Abstract
The study on the relationship between free curing contraction and effective curing contraction of the impression materials have not been so far reported.The purpose of this study was 1)to study the relationship between free curing contraction and effective curing contraction and 2)to evaluate the relationship between rheological properties and effective curing contraction.Three kinds of addition-type impression material;P, E and X, having characteristics of their contraction pattern were examined according to the following methods.Effective curing contraction was determined by measuring dimensional deviation of the stone dies and free curing contraction was measured by means of mercury bath method.Rheology of the impression materials during setting was studied by the oscillating rheometer and cone-plate rheometer.The findings were as follows:1)There was no correlation between on the one hand the free curing contracion of the three selected addition-type silicone impression materials and on the other hand the effective curing contraction.2)The coefficient of correlation between on the one hand free curing contraction of the impression materials during the time interval from 15 min to 24hrs after the start of mixing, and on the other hand differences in diameter of stone dies poured 24hrs and 10 min after removal of the impression was very high(r=0.83).3)Depending on specific rheological properties having a substantially high plasticity during setting process, free curing contraction of an impression material in the impression tray can be partly compensated for by flow which will be induced by an underpressure in the impression paste between the tray and teeth.
