Ultrasound has been shown to enhance the fluoride release of conventional glass ionomer cements (GICs). However it the mechanism of this effect is not clear.
Objectives: The aim of this study is to differentiate between greater reaction releasing more F from glass into matrix and changes in cement resulting in higher F diffusion.
Methods: Experimental GIC glass LG30 having only impurity level of F was formulated as water-mix GIC. It was mixed with either water (W) or 2% NaF (N) at a powder liquid ratio of 7:1. 2 x 2mm samples were made in cylindrical moulds .Samples (n=5) were either set with ultrasound for 55 seconds (U) or allowed to self-cure at room temperature (SC). The samples were de-moulded and placed in 10ml of deionsed water in an oven at 37 oC. The water was changed during intervals of 1,3,7,14,21 & 28 days. Aliquots were taken and measured with an Ion selective electrode for free fluoride in deionised water and total fluoride measured by buffering with TISAB IV. Results: The results showed that US set LG30 + NaF released 1.28 times more fluoride compared to SC set LG30 + NaF. However the LG30 cummulative fluoride release was ~ 3times than SC LG30. The cumulative fluoride release was linear to t1/2. The initial burst of fluoride (C=-intercept) and the total fluoride release (m=gradient) is as follows:
|
NU |
|
WU |
WSC |
|
|
m |
0.0046 |
0.0036 |
0.0009 |
0.0003 |
|
C |
0.0041 |
0.0035 |
0.0002 |
0.0004 |
Compared to a previous study the amount of fluoride released from N was very small because of the amount of fluoride present in the cement. The effect of ultrasound was very slight compared to cements with F in the glass.
Conclusion: Ultrasound has a direct effect on the GIC reaction rather than on the diffusion of F through the cement.