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

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.