The biocompatibility of resin-modified glass-ionomers has been assessed partly in terms of their cytotoxicity towards the pulp and partly in terms of their effects on dental personnel exposed to these materials in a regular basis [61].As we have seen, inorganic ions (Sr2 +, Al3 +, F−) are released from set resin-modified glass-ionomers, but at levels too low to have any cytotoxic effect [62]. However, several studies have shown that HEMA is released by resin-modified glass-ionomers [62–64] and this is the substance that compromises the biocompatibility of these materials [65]. HEMA released by fully set resin-modified glass-ionomers can penetrate the dentine and adversely affect the pulp [66–69]. It can also be distributed systemically from its location in the mouth, and can have the potential to cause damage [61]. Dental personnel may risk a variety of adverse effects from manual contact with the skin, ranging in severity from mild to severe dermatitis [70,71]. They are also at risk from inhalation of the volatile HEMA vapour.