## 4 Discussion  
Extraction of the mandibular third molar is the most commonly performed surgical procedure in oral and maxillofacial surgery. IAN injury can cause a lot of discomfort to the patient and lower the quality of life [35]. However, there are still not many studies on the relationship between the inferior alveolar nerve and mandibular third molars in populations. This study was to evaluate the pattern of mandibular third molar impaction in Korea and to evaluate the risk factors of inferior alveolar nerve damage that may occur during extraction. Prevalence of third molar impaction is reported to range from 30.3% to 68.6% [2; 3; 4; 5; 6]. The prevalence of impaction could not be determined in this study as it was intended for patients with impacted mandibular third molars. The gender difference regarding the impacted mandibular third molar varied from study to study. Previous studies showed that women have a higher prevalence of impaction [6; 36] and another study showed that men have a higher prevalence of impaction [37]. Impaction of the third molar was 52.1% in men, and the average age was 33.5 years. Patients 10 to 39 years old accounted for 88.4% of this study. The impaction pattern was varied according to the angulation. Most of studies showed that mesial angulation [6; 38; 39; 40; 41] and vertical impaction [42; 43] occur frequently. In this \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**P.G.A, Numbness** & \begin{tabular}{c} **Without** \\ **Numbes (\%)** \\ \end{tabular} & **Total (\%)** & \(p\) **Value** & \begin{tabular}{c} **P.G. I, II, III** \\ \end{tabular} & \
\begin{tabular}{c} **Numbes** \\ **(\%)** \\ \end{tabular} &
\begin{tabular}{c} **Without** \\ **Numbes (\%)** \\ \end{tabular} & **Total (\%)** & \(p\) **Value** \\ \hline A & 7 (0.1) & 5502 (99.9) & 5509 (100.0) & & I & 1(0.1) & 1203 (99.9) & 1204 (100.0) & \\ B & 16 (0.5) & 3487 (99.5) & 3503 (100.0) & \(p=0.004\) * & II & 21 (0.4) & 5683 (99.6) & 5704 (100.0) & \(p=0.189\) \\ C & 7 (0.5) & 1291 (99.5) & 1298 (100.0) & & III & 8 (0.2) & 3394 (99.8) & 3402 (100.0) & \\ Total & 30 (0.3) & 10,280 (99.7) & 10,310 (100.0) & & Total & 30 (0.3) & 10,280 (99.7) & 10,310 (100.0) & \\ \hline \end{tabular}
\end{table} 
Table 13: Association between the Pell and Gregory classification (P.G.) and numbness. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Risk Factors** & **Injury (\%)** & **Without Injury (\%)** & **Total (\%)** & \(p\) **Value** \\ \hline Both lingual pathway & & & & \\ and IAN narrowing & 24 (3.8) & 605 (96.0) & 629 (100.0) & \\ Only lingual pathway & 0 (0.0) & 592 (100.0) & 592 (100.0) & \\ Only IAN narrowing & 3 (0.0) & 8682 (100.0) & 8685 (100.0) & \(p<0.001\) * \\ No lingual pathway or & 3 (0.7) & 401 (99.3) & 404 (100.0) & \\ IAN narrowing & Total & 30 (0.3) & 10,280 (99.7) & 10,310 (100.0) & \\ \hline \end{tabular}  
* Statistical significance \(p<0.05\), [PERSON]’s chi-square test.  
\end{table} 
Table 14: Association between panoramic signs and inferior alveolar nerve (IAN) injury. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Risk Factors** & **Injury (\%)** & **Without Injury (\%)** & **Total (\%)** & \(p\) **Value** \\ \hline Both lingual pathway & & & & \\ and IAN narrowing & 24 (3.8) & 605 (96.0) & 629 (100.0) & \\ Only lingual pathway & 0 (0.0) & 592 (100.0) & 592 (100.0) & \\ Only IAN narrowing & 3 (0.0) & 8682 (100.0) & 8685 (100.0) & \(p<0.001\) * \\ No lingual pathway or & 3 (0.7) & 401 (99.3) & 404 (100.0) & \\ IAN narrowing & Total & 30 (0.3) & 10,280 (99.7) & 10,310 (100.0) & \\ \hline \end{tabular}  
* Statistical significance \(p<0.05\), [PERSON]’s chi-square test.  
\end{table} 
Table 15: Risk factors of inferior alveolar nerve (IAN) injury in cone beam computed tomography (CBCT). study, horizontal angulation was most popular. CBCT is taken when there is a suspicion of contact between the IAN and the mandibular third molar in panoramic radiographs, or when the third molars are completely impacted.