Thermo-hydrolytic stability of core foundation and restorative composites

STATEMENT OF PROBLEM: The use of weak and less durable materials in restoring teeth may result in weak restorations unable to withstand intraoral conditions. PURPOSE: The purposes of this study were to evaluate the effect of thermo-hydrolytic stress on the flexural strength and flexural modulus of core foundation composites with direct restorative composites and determine mass percentage of filler content. MATERIAL AND METHODS: A total of 216 specimens, from 9 brands of commercially available composites (Coreflo, DC Core, Photocore, APX, Litefil II A, Surefil, TPH Spectrum, Z100, and Z250) were fabricated following ISO Standard 4049. Flexural strength (MPa) and flexural modulus (GPa) were determined on bar-shaped specimens (25 x 2 x 2 mm) before and after storage in boiling water for 24 hours (n=12). The filler content in composite was determined by incineration using a thermogravimetric analyzer. The data were analyzed using 2-way analysis of variance and the Student t test (alpha=.05). RESULTS: Filler content of the tested composites was 66.6 to 81.8 mass %. Significant differences in both flexural strength and flexural modulus existed among materials, the effect of boiling and interaction (P<.05). Coreflo, DC Core, Z100, and Z250 demonstrated a significant decrease in flexural strength after boiling (P<.05). Z250 showed a significant decrease in flexural modulus after boiling (P=.001), while Surefil showed a significant increase in flexural modulus (P=.007). CONCLUSION: Within the limitations of this study, it can be concluded that composites were affected differently by moist heat stress. Some composites showed a degradation of flexural properties while some retained flexural properties. Stability of the composites varied among brands.