The Effect of Preheating of Nano-Filler Composite Resins on Their Degree of Conversion and Microfiltration in Dental Fillings

The study assessed microhardness, microleakage of Class I, and the degree of conversion of composite resins preheated at 55 °C. This in vitro study evaluated two nanofilled composite resins (NCR), Filtek™ P60 and Filtek™ Z350 XT, used in the restorations. The degree of conversion (DC) was determined by Raman spectroscopy; the study compared the vibrational bands of the residual unpolymerized methacrylate C=C stretching band at 1640 cm−1 to the aromatic C–C stretching band at 1610 cm−1, used as an internal standard. Microleakage tests considered standard Class 1 cavities prepared on human premolars randomly divided. Preheating Filtek™ P60 and Filtek™ Z350 XT increased significantly VMH values (p = 0.0001). The highest microleakage occurred in preheated Filtek™ Z350 XT, while the lowest was in unheated Filtek™ P60. Unheated Filtek™ Z350 XT showed a significant increase of microleakage than unheated Filtek™ P60. (p = 0.024). Preheating of composite resins improved mechanical properties increasing DC and VMH. However, it also increases microleakage promoting bacterial penetration, secondary caries, marginal discoloration and hypersensitivity.