Assessment of the Relationship between the Total Occlusal Area of the Human Permanent Upper First and Second Molars and the Robusticity of the Facial Skeleton in Sex-Different Cranial Samples of Homo Sapiens: A Preliminary Study

SIMPLE SUMMARY: So far, only a few studies have focused on the issue of the relationship between the size of the occlusal surface of human permanent upper first and second molars and facial robusticity, and in none of them was the area of this surface precisely measured. Additionally, in these studies the sex of the examined skulls was not taken into account. In our study, for the first time, a precise method for obtaining the values of the area of the occlusal surface of these two types of molars was used to assess the relationship mentioned above for adult male and female skulls of Homo sapiens from the 19th century (exhibiting a wide range of robusticity). For each specimen, the grades of massiveness of six regions of the facial skeleton and general facial robusticity were assessed. The results indicated a difference between male and female skulls, including the presence of a significant relationship between the analyzed traits, and most of them (except in relation to the robusticity of the trigone region of the frontal bone in male cranial samples) did not support the “localized-masticatory-stress hypothesis”, suggesting the importance of the occlusal area as the trait influencing the formation of robusticity of the human facial skeleton. ABSTRACT: The aim of this study was to establish whether there is a significant relationship between the total occlusal area (TOCA) of two types of permanent upper molars (first—M(1) and second—M(2)) and facial robusticity, as well as which of the examined facial regions indicate a relationship concerning the grade of their massiveness with the TOCA of analyzed molars in different sex adult Homo sapiens cranial samples. To obtain the values of the TOCA of the molars (n = 145), a morphometric method was performed based on the calibrated digital images of their occlusal surface using ImageJ software. The grades of the massiveness of six facial regions were assessed using qualitative scales of their expression, and an index of general facial robusticity was calculated. Two types of analyses were performed concerning standardized and non-standardized traits to the facial size, including Spearman’s/or Pearson’s correlations and partial rank correlations. The obtained results indicated the presence of a positive relationship between the relative TOCA of M(2)s and the relative general facial robusticity, as well as between the TOCA of both types of molars and the massiveness of trigone region of the facial skeleton in male crania. However, most of the obtained results were not consistent with the assumptions of the “localized masticatory stress hypothesis”.