Microleakage at the etched enamel-resin interface with bonded orthodontic brackets

This study was undertaken to investigate microleakage at the etched enamel-resin interface of directly bonded orthodontic brackets using a 2% aqueous fluorescein solution as a tracer. The buccal surfaces of 3 groups of30 extracted premolar teeth were etched and Begg plastic brackets were directly bonded. One group was kept in Hanks’ Balanced Salt solution for 24 hours at 37 degrees C (24 hour control group). Another group was thermally cycled between 4 degrees C and 60 degrees C for 200 minutes (thermal cycling group). The last group was aged in Hank’s Balanced Salt solution for 3 months at 37 degrees C (3 months aging group). Each tooth was then sectioned bucco-lingually through the centre of the bracket and the section was examined with an ultraviolet light microscope. The depth of fluorescein penetration along the enamel- resin interface was measured using a calibrated eyepiece graticule.

The results of this study showed that: (i) microleakage occurred in 93.3% of the 24 hour control group, 91.6% of the 3 month aging group and 100% of the thermal cycling group, (ii) large variations in the microleakage depths were observed although, in the majority of cases, the fluorescein penetrated less than 0.27mm, (iii) a significant difference (p <0.01) existed between the control teeth and the thermally cycled teeth with thermal cycling increasing the mean microleakage depth, and (iv) there was no significant difference between mean microleakage depth for the control teeth and teeth that were aged for 3 months but a tendency towards reduced microleakage after ageing was observed.