Factors responsible for pulp cell cytotoxicity induced by resin-modified glass ionomer cements

Resin-modified glass ionomer cements (RM-GICs) are the last generation of GICs commonly used in restorative dentistry. They contain various resins that improve their mechanical properties. These modifications, however, may also affect their biocompatibility. We compared the cytotoxicity of seven biomaterials (five RM-GICs, one metal-reinforced GIC (M-GIC), and a zinc-oxyphosphate cement) using an assay of pulp cell viability in vitro (MTT assay). The most toxic materials appeared to be the M-GIC Hi-Dense and the RM-GIC Vitremer. The less toxic ones appeared to be the RM-GICs Compoglass and Photac-Fil. Attempts made to identify the factors responsible for their cytotoxicity indicated that in vitro cytotoxicity did not seem to be caused by any change in pH of the biomaterial eluates. Adsorption of biomaterial eluates on dentin powder significantly reduced the cytotoxicity of all biomaterials. The concentration of F-, Sr2+, and Al3+ (major ionic elements present in GICs) in the eluate of six glass ionomer containing biomaterials was too low to be cytotoxic. However, Cu2+ and Ag+ (present in alloys of M-GIC) were present in toxic concentrations in Hi-Dense eluates. Unpolymerized monomers leached from resins were identified by Fourier transform IR spectroscopy in biomaterial eluates. The monomers hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA), and poly(acrylic) acid were identified in eluates of Vitremer, Compoglass, and Hi-Dense, respectively. After ethanol elution of HEMA and TEGDMA from Vitremer and Compoglass, respectively, the cytotoxicity of these two RM-GICs was drastically reduced. Our results suggest that the principal compounds responsible for cytotoxicity are unpolymerized resin monomers in the two RM-GICs and Cu2+ and Ag+ in the M-GIC.