Method: Light-cured resins and their ACP composites were extracted in either acetone (7 days, 23 oC, magnetic stirring) or saline/ethanol (1:1 mass ratio) mixture (14 days, 23 oC, 30 s mixing 2 times/day). The resins consisted of urethane dimethacrylate (UDMA), 2-hydroxyethyl methacrylate (HEMA), methacryloyloxyethyl phthalate (MEP) and poly(ethylene glycol) extended UDMA (PEG-U), with camphorquinone (CQ) and ethyl-4-N,N-dimethylamino benzoate (4EDMAB) as initiators and butylated hydroxytoluene (0.01 mass-%) as an inhibitor. 1H NMR spectroscopy was employed to qualify and quantify leachables. Data were statistically analyzed by ANOVA and multiple pair-wise comparisons (t-test).
Result: All monomers and 4EDMAB were identified in both extraction experiments, while CQ was not detected. Up to13.9 mass-% and 6.2 mass-% of the copolymers and composites, respectively, were extracted in acetone. Monomers varied between 0.30 % to 14.29 % (copolymers) and 0.12 % to 10.39 % (composites) of initial content. 4EDMAB showed the highest leachability (33.06 % and 24.66 % in copolymer and composite extracts, respectively). When composite data were normalized with respect to initial amounts of resin, the differences between copolymer and composite became marginal. In ethanol/saline experiments, the extractable portions were 2.5 mass-% and 7.3 mass-% of copolymers and composites, respectively. Monomers varied between 0.20 % to 37.32 % (copolymers) of initial content. 4EDMAB showed a leachability of 22.70 %. Composite samples are currently being analyzed.
Conclusion: Results exemplify a strong effect of the extraction conditions on leachability. The acetone extraction data suggest that in highly cross-linked experimental resins and composites, leachability is generally limited by the mobility of polymer chains which restricts pathways for monomer to leach out of the system.
Support: NIDCR Grant R01DE13169, ADAF and NIST.
Keywords: Composites, Leachability and Polymers
See more of: Dental Materials 6: Polymer-based Materials-Chemistry and Composition