Abstract
In order to establish direct firing method of precise porcelain jacket crown, some points were investigated using several investments as the direct refractory dies of porcelain jacket crowns.
The following results could be drawn.1.The dimensional change rates of directly fired porcelain jacket crowns were much correlated to the total expansion rates of refractory die materials.
2.The refractory die for direct firing method should have equal or slightly small heating expansion rate on cyclic heating compared with the porcelain.We could not make porcelain jacket crown on refractory dies which have more than 2.0% heating expansion.
3.All directly fired porcelain jacket crowns have a tendency to transform opening at cervical part. The degree of transformation became higher when total heating expansion rates of refractory dies grew larger.
4.When we use porcelain which have 0.88-1.11% heating expansion rates on cyclic heating, it would be possible to use investments which have 0.92-1.09 heating expantion rates as refractory dies for direct firing method.
