Accurate assessment of the three-dimensional shrinkage stress evolution for photopolymerized dental filling materials: Mechano-chemo-thermo-coupled finite element modeling and experimental validation

Abstract

Objective: Photopolymerized resin composites are widely used as dental filling materials. However, the shrinkage stress generated during photopolymerization can lead to marginal microcracks and eventual restoration failure. Accurate assessment of the stress evolution in dental restorations, particularly in complex cavity geometries, is critical for improving the performance and longevity of the dental filling materials. This study aims to develop a novel mechano-chemo-thermo-coupled finite element method (FEM) to accurately capture three-dimensional (3D) shrinkage stress of resin-based photopolymerized filling materials.

Methods: The FEM was established with consideration for the evolution of mechanical properties, thermal effects, and polymerization shrinkage during photopolymerization. Real-time material property evolution was derived from measurements of degree of conversion and temperature changes, and these were integrated into the FEM alongside thermal expansion/contraction effects. The FEM was parameterized through mechanical, chemical, and thermal experiments, then applied to simulate different photocuring protocols and boundary conditions. The accuracy of the predicted shrinkage stress was validated through three experiments: uniaxial shrinkage stress measurement, full-field optical measurement, and acoustic emission analysis using typical dimethacrylate-based dental filling materials.

Results: The coupled FEM model achieved predictive stress magnitudes in quantitative agreement with the experimental measurements (relative error ∼1 %), significantly improving upon existing methods (∼22.5 %). Furthermore, the FEM accurately predicted spatial debonding based on stress distribution, providing insights unattainable through current methods.

Significance: This experiment-modeling-combined study provides a valuable tool for accurately predicting the spatial and temporal evolution of the shrinkage stress in resin-based dental filling materials, thereby providing new insights for optimizing their clinical applications and enhancing durability.

Keywords: 3D shrinkage stress; Dental filling materials; Experimental validation; Mechano-chemo-thermo-coupled finite element method.