The effects of immersion disinfection of alginate impressions of various thicknesses on the reproducibility of stone models simulating a full crown preparation were investigated. Two types of alginate impression material : AROMA FINE DFIII (AFIII) characterized by smaller dimensional changes in water, and Jeltrate Plus (JLP) characterized by greater dimensional changes in water, were used. The impression thicknesses were adjusted to 1, 3, and 5mm. The impressions were immersed in 1% sodium hypochlorite solution for 10 min. The stone models obtained from treated impressions showed various dimensional changes and deformations depending on the type and thickness of impression. The effect of disinfection of AFIII on the dimensional change was small compared to JLP, and the disinfection of both impressions with 1 mm thickness had little effect.

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Fatigue tests in artificial saliva were carried out on variously heat-treated dental Ag-Pd-Cu-Au (12 mass% Au) type alloys. The effects of microstructures and artificial saliva on fatigue characteristics of dental Ag-Pd-Cu-Au type alloys are discussed, and fatigue fracture mechanism in artificial saliva is also analyzed. Fatigue strength in artificial saliva of the alloy after each heat treatment showed nealy the same result as that in air in the region showing a low cycle fatigue life. However, fatigue strength of aged alloy is, in particular, lower in artificial saliva than in air in high cycle fatigue life region. For the alloy contaning a large volume fraction of β phase, that is, for the aged alloy, corrosion may occur preferentially at the interface between the β phase and matrix. Then, the stress concentration at this site may be remarkable. Fatigue strength of the alloy in artificial saliva is reduced by the β phase.

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Titanium (Ti)/hydroxyapatite (HAP) functionally graded material (FGM) was fabricated by spark plasma sintering (SPS) and the mechanical properties and biocompatibility as an implant were evaluated. The FGM specimens were sintered at 850℃ under pressures of 40 and 80 MPa by SPS. Brinell hardness increased as the Ti content was increased. The FGM specimens fabricated at 80 MPa had higher compressive strength and flexural strength than those at 40 MPa. Histological observation after 4, 8 and 16 weeks implantation in rats showed that there was no inflammatory reaction and the extent of surface contact area with newly formed bone around the FGM gradually increased from 4 to 16 weeks for the entire range of compositions. Maturation of bone formed at the implant surface proceeded earlier in the HAP-rich part than in the Ti-rich part. These results showed that the Ti/HAP FGM implants made by the SPS method had strength, excellent biocompatibility and controllability for graded bio-reaction.

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To examine the effect of fine titanium particles, animal experiments (for 1〜30weeks) and cell functional test (TNF-α and superoxide anion release) were done. Animal experiments showed that each particle was englobed by fibrous connective tissue for the Ti particles (40, 150μm), whereas Ti particles (1〜3, 10μm) smaller than the inflammatory cells were englobed by connective tissue for their agglomeration and this occurred after being endocytosed by inflammatory cells for 1〜3μm particles. Cell functional test using human neutrophils revealed that fine particles of Ti-stimulated cells and increased the release of superoxide anion and TNF-α. Thus, fine particles of Ti smaller than cell size may cause a stronger inflammatory reaction.

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In recent years, titanium prosthetics have been widely used in clinical dentistry. However, there are reports that titanium plates were discolored by some denture cleaner. This study investigated the cause of discoloration by measuring the pH of denture cleaners and by surface analysis of discolored specimens using EPMA and XPS. Severe discoloration was observed with denture cleaners with a highly alkaline range. Discoloration was regarded as due to roughness caused by corrosion. The degree of discoloration depended on the thickness of the oxide film.

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A new suspensional type testing apparatus was designed to measure the frictional properties between orthodontic wires and brackets and frictional coefficients were obtained under conditions of single contact plane and double contact planes. Findings were compared for various combinations of brackets and wires, including the esthetic FRP wire that we manufactured. This testing equipment can eliminate geometric factors originating from sources other than the material properties. The frictional coefficients measured by the double contact test were larger than the expected value, √<2> times those by single contact test. The frictional coefficient between polycrystalline alumina bracket and FRP wire was larger than that of other combinations. The frictional properties of FRP wire with brackets were similar to those of metal wires except for the polycrystalline alumina bracket. Frictional properties between wires and brackets under clinical conditions could be affected by not only surface characteristics but the geometric relation and orthodontic force.

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Seven metallic and three polymeric prosthetic materials were examined for cytotoxicity by the cell recovery rate using a saliva/tissue combination as an in vitro model. Titanium was not cytotoxic regardless of the addition of the artificial saliva. A cobalt-chromium alloy, silver-palladium alloy, silver-tin alloy, heat-curing resin and self-curing resins showed only slight cytotoxicity. A silver-indium alloy and nickel-chromium alloy had a moderate effect, and copper had a marked effect. There was a significant difference in some findings after artificial saliva addition, although some samples were not affected. The present findings suggest the usefulness of the saliva/tissue combination model for cytotoxicity testing of dental materials.

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