their interaction with the stone at the interface. The roughness value of the stone model obtained from the agar impression became significantly larger than that from the rubber impression for the glass plate, and the roughness change of the former model was several per cent smaller than that of the latter for all the blocks. Alginate impression material yielded dramatically roughened surface and shallowed grooves on the stone model. The roughness of the model was significantly lowered by the sequent casting process. Especially the deepest grooves were markedly shallowed on the casting. It may be due to the breakdown of the convexes at their tops on removal of the wax pattern from the model in addition to many effects such as the poor abilities of the wax, investment and casting alloy to reproduce the detail of the sharp contour of the grooves. Different procedures or materials in each stage of casting and finishing process caused somewhat different roughness on the castings. Above all, the application of the wetting agent on the wax pattern and the use of the model investment were extremely effective to approximate the roughness of the casting to that of the model.
- 九州歯科学会の論文
- 1982-06-25
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