Methacrylate- and silorane-based composite restorations: Hardness, depth of cure and interfacial gap formation as a function of the energy dose

Abstract

Objectives To investigate the influence of the energy dose on the hardness, polymerization depth, and internal adaptation of silorane and methacrylate-based posterior composites in Class II restorations with different bonding approaches. Materials and methods Class II preparations were made on the mesial and distal surfaces of extracted third molars and randomly distributed into 6 groups ( n = 20), according to the restorative systems [methacrylate-based composite: Filtek P60 + Adper Single Bond 2 (etch-and-rinse adhesive) – P60/SB; Filtek P60 + Adper Easy One (self-etching adhesive) – P60/EO; silorane-based composite: Filtek P90 + P90 System Adhesive – P90 (self-etching adhesive)] and the energy dose (20 and 40 J/cm 2). Resin composites were applied in two increments, individually photoactivated using an LED light-curing unit. After 24 h, all restorations were mesio-distally sectioned. Hardness was evaluated along the transversal section of the fillings (1–4 mm below the restoration surface) using a load of 50 g for 5 s. In order to evaluate the internal gap formation, specimens were air dried and 1% acid red propylene glycol solution was applied to the internal margins for 20 s. Specimens were then water rinsed, air dried, and digitally image recorded. The internal gap (%) was calculated as the ratio between the stained margins and the total length of the internal margin. Kruskal–Wallis test was conducted to evaluate internal gap formation, and three-way ANOVA and Tukey's test were performed to evaluate hardness/polymerization depth ( α = 0.05). Results Regarding the internal gap formation, a significant difference was observed among all groups (P60/EO < P90 < P60/SB), regardless of the energy dose. For 40 J/cm 2, a significant increase in gap formation was seen for P60/EO and P90 when compared to 20 J/cm 2. The KHN of both resin composites was not affected by the depth of evaluation, but the influence of the material was significant (P60 > P90; p < 0.05). The highest energy dose (40 J/cm 2) produced significant increase in the KHN only for Filtek P90 ( p < 0.05). Significance Although a higher energy dose produces a slight increase in hardness for the silorane based composite, it also increases the internal gap formation. Dose of 20 J/cm 2 seems to be more suitable as it provides reduced internal gaps and satisfactory hardness. In addition, gap formation seems to be a consequence of an underperformed bonding approach rather than the differences in the resin-composite formulation.