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Simulating the effect of incremental layering on the shrinkage stress of dental resin-composite restorations

Author: Daniel Larrañaga-Ordaz - Minnesota Dental Research Center for Biomaterials and Biomechanics, School of Dentistry, University of Minnesota

Abstract

Dental caries is one of the most prevalent oral diseases due to increased sugar in the daily diet. Many different materials are used to fill dental cavities, the most common being resin composites due to their excellent aesthetic and mechanical properties. Resin composites require a curing process that generates polymerization shrinkage. Shrinkage stress thus occurs can cause failures of the restoration, the remaining tooth or the interface between them, leading to secondary caries. To reduce shrinkage stress and, hence, the risk of failure, the resin composite can be applied in incremental layers or it can be used in conjunction with a softer material that lines the cavity floor. To better understand how these different layering techniques affect the shrinkage stress, Finite Element Analysis (FEA) was used. Three static models were simulated using Abaqus (Dassault Systèmes SE, Île-de-France, France). Shrinkage of the restorative materials was modeled as thermal contraction with pseudo thermal expansion coefficients and a temperature drop. The thermal contractions prescribed were equal to 1/3 of the volumetric shrinkage strains, i.e. the effective linear shrinkage strains. The first model used only a single increment (4 mm thick) of a resin composite (E = 12 GPa, v = 0.3, and volumetric strain = 1.5%) to fill the cavity. In the second model, the same resin composite was applied in two sequentially cured layers, each 2 mm thick. In the third model, a 1 mm thick liner was used and co-cured with the upper layer of resin composite (3 mm thick). The properties of the liner were: E = 2 GPa, v = 0.3, and volumetric shrinkage strain = 0.5%. Both strategies were shown to be effective in reducing shrinkage stress.

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