title: 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.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Dpt of conservative dentistry and fixed prosthodontics, Fac of Dentistry, Univ. of Jordan, Amman, Jordan.
authors.forename: A
authors.initials: A
authors.lastname: Khraisat
authors.forename: F
authors.initials: F
authors.lastname: Alsoleihat
authors.forename: F A
authors.initials: FA
authors.lastname: Sawair
authors.forename: A I
authors.initials: AI
authors.lastname: Shaweesh
mesh_terms: D000293:Adolescent; D018912:Arabs / Q000235:genetics; D005260:Female; D015870:Gene Expression / Q000235:genetics; D051456:Gene Flow / Q000235:genetics; D005838:Genotype; D006801:Humans; D007597:Jordan; D008297:Male; D008334:Mandible; D003765:Models, Dental; D008963:Molar / Q000033:anatomy & histology*; D010641:Phenotype; D012737:Sex Factors; D019228:Tooth Crown / Q000033:anatomy & histology*