## 4 Discussion
Some studies reported the rate of patients with mandibular second molar root-lingual cortical bone contact [12; 13]. [PERSON] et al. showed that contact between mandibular second molar roots and lingual cortical bone was observed in 49.3% of adults [12]. [PERSON] et al. reported that contact between the mandibular second molar and lingual cortical bone was observed in 12.2%, 26.8%, and 65.9% of hypodivergent, normovergent, and hyperdivergent patients, respectively [13]. In our study, mandibular second molar roots were in contact with the lingual cortical bone in 30.6% (11 out of 36), 42.5% (34 out of 80), and 51.7% (15 out of 29) of young adults with hypodivergent, normovergent, and hyperdivergent facial patterns, respectively. The contact between the posterior mandibular teeth and the lingual cortical bone can also be inferred from previous clinical studies. [PERSON] et al. reported on the movement patterns of mandibular first molars after the mandibular teeth were moved posteriorly using ramal plates [23]. The crown area moved 1.9 times more than the root region, and distal inclination was observed in approximately 31% of the posteriorly moved mandibular first molars. These findings suggest that the proximity of the posterior mandibular roots to the lingual cortical bone may have resisted posterior movement. In the simple logistic regression analysis, only D7 MP was found to be a significant predictor of L7-LCC. However, when a receiver operating characteristic (ROC) curve was plotted using D7 MP as a predictor, the area under the curve (AUC) was only 0.68, suggesting that D7 MP may not be a reliable diagnostic tool for confirming the presence of L7-LCC. L7-LCC is likely influenced by various other factors, such as the buccal inclination of teeth, the shape of the lingual cortical bone, the location of the mandibular mylohydoid line, and the presence of submandibular glands, which have been previously reported in the literature. Therefore, although D7 MP can be used as a preliminary assessment tool, additional three-dimensional diagnostic imaging may be necessary to establish an accurate treatment plan. In this study, D7 MP was measured using the left and right hemifacial CBCT images, allowing for more accurate measurement without overlap due to teeth on the opposite side and the mandible. However, when using conventional two-dimensional lateral cephalograms, overlapping opposite structures can make it difficult to measure D7 MP accurately. Therefore, further studies using lateral cephalograms should be conducted to confirm the effectiveness of D7 MP in predicting L7-LCC. There are several limitations to this study. First, it was conducted using only young adults, so it may not apply to growing patients. Second, the sample groups were determined solely based on FHR, and other factors were not taken into account. The hyperdivergent group had a high mean ANB value and a higher proportion of females, which may have influenced the observed differences between the groups. Therefore, further studies are needed to investigate the relationship between the mandibular molar roots and lingual cortical bone based on age, sex, and the anteroposterior relationship between the maxilla and mandible.