Analyses of rampant corrosion in stainless-steel retainers of orthodontic patients

Effect of fluoride agents on surface characteristics of NiTi wires. An ex vivo investigation

Aim

To analyze the degree of corrosion of nickel titanium arch wires in patients with and without exposure to fluorides.

Material and methods

This was an ex vivo study comprising of 60 subjects undergoing fixed orthodontic treatment. Group 1(controls) comprised of 30 sets of new unused NiTi wires and unused 11, 15 brackets, Group 2(patients) comprised of 30 sets of non fluoridated NiTi wires and 11, 15 brackets and Group 3(patients) had 30 sets of fluoridated NiTi wires and 11, 15 brackets. NiTi wires were used over 6 months of treatment(0.014″,0.016″, 16 × 22", each wire was used for 2 months and replaced with the next size). All wires were retrieved, stored and analyzed. At 6 months, brackets from 11 to 15 were debonded in both treatment groups. Archwires and brackets in 3 groups were subjected to SEM analysis at 500 and 1000X to observe differences. Additionally, EDX Spectroscopy was undertaken to evaluate surface elemental compositional differences in groups.

Results

Significant differences among groups were evident in brackets and archwires tested. Maximum degradation, cracks and dark spots were seen in wires and brackets exposed to fluoride agents. EDX spectroscopy revealed least Ni% in fluoridated wires and brackets.

Conclusions

Increased leaching of metal ions was evident when wires and brackets are exposed to fluoride agents during treatment. Use of non fluoridated mouthwash and toothpastes may be considered in orthodontic patients without risk of caries to mitigate such effects.

Corrosion in Haas expanders with and without use of an antimicrobial agent: an in situ study

Objectives

The purpose of this study was to evaluate in situ the occurrence of corrosion in the soldering point areas between the wire, silver brazing and band in Haas expanders.

Material and Methods

Thirty-four 7-12-year-old patients who needed maxillary expansion with a Haas expander were randomly assigned to two groups of 17 individuals each, according to the oral hygiene protocol adopted during the orthodontic treatment: Group I (control), toothbrushing with a fluoride dentifrice and Group II (experimental), toothbrushing with the same dentifrice plus 0.12% chlorhexidine gluconate (Periogard^®) mouthrinses twice a week. The appliances were removed after approximately 4 months. Fragments of the appliances containing a metallic band with a soldered wire were sectioned at random for examination by stereomicroscopy, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Data were analyzed statistically by Fisher's test at 5% significance level.

Results

The analysis by optical microscopy revealed areas with color change suggestive of corrosion in the soldering point areas joining the band and the wire in all specimens of both groups, with no statistically significant difference between the groups (p=1). The peaks of chemical elements (Ni, Fe, Cr, O, C and P) revealed by EDS were also similar in both groups.

Conclusion:

Color changes and peaks of chemical elements suggestive of corrosion were observed in the soldering point areas between the wire, silver brazing and band in both control and experimental groups, which indicate that the 0.12% chlorhexidine gluconate mouthrinses did not influence the occurrence of corrosion in situ.