Cone-beam computed tomography evaluation of alveolar bone and root changes after clear aligner therapy with different extraction protocols: Balancing tissue loss, tooth control, and treatment alternatives

To evaluate changes in alveolar bone and tooth root dimensions in anterior teeth of patients with different tooth extraction types undergoing clear aligner therapy (CAT) and to provide reliable information for preventing tissue loss and providing tooth control in severe cases through a large-scale sample analysis of the clinical outcomes of CAT. We selected 281 patients (186 non-extraction [NE], 59 with two-premolar extraction [TPE] in both the maxilla and mandible, and 36 with TPE in the maxilla and one lower-incisor extraction [OLIE] in the mandible) from the records of recent three years. Quantitative changes in the dentoalveolar apparatus were analyzed using pre- (T1) and post-treatment (T2) cone-beam computed tomography. The measured parameters included the alveolar bone height and thickness, and root length in the anterior teeth in different types of tooth extraction. Alveolar bone height loss was common in all groups after CAT. Compared to patients with NE, patients with TPE showed a higher risk of lingual bone dehiscence and torque loss (P < 0.05), whereas those with OLIE showed a higher risk of open gingival embrasures (P < 0.05). A more severe alveolar bone loss was observed in the mandibular anterior teeth than in the maxillary anterior teeth (P < 0.05). Different tooth extraction types can lead to different degrees of bone loss in the direction of tooth movement, and orthodontists should adopt more cautious measures for mandibular anterior teeth. Despite numerous experimental studies for improving techniques and designs in CAT, tooth control and complication prevention in extraction cases remain challenging for orthodontists.