Surface Microhardness of Tetric N-Ceram Nanoparticulate Resin Photocured with LED Polywave N^® vs Monowave MN^® at Different Exposure Times

Aim: To explore how photopolymerization with monowave and polywave LEDs influences the surface microhardness of Tetric N-Ceram composite resin across varying exposure times, aiming to better understand how these factors affect material strength and contribute to improving its performance in clinical settings. Materials and methods: An in vitro study was carried out. One hundred sixty resin blocks were prepared, consisting of 80 samples of one nanohybrid composite and 80 samples of a universal composite, all in shade A2. The blocks were molded using stainless steel matrices with dimensions of 8 mm in diameter and 2 mm in height. Specimens were polymerized using different light-curing protocols with polywave and monowave LED units, applying various exposure times (10–40 seconds) to evaluate surface microhardness. Surface microhardness was measured using a Vickers microhardness tester with a 100-gm load applied for 10 seconds. Statistical analysis included three-way ANOVA, post hoc tests, and Shapiro–Wilk normality tests (p < 0.05). Results: The surface microhardness of the nanohybrid composite was significantly affected by the light-curing protocol. The high-power mode at 20 seconds produced the highest value (43.9 HV), while the low-power mode at the same duration yielded the lowest (37.9 HV, p < 0.05). For the universal composite, the high-power setting at 20 seconds resulted in the greatest hardness (51.4 HV). In contrast, curing with monowave LEDs showed no statistically significant differences between exposure times, with stable values recorded for both composites (34.1 HV and 34.7 HV for the nanohybrid; 50.1 HV and 48.7 HV for the universal composite, p > 0.05). Conclusions: Photopolymerization protocols significantly influence the surface microhardness of resin composites. Higher light intensity and longer exposure times improved hardness in both Tetric N-Ceram and Filtek Universal. Meanwhile, monowave LED curing showed stable results regardless of time, suggesting reliable performance. Clinical significance: The study offers valuable insights for clinical practice, demonstrating that adjusting light intensity and exposure time enhances composite resin hardness. This supports tailored photopolymerization protocols to improve restoration durability. Moreover, the stability of monowave LED results suggests its reliability for consistent outcomes, aiding material selection in restorative procedures.