| Objective:The position of the mental foramen and the anterior loop length of the inferior alveolar nerve serve as important anatomical landmarks for dental implant surgical procedures in the anterior mandibular region. This study was designed to reconstruct 3-dimensional the anterior loop of the inferior alveolar nerve by cone-beam CT (cone beam computed tomography, CBCT) combined with Mimics (Materiaise’s interactive medical image control system), measuring targets associated with dental implant surgery and anatomy, meanwhile, exploring relationship between the position of the mental foramen and the anterior loop of the inferior alveolar nerve.Methods:From 2011 to 2013 in the treatment of 60 patients of Departments of Implant Dentistry, Stomatology Hospital, Guangxi Medical University, were in line with the following inclusion criteria:(1) at least 18 years of age; (2) the mandible without congenital developmental defects or deformity; (3) no mandibular space-occupying lesion; (4) the mandible without visible scar of trauma or surgery; (5) clear CBCT images without pseudo shadow influenced the inferior alveolar canal and (or) mental foramen. Of which were 30 males,30 females, ranging in age from 21 years to 73 years, mean age 46.6 years.60 patients were divided into male and female group,30 patients were male,30 patients were female, divided into five groups by age, including 20-29 years of 9 cases,30-39 years of 19 cases,40-49 years of 16 cases,50-59 years of 8 cases, more than 60 years (including 60 years of age) of 8 cases, divided into two groups with 60 cases respectively, according to the left and right side of the inferior alveolar nerve.60 CBCT images data of the original volume were taken by professionals in Departments of Radiology, Stomatology Hospital, Guangxi Medical University. The researchers transformed CBCT data of 60 patients into digital imaging and communications in medicine (DICOM) format files for Mimics for 3-dimensional reconstruction and measured the following parameters:anterior loop length of the inferior alveolar nerve (ALL) and anterior loop angle of the inferior alveolar nerve (ALA); 2-dimensional mental foramen diameter (2D MFD),2-dimensional vertical height from the inferior border of the mental foramen to the inferior border of the mandible (2D H-MF), 3-dimensional mental foramen diameter (3D MFD), and 3-dimensional vertical height from the inferior border of the mental foramen to the inferior border of the mandible (3D H-MF); inferior alveolar canal diameter (IACD) and vertical height from the inferior border of the inferior alveolar canal to the inferior border of the mandible (H-IAC). In addition, mental foramen location (MFL) was measured directly in the GALAXY viewer.Results:1. ALL and ALA:ALL was 1.16±1.78mm, the maximum of 8.41mm. Analysis of ALL revealed no significant differences between sides of the mandible (p=0.722), sexes (p=0.071), or age groups (p=0.99). ALA was 19.13±26.89°, the maximum of 81.79°. There was no significant difference in ALA between the sides of the mandible (p=0.504). However, ALA in women (25.21±28.89°) was significantly higher than in men (13.06±23.43°) (p=0.013), and ALA showed significant difference between age groups as well (p=0.029).2. Diameter and height of the mental foramen:2D MFD was 2.97±0.61mm (range,1.28-4.53mm), and 3DMFD was 2.95±0.59mm (range,1.21-4.63mm). Paired-sample t test revealed no significant difference between 2DMFD and 3D MFD (p=0.293). The statistically significant variations observed in the 2D MFD include side (p=0.014), sex (p=0.015), and age (p=0.001). Similar observations were made with 3D MFD, and statistically significant differences were found in the side (p=0.019), sex (p=0.01), and age (p=0.001).2D H-MF was 14.67±1.67mm (range,10.73-19.55 mm), and 3D H-MF was 14.61±1.69mm (range,10.43-18.97mm). Paired-sample t test revealed that there was no significant difference between 2DH-MF contrasted with 3D H-MF measurements (p=0.127). Statistically significant variations were observed in 2D H-MF measurements based on the sex (p=0.000) and age groups (p=0.017), but no significant variations were observed between the sides of the mandible (p= 0.94). A similar statistical profile was observed, with 3D H-MF similar to 2D H-MF in sex (p=0.000), age groups (p=0.02), and sides of the mandible (p=0.859).3. Diameter and height of the inferior alveolar canal:IACD was 3.01±0.67mm (range,1.45-5.24mm). There was no statistically significant difference in IACD between the right and left sides of the mandible (p=0.397). However, the IACD in male was significantly greater than in female (p=0.006). Inferior alveolar canal diameter was found to be significantly different between the age groups (p=0.001) as well. H-IAC was 10.32±1.56mm (range,6.68-16.66mm). There was no significant difference in H-IAC between the sides of the mandibles (p=0.223) and between the age groups (p=0.834). The H-IAC was found to be significantly greater in male than in female (p=0.039).4. Location of the mental foramen and the anterior loop of the inferior alveolar nerve:the mental foramen was located apically between the first and second premolars in 51.67% of the cases and below the second premolar in 40.83% of the cases observed. The anterior loop of the inferior alveolar nerve was observed in 37.5% of the cases. The mental foramen was located below the second premolar in 73.33% and apically between the first premolar and the second premolar in 20% of the cases with an identifiable anterior loop. Unconditional logistic regression analysis confirmed a significant (p<0.05) relationship between the location of the mental foramen and the presence of the anterior loop of the inferior alveolar nerve.Conclusions:1. Using CBCT combined with Mimics for the anterior loop of the inferior alveolar nerve 3D reconstruction can be more visually measured to anterior loop length of the inferior alveolar nerve and anterior loop angle of the inferior alveolar nerve before dental implants surgery involving mental foramen region, improving the accuracy of measurement, providing accurate anatomical reference in order to avoid intraoperative injury to the anterior loop of inferior alveolar nerve.2. Diameter and height of the mental foramen in male were greater than female’s. Diameter and height of the mental foramen were measured by both 2D and 3D methods. On the basis of the observation made in the current study, we can conclude that there is no significant difference in the accuracy of 2D and 3D measurements, suggesting that in clinical dental implants surgery involving mental foramen region, the preoperative use of CBCT 2D coronary section measuring diameter and height of the mental foramen can provide reliable anatomical basis for clinical surgery involving mental foramen region.3. Diameter and height of the inferior alveolar canal correlated with gender, IACD and H-IAC in male were larger than female, H-IAC did not change with the growth of the age, but there were differences in the anatomy of the inferior alveolar canal without uniform standard reference, therefore, the preoperative CBCT scanning combined with accurate analysis by software for reducing the damage to the inferior alveolar canal.4. Location of the mental foramen correlated with the presence of anterior loop of the inferior alveolar nerve. When the mental foramen was located below the second premolar, there was a higher possibility of the presence of the anterior loop of the inferior alveolar nerve, suggesting that the implantologist needs to pay attention to the anterior loop during placements of implants in the region of the mental foramen to avoid injury to the inferior alveolar nerve and occurring postoperative complications. |
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