DualCure BulkFill Composite Adaptation and Bond Strength in Deep Cavities

Objectives: Polymerization shrinkage may cause gap formation between the cavity floor and bulkfill composites, depending on the polymerization mechanism. This study investigated the adaptation and bond strength of a newly developed dualcure composite with addition of 80 nm spherical zirconia fillers in 4-mm deep preparations compared to commercially available products using optical coherence tomography (OCT) and microtensile bond strength (MTBS).
Methods: Six bulkfill composite products were tested; Bulk EZ Plus prototype (BEZP, Zest), Surefil SDR Flow+ (SDRF, Dentsply), Surefil One self-adhesive capsule (SONE, Dentsply), Filtek One (FTON, 3M), Hyperfil (HYPF, Parkell), and Sonicfill 3 (SNCF, Kerr). Standard composite molds 4-mm in depth were used to observe and score separation of the bonded composite during the polymerization process under OCT (Octina, Yoshida Dental). Preparation 3x3x4 mm in dimensions were prepared in extracted posterior human teeth to conduct the MTBS test with each of the composites placed using ScotchBond Universal (3M) adhesive. OCT data was analyzed by Mann-Whitney U non-parametric tests while MTBS data was analyzed by one-way ANOVA with Bonferroni correction at 0.05 significance level.
Results: OCT data showed that the dualcure composites BEZP followed by HYPF had lowest gap formation during polymerization compared to all other groups (p<0.05). SONE self-adhesive demonstrated the highest debonding from the cavity floor (p<0.05). There was no difference between SDRF and FTON (p>0.05) which had 10% to 50% debonding from the cavity floor. For MTBS analysis excluding the pretest failures due to debonding, SONE showed the lowest bond strength, followed by SNCO both of which were significantly different from SDRF (p<0.05). There was no statistically significant difference among other groups (p>0.05).
Conclusions: The dual-cure bulk fill composites tested exhibited significantly better adaptation and less gap formation than the light cured ones. The difference was not reflected in the bond strength values with the universal adhesive used in the current study. The self-adhesive composite de-bonded frequently in both experiments.