Elution characteristics of residual monomers in different light- and auto-curing resins

The aim of this in vitro study was to assess different auto-curing resins based on methylmethacrylate (MMA) and new light-curing resins based on urethane dimethacrylate (UDMA) regarding the residual monomers remaining in the resin and their elution over time. Specimens from three auto-curing and three light-curing resins were produced following the manufacturer's instructions. The concentration of residual MMA and UDMA monomers present in the resins as well as the quantity of the residual monomers released into artificial saliva solution after immersion times of 1, 3, and 7 days were analyzed by high-performance liquid chromatography (HPLC). Data were statistically analyzed using ANOVA and the post hoc Student-Newman–Keuls test. The highest and lowest amounts of residual monomers were found in the group of light-curing resins (p < 0.05). The light-curing resins Triad Trans Sheet (0.06 wt%) and Primosplint (0.06 wt%) released over the entire immersion time of 7 days the smallest (p < 0.05) quantity of UDMA. These two light-curing resins based on UDMA exhibited lower elution of residual monomers than auto-curing resins (MMA). The elution characteristics of the residual monomers do not seem to correlate with the residual monomer concentration in resins. These observations demonstrate that the quantitative determination of residual monomers alone - as required by the ISO specification 20795-1 – does not seem to be sufficient for an assessment of the biological properties of different resins. Instead, the evaluation of elution characteristics appears to be of higher clinical relevance.