Effect of light curing protocol on degree of conversion of composites

To evaluate the degree of conversion (DC) of two light-cured composites with different protocols of light curing.One hundred and ninety two specimens (n = 8) were prepared (5 mm × 2 mm) according to experimental groups: two composite resins (Filtek Supreme and four seasons); three light curing protocols [20 s with the tip of the light curing unit (LCU) device touching composite surface (C); 20 s with the tip of the LCU at 8 mm distant from composite surface (D); and tip of the LCU at 8 mm distant from composite surface and polymerization time required to obtain a radiant exposure of 16 J/cm(2) (DS)]. Four LCUs (Bluephase 16i, Ultralume LED 5, XL 3000 and Optilux 501C) were used. DC of the bottom and top surface of specimens were measured using a FTIR spectrometer. Data were statistically analyzed by 3-way split splot ANOVA and Tukey's test (alpha = 0.05).The results showed that DC of the top surface was higher than the bottom at all experimental conditions (p0.0001). Overall, the curing at 8 mm of distance did not affect conversion rate on the top surface (p0.05), but bottom surfaces showed DC reduction (p0.05). The highest monomer conversion values were observed for C and DS situations.The distance between the LCU and material surface and radiant exposure can affect the DC. Polymerization at distance should be performed with curing units with higher light power and/or extended exposure time.