Microleakage between composite/wire and composite/enamel interfaces of flexible spiral wire retainers: direct versus indirect application methods

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The aim of this in vitro study was to compare the microleakage of flexible spiral wire retainers (FSWR) at composite/wire and composite/enamel interfaces produced by an indirect application method to that of a conventional direct application method. Forty freshly extracted human mandibular incisor teeth were randomly divided into two equal groups. Group 1 was bonded directly according to the manufacturer's recommendations. Group 2 consisted of 20 teeth bonded indirectly with Transbond LR as the adhesive and Sondhi Rapid Set A/B Primer (3M Unitek, Monrovia, CA, USA), a filled resin primer. After bonding, specimens were further sealed with nail varnish, stained with 0.5% basic fuchsine for 24 h, sectioned and examined under a stereomicroscope that measured microleakage at the composite/wire and composite/enamel interfaces from both mesial and distal margins. Statistical analyses were performed using Wilcoxon and Mann-Whitney U-tests with Bonferroni correction. Statistical comparisons indicated that no statistically significant differences were observed between composite/wire and composite/enamel interfaces for direct vs. indirect application procedures (Direct method p = 0.630 and Indirect method p = 0.930). Comparisons of the microleakage scores between direct and indirect FSWR application groups at composite/wire and composite/enamel interfaces indicated no statistically significant microleakage differences at mesial or distal margins (Composite/enamel interface p = 0.361 and Composite/wire interface p = 0.270). The type of FSWR application procedures (direct vs. indirect) did not significantly affect the amount of microleakage at the enamel/composite/wire complex.