Predictors of gingival margin migration after fixed orthodontic treatment: a linear mixed model analysis of labial...

This study evaluated the influence of clinical periodontal, radiological, and demographic factors on gingival margin migration after fixed orthodontic treatment using linear mixed model analysis, with separate assessments of labial and lingual surfaces.

This retrospective single-cohort study analyzed pre and post treatment changes in 88 patients who underwent orthodontic treatment without a non treated control group. Patients were periodontally healthy based on the absence of bone loss on panoramic radiographs and three dimensional intraoral scans. The mean age was 19.25 ± 7.46 years, and measurements were performed on mandibular anterior teeth. Clinical crown length and keratinized tissue width were measured using three dimensional intraoral scans, and cephalometric variables were obtained from lateral radiographs. Gingival margin migration was defined as the change in clinical crown length from before to after treatment. Predictor variables included dental crowding, alveolar ridge width, incisor mandibular plane angle, gonion-menton-sella-nasion angle, symphysis morphology, age, sex, treatment duration, and keratinized tissue width. Linear mixed models were used to assess gingival margin migration across all surfaces and separately for labial and lingual surfaces, using baseline and treatment related changes as predictors.

Of 530 screened patients, 88 were included (72% female). In baseline models, keratinized tissue width, dental crowding, and sex were significant predictors of gingival margin migration. Lingual migration was additionally associated with incisor mandibular plane angle, symphysis morphology, and age. On the labial surface, incisors showed more coronal gingival margin position than canines relative to baseline. In models based on treatment related changes, keratinized tissue width, dental crowding, and age were consistent predictors across all surfaces. Labial margins showed more coronal position than lingual margins, while lingual migration was negatively associated with changes in incisor mandibular plane angle. Changes in keratinized tissue width had the strongest effect.

Baseline keratinized tissue width and its increase during treatment were the strongest predictors of gingival margin stability. Dental crowding, incisor inclination, and symphysis morphology showed surface and tooth specific effects, whereas alveolar crest width had no significant impact.