showed that MCI yielded a total sensitivity of 65% (0.59, 0.71) and total specificity of 63% (0.56, 0.69).
Overall, the identification accuracy varied from 32% to 94% for the males and 24% to 87% for females indicating a wide variation.. To explain this heterogeneity/
variation subgroup analysis and sensitivity analysis were undertaken. However, both the analysis could not explain the variation as the subgroups itself did not demonstrate homogeneity.
The varying degree of diagnostic accuracy could be probably explained on the basis of lack of sexual dimorphism with regards the mesio-distal canine width and intercanine distance. This is further explained with an example: In a study by Hosmani JV et al 16, the sensitivity reported was 0.40 (40% males identified correctly) and specificity was 0.50 (50% females identified correctly). The measurement of their study participants were: mesio-distal width of the canine in males was 7.18(6.02,8.34) and in females was 6.95 (5.37, 8.53) and the inter-canine width of males was 27.17(22.03, 32.31) and females was 26.25 (21.58 , 31.31) respectively. Observing the values closely, one can appreciate that there is an overlap indicating lack of sexual dimorphism. All those participants falling in this overlap region are misdiagnosed (False positives
=50% and False negatives=60%). From this example one can interpret that only 40% males have unique bigger measurements and 50% females have unique smaller measurements and hence they have been identified correctly. While those in the overlap region, the 60% males have smaller measurements and are misdiagnosed as females and 50% females have bigger measurements of their teeth similar to males and hence are misdiagnosed as males. This accomplishes that only when there is distinct sexual dimorphism , MCI can have better accuracy in gender identification 8,30,32,33.
A varying range of Std MCI (cut off point values) from a minimum of 0.19 to a maximum of 0.3 has been observed across the different studies. Each study showed its own unique Std MCI value. This variation in the cut off points is the result of the varying mesio- distal canine width and the inter-canine distance of the population indicating that there is no one standard MCI value which is applicable to all the people from different geographical location. This can pose to be a major drawback while choosing of a cutoff point (Std MCI) value for making a decision while utilizing MCI as a tool for gender identification for a victim (from
unknown geographical location) in mass disasters.
All the 26 studies considered in the review have used MCI as a tool for gender estimation in a living population with known gender. No studies could be retrieved where MCI has been used for victim identification in mass disasters or in post mortem cases. The actual application for which MCI is designed has never been tested.
Rao et al7 proposed that MCI should be calculated in the well aligned mandibular arch. Three studies 8,9,22 have performed these calculations in the mal-aligned teeth.
Such malocclusion can affect the accuracy of the MCI.
More-so, this again limits the application of MCI in mass disasters, where there is a slender chance that the victim would have well aligned mandibular teeth available for estimation. Mandibular arch with missing teeth, rotated or crowed teeth limits the application of MCI.
The unique feature of this review is that, probably this is the first largest systematic review and meta-analysis with 26 studies. Because of lack of homogeneity in the data across the studies complex meta-analytic statistics could not be performed. Since only two databases were searched there is a possibility to miss on some more relevant articles.
cOncluSIOn
The fact that several studies13,16,19,30 have already refuted the application of MCI in sex estimation and synergistically the results of this systematic review and meta-analysis along with the explanation of its limitation in the above section clearly indicates that Mandibular Canine Index is not an accurate tool for gender identification.
Acknowledgement: The authors would like to
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