Chitosan film is characterized by both its elasticity and in vivo absorbtion capacity. Although the chitosan films become inelastic when dried, they will return to an elastic state when soaked in water. It is of practical importance to determine the amount of calcium ions dissolved from the hydroxyapatite (HA) which is kneaded with the chitosan film. In the present study, the relationship of various amounts of added HA to shrinkage, hardness, tensile strength and elongation of the dried chitosan film was determined in addition to the amount of dissolved calcium ions.
The following results were obtained. The shrinkage during drying was decreased by increasing the amount of HA added. The hardness showed a maximal value at a rate of 4:11. The tensile strength of the chitosan films kneaded with HA exhibited a higher value than those without HA. Elongation showed the highest value when the ratio of hydroxyapatite : chitosan sol=2:11. The amount of calcium ion dissolution showed the highest value when the ratio of hydroxyapatite : chitosan sol=4:11. When chitosan film was soaked in physiological saline, the original level of elasticity was restored.

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Alginate impressions, immersed in a glutaraldehyde solution for 30 minutes, were fixed with solutions of CaCl₂, K₂SO₄ and ZnSO₄ using respective concentrations of 2, 5 and 10% for 0.5, 1 and 5 minutes. A saturated CaSO₂ solution (clear slurry) was also applied. Surface roughness and waviness of the stone casts obtained from the fixed impressions were measured.
Fixing with ZnSO₄ was most effective in reducing the surface roughness of stone casts at any concentration or time without altering the surface waviness, while the roughness was reduced by fixing with CaCl₂ and K₂SO₄ solutions in relation to increases in the concentration or time. Applying clear slurry for 1 minute can be easily performed in clinical use.

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Two types of heterogeneous fluoridated hydroxyapatites (H-FAp and F-HAp) with relatively lower crystallinity were synthesized at 60℃ and pH7.4, using the 2-step fluoride supply system. The fluoride content was similar in both heterogeneous fluoridated hydroxyapatites and was only half the maximal fluoride content of fluorapatite. X-ray diffraction analysis indicated that they had wider peak breadths of the (300) reflection, which were not so different from each other. However, the scanning electron microphotographs (SEM) were quite different from each other. Energy dispersive spectroscopy attached to the SEM gave clearly different spectra and the fluoride peak of H-FAp was higher than that of F-HAp. H-FAp had a lower apparent solubility after one-month incubation in 0.5 M acetate buffer solution (37℃, pH4.0). These results suggested that hydroxyapatite covered with fluorapatite (H-FAp) and fluorapatite covered with hydroxyapatite (F-HAp) might be formed.

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This study investigated the effects of elapsed time and heating rate on dimensional change of a gypsum-bonded investment for quick heating by placing a mold directly in an electric furnace at 700℃.
The elapsed time after the start of mixing had no effect on thermal expansion. However, the setting expansion increased for 50 min, resulting in an increase in total expansion. The heating rate did not significantly affect either the thermal or total expansion at any elapsed time investigated.
In the case of quick heating, the expansion curve showed the dehydration of gypsum, the transformations of both cristobalite and quartz, and a plateau which indicated the completion of thermal expansion.

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This study classified non-asbestos casting ring liners using IR (ATR-method) and WDX spectra. Fifteen non-asbestos casting ring liners and three asbestos ribbons were used. Non-asbestos casting ring liners were classified into five groups by IR spectra. Detected elements were Ca, Si, Al and Mg in A group, Al, Si, Ca, K and Mg in B group, Al and Si in C group, Al, Si, Ca or Zr in D group and Al, Si and Fe in E group. Asbestos ribbons consisted of Si, Mg and Fe. We identified A group as a rock-wool type, B group as a low temperature ceramic fiber type, C group as a standard ceramic fiber type, D group as a low temperature or standard ceramic fiber type and E group as a kaolin type.

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We developed a new FRP flask with an injection molding system for microwave polymerization. This study evaluated the effects of additives to α-calcium sulphate hemihydrate combined with microwave powers on the temperature of the gypsum mold in the FRP flask during the polymerization process. The results were summarized as follows. 1. The use of the fiber optic thermometer allowed continuous temperature measurement of the gypsum mold in the flask during microwave irradiation, which exerted strong electromagnetic fields. This measurement was useful in accurately identifying the temperature distribution in the gypsum mold, which was affected by the rapid temperature rise and thermal conductivity during microwave polymerization. 2. The temperature of the gypsum mold was increased by electroconductive additives. The amount of the temperature increase was proportional to the quantity of additives. 3. Using 90W power for the microwave oven evenly decreased the magnitude of a rapid exotherm in gypsum mold, compared with that at 500 W power, leading to a more uniform temperature distribution inside the FRP flask.

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To join titanium and titanium alloy for a crown and bridge, soldering with titanium solder is desirable. Therefore, composition of titanium solder was analyzed and tensile soldering strength was measured. Wave dispersive electron probe X-ray microanalyzer was used for an analysis of the composition. Pure titanium bars (Type 3) were prepared and soldered in an argon gas atmosphere using an infrared soldering apparatus.
As a result, it appeared that the composition of commercial titanium solder was Ti, Ni and Cu and the structure of the layered solder was Ti and Ni-Cu alloy. The composition of Ti, Ni and Cu was 50〜67 wt%, 17〜30 wt% and 16〜20 wt%. The tensile strength of the soldered joint was 392〜516 MPa.

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The study investigated bamboo extract, which was distilled at 200℃ under a reduced pressure of 20 mmHg, as an antibacterial agent or disinfectant for dental use. Antibacterial and bactericidal activities of the bamboo extract against Staphylococcus aureus (S.aureus), Streptococcus mutans (S.mutans) and Candida albicans (C.albicans) were examined by measuring MIC (minimum inhibitory concentration) and MBC (minimum bactericidal concentration), respectively. Then the bamboo extract was tested for toxicity when administered orally to mice at a dosage of 2000 mg/kg.
The MIC of the bamboo extract was 5%, 0.625% and 2.5% against S.aureus, S.mutans and C.albicans, respectively. The bactericidal activity was confirmed by MBC, which was nearly equal to the MIC, against these microorganism. The 5% bamboo extract exhibited a marked antibacterial and bactericidal activity against these microorganism. The bamboo extract contained more than 40 components, which were mainly Furans or Phenols. All of the mice were in normal health before and after the toxicity tests. There was no detectable amount of arsenic, lead or mercury in the bamboo extract. These results suggest that the bamboo extract can be used safely as an antibacterial agent or disinfectant comparable to conventional compounds used for those purpose.

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The chipping behavior of twenty-one commercial dental stones including eleven high-strength dental stones was evaluated quantitatively using two previously reported testing methods. One method measured the average and maximum widths of chipped area cut with a rotating saw, and the other method measured the minimum thickness of a thin nubroken piece sliced with a rotating saw.
There were statistically significant differences between the products for the average width, maximum width, and minimum thickness. There was a significant difference between the groups of high-strength dental stones and other dental stones for the average and maximum widths, while there was no significant difference in minimum thickness between the two groups.
There were significant positive correlations between the average width, the maximum width, and the minimum thickness. The logarithm of cutting time statistically correlated with the average width, the maximum width, and the minimum thickness. It was suggested that the excess water present in the specimens affected the chipping behavior of dental stones.

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We previously reported that <Phytic acid (PYA)-SnF₂> primer is a useful tooth conditioner for bonding dental adhesives containing a functional monomer with phosphoric or carboxylic acid groups and glass polyalkenoate cements to tooth substrates. However, treatment with this primer requires two steps. Therefore, to simplify the conditioning steps, we prepared 4 tooth conditioners composed of a 10% aqueous solution of PYA mixed with 0.02〜0.5mol of SnF₂ to PYA and compared these with conventional <PYA-SnF₂> primer. The effects of these conditioners were evaluated by the bond strength of Photo Bond ^® to bovine dentin and enamel and by SEM observations of the treated tooth surface.
The bond strength to dentin and enamel treated with any of the 4 tooth conditoners was lower than that of specimens treated with conventional <PYA-SnF₂> primer, especially bond strength to enamel. The ability of these one-step conditioners to decalcify the treated surface decreased with increases in the concentration of SnF₂. In these one-step conditioners, Sn²⁺ seems to have reacted with PYA in solution thus resulting in a decreased ability to decalcify tooth. The chelate compounds of PYA and Sn²⁺resulting from this reaction seemed to be easily washed away by rinsing after treatment and not fixed on the treated surface. This could explain why one-step conditioners were less effective than two-step <PYA-SnF₂> primer.

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Using the single edge precracked beam (SEPB) method, the fracture toughness (K_IC) of porcelain-fused-to-metal (PFM) was measured to evaluate the effect of pop-precrack length. The K_IC was increased with increases in the pop-in precrack length, as observed in ceramics exhibiting R-curve behavior caused by the crack interface interaction force such as crack bridging due to interlocking grains. To investigate the effect of such an interaction force, a double notch was introduced. However, no decrease on K_IC was found despite exclusion of most of the precrack. Other experiments suggested that the growth of the pop-in precrack did not occur during the measurement of K_IC. From these results, it was concluded that the increase in K_IC with increases in the pop-in precrack length was due to the presence of the interaction force which had already reached the maximal value a very short distance from crack tip. After removing the resistance force, K_IC; was estimated as 0.85±0.06 MPam^1/2. Considering that such an interaction force should be also included as a part of K_IC, the length of the pop-in precrack should be as short as possible, when measuring the K_IC of ceramics such as PFM using the SEPB method.

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We studied the conditions of dynamic extraction in cytotoxicity testing of metallic biomaterials. Extraction was performed by gyrating specimens weighing 1.5 g and 2.0 g on alumina or zirconia balls for 1, 3 and 5 days at 200 rpm and 240 rpm. Extracts and filtrates were exposed to L-929 cells and cell viability after 72 hours was determined by neutral red assay. There was no significant difference in cell viability between extracts from specimens of different weights. Increasing the gyrating speed and extraction time resulted in a decrease in cell viability. Cell viability after extraction on alumina balls was lower than that after extraction on zirconia balls. By gyrating specimens on alumina balls at 240 rpm, ten types of metals were classified into four groups according to the effect of the extraction on cell viability. In these four groups, cell viability was decreased in the following order; a group that included titanium and Ti-6 Al-4 V alloy: a group that included cobalt-chromium alloy, nickel-titanium alloy, and 316L stainless steel; a group that included Type IV gold alloy and gold-silver-palladium alloy; and a group that included nickel-chromium alloy, siver-indium alloy, and silver-tin alloy. Cell viability after exposure to filtrates was greater than that after exposure to extracts. After gyrating specimens on alumina balls for 5 days at 240 rpm, copper was selectively dissolved in the filtrates from Type IV gold alloy and gold-silver-palladium alloy. Zinc was dissolved from silver-indium alloy and silver-tin alloy. Nickel was dissolved from nickel-chromium alloy, nickel-titanium alloy, and 316L stainless steel and cobalt from cobalt-chromium alloy. Dissolution from titanium and Ti-6 Al-4 V alloy was not recognized. The most efficient dynamic extraction condition for testing of cytotoxicity was found to include specimens weighing 1.5 g and extraction by gyrating on alumina balls at 240 rpm. These results might offer the potential to simulate the behavior of metallic biomaterials in vitro.

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We attempt to improve the adaptability of denture base resins by initiating the polymerization from the mucosal side using selective microwave-heating of the model and investing stones.
We also attempted to develop resins suitable for microwave polymerization.
This investigation used differential scanning calorimetry (DSC) to evaluate the relationship between the heating rate and initiation temperature of polymerization. We also controlled the initiation temperature of polymerization by adding an activator, dimethyl-p-toluidine (DMPT) and an inhibitor, hydroquinone (HQ) to freshly-distilled methylmethacrylate (MMA).
The results were summarized as follows.
1. The initiation temperature of polymerization increased with the heating rate. Acron had the highest initiation temperature for polymerization, followed by freshly-distilled MMA containing 0.0050 wt% HQ, while freshly-distilled MMA and Quick Acron did the lowest. The difference in the initiation temperature between resins remained constant irrespective of the heating rate.
2. The initiation temperature for polymerization increased 10℃ with increments in the HQ concentration up to 0.0050 wt%.
3. The initiation temperature for polymerization decreased 35℃ with increments in the DMPT concentration up to 1.00 wt%.
4. The effect of the dual addition of HQ and DMPT on the initiation temperature for polymerization did not differ significantly from the effect of single additions of HQ and DMPT.

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