Influence of photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites

Objective. To establish the relationship between photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites. Methods. Model composites based on BisGMA/TEGDMA (60:40 mol%) were loaded with 40 wt% of 7 nm or 16 nm-sized filler particles. One of the following photoinitiator systems was added: camphorquinone (CQ) associated with an amine (EDMAB), monoacylphosphine oxide (TPO), or bysacylphosphine oxide (BAPO). The optical properties of disk-shaped specimens were measured 24 h after curing and repeated after storage in water for 90 days and coffee for 15 days. A large spectrum LED unit (Bluephase G2, Ivoclar Vivadent) was used for photoactivation. CIE L∗a∗b∗ parameters, color difference (ΔE), and translucency parameter (TP) were calculated. Knoop hardness readings were taken at top and bottom composite surfaces. Cure efficiency was determined by bottom/top hardness ratio. Data were statistically analyzed at α = 0.05 significance level. Results. Composites formulated with 16 nm particles had higher CIE L∗ than those with 7 nm particles in all storage conditions. BAPO-based composites generally had lower CIE a∗ than the other composites. The group TPO + 16 nm before storage and all groups with 16 nm-sized particles after storage had lower CIE b∗ (i.e. lower degree of yellowing) than the other groups. TPO-based materials had higher color stability. The cure efficiency was not significantly affected by photoinitiator system or particle size. CQ + 7 nm had the lowest and BAPO + 16 nm the highest hardness values. Significance. Combination of photoinitiator system and filler particle size might affect the optical properties of composites, with low influence on cure efficiency.