A Branemark dental implant, which broke in the mouth, was investigated and the fracture process was examined. The implant had functioned as a dental root, but it was broken after a decrease in the marginal bone. In the fracture area, the outer screw trough of the implant's fixture developed along the inside screw trough, then the fixture broke around the weakened area under high stress. The dentail structure, which should have yielded at the same time as the fracture, disappeared. However the implant's central screw area had small wave-like structures, indicating that the central screw received repetitive stress and ruptured. The results indicate the fracture process is as follow:first, a crack appeared along the screw trough of the fixture, then, the fracture surface was plastically deformed, and the center screw finally ruptured by repetitive stress.

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This study evaluated the electrrochemical properties affecting the corrosion resistance of free-machining titanium alloy for dental application. Pure titanium, Ti-3Al-2V alloy and two free-machining titanium alloys(DT 2F, DAT 52F:Daido steel)were used in this experiment. Polarization resistance and the potentiodynamic polarization profile were measured using an electrochemical device and test solutions consisted of 0.9% NaCl and 1.0% lactic acid. The natural electrode potential and the polarization resistance of free-machining titanium alloys were lower than those of titanium and Ti-3Al-2V alloy. From the potentiodynamic polarization behavior, free-machining titanium alloys showed high passive current density in the 0.9% NaCl solution. The transpassive potential was nearly the same for all alloys. The pits were recognized on the surface of free-machining titanium alloy which was tested in the 0.9% NaCl solution. Accordingly, it was estimated that the corrosion resistance of free-machining titanium alloy was inferior to pure titanium and Ti-3Al-2V alloy.

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The objective of this study was to investigate the effects of manipulative conditions in air abrasion equipment on abrasion of tooth to obtain fundamental knowledge of the optimum conditions for air abrasion systems in clinical use. Bovine enamel and dentin surfaces were air-abraded with alumina particles using currently commercially available Painless-Jet equipment under different settings for air abrasion pressures, time periods, distances, diameters of abrasive tip nozzle, sizes of particles and abrasive angles. The depth of the abraded area was determined after abrasion. Effective abrasive results could be obtained at manipulating conditions where the larger the air pressure and nozzle size, the longer the abrasive time and 60-degree abrasive angles were employed. The shapes of the abraded tooth surface were notably more affected by the abrasive angle, rather than abrasive pressure and particle size.

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To investigate the influence of light intensity exposed to a photo-cured composite resin on the behavior of photo-polymerization, the heat flow during polymerization of photo-cured composite resin was measured by a modified differential scanning calorimeter(DSC) which installed the light curing unit with a high light intensity. Moreover, the relationship of the behavior of photo-polymerization to knoop hardness after hardening of the composite resin was investigated. In the results, the heat flow during photo-polymerization from starting the light exposure to the composite resin could be precisely obtained by modified equipment. There was significant correlation between the peak time of heat flow during the photo-polymerization and the inverse of the light intensity, and the peak time was close to 9 seconds with increased light intensity. The logarithm of the light intensity was also significantly related to the heat flow during the photo-polymerization and knoop hardness. Therefore, it was considered that photo-polymerization was simulated by the measurement of light intensity exposed to the composite resin.

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The original measuring device(OH)of the Notchless Triangular Prism fracture toughness test(NTP) was modified to a design(TH)with a 15° inclined plane at the holder assembly(HA) of the NTP specimen(Prism). This new design was compared with OH. Consequently the experimental conditions using TH;the cross head spped(Chs), the surface roughness of Prism(R)and the space of the measuring device(HD);were evaluated by three-way ANOVA and observation of the fractured surface. Since the interference of the HA affected the stress distribution before fracture, the maximal fracture load using OH was significantly higher than TH. Therefore, TH which can for prevent interference was considered more effective than OH. As in a rarge of the experimental conditions using TH, Chs and R should be controlled 0.5〜1.0 mm/min and 0.19〜0.62 μm, respectively.

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