Influence of additional heating on the microhardness of glass-ionomer cements

The objectives of this study were to verify for various GIC products, whether the application of external heat on the initial curing material, produces an increase in microhardness, and to determine whether this hardness varies, dependent of the depths in the GIC samples. Moreover, the efficacy was examined of various polymerization units on this additional hardening. 

Method:

The GICs samples were thermo-cured for 60s with three polymerization units. The Vickers micro-hardness was measured at three different depths: 2, 3 and 4 mm. The statistical analysis was performed by one-way ANOVA, Newman-Keuls test and linear regression analysis. Statistical significance was set to p<0.05.

Result: Analysis of variance and Newman-Keuls test showed statistically significant difference among tested groups for all three GICs. The results of linear regression analysis showed statistically significant correlation between the hardness of the material and temperature for 2 mm (R=0.78; p=0.0028) and 3 mm depth (R=0.59; p=0.045).  

Conclusion: The results of this study indicate that thermal-curing of GIC with different polymerization units for 60s during setting reaction increases the microhardness of the GICs at all depths, and consequently resistance to mastication forces which is extremely important for clinical success of restorations