The effect of curing regime on the release of hydroxyethyl methacrylate (HEMA) from resin-modified glass-ionomer cements

This study investigated the effects of degree of cure and specimen maturation on the release of HEMA from four resin-modified glass-ionomer cements. Disc specimens were light-cured for either the manufacturersʹ recommended time (MRT) for that material, or were under-cured (irradiated for 0.5MRT), over-cured (1.5MRT) or allowed to dark-cure (0MRT). Specimens were matured in the mould at 37°C until set or for 10 min, 40 min or 24 h prior to immersion in distilled water (at 37°C) for 4 h. The HEMA release was determined by measuring the HEMA concentration in the storage water by HPLC. Vitremer, Fuji II LC and Fuji Lining LC set without light-curing (0MRT) in less than 6 min and these specimens released low levels of HEMA (not, vert, similar1, 7 and 4% of the included HEMA, respectively). Dark-cured Vitrebond took 15 min to set and the HEMA release was high (not, vert, similar50% of the included HEMA) indicating that the material had only set by the acid–base reaction. HEMA release from light-cured Vitremer or Vitrebond was not affected by under- or over-curing but release from Fuji II LC was reduced by over-curing (1.5MRT). Under-curing Fuji Lining LC caused a significant increase in HEMA release. Specimen maturation times of 10 min, or longer, had little effect on the measured HEMA release. All the materials released HEMA into their storage solutions. In order to minimise HEMA release, resin-modified glass-ionomers should always be cured for at least the manufacturersʹ recommended time at thicknesses no greater than the maximum recommended.