Polymerizable inhibitor can reduce shrinkage stress of resin composite

The purpose of this study was to prepare dental resin composites (DRCs) with low shrinkage stress and limited leachable inhibitor content by incorporating a synthesized polymerizable inhibitor PBHT (2,6-di-tert-butyl-4-(methacryloyloxy-ethyl-carbamate-methyl)phenol).

The PBHT was synthesized via the reaction between 2,6-di-tert-butyl-4-hydroxymethylphenol and 2-(methacryloyloxy)ethyl isocyanate. The structure of PBHT was confirmed by FT-IR and ¹H-NMR spectra. The PBHT was added to the resin matrix of the DRCs at mass ratios of 1, 2, and 3 wt%. Double bond conversion (DC), volumetric shrinkage (VS), shrinkage stress (SS), flexural properties, water sorption (WS) and solubility (SL) of the prepared DRCs were investigated according to standard or referenced methods. The amount of leachable inhibitors in DRCs was determined by gas chromatography-mass spectrometry using the selected ion monitoring method. For comparative purposes, the DRCs containing the commercial inhibitor butylated hydroxytoluene (BHT) were also prepared, while a DRC without any extra inhibitor was used as the control.

Adding PBHT to the resin matrix significantly reduced the DC of DRCs (p < 0.05). The PBHT lowered VS and SS of DRCs (p < 0.05), in contrast to BHT, which showed no significant effect (p > 0.05). Neither PBHT nor BHT affected flexural properties of DRCs (p > 0.05). The WS of DRCs was significantly increased after adding 3 wt% of either inhibitor (p < 0.05). While both PBHT and BHT significantly raised SL (p < 0.05), the PBHT-containing DRCs showed significantly lower SL than the BHT-containing ones at the same concentration (p < 0.05). Compared with the BHT-containing DRCs, PBHT-containing DRCs had lower leachable inhibitors (p < 0.05).

The PBHT-containing DRCs achieved low shrinkage stress and limited amount of leachable inhibitors. At the optimal concentration of 1 wt%, PBHT had no significant effect on the physicochemical properties other than SL.