Examining the Impact of Preheating on the Fracture Toughness and Microhardness of Composite Resin: A Systematic Review

The objective of this comprehensive study was to systematically evaluate the effects of preheating on two critical mechanical properties, microhardness and fracture toughness, in resin composite materials. The overarching goal was to provide valuable insights into the potential benefits and limitations of this technique for enhancing the overall mechanical performance of such materials. To achieve this, an extensive and systematic electronic search was conducted across multiple reputable databases, including MEDLINE/PubMed, SCOPUS, ProQuest, SpringerLink, Web of Science, ScienceDirect, and Google Scholar, with data collection extending until June 2023. This rigorous search process resulted in the identification of 29 pertinent articles, which were subjected to a thorough risk of bias assessment employing the Quality Assessment Tool For In Vitro Studies (QUIN). The findings of this comprehensive investigation revealed several noteworthy trends. First, concerning microhardness, all the studies consistently demonstrated a positive effect of preheating on this mechanical property. This uniformity in results corroborates the initial hypothesis that preheating indeed enhances microhardness in resin composite materials. Second, with respect to fracture toughness, a majority of the studies provided evidence supporting the notion that preheating has a favorable influence on this particular mechanical property. This alignment of outcomes suggests that preheating can be a beneficial technique for improving fracture toughness in resin composites. However, it is essential to note that there were a few exceptions within the collected data, where preheating appeared to lead to a decrease in fracture toughness. Additionally, one study reported no statistically significant effect on fracture toughness. These deviations from the general trend highlight the complexity of the relationship between preheating and fracture toughness, indicating that other factors or material-specific nuances may come into play. In conclusion, the results of this study indicate that preheating resin composites can improve microhardness and fracture toughness, offering potential benefits for dental restorations. Yet, conflicting data warrants further research to uncover the reasons behind these discrepancies. Future studies should also investigate preheating's broader impact on composite resin materials to gain a comprehensive understanding of its applications and limitations in the field.