In this study we examined the optimal design of glass fiber reinforcement for a hybrid resin fixed partial dentures by FEM (finite element method) analysis. We found that the configuration and position of the glass fiber reinforcement affected the stress distribution. The maximum principal stress on top of the lower embrasure was decreased from 106.82 MPa to 75.45 MPa with fiber reinforcment Thus, fiber reinforcement results in 29% reduction of stress concentration.

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The objective of this study was to determine the surface conditions of discolored metallic prostheses in the oral cavity. Pure titanium and Ag-Pd-Cu-Au alloy were installed in the partial dentures of three patients by informed consent and each denture was used as usual for two months. Each specimen was discolored visually after two months, and the discoloration layers and their thicknesses were observed and measured by scanning probe microscope (SPM) and X-ray photoelectron spectroscopy (XPS). The surfaces of the discolored specimens were found to be covered with spherical accretion. No constituent elements common to acceptions on both types of specimens were detected, but 0, C, N, and S were detected. The accretion on Ti prostheses was removed by Argon ion etching under XPS and its thickness was confirmed to be 0.2-0.5 μm. However, the thickness of the accretion on Ag-Pd-Cu-Au alloy could not been estimated because it was not fully removed by Argon ion etching.

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Indirect composites are classified as light-curing type, light-and heat-curing type and light-and heat-curing under pressure type, and conversion depends on the curing conditions. The present study evaluated infrared absorbance values of indirect composites by the Fourier transform infrared spectrophotometer single beam method before and after polymerization, and then their conversions were calculated from residual double bonds. The conversion of enamel pastes showed 42.2-75.7%, and that of dentin pastes showed 35.4-84.7%. A significant difference in curing between enamel paste and dentin paste was recognized in some indirect composites. The light-and heat-curing under pressure type had the largest value, light-and heat-curing type was second, and light-curing type had significantly lower conversion than the others.

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In this study we investigated endocrine-disrupting phthalate esters in the liquid of resinous temporary sealing materials. We found that they contained 40-50% phthalate esters such as dibutyl phthalate (DBF) or butyl phthalyl butyl glycolate (BPBG). We also measured the leached phthalate esters immediately after mixing in distilled water or artificial saliva. While stationary, the esters were almost undetectable. On the other hand, a quantity of esters was detected within 20 seconds after mixing by shaking, but the quantity decreased considerably after that. Moreover, to simulate accidental swallowing, we inserted a cured sample directly into the stomach of a rat. This sample was found in the feces almost unchanged, and more than 92% phthalate ester was recovered. This experiment suggested that if the contact with saliva is avoided during the 20 seconds after application, the leaching of phthalate esters is reduced, and the elution would be very small in cases of accidental swallowing. However, temporary sealing materials should be handled carefully in the case of youth or pregnant women, and it is clear that materials free of phthalate ester need to be developed.

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We examined the mechanical properties of thermally degraded resin composite materials for core build-up. Six different types of resin composites for core build-up were tested. The diametral tensile strength (DTS) and fracture toughness (K_IC) of each material were determined. The specimens were immersed in deionized water at 37°C for 28 days (Control) or were subjected to continuous water flow for 28 days in a Soxhlet extraction apparatus to accelerate degradation (Td). Significant decreases in DTS and K_IC values were found in materials CP, and CN and CP, respectively after thermal degradation (p<0.05) ; however, there were no statistical differences in DTS among the Control, Td for CN, MII , BC, UC and DC and toughness among the Control, Td for M II , BC, UC and DC (p>0.05). No significant differences in the values were found among all materials tested after Td (p>0.05, ANOVA). Although this method for examining the mechanical properties of the resin composites for core build-up did not simulate regular thermal degradation behavior, it may be effective as a deterioration test.

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