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

Objectives. The objectives of this study were to (1) demonstrate X-ray micro-computed tomography (mu CT) 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. Methods. Composites placed in a series of model cavities of controlled C-factors and volumes were imaged using mu CT 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 mu CT results. Results. The 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 mu CT 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 mu CT agreed well with results determined by dye penetration. Significance. mu CT has proven to be a powerful technique in quantifying polymerization shrinkage and corresponding microleakage for clinically relevant cavity geometries. Published by Elsevier Ltd on behalf of Academy of Dental Materials.