Influence of power density on the setting behaviour of light-cured glass-ionomer cements monitored by ultrasound measurements

ObjectivesTo monitor the influence of the power density of the curing unit on the setting behaviour of light-cured glass-ionomer cements (LCGICs) using ultrasound measurements.MethodsThe ultrasound equipment comprised a pulser–receiver, transducers and an oscilloscope. The LCGICs used were Fuji II LC, Fuji II LC EM and Fuji Filling LC. The cements were mixed according to the manufacturer's instructions and then inserted into a transparent mould. The specimens were placed on the sample stage and cured with power densities of 0 (no irradiation), 200 or 600 mW/cm2. The transit time through the cement disk was divided by the specimen thickness and then the longitudinal ultrasound velocity (V) within the material was obtained. Analysis of variance and Tukey's Honestly Significantly Different test were used to compare the V values between the set cements.ResultsWhen the LCGICs were light-irradiated, each curve displayed an initial plateau at ∼1500 m/s and then rapidly increased to a second plateau at ∼2600 m/s. The rate of increase of V was retarded when the cements were light-irradiated with a power density of 200 mW/cm2 than with a power density of 600 mW/cm2. Although sonic echoes were detected from the beginning of the measurements, the rates of increase of the sonic velocity were relatively slow when the cement was not light-irradiated.ConclusionsThe ultrasound device monitored the setting processes of LCGICs accurately based on the longitudinal V. The polymerization behaviour of LCGICs was shown to be affected by the power density of the curing unit.