In this study we evaluated fiber reinforced posterior hybrid resin. Two fibers (E glass, polyethylene), bonding agents (modeling liquid, DE bonding liquid) and three different lengths of fibers (20, 30, 40 mm) were used. Moreover, the influence of the fiber bundle inside the posterior hybrid resin on the bending (flexural) strength of the test specimen was studied. The bending strength of the posterior hybrid resin changed from 81.1 to 540.7 Mpa when fibers and additional bonding agent were added. The length of the fiber bundle also affected the bending strength of the test specimen, the strength increasing serially from 95.8 to 415.2 Mpa when 20, 30 and 40 mm long glass fiber bundles were applied. These results suggest the value of fiber reinforcement.

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The cushioning effects of casting ring liners on the setting expansion of the investment material in a split metal mould 30 mm in diameter and 40 mm in height were evaluated for the decrease in the thickness of wet ceramic liners and asbestos ribbons. The setting expansion of investment material was 0.35%, and the required decrease in thickness of liners was 0.05 mm. Decreases in the thickness of liners (δTs) were within -0.007 to 0.255 mm. With the exception of A-group (Rockwool-type) liners, δTs at the bottom side were larger than those of the upper side. (δTs tended to increase with the original thickness of the liner. In the liners with high water sorption, it was found that water absorbency and water retentiveness of the liner influences the setting and hygroscopic expansion of investment material. The correlation between δTs and cushioning effects using setting expansion measurement apparatus was significant in B-group (ceramic fiber low temperature type), C-group (ceramic fiber standard type), D-group (ceramic fiber low temperature-standard type) and AS-Group (asbestos ribbon) liners.

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The purpose of this study was to confirm the effect of filler shape and filler contents on the machinability of composite resins. Bis-GMA based resin was used for matrix resin. Two types of spherical-shaped fillers with average particle sizes of 0.2 and 4.3μm, and one type of irregular-shaped hybrid filler with an average particle size of 6.6μm were selected. Silanized filler loadings were 50% and 80 mass%. Bar-shaped specimens (3x3x25mm) of composites were prepared. The machinability was evaluated as a volumetric grinding amount after a machinability test at a 40-gf load. The grinding amounts of composite resins using the spherical-shaped filler were greater than those using the irregular-shaped hybrid filler. The large spherical-shaped filler showed greater grinding amounts than that the small spherical- shaped filler. The grinding amounts were greater when the filler content was higher.

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The electrodeposition (ED) of adhesive monomer on dental alloy surfaces has been investigated to improve the adhesion of dental resin to dental alloy. In this study, the relationship between the ED treatment conditions and bond strengths was investigated by FT-IR using an aromatic carboxylate monomer (4-methacryloxyethy1 trimellitic acid, 4-MET). As a result, when the 4-MET was electrodeposited on the alloy surfaces, its carboxylate group and double bond of methacry1 group were detected on the alloy surfaces. Effective treatment conditions for each alloy differed depending on the type of alloy ; in a solution concentration of 10% 4-MET, and treatment current of 10-100 mA/cm², 15%-1〜100mA/cm² and 20%-1〜5mA/cm², the maximum shear bond strength was 9.4 Mpa for 12% Au-Ag-Pd alloy. Similarly, at 5〜20%-1 mA/cm² it was 11.6 MPa for pure titanium.

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Fatigue tests were carried out on various heat-treated dental Au-Ag-Pd (12 mass% Au) type cast alloys in air. The effects of microstructures on the fatigue characteristics of dental Au-Ag-Pd type cast alloys were discussed, and the relationship between casting defect and fatigue fracture mechanism was also analyzed. The effect of micro shrinkage cavity on the fatigue strength is greater in the low cycle fatigue life region than in the high cycle fatigue life region. The fatigue strength of solutionized cast specimen at 1123 K (1123 WQ) is the greatest in the high cycle fatigue life region. The effect of casting defect on the fatigue strength of casting alloy can be reduced by solutionizing at 1123 K followed by water quenching, and the fatigue strength of this cast alloy is improved.

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In this study we compared the mechanical properties of pressable ceramic restorations. Four crystallization temperatures (890,900,910,920℃) and durations (1,10,20,30 min) were used to evaluate the effects on fracture toughness of Diopside crystallized ceramics. Three pressable ceramics, Diopceram (DI), IPS Empress2 Layering (EL), and IPS Empress Staining (ES) were selected for comparison of the mechanical properties. The fracture toughness increased as a function of both increasing crystallization time and temperature. The fracture toughnesses (MNm^-3/2) of DI, EL and ES were 1.97, 2.79 and 2.39, respectively. The compressive strength, diametral strength and bending strength of these materials were 1183-1344 MPa, 29-42 MPa and 143-306 MPa, respectively. According to the results obtained, there were statistically significant differences among the mechanical properties of DI, EL and ES.

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