Effect of Alkaline Components on Dental Filling Glass

The influence of the modification of glass in the strontium-aluminum-boron-silicate system (SABS) on technological and physicochemical properties was investigated. Introducing two alkalis into the glass makeup significantly lowered the melting temperature, from 1500 to 1450°C, which effected changes in the properties of the glass. On introducing alkalis in amounts up to 5 mol.% the thermal linear expansion coefficient (LTEC) decreased from 58 to 50 (α × 10 ^{– 7} K^{– 1}) and the refractive index n_D from 1.551 to 1.528. However, alkaline components adversely affect the hydrolytic resistance of the glass, transferring it from hydrolytic class I to II. The solution to this problem was to: (1) employ the polyalkaline effect, (2) maintain high radiopacity of the glass by introducing a small amount of highly effective radiopaque barium oxide into the makeup and significant strontium oxide reduction, and (3) increase the aluminum oxide content, which ordinarily increases the chemical resistance of the glass. The result was improved melting properties on lower melting temperatures and glass with high values of x-ray contrast (about 550%), light transmission (T = 90%), refractive index values n_D = 1.530 and LTEC = 56 (α × 10 ^{– 7} K^{– 1}) were obtained while maintaining chemical stability with respect to water the corresponding hydrolytic class I.