Tensile Strength of Fluoride-releasing Restorative Materials after Thermal Degradation

Objectives: This study examined the diametral tensile strength of thermally degraded fluoride-releasing restorative materials. Methods: Commercially available fluoride-releasing restorative materials were used: three different compomers [Reactmer (RE, Shofu), Dyract AP (AP, DENTSPLY-Sankin), and Xeno CF (XE, DENTSPLY-Sankin)] and two different light-cured glass ionomers [Fuji II LC EM (LC, GC) and Vitremer (VT, 3M)]. Disc specimens (6mm in diameter, 3mm thick) of each material were prepared according to the manufacturers’ instructions. One hour after preparation, the specimens were immersed in deionized water at 37°C for 28 days (Control) or were subjected to continuous hot water (90°C) flow for 28 days in the Soxhlet extraction apparatus to accelerate degradation (Td). The diametral tensile strength of each specimen was then measured. Results: The strength values (MPa, mean±sd, n=5) were as follows (Control vs. Td): 38.0±3.5 vs. 27.2±3.0 for RE, 45.1±2.6 vs. 36.5±4.9 for AP, 48.8±1.7 vs. 44.0±3.2 for XE, 38.9±1.6 vs. 32.1±0.4 for LC and 38.5±4.7 vs. 30.6±2.7 for VT. For all materials tested, a significant reduction in the strength was observed after Td (p<0.05). In our previous study (Harashima et al., J.J. Dent. Mater. 22. SI. 41. 2003), the resin composites did not thermally degrade under experimental conditions identical to those used in this study. The range of average values found for these resin composites after thermal degradation was 53.4–61.7 MPa. Conclusion: The matrix components of the fluoride-releasing restorative materials tested appeared to be prone to thermal degradation compared to those of resin composites.