Background Previous studies have reported incidence rates of dehiscence (DEH) and fenestration (FEN) as high as 36.51 and 51.09%, respectively. Only a few studies comparing DEH and FEN before and after orthodontic treatment (OT) are available in the literature. Purpose The aim of this study was to evaluate the occurrence of DEH and FEN in anterior teeth, before and after OT, using cone-beam computed tomography (CBCT). In addition, findings may provide a clinical basis for avoiding DEH and FEN during therapeutic tooth alignment. Patients and methods CBCT images of 21 patients near the end of their peak growth and development were included. DEH and FEN in the anterior teeth and thicknesses of the alveolar bone at the palatal (TP) and labiolingual (LL) sides of each anterior tooth were measured before and after OT. Results After OT, the incidence rates of mandibular anterior labial DEH, maxillary anterior TP-bone defect, and mandibular anterior lingual bone defect were increased by 20, 19, and 30%, respectively. Assessment of CT images prior to treatment showed that the teeth developing bone defects were significantly different regarding the apical alveolar bone thicknesses compared to the teeth that did not develop bone defects after OT, i.e., the incidence of DEH and FEN after OT was lower if the thickness of the apex to labiolingual alveolar bone before OT was as follows: the apex to labial alveolar bone thickness of the maxillary central incisor and maxillary lateral incisor was >4 & x202f;mm, the apex to palatal alveolar bone thickness of the maxillary lateral incisor was >3 & x202f;mm; the apex to labiolingual alveolar bone thickness of the lower incisor was >5 & x202f;mm. Conclusion The incidence of post-OT DEH at the maxillary anterior and mandibular anterior lingual surfaces were increased significantly compared to before treatment. In general, the smaller the apex to labiolingual alveolar bone thickness, the greater the likelihood of bone defects occurring after OT. Evaluation of the apical position of anterior teeth in alveolar bone can help minimize the occurrence of bone defects after OT.