Post-cure heat treatments influence on mechanical and optical properties of resin composites

Abstract

This study evaluated the effect of post-eure heat treatment (PCHT) on the Knoop mierohardness (KHN), degree of conversion (DC), color changes, and contrast ratio (CR) of four resin composites (RCs): Z100 (3M ESPE), Z350 XT (3M ESPE), Estelite Omega (Tokuyama) and Empress Direct (Ivoclar Vivadent). Specimens (12x1 mm) were prepared for each material (n = 10/group). After curing, samples were subjected to PCHT for 10 min at 100°C or 170°C. Control group was maintained at room temperature (24°C) for the same time. The DC was analyzed by FT-NIR immediately and 24 h after the PCHT (n = 3/group). KHN was analyzed 24 h after PCHT (n = 10/group). According to CIEDE2000 (AE oo), color measurements were obtained immediately after curing, five minutes after PCHT, and after seven days of storage in water, coffee, and red wine. Data were analyzed by One and Two-Way ANOVA (p < 0.05). Z100, Z350, and Estelite Omega showed increases in KHN with increased temperature (p < 0.05). PCHT at 100°C and 170°C led to a higher DC of all RCs (p < 0.05). Initially, the PCHT lead to increased AEoo values (p < 0.05), which was decreased after immersion in coffee and wine (p < 0.05). Considering the effect of PCHT and staining solutions, lower color changes were observed in the thermally treated specimens (p < 0.05). Taken collectively, the results suggest the PCHT as an economical and practical alternative to enhance direct RC’s properties in direct-indirect and indirect restorations.