Influence of prolonged heating protocols on the physico-mechanical properties of resin composites

This study aimed to evaluate the physical-mechanical behavior of resin composites when subjected to different prolonged heating protocols.

A total of 150 specimens were divided into 15 groups (n = 10 per group) based on the restorative materials (Filtek Supreme, VisCalor, and Grandioso) and heating protocols: room temperature (22°C), 24 hours at 68°C, 7 days at 68°C, 30- and 100- cycles of artificial aging by thermocycling (5 and 68°C for 10 minutes each). The materials were inserted into a PVS matrix, cured for 20 seconds using a 1,000 mW/cm2 LED light-curing unit, and stored for 24 hours. The response variables measured were flexural strength and Knoop microhardness.

The flexural strength evaluation showed that Grandioso exhibited higher strength compared to Filtek Supreme and VisCalor, with no significant differences observed across the heating protocols. This indicates that prolonged heating did not affect the flexural strength of any of the tested resins. Knoop microhardness testing revealed significant differences among resins and heating protocols. Grandioso demonstrated the highest surface hardness across all protocols, whereas Filtek Supreme showed a decrease in hardness after 100 thermocycling cycles. Prolonged heating reduced surface hardness for Grandioso and VisCalor compared to room temperature, whereas Filtek Supreme maintained its hardness under extended heat exposure.

These findings suggest that while flexural strength remains unaffected by heating, surface hardness varies depending on the resin type and the heating duration.