Monomer elution and shrinkage stress analysis of addition-fragmentation chain-transfer-modified resin composites in relation to the curing protocol.

OBJECTIVE

The purpose was to compare the effects of rapid (3 s) and conventional (20 s) polymerization protocols (PP) of mono- and multichip LED curing units (LCU) on shrinkage stress (SS) and monomer elution (ME) in bulk-fill resin-based composites (RBC) with and without addition-fragmentation chain-transfer (AFCT) monomer.

METHODS

Cylindrical (5x4mm) specimens were prepared from two RBCs containing different AFCT monomers (Filtek OneBulk-FOB; Tetric PowerFill-TPF) and one without (Tetric EvoCeram Bulk-TEC). After soaking for 3, 10, and 14 days (75 % ethanol), ME was quantified using standard monomers by High-Performance Liquid Chromatography. SS was measured from the start of polymerization to 5 min using a Materials Testing Machine. The radiant exitance of LCUs was measured using a spectrophotometer. ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05).

RESULTS

AFCT-modification significantly decreased ME (p < 0.001). ME was reduced by half by day 10 and by one tenth by the end of the 14-day compared to the 3-day sampling. ME itself was dependent, whereas the percentage of monomers released was independent of the PP used (p > 0.05). FOB showed the lowest SS (p < 0.001), while there was no significant difference between TPF and TEC (p = 0.124). Both ME and SS were significantly influenced by material type and PP.

SIGNIFICANCE

The incorporation of the AFCT monomer reduced ME, but this was inversely related to a decrease in exposure time. SS values reduced by rapid PP in parallel with increasing ME values. The utilization of the AFCT molecule in conjunction with an appropriate resin-, initiator-system is of significant consequence for the kinetics of polymerization and the incorporation of monomers into the network.