Resin Viscosity Determines the Condition for a Valid Exposure Reciprocity Law in Dental Composites

Published

January 28, 2022

Author(s)

Sri Vikram Palagummi, Martin Chiang, Taeseung Hong, Zhengzhi Wang, Chang Kwon Moon

Abstract

Objective: To provide conditions for the validity of the exposure reciprocity law as it pertains to the photopolymerization of dimethacrylate-based dental composites Methods: Composites made from different mass ratios of resin blends (Bis-GMA/TEGDMA and UDMA/TEGDMA) and silanized micro-sized glass fillers were used. All the composites used camphorquinone and ethyl 4-dimethylaminobenzoate as the photo initiator system. A cantilever beam-based instrument (NIST SRI 6005) coupled with NIR spectroscopy and a microprobe thermocouple was used to simultaneously measure the degree of conversion (DC), the polymerization stress (PS) due to the shrinkage, and the temperature change (TC) in real time during the photocuring process. The instrument had an integrated LED light curing unit providing irradiances ranging from 0.01 W/cm2 to 4 W/cm2 at a peak wavelength of 460 nm (blue light). Vickers hardness of the composites was also measured. Results: For every dental composite there exists a minimum radiant exposure required for an adequate polymerization (i.e., insignificant increase in polymerization with any further increase in the radiant exposure). This minimum predominantly depends on the resin viscosity of composite and can be predicted using an empirical equation established based on the test results. If the radiant exposure is above this minimum, the exposure reciprocity law is valid with respect to DC for high-fill composites (filler contents > 50% by mass) while invalid for low-fill composites (that are clinically irrelevant). Significance: The study promotes better understanding on the applicability of the exposure reciprocity law for dental composites. It also provides a guidance for altering the radiant exposure, with the clinically available curing light unit, needed to adequately cure the dental composite in question.

Citation

Dental Materials

Pub Type

Journals

Download Paper

DOI Link

Keywords

photopolymerization, exposure reciprocity law, radiant exposure, irradiance, autodeceleration, polymerization exotherm

Citation

Palagummi, S. , Chiang, M. , Hong, T. , Wang, Z. and Moon, C. (2022), Resin Viscosity Determines the Condition for a Valid Exposure Reciprocity Law in Dental Composites, Dental Materials, [online], https://doi.org/10.1016/j.dental.2019.12.003 (Accessed March 13, 2025)