Does orthodontic treatment using fixed appliances cause initial caries lesions?

Design: Systematic review and meta-analysis of randomized clinical trials (RCTs), non-randomized studies of intervention (NRSIs), cohort and cross-sectional studies. The systematic review was registered in advance on PROSPERO, and was conducted following the Cochrane Handbook of Systematic Reviews of Interventions and PRISMA checklist. Data sources: An electronic search in three databases (PubMed, Scopus, and Embase) was conducted by two authors to evaluate studies published from 1990 until May 2023. Study selection: The review question was defined in PICOS format as follows: Population (P), subjects with permanent dentition who having/had orthodontic therapy; Exposure (E), orthodontic therapy with fixed orthodontic appliance; Comparison/Control (C), no orthodontic treatment or intervention; Outcome (O), assessing incidence and/or prevalence of initial caries lesions (ICLs) at subject and teeth levels was the primary outcome, whereas evaluating the influence of demographics and treatment-related variables were secondary outcomes; studies (S), randomized clinical trials, non-randomized clinical studies, cohort and cross-sectional studies. Data analysis: Meta-analysis was conducted of three or more included studies had comparable findings. The following factors were calculated for each study; sample size, number of patients with ICLs, number of teeth with ICLs, number of teeth affected per patient, and number of surfaces affected. Statistical heterogeneity of effects among studies was assessed by means of the Cochran's test was used to evaluate the statistical heterogeneity of effects in the included studies. Funnel plot approach was used to assess publication bias, whereas Begg's and Egger's correlation test were used to identify asymmetry. Meta-analysis was conducted using a random effects model owing to high methodological and clinical heterogeneity. A descriptive analysis was presented when the meta-analyses appeared inappropriate. Statistical significance level was set at p < 0.05 for all statistical analyses. Results: 21 studies were included in the qualitative synthesis (systematic review); 11 RCTs; 7 NRSIs, and 3 observation studies. Of the included studies, 19 studies were analyzed in the quantitative synthesis (meta-analysis). In regard to the prevalence rate of ICLs; 57% of patients had ICLs, with a mean of 2.24 lesions per patient and 22% of surfaces were affected. In regard to the incidence rate; 48% of patients developed new ICLs, with a mean of 2.29 new lesions per patient, and 15% of surfaces became affected. Both prevalence and incidence rates were positively associated with the duration of the orthodontic therapy (P = 0.01 and P < 0.01, respectively), illustrating an elevation in the ICLs numbers as the treatment duration (number of months) increases. There was no association between patients' age and ICLs numbers. Conclusions: Orthodontic therapy using fixed appliances can increase the risk of accumulating plaque and developing caries lesion. However, other risk factors may play a role in developing ICLs; thus, controlling for these factors is paramount to better evaluate the true influence of orthodontic therapy on the ICLs development. Implementing caries preventive measures during orthodontic treatment may be needed to minimize the potential risks.