Effect of Polywave LED Activation on a Bulk-fill Composite Degradation

Objectives: Bulk-fill composite resins present as advantage low polymerization shrinkage and allows their application in deep cavities in thicker layers due to monomer and initiators changes, but there are concerns on long term mechanical properties maintenance. This research assessed the resistance to degradation by microhardness test of a Bulk-Fill composite resin (Tetric N Ceram Bulk Fill) activated with a mono- or polywave LED.
Methods: Fourteen specimens with 1.5.x1.5x6.5mm (n= 7) were tested in a factorial design considering composite in “light” in 2 levels: monowave (Radii Plus; SDI ±1,250mW/cm²) or polywave (Bluephase G2; Ivoclar-Vivadent ±1,450mW/cm²), repeated measures of in vitro degradation in 2 levels: baseline and degradation (24h in 100% ethanol), and Depth in 7 levels at 0.1; 1.0; 2.0; 3.0; 4.0; 5.0; and 6.0mm from the irradiated surface by microhardness. Custom molds were bulk filled with composite resin and activated for 10s with respective LED. Baseline microhardness were evaluated after 24h, by 3 profiles per depth. Specimens were immersed in 100% ethanol for 24h and the microhardness after degradation was evaluated. Data showed normal distribution (Levine test) and were analyzed by repeated measurements ANOVA and Bonferroni (α=0.05).
Results: Statistical significant differences were observed to interaction between Depth*Degradation (p<0.01), no statistical significant differences were observed to other interactions. The main factor Light showed statistical significant difference (monowave= 23.4[5.0]; polywave 24.2[5.5]; p=0.02).
Conclusions: The use of polywave LED may result in higher hardness. All specimens degraded after chemical degradation. Degradation increases in function of Depth.