| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1988: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1987: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
This study investigated the role of the filler content in the marginal adaptation of light-cured composite resin restorations. silanized quartz powder was incorporated in Bis-GMA and TEGDMA resin. The filler content levels were 0, 22.4, 39.5, 50.3, 63.5, 69.5, and 71.1 vo1%.
Polymerization shrinkage, hygroscopic expansion, and thermal expansion decreased linearly with increased filler content. The shear bond strength to the bovine enamel increased when the filler content increased up to 63.5 vo1%, but thereafter no significant differences were detected. The stress relaxation rate decreased at the filler content increased. That was about 20-50% after 5 minutes and about 45-70% after 24 houres. Independently of filler content, the marginal sealing in class V restorations was poor when the restorations were polished or/and thermal cycled immediately after irradiation, and it was excellent when the restorations were only polished after a one-day immersion in water. Microleakage and enamel cracks increased in the below 39.5 vo1% and 50.3 vo1%-filled resin restorations, respectively, when the restorations were polished and thermal cycled after a one-day immersion in water. The immersion of restorations in water for 3 months before thermal cycling improved the marginal sealing at lower filler levels as compared with one-day immersion in water.
It was suggested that the factor affecting the marginal sealing the most immediately after irradiation was polymerization shrinkage stress, and that additional stresses caused by polishing or thermal cycling can destroy the marginal sealing. However, after a one-day immersion in water, shrinkage stress was almost eliminated and the factor with the greatest influence was the difference in thermal expansion between the resin and the tooth structure. Hygroscopic expansion caused by threemonths immersion in water can eliminate the influence of thermal expansion even at lower filler levels.
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