Effect of temperature on fluoride release from orthodontic adhesives

Objectives: To investigate the effect of recharging temperature on the level of fluoride release from a number of fluoride releasing adhesives.

Methods: Three fluoride releasing orthodontic adhesives; Conventional glass ionomer (Ketac Cem µ®), resin modified glass ionomer (Fuji Ortho LC) and compomer (Dyract ® Cem Plus) were tested and a composite resin (Transbond™) was used as a control. Two groups of 5 disc specimens of each material were prepared and stored in deionised water at 37°C. The discs in group A and B were soaked daily for 21 days in a 250ppm Fˉ solution at 37°C and 55°C respectively. The daily fluoride release from specimens for 28 days was measured using an ion selective electrode (ISE). Results were statistically analyzed using ANOVA and t-test at (p< 0.05).

Results: The cumulative amounts of daily fluoride released (µg/cm²) from each material during the 21 days recharging period are given in the table below.

Recharging temperature	Fuji Ortho Mean   SD	Ketac Cem Mean     SD	Dyract Mean     SD	Transbond Mean    SD
37º C	158.92   10.07	189.41    24.73	53.48       2.60	1.46         0.74
55º C	188.47*  9.99	228.71*  17.20	85.88*     8.49	2.10         0.67

* Indicates a significant difference between values in the two temperature groups.

Through out the study, the control material showed a negligible rechargeability at all times. During daily recharging period, the three fluoride releasing materials showed a sustained fluoride release. When recharging was stopped, the level of fluoride release dropped dramatically to a low level. All three materials showed significantly higher levels of fluoride release with the increase in recharging temperature from 37º C to 55º C. At both recharging temperatures, there were significant differences in the cumulative amount of fluoride released from the 3 materials.

Conclusions: Increasing the recharging temperature significantly increased the amount of fluoride released from fluoride releasing adhesives.