Changes in weight, dietary habits, and oral health-related quality of life in adolescents undergoing fixed orthodontic treatment in relation to body mass index: a prospective cohort study

The relationship between body mass index (BMI) and orthodontic treatment (OT) with respect to adolescents’ dietary habits and oral health-related quality of life (OHRQoL) remains underexplored. This prospective cohort study in adolescents aimed to evaluate changes in weight, dietary habits, and OHRQoL during the leveling and alignment phase of fixed OT, in relation to BMI status. Fifty adolescents (mean age 13.54 ± 1.39 years, 48% females) were consecutively enrolled and categorized into a normal BMI group (mean 19.73 ± 2.21 kg/m²; n = 26) and an increased BMI group (mean 29.57 ± 4.78 kg/m²; n = 24). Data collection occurred at baseline (T1) and at follow-up (T2, 5–14 months after comprehensive fixed OT initiation). Weight, height, and BMI were measured, and dietary habits were assessed using the Food Consumption Frequency Questionnaire. OHRQoL was evaluated using the Oral Health Impact Profile-14 (OHIP-14). Linear mixed-effects models were used for weight-related outcomes, ordinal mixed-effects models for dietary data, and mixed-effects Poisson regression models for OHIP-14 data. All models included random intercepts for subjects and fixed effects for study group, timepoint, and their interaction. There were no significant baseline group differences except for BMI status ( p < 0.001). Participants’ weight and BMI remained stable from T1 to T2 in both groups, with no significant timepoint effect or group × timepoint interaction. Dietary habits were not significantly influenced by BMI group, timepoint, or their interaction across all nine food categories. BMI status did not significantly affect any OHIP-14 items, domains, or the total score. The total OHIP-14 score did not change significantly over time (incidence rate ratio (IRR) = 1.04, p = 0.622). There was a significant increase in the physical pain (IRR = 1.61, p = 0.015) and physical disability (IRR = 1.79, p = 0.019) domain scores, while embarrassment about teeth decreased (IRR = 0.54, p = 0.005) during the leveling and alignment phase. Increased BMI was not associated with significant differences in weight changes, dietary habits, or OHRQoL during the leveling and alignment phase of fixed OT in this cohort of adolescents. However, this study was not powered to exclude smaller effects. Increases in physical discomfort and a decrease in embarrassment about teeth occurred during the leveling and alignment phase, regardless of BMI status. ClinicalTrials.gov (NCT07217756).