Entoconulid (cusp 6), metaconulid (cusp 7), post-metaconulid and pre-entoconulid expression on permanent mandibular first molar in the living Jordanian population and inter-trait interactions.

Objectives: To determine the frequency of expression and sexual dimorphism of the following dental morphological traits on the permanent mandibular first molar (LM1) in the living Jordanians: Entoconulid (cusp 6; tuberculum sextum), metaconulid (cusp 7, tuberculum intermedium), post-metaconulid and pre-entoconulid (entostylid) traits. In addition, to analyze inter-trait interactions whenever possible was one of the aims.

Methods: Three hundred sixty school children (176 males, 184 females, ages 15.5 +/- 0.4 years) from the middle of Jordan were involved. Impressions for the mandibular dental arches were taken, and dental casts were produced in 2009. The above-mentioned traits were observed. Z-value test between two proportions and nonparametric correlation analysis were used for data analysis.

Results: Cusp 7 on LM1 was found in 15.83 %, while cusp 6 on this tooth was found in 21.67% of the examined students. In comparison, both post-metaconulid and pre-entoconulid traits were found to be absent on LM1 in all observed subjects. Nonparametric correlation analysis revealed weak negative and statistically insignificant association between the expression of cusp 6 and 7 on LM1 among the living Jordanians.

Conclusion: Both cusp 6 and cusp 7 on LM1 are expressed in a relatively higher rate among the living Jordanian Arabs than other studied Western Eurasians, suggesting a significant gene flow from Sub-Saharan Africans and Mongolians to the Middle East. In addition, the insignificant weak correlation between cusp 6 and 7 on LM1 suggests that these two dental morphological traits are both genetically and phenotypically independent.