Double inferior alveolar nerve canals and mental foramina in the mandible : a computed tomography study at a private dental clinic in Kenya

Abstract

Aberrant inferior alveolar nerve canals (IANC) and mental foramina (MF) have been well documented and can have significant implications if injured during invasive procedures of the human mandible. Geographical and ethnic differences have been observed in the occurrence of these variations. The primary objective of this study was to determine the pattern of occurrence of double IANC and MF among a sample of patients attending a dental clinic in Kenya through cone beam computed tomography (CBCT) image analysis. The occurrence, location, configuration and morphometric measurements of double inferior alveolar canals and mental foramina were recorded in a data extraction form (Appendix 1). Data was captured in a Microsoft Excel 2010 data sheet. With the use of Bayesian statistics, exploratory and inferential data analysis was done in R (R Development Core Team, Vienna, Austria) software version 3.1.2. The results were presented as posterior distributions of means and mean differences including standard deviations (SD), Credible Intervals (CrI) and effect sizes (ES). In all outputs, the 95% most credible values (CrI) were shown as a High-Density Interval (HDI) in the respective histograms. Gender and side differences were rated. A total of 800 images were included in the present study of 347(43.38%) male and 453(56.62%) female patients. The mean age was 39.18 years+12 SD while median age was 39 years (range: 19 to 67 years). Double IANC were observed in 26 (3.25%) of the 800 images (29 of 1600 sides, 1.81%). The most frequently encountered type of double IANC was type 1 (23 / 29, 79.31%), followed by type 3 (4 /29, 13.79%) and then type 2 (2 / 29, 6.9%). The double IANC were more in the angle region than at the body area of the mandible. The mean diameter and length of the double IANC were 1.57+0.41mm (95% CrI: 1.40, 1.73) and 13.10 +3.45mm (95% CrI:11.60, 14.5) respectively. In total, 21 double MF were found in 19(2.4%) patients, with 11 being posterior, seven anterior and three superior to the main mental foramen (MF). The mean diameter of double MF was 1.27 [95% CrI: 1.05, 1.47] mm with a standard deviation of +0.41mm. The mean distance between double MF and the main MF was 4.69mm [95% CrI: 3.47, 5.59] with a standard deviation of 2.26mm. Based on the findings reported in this study, the rate of occurrence of double IANC and double MF was typically low in the study population. The diameter of the main MF was always smaller than that of the side without the double MF. This was not the case with the IANC. There was also no gender predilection elicited in any of these occurrences. CBCT imaging is recommended as it has better resolution to enable detailed analysis of structures that are less than a millimeter in diameter. Ensuring a safe distance of 9 mm from the walls of the main MF would greatly reduce the risk of injury to the neurovascular contents of the double MF in case CBCT imaging is not available.