## 3 Discussion  
This case report describes the unusual occurrence of ECR of an impacted tooth, mimicking the symptoms of tooth ankylosis. Due to the scarcity of literature, the etiology of this rare phenomenon remains questionable. Root resorption might be classified according to the location of the root surface (internal/external). Further, external root resorption can be subclassified into surface, inflammatory, replacement, cervical, and transient apical breakdown [23]. External cervical root resorption usually manifests in the cervical area of teeth and appears in most cases due to the periodontal ligament and subepithelial cementum damage [24]. The early diagnosis of ECR improves tooth prognosis. However, no specific symptoms or radiographic features can usually be observed in the initial stages [25]. Therefore, CBCT is a _gold standard_ in the diagnostics and treatment planning of ECR lesions [21]. The present case confirms the diagnosis of ECR during orthodontic treatment, which was determined through CBCT. While a minor radiolucent shadow was retrospectively observed distally to the impacted second premolar in the pre-treatment panoramic radiograph (Figure 1A), this finding raises doubts about the etiology of ECR, as the initial lesion may have already been present before the orthodontic treatment. Despite surgical exposure, the tooth did not erupt spontaneously, and a subsequent X-ray taken after activation of the traction revealed a radiolucent shadow in the distal cervical area (Figure 2D). [PERSON] and [PERSON] emphasized the importance of orthodontically induced inflammatory root resorptions (OIIRR) in 2002 [26]. Although commonly associated with apical resorption, cervical resorption is also a consequence, and patients who received earlier orthodontic treatment are at a higher risk, according to [PERSON]'s research [27]. The progression of cervical resorption plays a significant role in its development, and it is subject to bacterial infestation through the sulci, which promotes inflammation and subsequent resorption even after the movement forces have been stopped. In this particular case, the impacted tooth was considered ankylosed empirically when no tooth mobility was observed, and the adjacent teeth had been intruded during the orthodontic traction instead of extrusion of the affected tooth [28]. As mentioned above, in advanced stages of ECR, bone-like resorptive tissue may be observed at the defect site [29]. This might have resulted in the absence of physiological mobility during following appointments after the surgical exposure of the second premolar. Since the tooth  
Figure 3: Reconstructed CBCT images of the #45 tooth, showing signs of the external cervical resorption (ECR): portal of entry (white arrows), bone-like tissue apposition (red arrows), the extent of the resorption (blue arrow). (**A**)—coronal; (**B**)—sagittal; (**C**)—axial slices. was identified as ankylosed, surgical luxation was performed to facilitate the eruption of the impacted premolar based on the evidence from the literature [20]. Considering the aforementioned relationship between the ECR and the damage of the cervical tooth region, the following aspects could contribute to the damage of cemento-namel junction (CEJ) structures in the present case: (1) chemical trauma (35% phosphoric acid), (2) mechanical trauma (during luxation), and (3) orthodontic movements [7]. A clinical study by [PERSON] et al. (2013) showed a higher risk for ankylosis for closed surgical procedure performed compared with an open surgical technique [7]. In the present case, a closed surgical technique and forced eruption were performed. Damage to the CEJ area during surgical exposure of an impacted tooth is described as a potential risk factor for ECR. It should be noted that in our case, the periodontitis has not reported any trauma or exposure of CEJ during the first surgical intervention.