Validity of the mandibular canine index (MCI) in sex prediction: Reassessment in an Indian sample.

The dentition's use in sex assessment has been explored and advocated owing to its strength and resistance to peri- and postmortem insults. Among the teeth, canines have shown the greatest sexual dimorphism; they are also known for greater resistance to pathological alterations and trauma. These factors have prompted some researchers to explore its use alone in sex prediction. Specifically the mandibular canine index (MCI), which is the ratio of the mesiodistal (MD) dimension of the lower right canine and the inter-canine arch width, was developed by Rao et al. [Forensic Sci. Int. 42 (1989) 249-254] who predicted sex correctly in ∼86% of cases in a South Indian sample. These results were verified subsequently by other Indian researchers, both on southern and on northern Indians, although such success rates were not apparent in another South-Asian population as well as a European group. The present study re-examined the method in 203 Indians (103 males, 100 females) of age 19-32 years who originated from diverse states of the country, constituting all major religious and caste affiliations, and found relatively low sex estimation accuracy using the MCI (∼51%). This is in spite of the MD dimension of canines as well as inter-canine arch width - the absolute measurements used for deriving the MCI - showing statistically significant sex differences (p<0.05); also, the application of multivariate statistics, viz. logistic regression analysis, revealed higher accuracy levels of sex estimation for the absolute measurements (∼62-66%) vis-à-vis the MCI (∼50%). The results herein reinforce recent observations that ratios obtained from teeth, such as the MCI, do not reflect sexual dimorphism that may be present in absolute measurements. Furthermore, we believe that the basis for using MCI as a sex assessment tool is questionable, since it depends on the levels of sexual dimorphism between the absolute dimensions-low sexual dimorphism in one (e.g. MD measurement of canines) and proportionately high sexual differences in the other (e.g. inter-canine arch width), or vice versa, would lead to higher sex estimation accuracy of the MCI; on the other hand, relatively equal levels of sexual dimorphism in both would negate the ability of the MCI to accurately estimate sex. These suggest that the MCI has little utility in sex estimation and that its application should be restricted, if not discontinued altogether, in forensic and anthropological sex prediction.