The fracture process in dental Ni-Cr casting alloy was investigated metallographically on the basis of dislocation theory. As a result, the pile-ups of slip trace due to dislocation on {111} planes were found within the cell structures near the voids, while the dislocation-free region was locally observed inside the cell structures at the tip of void. The morphology of void was identified to be both the type taken off to the tensile axis along the cell-interfaces and the wavy type at the interior of the cell structure. As the mechanism of void formation, stress-concentration due to both the piled-up dislocation to the cell-interfaces and the stress field near the inclusion was found. It was, in addition, clarified that the rapid coalescence and propagation of void occurred alternatively along the cell-interfaces which had approximate 45 degrees to tensile axis.

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　The structure change of dental Ni-base casting alloys as low-melting 32Ni-23Cu-25Mn and high-melting 84Ni-9Cr alloys was investigated on the effect of two different types of sprue position and direction systems (The sprue wires were set with angles of 0 and 45 degrees to longitudinal center axis of casting ring). At first, as the change of internal structure, the low-melting 32Ni-23Cu-25Mn alloy had three kinds of crystal grains in two sprue systems, but the high-melting 84Ni-9Cr alloy was composed of cell structure (0 degree-sprue system) and cellular dendrite structure (45 degree-sprue system). Secondly, the morphology of structure at the surface layer of casting specimens and the crystal grain-size distribution were notably affected by sprue systems in two Ni-base casting alloys. At third, it was clarified that the corrosion tendency of B-grain in 0 degree-sprue system increased more than that of 45 degree-sprue system in the low-melting alloy, and on the contrary the corrosion tendency for the high-melting alloy was not so clear as for the low-melting alloy.

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　The sintered composite were made from mixed powder compacts prepared from low fusing glass powders and each one of alumina powder, quartz powder, silica glass powder using sintering method at the temperature to 1000℃, and the affections of physical properties of sintered composite were investigated by measurements of transverse strength and transparency.
　Transverse strength value of sintered composite of alumina and pyrex glass (expansion coefficient 3.6×10^-6) or soda-lime-silica glass (10.7×10^-6) increased with increase alumina content, particularly sintered composite with 50wt% alumina addition showed the transverse strength value of 170-180 MPa. The addition of alumina was more effective on the strength of sintered composite comparing with quartz and silica glass, inversely, transparency of sintered composite decreased with increase of alumina content.
　In the case of the sintered composite of silica glass and low fusing glass, transverse strength velue decreased with increase of silica glass content. The sintered composite with silica glass addition showed smaller transparency value by difference of the refractive index due to the generation of cristobalite followed with the crystallization of cristobalite than that without crystallizing property.

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　Effect of irradiation with ⁶⁰Coγ-ray as a medical treatment to cancer in oral cavity has been proven, but this treatment often causes to develop complication of periodontal disease. Reported in this article are some results obtained in fundamental study to find out relation between irradiation with ⁶⁰Coγ-ray and neutron beam as a treatment against cancer and damages of dentin. Human and bovine incisors were cut to get specimen of dentin of about 0.8×4.5×6.5 mm. The long axis of specimen was equal to main axis of incisor. Those specimens were subjected in wet condition to irradiation of ⁶⁰Coγ-ray for 1×10⁵ to 1×10⁷r and thermal neutron flux of 8×10¹³n/cm²・sec with JRR-4 for 1 to 40 minutes. Effect of irradiation with ⁶⁰Coγ-ray and neutron beam was studied with tension test, X-ray diffraction analysis, X-ray microanalysis, TG-DSC, infrared absorption analysis and observation with scanning electron microscope. As the irradiation dose is less than 1×10⁶ by ⁶⁰Coγ-ray and 8×10¹³n/cm²・sec×10 min by neutron beam, it seems reasonable to assume that cross-linking was in luced in collagen. By further addition of irradiation dose, collagen molecules were severed and the dentin was collaped. Consequently, collagen in dentin seems to make large contributions to strength of dentin.

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The methacryloyl fluoride(MF)-methyl methacrylate(MMA) copolymer was prepared and the rates of fluoride ion release from the copolymer and the blended polymer with poly(methylmethacrylate) (PMMA)were determined by the use of a fluoride electrode. The rates were found to be constant over 60 days.Infrared analysis revealed that the fluoride ion was released by the hydrolysis occurred exclusively at the MF-MF configurations, followed by an anhydride formation. The dentins of extracted bovine teeth were treated with 3% of various metal chlorides in a 10% citric acid aqueous solution, and the effect of the formulations of cleaning solution on the adhesive strength of 5%-4-META/MMA/TBB-O resin to the treated dentin surface was examined. The highest adhesive strength was obtained for 3% ferric chloride or 3% cupric chloride. The adhesive strengths of the fluoride-containing resin to human enamel treated with a 65% phosphoric acid aqueous solution and human dentin treated with 3% cupric chloride in a 10% citric acid aqueous solution were 8.3 MPa and 12.2 MPa, respectively.

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We have studied on the physicochemical characters of the porcelain materials in order to recognize the important factors concerning the bonding mechanism between porcelains and base-metal alloys at the metal/ceramic veneering technique.
The results were as follows.
By the X-ray Fluorescence analysis, main constituents of the every porcelain materials are SiO₂ and Al₂O₃. SnO₂, which is considered to effect on the bonding mechanism, was mainly contained in the opaque porcelains and its maximum content was 23.75%.
The composition of the so-called Metal Conditioner was similar to that of the dental porcelains.The particle sizes of the se porcelains were mainly classified in four kinds.
On the thermal expansion, the metastatic temperature was 500-600℃ and the coefficient of expansion was 0.73-1.36%.In the case of some base-metal elements were added to the porcelain materials, there was no remarkable change in the metastatic point and the thermal expansion.
But, the softening point shift to some higher temperature, the degree of the thermal expansion increase and also the fusible point somewhat rise.
The mechanical surface treatment of the alloys had more effect on the bonding strength than the chemical surface treatment.
As to the metal/ceramic boundary analysis by the electron probe X-ray microanalyser, the joint investigation of characteristic X-ray image and X-ray diffraction intensity map was a useful means to explain the diffusion state of elements at the both sides of the interface.

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A new dental cement composed of hydroxyapatite, zinc oxide, and acrylic acid copolymer was developed. Setting time and consistency of the hydroxyapatite cement were tested by JIS method. Compressive, 4-point bending and diametral tensile strengths of the cement were about 700, 250, and 80 kg/cm², respectively.These physical properties showed that the cement can be applied to the clinical dental uses. As increasing the contents of hydroxyapatite, setting time of the cement was prolonged and the modulus of elasticity was elevated. Compressive strength of the cement decreased, as the ratio of water/powder (W/P) increased.The hydroxyapatite cement was incubated at 37℃ in distilled water, physiological salt solution and human parotid saliva for 6 days.The texture of cement was not changed and the compressive strength increased in each incubation condition.

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