Setting expansion of gypsum-bonded investment in dental casting

Abstract

The values of setting expansion of investment under uniaxial stress have been determined at conditions designed to obtain the difference of setting expansion between that parallel to the loading direction and that perpendicular to the loading axis. The setting expansion curves were represented by $$a(t) = a_0 (1 - P/E')[1 - exp( - kt)]$$ along the loading direction and $$a(t) = a_0 (1 + \nu 'P/E')[1 - exp( - kt)]$$ perpendicular to the loading direction, wherea(t) is a setting expansion,a0 = 0.009,ν′ = 0.2,E′ = 5 kg cm−2,k = 0.032 min−1,P applied stress, andt the time (min). On the basis of these results, a method to estimate the value of setting expansion under restrictive force was developed. According to this method, the setting expansion of the investment could be calculated by substitutingϱe/ϱt fore, ka0 exp (−kt)/E′ for 1/E, ν′ forν, andka0 exp (−kt) forαT in the theory of elasticity.