3D mapping of polymerization shrinkage using X-ray micro-computed tomography to predict microleakage

ObjectivesThe objectives of this study were to (1) demonstrate X-ray micro-computed tomography (μCT) as a viable method for determining the polymerization shrinkage and microleakage on the same sample accurately and non-destructively, and (2) investigate the effect of sample geometry (e.g., C-factor and volume) on polymerization shrinkage and microleakage.MethodsComposites placed in a series of model cavities of controlled C-factors and volumes were imaged using μCT to determine their precise location and volume before and after photopolymerization. Shrinkage was calculated by comparing the volume of composites before and after polymerization and leakage was predicted based on gap formation between composites and cavity walls as a function of position. Dye penetration experiments were used to validate μCT results.ResultsThe degree of conversion (DC) of composites measured using FTIR microspectroscopy in reflectance mode was nearly identical for composites filled in all model cavity geometries. The shrinkage of composites calculated based on μCT results was statistically identical regardless of sample geometry. Microleakage, on the other hand, was highly dependent on the C-factor as well as the composite volume, with higher C-factors and larger volumes leading to a greater probability of microleakage. Spatial distribution of microleakage determined by μCT agreed well with results determined by dye penetration.SignificanceμCT has proven to be a powerful technique in quantifying polymerization shrinkage and corresponding microleakage for clinically relevant cavity geometries.