Light transmission through resin composites

What is it about?

Introduction: The study aimed to quantify the amount of light that passes through different resin-based composite (RBC) types and to assess if a clinically used polymerization procedure in curing incrementally filled deep cavities is justified. Methodology: Light transmission through 2-mm thick specimens made of three regular RBCs – a nano, a flowable nano and a microhybrid – of the same shade A3, was analyzed under 24 different curing conditions, that resulted by varying the curing mode, exposure distance and exposure time when using a violet-blue LED light curing unit. Incident and transmitted irradiances were assessed in real-time on a spectrophotometer and radiant exposure, transmittance (T) and absorbance (A) were calculated. A multivariate analysis assessed the effects of various parameters on T and A. Results: Incident irradiance varied among 656.4 (8.1) mW/cm² (Standard mode, exposure distance = 7 mm) and 3361.5 (33.6) mW/cm² (Plasma Emulation mode, 0 mm). The filler amount (weight and volume %) exerted a significant effect on transmitted irradiance (p < 0.001; partial eta squared ηP² = 0.400 and 0.362, respectively) while the effect of exposure distance was low (p < 0.001, ηP² = 0.141). Light transmittance was material-dependent and very low. The significant lowest absorbance was identified in Filtek Supreme XTE flow (1.11 ± 0.09), followed by Filtek Silorane (1.21 ± 0.03) and Filtek Supreme XTE (1.62 ± 0.13). Incident and transmitted radiant exposure correlated exceptionally well in each RBC (Pearson correlations coefficient > 0.99). Conclusion: When restoring a deep cavity with regular RBCs, each increment needs to be cured adequately, since final curing to compensate for deficits in polymerisation is insufficient. Keywords: resin-based composites, light curing unit, irradiance, radiant exposure, transmittance, absorbance.

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