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 maturati on on the release of HEMA from four resin-modified glass ionomer cements. D isc specimens were light-cured for either the manufacturers' recommended ti me (MRT) for that material, or were undercured (irradiated for O.5MRT), ove r-cured (1.5MRT) or allowed to dark-cure (0MRT). Specimens were matured in the mould at 37 degrees C until set or for 10 min, 40 min or 24 h prior to immersion in distilled water (at 37 degrees C) for 4 h. The HEMA release wa s determined by measuring the HEMA concentration in the storage water by HP LC. 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 (simila r to 1, 7 and 4% of thr included HEMA, respectively). Dark-cured Vitrebond took 15 min to set and the HEMA release was high (similar to 50% of the inc luded HEMA) indicating that the material had only set by the acid-base reac tion. HEMA release from light-cured Vitremer or Vitrebond was nor affected by under- or over-curing but release from Fuji II LC was reduced by over-cu ring (1.5MRT). Under-curing Fuji Lining LC caused a significant increase in HEMA release. Specimen maturation times of 10 min, or longer, had little e ffect on the measured HEMA release. All the materials released HEMA into th eir storage solutions. In order to minimise HEMA release, resin-modified gl ass-ionomers should always be cured for at least the manufacturers' recomme nded time at thicknesses no greater than the maximum recommended. (C) 1999 Elsevier Science Ltd. All rights reserved.