Variation of 3D outer and inner crown morphology in modern human mandibular premolars

Abstract

ObjectivesThis study explores the outer and inner crown of lower third and fourth premolars (P3, P4) by analyzing the morphological variation among diverse modern human groups.Materials and MethodsWe studied three‐dimensional models of the outer enamel surface and the enamel–dentine junction (EDJ) from μCT datasets of 77 recent humans using both an assessment of seven nonmetric traits and a standard geometric morphometric (GM) analysis. For the latter, the dental crown was represented by four landmarks (dentine horns and fossae), 20 semilandmarks along the EDJ marginal ridge, and pseudolandmarks along the crown and cervical outlines.ResultsCertain discrete traits showed significantly different regional frequencies and sexual dimorphism. The GM analyses of both P3s and P4s showed extensive overlap in shape variation of the various populations (classification accuracy 15–69%). The first principal components explained about 40% of shape variance with a correlation between 0.59 and 0.87 of the features of P3s and P4s. Shape covariation between P3s and P4s expressed concordance of high and narrow or low and broad crowns.ConclusionsDue to marked intragroup and intergroup variation in GM analyses of lower premolars, discrete traits such as the number of lingual cusps and mesiolingual groove expression provide better geographic separation of modern human populations. The greater variability of the lingual region suggests a dominance of functional constraints over geographic provenience or sex. Additional information about functionally relevant aspects of the crown surface and odontogenetic data are needed to unravel the factors underlying dental morphology in modern humans.

Morphological Variation of the Baka Pygmies’ Deciduous Second Molars 

“…South Americans showed the largest tooth size. Our results matched these ndings using a different measure of size, namely the lnCS, which depends also on the landmark con guration 25 . The dental size of the Baka and other pygmies was studied also in relation to their body size and developmental patterns 18,19 .…”

“…In fact, we observed a great overlap between populations in our lower deciduous second molars sample, which hampered the possibility to distinguish the diverse geographical groups based only on their tooth shape. Similar ndings were made by Buchegger 23 , Teplanova 24 , Krenn et al 25 and Halász 26 for permanent upper and lower premolars, and rst and second molars.…”

“…High pairwise correlation between opposing teeth developing in different jaws can be interpreted as a strong hint to a tight genetic control over the dental development, and is explained by the fact that antagonists have to t optimally to facilitate an effective mastication. These constraints are likely similar for any tooth type, as similar results were achieved for dyads of other dental types 25,26 .…”

A Neanderthal from the Central Western Zagros, Iran. Structural reassessment of the Wezmeh 1 maxillary premolar

“…Geometric morphometric (GM) analyses of EDJ were performed on the virtual surface by placing two landmarks at the apices of the paracone and protocone dentine horns and 71 semilandmarks along the marginal ridges (33 on the mesial marginal ridge and 38 on the distal one). We performed the generalized Procrustes analyses, followed by between-group principal component analyses (bgPCA) and Jackknife cross-validated canonical variate analyses (CVA) based on the first 9 (for the separate P 3 and P 4 samples) to 12 (for the combined P 3 -P 4 samples) first principal components explaining ~90% of the total variance (Mitteroecker and Bookstein, 2011;Krenn et al, 2019). Wezmeh 1 was included a posteriori in the analyses.…”

Distinct mandibular premolar crown morphology in Homo naledi and its implications for the evolution of Homo species in southern Africa

“…In African apes, it seems that population structure is important in understanding levels of dental variation; gorillas show hierarchical levels of dental variation such that there is more variation at the species than subspecies level, while in chimpanzees the subspecies and species levels of variation are roughly similar. Similarly, in modern humans there appears to be high levels of intra-population variability in premolar EDJ shape 38 . In sum, low levels of dental variability could suggest the H. naledi remains are from relatively closely related individuals in a single population.…”