Multidimensional tooth movement boundaries in the extended aesthetic zone: a cone-beam computed tomography study

Purpose To establish tooth movement boundaries in four directions by a novel morphometric analysis of alveolar bone using conebeam computed tomography (CBCT) images. The aim was to assist clinicians in minimising the occurrence of bone fenestration and dehiscence, thereby facilitating safe and efficient orthodontic treatment. Methods CBCT images of 123 male volunteers comprising 55 individuals with hypodivergent vertical skeletal patterns and 68 individuals with normodivergent vertical skeletal patterns and normal occlusions but without a history of previous orthodontic treatment, were analysed. The mesiodistal and labiolingual alveolar bone height (ABH) as well as the labiolingual cancellous bone thickness (CBT) were measured in relation to the maxillary and mandibular anterior teeth and premolars. These parameters were subsequently compared between the different vertical skeletal patterns. Results Teeth within the extended aesthetic zone exhibited a limited range of safe movement on the labial aspect across all three root aspects, with 97.6% of the upper lateral incisors and 98.4% of the lower lateral incisors positioned against the labial cortical plate (<0.5 mm). The lingual aspects had significantly more space for tooth movement compared with the labial aspects (P < 0.05). The ABH was significantly greater in the hypodivergent group than the normodivergent group involving particular teeth and sites in the maxilla (P < 0.05), while no significant difference was noted in the mandible. The hypodivergent group also exhibited thicker cancellous bone on most labial and some lingual aspects. Conclusions The findings provided the average tooth movement range in the horizontal and vertical directions within the extended aesthetic zone in male individuals presenting with a normal occlusion. It was concluded that a hypodivergent growth pattern may have a relatively large range of safe tooth movement in the sagittal and vertical directions.