Real-time Imaging and Quantitative Analysis of Internal Gap Formation in Bulk-fill and Conventional Resin Composites: An OCT Evaluation

Background This study used optical coherence tomography (OCT) to observe real-time internal gap formation in both bulk-fill and conventional resin composites. It aimed to provide a quantitative analysis of variations, addressing the inconclusive nature of microleakage assessment caused by differences in testing methods. Methods Fifty extracted third molars prepared with Class I cavities, were divided into five groups (n=10). Conventional resin Filtek Z350 XT (FZX) was applied with a double-layer filling of 2 mm per layer. Bulk-fill resins X-tra fil (XTF), Filtek Bulk Fill Posterior Restorative (FBP), Surefil SDR Flow + (SDR), and Filtek Flowable Restorative (FFR) were applied with a single-layer filling of 4 mm. Real-time OCT imaging was conducted during light curing. Post-curing, the entire sample was OCT-scanned. Following this, ImageJ software was used to measure the gap (G1%). Subsequently, thermal cycling (TC) (5000 times, 5°C–55°C) was applied, followed by OCT scanning to calculate the gap (G2%) and ΔG%. Data were analyzed using two-way repeated measures ANOVA, Kruskal-Wallis test, and Duncan's test (α=0.05). Results There was no significant difference in G1% among the groups (p>0.05). Following TC, FZX exhibited the highest G2%, succeeded by FFR, FBP, XTF, and SDR, with SDR demonstrating the lowest G2% (p<0.05). FZX showed the highest ΔG% (p<0.05), while SDR exhibited the lowest ΔG% (p<0.05). Conclusion OCT proves to be a promising tool for detecting microleakage. TC exerted a more significant negative impact on conventional resin. Surefil SDR Flow + displayed the least microleakage, both before and after TC.