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The objective was to determine the expression and fluctuating asymmetry of two dental morphological traits in the living Jordanians: The lingual cusp number on the lower premolars (LP1 and LP2) and the hypoconulid (distal cusp) reduction on the lower first molar (LM1). In addition, both intra- trait and inter- trait interactions were analyzed. Three hundred school children (15.5 +/- 0.4 years) were involved. Impressions for the mandibular dental arches were taken, and dental casts were reproduced. The above-mentioned traits were observed. Paired sample t test and nonparametric correlation analysis were used for data analysis. Three-cusped LP1 was found in 11.40 % of the examined students, while the two-cusped LP1 was found in 88.60%. In comparison, the Three-cusped LP2 was found in 61.40% while the two-cusped LP2 was found in 38.60% of the observed subjects. The frequencies of the 4-cusped and 5-cusped LM1 were found to be 8.65% and 91.35%, respectively. Nonparametric correlation analysis revealed positive and statistically significant association between the expression of two lingual cusps on LP1 and on LP2 in both genders (p < 0.01), while there was no significant correlation between expression of two lingual cusps on either LP1 or LP2 and the hypoconulid loss on LM1 in both genders (p > 0.05). Bilateralism was highly significant in the tested traits in both genders (p < 0.001). This finding might be a sign of relatively low environmental stresses experienced by the living Jordanians and/or great ability of its individuals to buffer the adverse effects of such stresses on dental development. This study is a useful addition to the existing literature in that it examines a previously poorly characterized population and assists in placing the contemporary Jordanian population within the current framework of human population groups globally.

The objective of this study is to determine the prevalence of expression and bilateralism of two dental morphological traits in contemporary Jordanians: The hypocone reduction trait on the maxillary second permanent molar and Carabelli's trait on maxillary permanent first and second molars. Furthermore, inter-trait correlation and the relationship of Carabelli's traits with upper first molar dimensions were investigated. Three hundred subjects of school children at their 10th grade and of an average age of 15.5 +/- 0.4 years were involved. Alginate impressions for the maxillary arch were taken, dental casts were reproduced. The selected accurate casts were of 132 male- and 155 female-students. The frequencies of hypocone reduction trait on the maxillary second molar and Carabelli's trait on the maxillary molars were examined. Buccolingual and mesiodistal diameters of the maxillary first molar were measured and recorded. Paired Sample t test and Nonparametric Correlation analysis were used for data analysis. Hypocone reduction trait on the maxillary second molar was found in 29.8% of the examined students. Positive forms of Carabelli's trait on first and second molars were observed in 65.0% and 3.8%, respectively. Nonparametric correlation analysis revealed positive association between Carabelli's trait on first molar and hypocone reduction trait on the maxillary second molar. The presence of Carabelli's trait on first molar was strongly associated with the increase of buccolingual, but not the mesiodistal, diameter. Bilateralism was found highly significant in the tested traits and both genders (p < 0.001). This finding might be a sign of relatively low environmental stresses in the living Jordanian population and/or great ability of its individuals to buffer the adverse effects of such stresses.