|Budget Amount *help
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 2002: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2001: ¥1,400,000 (Direct Cost: ¥1,400,000)
This research was projected to establish a quantitative primary screening for the survey of marginal sealability of dental materials. An automated testing apparatus was developed, in which cool and hot water baths, six solenoid valves, three pumps an electroconductivity meter and their controller were assembled.
The testing apparatus could load reproducibly 50,000 cyclic thermal changes, loadable temperature 7-54 C at frequency of 33.3 mHz, to a specimen. However some modification was required to ensure prolonged stable monitoring more than 100,000 thermocycles. Obtained conductivity changes related quantitatively to leakage volume of physiological saline.
Disc-shape specimen was made of a bovine tooth plate and light-curing resin. The tooth plate was drilled through a hole to be filled with a dental light-cured restorative composite.
When there was a bubble in the vicinity of specimen surface at the detection side, leakage volume increased with convex curve. Leaked saline forms a droplet in the bubble in no contact with circulating water. Mixing of grew droplet into circulating water results steep rise of conductivity. In normally, leakage volume increased with concave curve after an induction period. Leakage volume increase could be regressed to two-order polynominal expression of thermocycle. The durability of marginal seal was able to estimate the thermocycle showing zero of leakage volume in the polynominal. Examined dental composites showed 30,000 to 50,000 cycles of the sealing durability for acid-ethed cavity.
The two-order leakage curves were gradually asymptotic to lines with prolongation of monitoring. The slope of asymptotic line might be equivalent to the width of marginal gap. The obtained normal leakage behaviors might be explained that ; first adhesion break yields a micro-crack, then the crack grows, and finally marginal gap with a constant width generates at every thermal cycle.