Correlations Between Mandibular Third Molars to Inferior Alveolar Nerve Locations in Vietnamese Population

One of the probable complications in mandibular third molar extraction is the damage to the inferior alveolar nerve (IAN). Calculating the distance between IAN and third mandibular can decrease the complication risk. In this study, cone beam computed tomography (CBCT) scans were used to evaluate several factors related to the positional relationship between mandibular third molar and IAN in the Vietnamese population. One-hundred-seventy-eight CBCT scans were collected from dental clinics at Ho Chi Minh City, from 1st January 2018 to 28th February 2021. Only 100 scans were included in this study, 55 scans of female and 45 scans of male patients. The age of the patients ranged from 19 to 59 years old. From this study, the most common location of IAN relative to the roots of the mandibular third molar was on the apical side (60.5%), followed by the buccal side (21.5%), the lingual side (16%), and the least common located between the roots (2%). Overall, the mean distance between mandibular third molar roots to IAN was 3.19 ±1.85mm. There was a significant correlation between the left and right sides of the IAN location, indicating symmetry. Moreover, there is no association was found between gender and the location of IAN


Introduction
The extraction of the mandibular third molar is the most frequent intervention in oral surgery. A cohort study evaluated those general dentists recommend extraction of third molars in 59% of patients, mainly to prevent future problems or because a third molar had an unfavorable orientation or was unlikely to erupt 1 .
Unfortunately, a common problem after oral and maxillofacial surgery and even sometimes during routine dental treatment is the inferior alveolar nerve damage 2 . Inferior alveolar nerve damage can lead to numbness in the region supplied by the inferior alveolar nerve, which may be temporary or even

Method
This research design is a cross-sectional study, conducted from February to April 2021 at Ho Chi Minh City. The sampling method is purposive sampling.

Population and sample
The population observed was the Ho Chi Minh City commuter, who had taken CBCT radiographic scans for various treatments at Dental Clinics from 1 st January 2018 to 28 th February 2021. The CBCT radiographic images were taken from the same machine (Newtom GIANO HR), at the same settings. CBCT files were collected in DICOM format. Images were processed using NNT 3D Imaging software. Apart from CBCT scan images, medical records were used to confirm the patient's gender.

Data collection method
From one-hundred-and-seventy-eight CBCT scans collected in the clinic. Only one hundred were selected in this study, based on the inclusion and exclusion criteria. Fifty-five (55) patients were female, and fortyfive (45) patients were male. The CBCT images were analyzed twice by two observers, one dental student and one experience radiologist, to classify the threedimensional relationship of the mandibular third molar and the IAN.

Data analysis method
The selected data were categorized for the position of the mandibular canal relative to the roots of the mandibular third molar, based on the 4 classes of the Cartesian Coordinate System Concept. Afterward, the distance between the IAN to the root of the mandibular third molar was also being measured in millimeters. If the mandibular has only one root, the distance is taken from the distance between the root to the closest point of the IAN. For the mandibular with more than one root, the closest root to the IAN will be chosen as the reference point.
The data collected in this study were analyzed statistically using the SPSS software version 24.0 (IBM Corporation, USA) program.

Result
The prevalence of each classification and contact relation of the ian position relative to the roots of the mandibular third molar, based on the cartesian coordinate system concept in the vietnamese population.
This study revealed that IAN is commonly located on the apical side of the mandibular third molar (60.5%), followed by the buccal side (21.5%), the lingual side (16%), and between the roots (2%). In terms of contact relationship, 94.5% of the IAN does not have any contact relation with mandibular third molar roots (Table 1) The distance between the IAN to the root of the mandibular third molar was also being measured in millimeters in the Vietnamese population.
The distance from the root of the third mandibular molar root and IAN is measured in mm. Table 2 summarized all data in a detailed manner. From the table, data illustrated that the mean distance in each class I, class II and class III cases is 3.47mm, 2.81mm, and 3.08mm, respectively. Overall, the mean distance is 3.19 ±1.85mm However, the distance between IAN and mandibular third molar is 0 in all class IV cases.
This means that the IAN is in contact relation with mandibular third molars when the IAN is between the roots of mandibular third molars ( Table 2).
The normality of data distribution was being analysed. Since the p-value is greater than 0.05, we can conclude that the distance is normally distributed in all the samples. The symmetrical relationships between the left and right side of the mandibular third molar to IAN were evaluated using the Pearson correlation coefficient test (Table 3). The statistical analysis showed that the location of IAN between the right side and left side is .607, which is significant (p < .001 for a two-tailed test), based on 100 complete observations. There were also statistically significant correlations of the location of IAN between the left and right sides, indicating symmetry.
The gender factor related to IAN and mandibular third molar position in the Vietnamese population.
The distribution of IAN classification was similar between two gender groups (female and male) as shown in Table 4. In both groups, the location of IAN was found more common in the apical position of the mandibular third molar, approximately 60% of total cases. While Class II and III classifications were seen in 1 out of 5 cases (approximately 20%). Class IV classification was rarely found in both groups.

Conclusion
This research is conducted to analyse the positional relationship between IAN to mandibular third molar.
Besides, a various factor is evaluated. From the statistical analysis, we concluded that the most common location of IAN relative to the roots of the mandibular third molar was on the apical side (60%), followed by the buccal side (22%), the lingual side (16%), and then between the roots (2%