The aim of the experiments was to establish the basis of low-fusing porcelain produced by the use of inorganic reagents on the market, therefore the fusing temperature, the compressive strength of fired products and the fusing shrinkage were observed in the porcelain specimens composed of various compositions. From the experimental findings, the following results were obtained. 1. The fusing temperature and compressive strength of fired products were decreased with the increase of the amount of fluxes. 2. In the case of using B2O3, as a flux, in comparison with the case of using K2O or Na2O, the fusing temperature and the compressive strength of fired products were comparatively slightly decreased. 3. The fusing shrinkage of porcelain powder began at around 700°C, and it increased, as the fusing temperature rose. 4. The fusing shrinkage changed, as the ingredient of flux or its amount differed, for example, when the amount of B2O3 was large, the fusing shrinkage was decreased. 5. For the low-fusing porcelain, the most suitable composition was as follows; SiO2 : 58.8%, Al2O3 : 19.5%, Na2O : 7.9%, K2O : 9.3% and B2O3 : 4.5%, in using inorganic reagents on the market. 6. In the fired product in specimen No.5, the fusing temperature was 880°C, the compressive strength was 3250 kg/cm2 and the fusing shrinkage was 12% in dimension at 830°C.
Predentin, intertubular dentin, and peritubular dentin of successional tooth germ of puppies at the stage of mantle dentin formation and permanent tooth of adult dogs were studied by means of SEM and the following conclusions were drawn. 1) Peritubular dentin was present in mantle dentin but not in circumpulpal dentin. Dentinal tubular wall was smooth and glistening in the mantle dentin but shows a fibrous structure in the circumpulpal dentin. 2) The matrix fibers of peritubular dentin were thinner than the matrix fibers of intertubular dentin, with a dense distribution and different course. Around these fibers, granular substances measuring 300-700 Å, smaller than those in the inter-tubular dentin, accumulate, burying the fibers and forming the first peritubular dentin. These are calcified and subsequently covered by small granular substances on the surface, which become smooth and glistening, forming peritubular dentin of approximately constant thickness. 3) The end of formation of peritubular dentin was more readily distinguished than the interlobular dentin. The end of formation is irregular with occasional island formation, some being formed simultaneously with interlobular dentin but mostly with delay.