Three-dimensional assessment of root migration and rotation patterns after coronectomy: bone-embedded roots versus soft tissue-covered roots

In this study, a three-dimensional evaluation was performed to explore differences between bone-embedded and soft tissue-covered roots after mandibular third molar (M3M) coronectomy. Patients were recruited according to the results of cone-beam computed tomography, 6 months after coronectomy. Completely bone-embedded M3Ms were assigned to group B, while completely soft tissue-covered M3Ms were assigned to group S. Data were recorded using digital software. A total of 213 M3Ms in 181 patients were investigated, of which 170 were assigned to the two study groups. Age was the primary factor influencing root migration (P < 0.001). The smaller the degree of angulation of the M3M, the more likely was the root complex to rotate distally (r = ?0.37, P < 0.001). The depth of the impacted M3M contributed to the regeneration of new bone (P ≤ 0.008). The length of the root complex (odds ratio 0.82, P = 0.048) and distance from the root to the alveolar crest (odds ratio 1.23, P = 0.026) were two critical factors influencing whether the root complex was bone-embedded. Ensuring that the length of the root complex is <7.6 mm and the distance between the root and alveolar crest is ≥5 mm were both found to be critical to the remaining root being completely bone-embedded and thus preventing eruption and the need for secondary surgery.