陶材焼付連結冠の適合性の変化に関する研究
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概要
- 論文の詳細を見る
In manufacturing ceramo-metal restoration, the metal coping is subjected to several mechanical and thermal treatments after cast for fusing porcelain. Several reports have demonstrated some changes in the fit of the single ceramo-metal crown during such procedures. The potential disturbance of the fit in the case of the connected crowns was examined in this study. The model was composed of two abutments for connected crowns with an interspace of 1 mm. Both the abutments were of shouldered type, 6 mm in height and 5°in taper. The pattern was prepared using a spacer to ensure the specified thickness for full-baked or veneered type. The investments used were two brands of phosphate-bonded investments-Uni vest non-precious (UN) and Blue vest (BV) having different compressive strength. Nickelchromium alloy was employed as the coping metal. The vertical gap at the margin between the coping and the abutment shoulder was measured after each stage of the procedures : casting, cutting of sprue, treating of metal surface, degassing, fusing of opaque porcelain, fusing of body porcelain, adjusting of body porcelain, and glazing. The as-cast connected crowns were in mesio-distally warped shape showing larger gap at the proximal margin than at the connected margin. The subsequent mechanical and thermal treatments caused deformation of the crowns to correct the warpage to some extent, resulting in the decreased gap as a whole. The largest decrease in the gap was generally found at the stage of sprue cutting, and the second at those of degassing and sandblasting for metal surface treatment. The decrement at each stage was changed by altering the processing order in association with the amount of residual stresses in the casting involving uncut sprue and runner bar, relaxation and release of the stresses, and development of new stresses in the previous treatments. The changes in the fit were marked in the full-baked type with the coping being thinner, especially cast with the investment UN when compared with that in the veneered-type. It is because a larger residual stress might be introduced in the casting with use of the stronger investment UN than BV, which was suggested from the cast tearing test. The compressive strength of BV is intentionally lowered by the manufacturer for the purpose of making it easy to take out the casting from the mold. The lowered strength of this investment showed additional effect of reducing the residual stress and hence minimizing the fit changes in the subsequent procedures. The application of the stress relief annealing to the casting before cutting the sprue was also found to be effective for maintaining the as-cast fit of the casting.
- 九州歯科学会の論文
- 1992-12-25