Effect of Repeated Heat-Pressing on Mechanic Properties of Pressable Ceramic

Objectives: The aim of this study was to evaluate the Vickers hardness (VH) and biaxial flexural strength (BFS) of heat-pressed glass-ceramic IPS Empress Esthetic after repeated pressing.
Methods: Specimens (12 mm diameter, 0.9 mm thick) of heat-pressed glass-ceramic IPS Empress Esthetic (Ivoclar vivadent) were heat-pressed and used as control (HP1). Button and sprue parts of the glass-ceramic IPS Empress Esthetic were retrieved and used for repeated heat-pressing to fabricated specimens of two and three re-pressed groups (HP2 and HP3). All the heat-pressed casting procedures were performed according to the manufacturers' instructions. Vickers hardness test was conducted in a microhardness tester HMV-2 (Shimadzu) with a load of 500g applied for 15 seconds. Five indentations were made for each specimen. Twelve glass-ceramic discs were made for pressed (HP1) and twelve for re-pressed (HP2 and HP3). A BFS test was performed to determine the strength of pressed (HP1) and re-pressed (HP2 and HP3) glass-ceramic IPS Empress Esthetic specimens (n = 12) at a crosshead speed of 1.0 mm/min. Data were submitted to ANOVA and Tukey’s post-hoc test (α=0.05).
Results: The VH values (mean ± standard deviation) were HP1 (589.1±14.1); HP2 (551.8±13.9) and HP3 (552.0±12.6). HP1 was significantly higher than HP2 and HP3. The BFS values in MPa were HP1 (219.7±17.9); HP2 (180.6±14.7) and HP3 (171.8±9.6). HP1 was significantly higher than HP2 and HP3.


Conclusions: Repeated heat-pressing treatment produce a statistically significant decreased in the VH and BFS of the IPS Empress Esthetic glass-ceramic.