Influence of Repeated Heat-Pressing on Properties of Pressable Ceramic

Objectives: The purpose of this study was to evaluate the biaxial flexural strength (BFS) and Vickers hardness (VH) of heat-pressed glass-ceramic material after repeated pressing.
Methods: Ceramic discs of IPS e.max Press (12 mm in diameter x 0.9 mm thickness) were heat-pressed and used as control (HP1). Sprue and button parts of the heat-pressed material were retrieved and used for repeated heat-pressing to construct discs of two and three re-pressed groups (HP2 and HP3). All the heat-pressed casting procedures were performed according to the manufacturers' instructions. A biaxial flexural strength (BFS) test was performed to determine the strength of pressed (HP1) and re-pressed (HP2 and HP3) glass-ceramic disc specimens (n = 12) at a crosshead speed of 0.5 mm/min. Vickers hardness test was conducted in a microhardness tester HMV-2 (Shimadzu) with a load of 500 g applied for 15 s. Twelve glass-ceramic discs were made for pressed (HP1) and twelve for re-pressed (HP2 and HP3) and five indentations were made for each disc. Data were submitted to ANOVA and Tukey’s post-hoc test (p<0.05).
Results: The BFS values in MPa (mean ± standard deviation) were HP1 (279.7±12.5); HP2 (230.3±7.1) and HP3 (220.8±8.6). HP1 was significantly higher than HP2 and HP3. The VH values were HP1 (638.1±11.5); HP2 (592.6±6.6) and HP3 (590.4±7.6). HP1 was significantly higher than HP2 and HP3.
Conclusions: Repeated heat-pressing treatment produce a statistically significant decreased in the biaxial flexural strength and Vickers hardness of the IPS e.max Press glass-ceramic.