Introduction: In spite of growing concern of routine mechanotherapy modalities in patients' health and recent regulations on nickel exposure, there has been no relevant meta-analysis. The aim of this study, therefore, was to investigate the effect of orthodontic therapy on the prevalence of nickel hypersensitivity and compare it with the prevalence in the general population.
Methods: Several electronic databases were searched. Hand-searching was also performed to identify additional relevant studies. Initially, 324 articles were retrieved. After applying specific inclusion criteria, 8 studies were eligible for the meta-analysis. Meta-analysis was performed with Comprehensive Meta-Analysis software (version 2.2.046, Biostat, Englewood, NJ). Evaluations of the validity of the included articles and of publication bias were also performed.
Results: A lack of high-validity longitudinal studies of the prevalence of nickel hypersensitivity in patients before and after orthodontic treatment and in appropriate controls was noted. From the studies retrieved, no statistically significant difference between the odds for a positive patch-test result before orthodontic treatment and after the placement of the appliances was observed. Orthodontic patients with no cutaneous piercing or with skin pierced have no statistically significant differences of nickel hypersensitivity after treatment compared with the general population.
Conclusions: Orthodontic treatment is not associated with an increase in the prevalence of nickel hypersensitivity unless subjects have a history of cutaneous piercing. High-validity studies are needed to produce strong evidence to further support the results of this meta-analysis.