Phenyl-propanedione and curing light influence experimental resin’s physical-mechanical properties

Objective: The aim of this study was to evaluate the influence of photoinitiator type and curing light on the Knoop Hardness (KHN), cross-link density (CLD) and yellowing of experimental resins.

Method: Three resins were prepared containing BisGMA, UDMA, BisEMA and TEGDMA. The photoinitiators used were camphorquinone (CQ), Phenyl-propanedione (PPD) and the association (CQ/PPD). These photoinitiators were used in combination with an aliphatic amine (DMAEMA). The Ninety cylindrical specimens (n=10) were made and photocured by different curing lights: Quartz-halogen-tungsten light (XL3000), a second generation LED (Radii Cal) and a polywave LED (Valo). The energy dose was standardized at 32J. After 24hs, the yellowing effect was analyzed by spectrophotometer and the initial KHN in a microhardener tester. Next, specimens were immersed in 100% ethanol for 24hs and the KHN was measured again. The cross-link density was measured as the softening effect of the resins (decrease of KHN). Data were submitted to two-way ANOVA and Tukey test (α = 0.05).

Result: For the KHN, the presence of CQ and photocuring with Valo unit provided higher KHN values compared to the other groups. For the CLD, there were no difference among the groups tested (p ≥ 0.05). In general, the yellowing effect, analyzed by the b* axis of the CIELAB color system was higher when the resin blend contained CQ or the association CQ/PPD, compared to the resin with only PPD as the photoinitiator.

Conclusion: The use of CQ as photoinitiator promoted higher hardness values, however allowed a higher yellowing of the resin material. The light curing unit Valo promoted better results of Knoop hardness, even with the resin contained PPD in its formulation.