Composite curing transmission, cure depth and filler-resin refractive index mis-match

Objectives: To relate monomer reactivity to light transmission (LT) changes during cure and assess the influence of filler/resin matrix refractive index mis-match on cure depth (CD) for experimental resin based composites (RBCs). Methods: Eight experimental RBCs were prepared from two fillers; Sr-(S) and Ba-Glass (B) with refractive indices (RIs) of 1.51 and 1.53 respectively. Each filler was mixed (70wt%) with one of four monomer formulations (BisGMA, TEGDMA mixtures) of RI's 1.537 (1), 1.5233 (2), 1.497 (3) and 1.470 (4). Each RBC (S1-S4 & B1-B4; n=3) was cured for 60s with an 843 (13) mW/cm² LED light. Curing resin LT was recorded using a computer based diode technique. CD was recorded with a penetrometer, and pre- & post-cure Translucency Parameter (TP) with a tristimulus colorimeter. Data was analysed by ANOVA and post-hoc Tukey tests (P<0.05). Results: Total curing LT did not differ significantly (P>0.05) between resins. Mean (S.D.) time to 90% of peak transmittance ranged from 5.9s (0.6s) for monomer 1 to 26.3s (0.6s) for monomer 4. Monomer four was significantly (P<0.05) less reactive than the other three monomers. TP ranged from 1.82 (0.17) for B4 pre-cure to 39.7 (1.75) for B3 after 60s irradiation. B1, B2, S1, S2 became more opaque (P<0.05) on curing whereas B3, B4, S3, S4 became more translucent. CD ranged from 3.75mm (0.04mm) for S1 to 6.54mm (0.05mm) for S3 and 3.27mm (0.04mm) for B4 to 8.10mm (0.02mm) for B3. Two-way ANOVA revealed that resin matrix formulation and filler type were both significant factors with regard to CD, with a significant interaction (P<0.001) present. CD for RBCs based on monomer 4 cured significantly deeper with filler S (P<0.001) whereas the converse applied for the other RBCs. Conclusions: Resin matrix reactivity and filler-resin refractive index mis-match influence curing light transmittance changes and depth of cure.