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

The setting reaction of two light-activated glass polyalkenoate cement s has been investigated using differential thermal analysis and surfac e hardness measurements. One material was found to have two distinct p hases to its setting reaction. Light activation resulted in a rapid in itial set with a large exotherm. A slower setting reaction was detecta ble when the cement was allowed to set in the absence of light. The su rface hardness of this cement increased for some time after the cessat ion of light activation, indicating continuation of the chemical setti ng reaction within the material. The ultimate hardness of the cement w as 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 o bserved. This material remained very soft and flexible for over 1 h af ter light activation. A 30 s exposure with a visible light source prod uced some immediate hardening up to 1.5-2.0 mm below the surface for b oth materials.