Combined OCT-DIC Image Analysis of Shrinkage Behaviors of Composite Restorations

Objectives: Polymerization shrinkage behaviors of resin composite restorations may affect their interfacial integrity. The optical coherence tomography (OCT) imaging has revealed the changes in polymerization process, which can be integrated with the digital image analysis (DIC) to investigate the shrinkage kinetics. The purpose of this study was to examine the shrinkage behaviors of different resin-base composites restorations by using combined OCT-DIC analysis.
Methods: The accuracy of OCT images used for DIC analysis was verified by determining the displacements of a polymerized restoration. Three kinds of composites were examined: Filtek Z350XT Flowable (Z350F), Z350XT Universal (Z350), and BulkFill Posterior (BF) (all from 3M ESPE). Each composite was filled into a tapered cylindrical cavity (3 mm diameter and 1 mm deep) on the labial surface of an extracted incisor either without or with adhesive treatment. During a 20-s light curing, an OCT scanned the restoration and the images were used for the analysis of shrinkage behaviors by a DIC software (VIC-2D).

Results: The combination of OCT-DIC analysis showed errors less than 0.01% when the displacements were within 132 µm. Three composites Z350F, Z350, and BF presented maximal downward displacements of 22.97, 8.16, and 12.60 µm on the top surfaces in the unbonded conditions; and larger displacements (28.38, 16.32, and 14.77 µm) in their bonded conditions. In the bond conditions, three composites reached 95% of maximal displacements of top surfaces within 10 s after curing. In unbonded conditions, Z350F and BF presented similar patterns but Z350 presented reversed upward displacement at 8.8 s. The displacements at the bottoms were 3-5 µm upward for all composites, except that unbonded Z350 revealed an abruptly increased upward displacement at 8.8 s as well.


Conclusions: The combined OCT-DIC analysis revealed the temporal information about the shrinkage patterns of composite restorations in regards of displacements and directions.