Abstract This article aims to compare the polymerization effectiveness of two curing modes of a polywave LED unit in four conventional resin composites at a 2-mm increment thickness, using bottom/top microhardness ratios as the evaluation method. Cylindrical specimens (5 mm in diameter and 2 mm in thickness; n = 20 per material) were prepared from four composites: Charisma Classic (CC), Filtek Ultimate (FU), G-aenial Posterior (GP), and Clearfil Photo Posterior (CP). According to the curing protocol, each material was assigned to two subgroups (n = 10 per subgroup), resulting in eight groups and a total of 80 specimens using a Valo PolyWave LED: standard mode (Mode 1: ≈ 1,200 mW/cm2, 20 seconds and high-power mode (Mode 2; ≈3,200 mW/cm2, 12 seconds. Light output and spectral distribution were verified with a radiometer and spectrometer. After storing the specimens for 24 hours in water at 37 °C, Vickers microhardness was measured on the top and bottom surfaces. Then, the bottom:top hardness ratios were calculated. A ratio ≥0.80 was considered indicative of clinically acceptable curing. Data were analyzed using two-way ANOVA (curing mode × composite type), with additional post hoc comparisons performed where appropriate; categorical outcomes were evaluated using Fisher's exact test (α = 0.05). No significant difference was found in bottom:top hardness ratios between Mode 1 and Mode 2 within FU, GP, or CP (p > 0.05). However, CC showed a significant reduction with Mode 2 (p = 0.022). The mean ratios for Mode 1 were ≥0.80 for CC, FU, and CP (ranging from 0.84 to 0.85), and were slightly below 0.80 for GP (0.79). In contrast, all materials in Mode 2 exhibited mean ratios below 0.80 (ranging from 0.75 to 0.78). The proportion of specimens with ratios ≥0.80 in Mode 1 ranged from 30% (GP) to 90% (FU); however, it was lower in Mode 2 for all materials. CP exhibited the highest hardness values and GP the lowest, irrespective of curing mode. Despite delivering higher total radiant exposure, the high-power/short-time mode of the PolyWave LED did not improve deep polymerization of 2-mm increments; often, it compromised it. For conventional resin composites, standard power with longer exposure is a more reliable method of achieving clinically acceptable curing at a 2-mm depth. High-power modes should only be used for thin surface layers or repair procedures.
Hatice Sümeyye Kiliç (Thu,) studied this question.