Risk of alveolar bone loss during orthodontic treatment of lower anterior teeth – a prospective CBCT study on predisposing factors

Abstract

BACKGROUND: Larger degrees of tooth movements in thin alveolar bone may exceed limits of bony envelope, cause fenestrations and dehiscences, which consequently increase risk for gingival recession and overall long-term prognosis. The aim was to study changes of alveolar bone level (ABL) of lower anterior teeth (AT) during orthodontic treatment (OT) and predisposing factors for the ABL loss. METHODS: The study included 141 patients, ≤18 years, with Class I malocclusion, maxillary and/or mandibular AT crowding that required extraction of four premolars. ABL measurements on lower AT were performed on CBCT images before (T0) and after (T1) OT. Changes in ABL height and the presence of ABL at three different levels (marginal ABL at 2 mm from CEJ, at halfroot and apical level) were analysed. Factors, such as facial height, pre-treatment buco-lingual ABL width, inter-canine distance, Little’s irregularity index, gender and age were also analysed. RESULTS: Mean loss of ABL (T0-T1) was found on lingual (4.1 mm, SD 3.70) and buccal (1.1 mm; SD 2.13) surfaces (p<0.05) of all lower AT, significantly more on incisors (p<0.05). Already pre-treatment 1/3 of lingual and buccal surfaces of central incisors had missing marginal alveolar bone at 2 mm from CEJ. Change (T0-T1) in the presence of lingual marginal ABL in central and lateral incisors was >50%, however change (T0-T1) in presence of buccal marginal ABL was significantly less (>15%) (p<0.05). Change in the presence of marginal ABL on buccal and lingual surfaces of lower canines was only up to 15%. At halfroot level ABL coverage was lost in >70% of lingual surfaces of lower central incisors and >50% of lingual surfaces of lateral incisors. Bucco-lingual ABL width at apical level and 20 mm inferior CEJ, also facial height were predisposing factors for ABL loss on lingual and/or buccal surfaces, with more tendency to ABL loss in increased facial height and narrow ABL cases. CONCLUSIONS: OT with lower premolar extractions has increased risk for lingual ABL loss of lower incisors. Facial height and bucco-lingual width of alveolar process at apical level and at the level 20 mm inferior CEJ were predisposing factors for ABL loss.