The effect of re-pressing and glazing on the optical properties of high-density micronized heat-pressed glass ceramic

Abstract

Recycling high-density micronized (HDM) heat-press glass ceramic ingots to press several restorations would be economical and reduce waste. However, to achieve this, the effects of re-pressing on the optical properties and long-term durability of HDM glass ceramics must be completely understood. The aim of this study was to assess the effects of re-pressing and glazing on the optical properties of HDM heat-press glass ceramic. Twenty-one HDM glass ceramic (Initial LiSi Press) discs were prepared and randomly divided into three groups (n = 7 per group): single heat pressing, double heat pressing, and triple heat pressing. Optical properties, surface roughness, and crystalline structure were measured for each group at three time points: before glazing and thermocycling, after glazing, and after thermocycling. The effect of these independent variables on optical properties were assessed by two-way ANOVA, and Tukey's post hoc test assessed the differences between groups. Heat re-pressing HDM glass ceramic significantly altered its color, reduced translucency, and reduced surface roughness (P < 0.001). After the second heat-press, the color (ΔΕ00) and translucency parameter changes (ΔTP00) exceeded perceptible thresholds but not clinically acceptable thresholds, but these were exceeded after the third press for ΔΕ00. Additionally, glazing lightened the shade of the ceramic, reduced translucency, and reduced surface roughness (P < 0.001), with ΔΕ00 and ΔTP00 changes exceeding the perceptible but not the clinically acceptable threshold. Thermocycling produced ΔTP00 changes that exceeded the clinically acceptable threshold. Further studies of the effects of heat re-pressing on HDM glass ceramic are now needed to progress toward clinical translation.