## 4 Discussion
In the fixed appliance group, all teeth examined before and after treatment showed a statistically significant reduction in root length, whereas in the clear aligner group, only the maxillary incisors and mandibular central incisors exhibited a statistically significant change in root length [35]. [PERSON] et al. compared the severity of root resorption in individuals undergoing treatment with fixed braces versus transparent aligners. The maxillary canine and lateral incisor in the fixed appliance group experienced the most severe root resorption, while the mandibular canine and lateral incisor in the transparent aligner group displayed the least severe root resorption [35]. They observed reduced severity and lower prevalence of root resorption in patients who were treated with aligners. In contrast, [PERSON] et al. employed panoramic X-rays to compare the lengths of 1083 teeth (incisors, canines, and premolars) before and after aligner therapy [31]. All 71 adult patients examined in their study showed a minimal reduction in root length, where root length is considered the distance between the apex and the cement-enamel junction. However, only 3.69% of the assessed teeth (41.81%) had roots shorter than 20% of their original pre-treatment length. This incidence of root resorption can be compared to any orthodontic therapy with light orthodontic forces. Upper lateral incisors, lower lateral incisors, and central incisors were the teeth most affected by severe root resorption [31]. [PERSON] et al. 's study exclusively evaluated incisors in patients who used aligners to address class II malocclusion. They defined root resorption as the difference in root volume before and after treatment [62]. Following treatment with clear aligners, most teeth exhibited mild to moderate resorption, with only a few displaying severe resorption. Risk factors for root volume loss included tooth type and intrusion-extrusion changes [62]. In 2023, [PERSON] et al. conducted a retrospective study to assess the dimensions of alveolar bone alterations associated with orthodontic tooth movement (OTM), as well as the prevalence and severity of orthodontically induced inflammatory root resorption (OIIRR) in maxillary incisors treated with clear aligners (CA) or fixed orthodontic appliances (FA) [64]. The secondary goal of this study was to compare post-treatment alveolar bone alterations and root resorption in maxillary incisors treated with either approach. A total of 40 patients were randomly assigned to one of two groups (CA or FA). In the CA group, 20 patients were treated with Invisalign (Align Technology, San Jose, CA, USA). The FA group included 20 patients (29.67 \(\pm\) 7.71 months) who had fixed orthodontic appliances (Victory Series; 3 M Unitek, San Jose, CA, USA). Baseline characteristics and treatment duration were identical across both groups; moreover, both groups were treated with mild to moderate crowding on a non-extraction basis. Crowding was reduced by posterior teeth distalization, dental arch expansion, and anterior tooth proclination. Pre-treatment (T0) and post-treatment (T1) CBCT was used to assess dentoalveolar quantitative alterations. Alveolar bone thickness (ABT), alveolar bone height (ABH), root length (OIIRR), and maxillary incisor inclinations were among the parameters assessed. CA and FA treatments appeared to generate a substantial reduction in ABT, and both treatment methods reduced ABH significantly, with the greatest reduction reported on the labial side of the lateral incisors in the CA group. FA and CA treatments resulted in statistically significant increases in OIIRR in the maxillary incisor area, with FA patients displaying a greater frequency and severity of OIIRR. CBCT was also used in [PERSON] et al. 's study to investigate the occurrence and severity of OIIRR in patients who had undergone complete treatment with clear aligners (Invisalign; Align Technologies, Santa Clara, CA, USA), and to identify potential risk factors for OIIRR [60].