A method of continuously measuring temperature during microwave irradiation was developed using a metal sheathed thermocouple. The temperatures recorded by this method were compared with those measured intermittently with a mercury thermometer. Samples of Sydney tap water (50ml) were heated using a domestic microwave oven at High and Low powers which were the maximum (500W) and minimum (50W or 10%) powers of the oven, respectively. At 500W, boiling was seen to occur within 1min and the measurement with the mercury thermometer was omitted. The continuous temperature measurement with the thermocouple showed that the boiling point was reached at about 45s. At 50W the 10% work was shown by the delivery of 3s microwave radiation which was repeated every 32s. The boiling point was recorded at about 6min, which was much earlier than the time (10min) noted visually. The boiling point could not be registered with the mercury thermometer method. Visual observation or intermittent temperature measurement can result in an underestimation of temperature reached during microwave irradiation.

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The bond strength of resins (MMA-TBB resin system), containing 2-hydroxyethyl methacrylate (2-HEMA), 3-methacryloyloxypropionic acid (3MPA), 2-phenylethyl methacrylate (PylEM) and 2-(1-naphthyl) ethyl methacrylate (NEM), to dentin treated with a solution of 10% citric acid and 3% ferric chloride was measured after being immersed in water at 37°C for a long period of time to investigate the influence of water on bonding, and the relationship between the monomer structure and the decrease in bond strength in water. The bond strength of the resins did not change with the time spent immersed in water up to 6 months, but decreased with any further increase in time. The decrease in bond strength of all the resins tested was caused by either the degeneration and swelling of collagen or a difference in the degradation of the resin inside and outside the acid-proof dentin layer. There was no significant relationship between the decrease in bond strength in water and the monomer structure.

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We examined the effects of various denture base resin surface textures on the adherence of microorganisms.
S. sanguis and B. gingivalis adhered in greater amounts to the denture base resin than the other microorganisms tested. As to bacterial adherence according to polishing state, S. oralis, B. gingivalis C-101, and B. intermedius C-001 more adhered to the No.400 paper-polished surface than to the buff-polished and smoothening-treated surfaces. S. sanguis less adhered to the smoothening-treated surface. S. mitis and C. albicans, on the other hand, more adhered to the smoothening-treated surface. For the other microorganisms tested, no relationship was observed between surface texture and bacterial adherence. The fall-off test revealed no remarkable differences in the fall-off of S. sanguis and B. gingivalis C-101 by the types of surface treatment. However, the fall-off of C. albicans was poorest from the No.400 paper-polished surface. These results indicate that smoothening the denture base surface is important for denture plaque control.

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A new type of metal bracket was prepared to minimize the destruction at the bracket-resin interface and to suppress resin from remaining on the tooth surface in debonding. The brackets were made of stainless steel and had a modified cylindrical outward shape (φ3.8mm×1.8mm), twin-type wings, and a 0.018 inch (0.457mm) slot. Retentive forces and debonding aspects of residual resin for the brackets were studied using three representative adhesives. The mean tensile strengths at the bracket-resin interface were over 80kgf/cm² for all three resins. As the quantitative evaluation for the residual resin condition, a resin remaining ratio (RRR) was adopted. The aspects of the residual resin differed according to the type of adhesive resin used. Almost no resin was detected on the tooth surface just below the central part of the bracket, and even for the peripheral part which did not have an effective resin retention form, the RRR was under 30% for the heavily filled resin.

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The adsorption of 2-hydroxyethyl methacrylate (HEMA) on bovine dentin from aqueous solution was examined to clarify the priming effects of HEMA on dentin bonding.
HEMA adsorption was characterized by: (1) slow attainment of equilibrium at higher concentrations (after 72h); (2) a linear isotherm with a maximum possible adsorption, where an abrupt horizontal plateau occurred; (3) the large adsorption of ca. 2.5% by weight at the plateau; and (4) a vertical initial slope of the isotherm. The morphological difference between dentin powder surfaces before and after adsorption could not be determined. After heating, however, dentin powder which adsorbed HEMA was more resistant to demineralization with 6N HCl than the powder which did not adsorb. SEM examinations demonstrated that there was a demineralization-resistant dentin layer in tooth which adsorbed HEMA. The results indicated that HEMA infiltrated into intertubular dentin during adsorption.

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Temperature dependencies of thermal expansion coefficients for the alloys of Pd-Ag, Pd-Cu and Pd-Co binary systems were measured at temperatures up to 900°C, with heating and cooling rates of 5°C/min. The coefficient of thermal expansion of alloys with no transformation in the temperature range of interest in porcelain firing was well approximated by a linear equation of temperature. The constants in the equation were shown as a function of the weight for the added element. Thermal expansion of the palladium-based alloy with no transformation was well estimated at any temperature range and at any composition by using the constants represented here.
The coefficients of thermal expansion before and after order-disorder transformation and magnetic transformation were measured in Pd-Cu and Pd-Co alloys, respectively. The results suggest that transient and residual stresses in porcelain-fused-to-metal restorations can be effectively controlled by making use of transformation of the alloy.

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Hydroxyapatite powders (HAP: Ca₁₀(PO₄)₆(OH)₂) were prepared from calcium nitrate and di-ammonium hydrogen phosphate at various temperatures in aqueous solution in the absence and presence of carbon dioxide. In the absence of carbon dioxide, the crystallinities as well as the calcium to phosphate ratio (Ca/P ratio) of HAP powders increased with an increase in the preparation temperature. Calcium ion deficiency caused low Ca/P ratios of HAP powders. Such HAP powders decomposed thermally to β-tricalcium phosphate (β-TCP: Ca₃(PO₄)₂) at 800°C in 3 hours whereas HAP powders with sufficient calcium were stable at 1200°C for 3 hours.
In the presence of carbon dioxide as well the crystallinities of HAP powders increased with an increase in the preparation temperature, but carbonate-bearing HAPs were obtained instead of pure HAP. In addition, calcium carbonate was obtained along with carbonate-bearing HAP prepared below 60°C.

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The time dependency of stress distribution in the supporting structures under dentures was simulated, under three loading conditions, by visco-elastic finite element stress analysis. In this simulation, viscoelastic material, was used as a model for soft tissue.
The results indicate that the viscous flow of soft tissue and the loading position are factors determining stress intensity in the supporting structures under the denture. The stress intensity in the supporting structures was lowered when the occlusal force shifted towards the palatal side. Simulated results support Pound's lingualized occlusion theory.

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A very effective method for removing a denture from its cast after curing has been developed using a static expansive agent for hydration. Three filling hole designs for packing the expansive agent into a stone cast were examined to obtain the most effective method of splitting the cast for clinical application. The dynamic strain in the resin denture base was measured during static splitting one filling hole design was the safest for handling and the most effective for removing the denture. The upper tolerance limits for the maximum strain were estimated to be 2.9×10^-3 in the upper denture and 3.4×10^-3 in the lower denture. These values were lower than one-third of the critical strain corresponding to the proportinal limit of the denture resin.

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Titanium is strong, resists corrosion and has a low density and excellent biocompatibility. Conventional ceramic-metal restorations have been extensively used in dentistry because of their esthetic appearance and good mechanical properties. This study investigates oxidation effects on the porcelain-titanium interface reactions and bond strength. Pure titanium was treated in a porcelain furnace at temperatures of 600 to 1000°C under either vacuum or air. X-ray diffraction analysis of the surface of pure titanium revealed that the relative peak intensity of α-Ti decreased and that of TiO₂ increased, with increasing firing temperature. The Vickers hardness number of titanium increased with temperature especially over 900°C, and was harder in air than in vacuum. The tension-shear bond strength of the porcelain-titanium system was the highest in the green stage and lowest after 900°C treatment. Metallographic microscopy of the porcelain-titanium interface revealed a thick band-like zone in the sample treated over 900°C. The excess thick layer of TiO₂ apparently weakened the bond strength of porcelain-titanium. Unlike the conventional ceramic-gold alloy system the recommended degassing procedure was not suitable for porcelain-pure titanium restoration.

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The interaction of methyl methacrylate (MMA), ethylene dimethacrylate (EDMA) and triethyleneglycol dimethacrylate (TEGDMA), which are widely used in dentistry, with the dipalmitoyl phosphatidylcholine (DPPC) and the DPPC/cholesterol (CS) liposome system was studied by ¹H and ¹³C nuclear magnetic resonance spectroscopy (NMR). EDMA and TEGDMA have a larger interaction with the DPPC liposome system compared to MMA, resulting in changes in chemical shifts. The ¹³C chemical shift differences of C=C-C-O were larger than those of other carbon portions in methacrylate, indicating that double bonds interact predominantly with DPPC liposomes due to the hydrophobicity of methacrylates. At 37°C, ¹H signals from TEGDMA appeared in the DPPC/CS/TEGDMA liposome system, while signals due to H₂C=C-C-OCH₂CH₂ did not appear in the DPPC/TEGDMA liposome system.

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