## 4 Discussion
In addition, when examining the relationship between perforonins and impaction angulation in various studies, it was reported that vertical impaction was the most common, followed by mesial impaction, and bone loss was most observed in mesial impaction [53,54]. In this study, horizontal impaction was the most common (39.4%),followed by vertical impaction (25.0%) and mesial impaction (23.2%). Out of 158 distal impactions, 38 cases had pericoronitis, showing a high morbidity rate of about 24%. The incidence of IAN injury was 0.637%, which is similar to or lower than that reported in other studies [9; 10; 11; 12; 13; 14; 15]. Of the 30 patients with IAN injury, there was a statistically significant correlation with gender (\(p=0.038\)), with risk of nerve damage being higher in women than men. Other studies reported that there was no correlation between gender and nerve injury [31], but many studies have reported that women have a higher risk of nerve injury [23; 24; 55]. In addition, there was a significant correlation between age and IAN injury. It can be seen that the possibility IAN injury increases with age. There was also literature reporting that the age and risk of nerve injury were not correlated [55; 56]. However, many studies have shown that the risk of IAN injury increases in those over 25 years of age, and age is a risk factor for nerve injury [15; 23; 57; 58; 59; 60; 61]. Age-related changes such as a decrease in bone elasticity, an increase in the occurrence of hypercmentosis, and an increase in the amount of bone removal are thought to be the major causes of the increase in the difficulty of surgery. There are studies suggesting a relationship between the depth of impaction and the incidence of IAN injury [9; 13; 23; 30; 55; 56; 58; 60], and a study suggesting no relationship [31]. In the present study, it was found that there is a relationship between the depth of impaction and the incidence of IAN injury. Naturally, the deeper the impaction depth, the closer it is to the inferior alveolar nerve, and therefore, the probability of nerve injury is thought to increase. No significant correlation was found between the signs of panoramic radiographs and the incidence of IAN injury. This result is similar to most studies [9; 11; 20; 23; 26; 28; 31]. It is considered that the prediction of IAN injury is inadequate, as a panoramic radiograph sign has low sensitivity and high specificity. In this study, among 30 patients with IAN injury, 24 showed that the IAN was driven to the lingual side of the mandibular third molar root in CBCT, and at the same time, a narrowing of the IAN was observed. When these two features are observed at the same time, it can be said that the incidence of IAN injury increases. The narrowed IAN in CBCT and the lingual pathway of the IAN is consistent with other studies that suggested increased risk of IAN injury [27; 23; 62; 63]. The narrowing of the IAN canal means that the distance between the root of the mandibular third molar and the IAN canal is less. Clinically, when the mandibular third molar is extracted, most of the instrumentation is performed on the buccal side. Because of this, there are many cases where the tooth comes out while applying force in the lingual direction. Due to this effect, it is thought that the lingual movement and narrowing of the IAN cause IAN injury during extraction. This is thought to be a good factor in predicting the occurrence of nerve injury. This study examined the impaction pattern and the risk factors affecting injury to the IAN in Koreans. The study had several limitations. First, it cannot be concluded that the study reflects the overall characteristics of Koreans, as it was short-term research by a single institution. Second, the study only included patients who underwent panoramic radiography and CBCT, instead of using random target collection.