LIGHT-ACTIVATED GLASS POLYALKENOATE (IONOMER) CEMENTS - THE SETTING REACTION

The setting reaction of two light-activated glass polyalkenoate cements has been investigated using differential thermal analysis and surface hardness measurements. One material was found to have two distinct phases to its setting reaction. Light activation resulted in a rapid initial set with a large exotherm. A slower setting reaction was detectable when the cement was allowed to set in the absence of light. The surface hardness of this cement increased for some time after the cessation of light activation, indicating continuation of the chemical setting reaction within the material. The ultimate hardness of the cement was significantly higher than its hardness at the termination of light activation. Light activation of the second material increased the rate of set of the cement but no evidence of a dual setting reaction was observed. This material remained very soft and flexible for over 1 h after light activation. A 30 s exposure with a visible light source produced some immediate hardening up to 1.5-2.0 mm below the surface for both materials.