## 4 Discussion
They observed a significant increase in CCH on the labial side of the lateral incisor, which aligns with this study's findings. Considering the findings of this and the previous studies, OT would not cause APE, particularly in the maxillary lateral incisors. In the comparison of CBCT measurements of teeth between OT-treated and untreated subjects in the current study, no significant difference was observed for the BCT of the maxillary incisor teeth, which is another important finding. This parallels the findings of [PERSON] et al., where labial bone thickness remained the same after OT [40]. In addition, [PERSON] et al. [41] found that the bone density around the teeth remained the same before and after OT using CBCT analysis of the grayscale value of bone tissue. In contrast to the previous findings, some studies suggest that OT can substantially reduce alveolar bone density. [PERSON] and colleagues found a decrease in bone density around the teeth, with the greatest reduction seen in the upper-right and upper-left central incisors after seven months of treatment, as measured by CBCT scans [42]. Another study also reported similar findings, showing that orthodontic-induced reduction in the alveolar bone density around the teeth can recover into its original state after two years of retention [43]. [PERSON] et al. [44] substantiate an inverse relationship between the CEJ-BC distance and alveolar BCT through their tomographic study. Meanwhile, in this study, a reduction in the mean maxillary BCT in the case group was observed, compared with controls but not to a statistically significant degree. OT-induced bone loss is always a controversial topic. Normally, during OT, the movement of teeth is carried out through efficient and coordinated bone remodeling, which involves both bone resorption and formation [45]. Some studies have suggested that OT can decrease bone density around the teeth [46; 47] while others have found the opposite to be true [48; 49]. This systematic review aims to scrutinize the available evidence and check whether OT could be a causative factor for APE. It is important to note that the occurrence of APE among the adult population has received limited attention in research. This review includes two observational studies that examine this topic. The prevalence of APE was found to be 35.8%, with the OT group having a prevalence of 42.1% and the control group reaching 29.5%. However, the difference was not statistically significant, as reported by [PERSON] et al. [7]. The study included 190 patients aged 22-38 and examined 1140 anterior teeth. Various clinical factors, such as the presence of APE, clinical crown length, and gingival biotype, were evaluated. However, there was a major correlation between APE and the thick-flat gingival biotype, with 75.6% of patients with this biotype being diagnosed with APE. These findings align with the clinical observations of some authors [22; 23] who state that patients often develop a gummy smile after OT. The prevalence of APE in adults is not well studied, possibly due to undefined diagnostic criteria [7]. Some clinical features, such as a short clinical crown and flat gingival architecture, are commonly used to diagnose APE. However,these features are based on individual perceptions, can vary from person to person, and could be linked to specific anatomical structures. To make a clinical diagnosis, a probe should be used to find the position of the CEJ. If the distance from the gingival margin to the CEJ is 0.5-2 mm, it would be appropriate to use a greater distance than 2 mm as a criterion for an APE diagnosis [7]. Pre- and post-orthodontics clinical crown length of anterior maxillary teeth of the subjects under 18 years old was evaluated by [PERSON] et al. [28]. After OT, there was no change in the clinical crown length of the central incisors, but the lateral incisors and canines increased. Five years after, all maxillary anterior teeth had increased in clinical crown length but were still 1.5 mm shorter than ideal. In their longitudinal study, [PERSON] et al.