Shrinkage of Dental Composite in Simulated Cavity Measured with Digital Image Correlation

Abstract

Polymerization shrinkage of dental resin composites can lead to restoration debonding or cracked tooth tissues in composite-restored teeth. In order to understand where and how shrinkage strain and stress develop in such restored teeth, Digital Image Correlation (DIC) was used to provide a comprehensive view of the displacement and strain distributions within model restorations that had undergone polymerization shrinkage. Specimens with model cavities were made of cylindrical glass rods with both diameter and length being 10 mm. The dimensions of the mesial-occlusal-distal (MOD) cavity prepared in each specimen measured 3 mm and 2 mm in width and depth, respectively. After filling the cavity with resin composite, the surface under observation was sprayed with first a thin layer of white paint and then fine black charcoal powder to create high-contrast speckles. Pictures of that surface were then taken before curing and 5 min after. Finally, the two pictures were correlated using DIC software to calculate the displacement and strain distributions. The resin composite shrunk vertically towards the bottom of the cavity, with the top center portion of the restoration having the largest downward displacement. At the same time, it shrunk horizontally towards its vertical midline. Shrinkage of the composite stretched the material in the vicinity of the "tooth-restoration" interface, resulting in cuspal deflections and high tensile strains around the restoration. Material close to the cavity walls or floor had direct strains mostly in the directions perpendicular to the interfaces. Summation of the two direct strain components showed a relatively uniform distribution around the restoration and its magnitude equaled approximately to the volumetric shrinkage strain of the material.

Expanding Monomers as Anti-Shrinkage Additives

“…Digital image correlation DIC is a full-field image analysis method, which enables the measurement of the three-dimensional deformation of a sample [ 40 , 41 ]. By tracking the movement of visible patterns on the sample surface with cameras, the deformation of the sample can be determined during the curing process.…”

Analytical methods for the measurement of polymerization kinetics and stresses of dental resin-based composites: A review

“…In addition, they do not display how the cavity walls constrain the shrinkage of composites and would lead to the creation of shrinkage stress in restorations. [ 44 ] The basic idea of DIC is to compare visible patterns on the sample surface from sequential images taken during the deformation of material. Thus, displacement and strain fields can be determined through tracing the movement of the visible points on a specimen's surface.…”

“…[ 43 ] One of the main advantages of this method is full-field measurement which is very beneficial in observing nonuniform deformation and strain patterns. [ 44 ] Figure 2 shows schematic presentation of the images taken before and after the deformation of a specimen and procedures for showing the displacement vectors by DIC method.…”

“…In 2014, Li et al . [ 44 ] prepared specimens with model cavities making of cylindrical glass rods. To obtain high-contrast speckles, after filling the cavity with composites, the surfaces were sprayed with a thin layer of white paint followed by fine black charcoal powder.…”

Comparison of marginal adaptation between a monoincremental resin with sonic activation and a conventional resin.

“…In the 1980s their use was extended to posterior teeth because of their reduced particle size and increased filler loading 3 . However, one limitation of this material is the generation of stress in the tooth-restoration interface caused by polymerization shrinkage 4 , which may produce loss of chemical and mechanical stability, resulting in the loss of marginal integrity and the appearance of a gap, followed by marginal filtration and secondary caries 5 . The intensity of the generated stress depends, among other factors, on the modulus of elasticity of the material, and the latter, in turn, is dependent on the amount of filling 6,7 .…”