Morphometric Analysis of the Inferior Alveolar Nerve Fails to Demonstrate Sexual Dimorphism

Abstract

With regard to the incidence of inferior alveolar nerve (IAN) damage after an IAN block or following oral and maxillofacial surgical procedures, there are reports of sexual dimorphism, no sexual dimorphism, and little sexual dimorphism. However, details of the morphology and sexual dimorphism in the characteristics of the IAN have not been available in textbooks. We morphometrically analyzed the human IAN and clarified these issues. The materials were obtained from 22 cadavers (11 female and 11 male), aged 59 to 84 years (average age: 74.1 yr), and dentulous. The causes of death did not influence the nervous system, so the IANs were considered to be normal. Human IANs were resected at the mandibular foramen. We counted the myelinated axons and measured the transverse area, perimeter, and circularity ratio of the myelinated axons. We estimated the average total number of myelinated axons in the female IAN to be 25,230, with an average transverse area of 34.1 microm(2), an average perimeter of 21.8 microm, and an average circularity ratio of 0.86, with the same measurements in the male IAN being 20,278, 31.7 microm(2), 20.7 microm, and 0.87, respectively. Our data showed no significant difference between the female and male specimens in any measured item (P < .05). We assumed that the sex difference in the incidence of IAN damage was not affected by the morphometric findings. Our findings might partly explain why there is no significant sex difference in the incidence of IAN damage.