Effect of photoinitiator combinations on hardness, depth of cure, and color of model resin composites.

OBJECTIVE This study aims to determine the influence of photoinitiators' combinations on the hardness, depth of cure, and color of model resin composites. MATERIALS AND METHODS The composites were formulated by a mixture of BisGMA and triethyleneglycol dimethacrylate (60:40 mol), with barium-aluminum-silicate glass and silicon dioxide particles as inorganic fillers (60 wt%). Three photoinitiator types were tested: camphorquinone/amine (CQ), monoacylphosphine oxide (TPO), and bysacylphosphine oxide (BAPO). Six experimental groups were formed by differences in photoinitiator systems: CQ, TPO, BAPO, CQ+TPO, CQ+BAPO, and CQ+TPO+BAPO. Hardness was determined by Knoop indentation at the top and bottom surfaces (n = 5). Depth of cure was performed according to ISO 4049 scraping method (n = 5). Color was obtained by the CIELAB method (n = 10), 24 hours after curing (baseline), after 30 days storage in distilled water, and after 30 days storage in coffee solution. CIELAB color difference (ΔE*) was calculated for both periods. Data were submitted to analysis of variance, followed by Student-Newman-Keuls method (α = 0.05). RESULTS The photoinitiator system influenced hardness, where CQ presented the lowest top and bottom values. No statistical difference among groups was observed for the bottom/top hardness ratio. Regarding the depth of cure, the CQ and those formulated with CQ associations presented higher values than TPO and BAPO. Regarding color, BAPO and CQ+BAPO presented the highest ΔE* after 30 days in water immersion, whereas CQ+TPO and CQ+TPO+BAPO presented the lowest after 30 days in coffee immersion. CONCLUSION The associations CQ+TPO and CQ+TPO+BAPO presented improved color stability and hardness when compared with CQ, and did not influence the depth of cure. CLINICAL SIGNIFICANCE The combination of alternative photoinitiators with the traditional camphorquinone/amine system improved the color stability of the model resin composites and maintaining their mechanical properties.

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