Objective: To investigate the effect of repeated heat treatments on flexural strength and hardness of a new lithium disilicate ceramic. Materials and Methods: Thirty specimens of pressable lithium disilicate were prepared in the form of discs 15 mm in diameter and 1 mm in thickness and were fabricated using heat pressing technique. The discs were randomly divided into three groups (n=10); Press group (P1), 1st Repress group (P2), and 2nd Repress group (P3). For (P1), disc-shaped wax patterns were invested and heat-pressed according to the manufacturer's recommendations. For (P2) group, the leftover material from 1st pressing was recovered and the buttons were adjusted to fabricate the specimens by repeated heat-pressing using the same procedure as for (P1). The same procedure was repeated for (P3) group specimens fabrication. All specimens were tested for biaxial flexural strength. For the Vickers Hardness test, one fractured segment of each specimen was chosen randomly for the test and hardness was measured using Vickers hardness tester. Data was statistically analyzed by ANOVA and Tukey's post hoc analysis (α = 0.05). Results: For biaxial flexural strength, there was a significant difference (P <0.05) between tested groups. (P2) group showed the highest flexural strength value (403.69) while (P3) group showed the lowest value (353.22). For hardness, there was no significant difference between tested groups (p=0.055).
Conclusions: The optimum properties for LiSi Press are obtained with the first pressing. However, multiple heat repressing could significantly affect the strength of LiSi Press, but with no noticeable effect on surface hardness.