Effect of Heat Treatment on Physical and Mechanical Properties of Regular and Bulk-fill Resin Composites

Objectives: The aim of this study was to determine the influence of heat treatment on the volumetric polymerization shrinkage, presence and quantification of internal voids and flexural strength of a regular and a bulk fill composite placed in a class-I cavity using micro-computed tomography and three-point bending test.

Methods: 24 standardized class-I cavities (4 mm depth x 4 mm length x 4 mm wide) were made in caries-free extracted human third molars, restored with the bonding agent Adhese Universal (Ivoclar Vivadent) and the resin composites Tetric EvoCeram (TEC - Ivoclar Vivadent) and Tetric EvoCeram Bulk Fill (TEB), which were divided in 4 groups, regarding the restoration material used: G1 – TEC, G2 – TEC Heated, G3 – TEB, G4 – TEB Heated. Each group was scanned three times using a micro-computed tomography (μCT 35, Scanco Medical). First scan was done of the empty cavity, second after placing the composite in the cavity (uncured) and the third after curing (cured). 3D images were imported into Amira 3D software (Amira, Mercury Computer Systems) for 3D visualization, identification of voids and volumetric polymerization shrinkage analysis. Three-point bending test in a universal testing machine (Instron 5566, Norwood, MA, USA) was performed. Data were analyzed using one-way ANOVA and Tukey post-hoc test (p<0.05).

Results: Statistical analysis failed to show a significant statistical difference in VS either by material, heat treatment or the interaction between them (p > 0.05). G2 presented greater percentage of internal void formation and G4 presented a decrease in flexural strength

Conclusions: The use of pre-heating treatment did not affect relevantly the volumetric shrinkage polymerization and void formation of any of the studied composites, but it suggested that could have a negative effect on the flexural strength.