Light transmission through resin composites

Abstract

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.

Susceptibility of RBC to various clinical relevant curing conditions: Effect of filler amount and chemical composition of the organic matrix

“…In a nano RBC (Filtek Supreme XTE), the transmitted light through 2-mm thick increments amounted only 1.4% to 2.1% of the incident light and was merely slightly higher (4.2% to 7.4%) in the more translucent, low viscous version of the same material (flowable nano RBC Filtek Supreme XTE flow) [8]. The same applies for RBCs with a non-methacrylate polymer matrix, such as the micro-hybrid Filtek Silorane (4.2% to 6.5%) [8]. Note that a variety of clinical relevant irradiances (= radiant flux or power received by a surface per unit area; 656.4 mW/cm² to 3361.5 mW/cm²), radiant exposures (46.96 to 0.99 J/ cm 2 ) and exposure distances (0 to 7 mm) were considered in these calculations.…”

“…A very low transmitted irradiance was identified through 2-mm thick layers of various RBCs as well as through the tooth structure [8,9]. In a nano RBC (Filtek Supreme XTE), the transmitted light through 2-mm thick increments amounted only 1.4% to 2.1% of the incident light and was merely slightly higher (4.2% to 7.4%) in the more translucent, low viscous version of the same material (flowable nano RBC Filtek Supreme XTE flow) [8]. The same applies for RBCs with a non-methacrylate polymer matrix, such as the micro-hybrid Filtek Silorane (4.2% to 6.5%) [8].…”

“…Note that a variety of clinical relevant irradiances (= radiant flux or power received by a surface per unit area; 656.4 mW/cm² to 3361.5 mW/cm²), radiant exposures (46.96 to 0.99 J/ cm 2 ) and exposure distances (0 to 7 mm) were considered in these calculations. The indicated % limits for the light transmittance through the various materials are related to the irradiance while the lower the irradiance, the higher the % transmitted light in the above indicated interval [8]. Based on these calculations, it was assumed that the low light transmittance will be directly reflected in the mechanical properties of the RBCs [8].…”

“…The indicated % limits for the light transmittance through the various materials are related to the irradiance while the lower the irradiance, the higher the % transmitted light in the above indicated interval [8]. Based on these calculations, it was assumed that the low light transmittance will be directly reflected in the mechanical properties of the RBCs [8]. When transferring the transmitted irradiance to the more clinically relevant term of radiant exposure, the transmitted light at the bottom of 2-mm thick increments is quantified as to not exceed 4 J/cm² at an ideal exposure distance.…”

“…Particularly in posterior cavities that are difficult to access, where the light curing unit (LCU) may not be placed perpendicularly to the restoration, the exposure distance may vary from an ideal position, the exposure time may be chosen too short or the LCU be contaminated with resins. The total amount of light received by the material may be further reduced by using curing strategies involving a pre-curing of the lowest increment when incrementally reconstructing a deep cavity, based on the wrong estimate [8] that the lowest increment will receive enough light when curing the upper increments or when curing through the tooth structure [9].…”