| Budget Amount *help |
¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 1999: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1998: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
In Part I, effect of film thickness on retentive strength of castings were studied. 1. Differences in cement film thickness did not affect the retentive strength in two kinds of cement used, composite type and MMA type. 2. Actual cement space was smaller than that determined by calculation. The ratio of Actual/ calculated cement space was 0.85±0.09. 3. Super Bond C/B exhibited higher bond strength than Panavia 21. The tensile bond strength converted from the surface area was 10 and 6 Mpa, respectively. 4. In most cases, the interfacial fracture between tooth substance and cement was observed with nakied eye.
In Part II, effects of film thickness on retentive strength and marinal leakage was investigated under the thermal stress (5〜58℃, 1,000 or 10,000 times). 1. In general, effect of film thickness on retentive strength was not clearly observed except Fuji Lute, and the effect of film thickness on marginal leakage also was not clear except Super Bond, 2. In the case of Panavia, the retentive strength of approximately 20 kg was exhibited. Marginal leakage increased significantly after 10,000 cycles of thermal stress, and the dye penetration was three times deeper compared that of 1,000 cycle. 3. In the case of Super bond, the highest retentive strength of approximately 35 kg was exerted. The correlation between the film thickness and marginal leakage was close to the significant level, that is, the thicker the film thickness, the lesser the marginal leakage. 4. In the case of Fuji Lute, the retentive strength increased in accordance with the film thickness. The retentive strength was comparative to that of Panavia. Relatively higher marginal leakage was observed beyond the side wall to the cavity floor even after 1,000 cycles of thermal stress. 5. Correlation between the retentive strength and marginal leakage was low for Panavia and Fuji Lute, and close to significant level for Super Bond.
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