Date of Graduation

5-2024

Document Type

Thesis

Degree Name

Master of Arts in Anthropology (MA)

Degree Level

Graduate

Department

Anthropology

Advisor/Mentor

Kathleen S. Paul

Committee Member

Lucas K. Delezene

Second Committee Member

Peter S. Ungar

Keywords

Cusp Patterning; Dental Development; Dental Morphology; Enamel Knot; Patterning Cascade Model; Premolars

Abstract

Human mandibular premolars represent a morphologically transitional tooth class, possessing a relatively caniniform third premolar (P3) and a more molariform fourth premolar (P4). Marked variation in cusp height and lingual cusp number are characteristics unique to these postcanine teeth. The aim of this study is to determine if human premolar variation aligns with predictions outlined by the patterning cascade model (PCM). The PCM posits that tooth size and enamel knot spacing/surrounding inhibitory fields (approximated by cusp tip positioning) play a role in determining ultimate crown morphology, providing a predictive framework for examining crown variation within and between individuals. While there has been considerable research focused on bunodont, quadrate molars, there is a significant lack of studies on human mandibular premolar anatomy and development. Importantly, mandibular premolars may be a more appropriate tooth class to test predictions of the PCM, as their cusp height disparity makes them similar in morphology to seal teeth, to which the model was originally applied. Using three-dimensional (3D) scans and two-dimensional (2D) images of mandibular casts representing contemporary Solomon Islander individuals (n=63), We collected 2D crown area, cusp area, and ICD measurements, as well as 3D intercusp distance (ICD) measurements to account for differential cusp height. To control for size variation, relative cusp areas (RCA) and relative ICDs (RICD) were calculated and subjected to ANOVAs, independent sample t-tests, dichotomized generalized linear model regressions, and linear regressions to determine the variables with significant relationships to later-forming lingual cusp number. RICD between the mesiolingual cusp and its distal neighbor differ significantly as a function of lingual cusp number, with two lingual cusped premolars exhibiting greater RICDs on average than three lingual cusped premolars. These results were consistent across the 2D and 3D datasets for P3s and P4s. For P4s, individuals possessing two versus three lingual cusps differ significantly in 2D buccal to mesiolingual cusp RICD, with two lingual cusped teeth exhibiting greater RICDs, on average. Models involving RCAs of the mesiolingual cusp and its distal neighbor were significant, with three lingual cusped P4s having smaller RCAs than two lingual cusped P4s. These findings align with PCM expectations and demonstrate the potential use of RICD and RCA as predictors for lingual cusp number. The mesiolingual cusp was involved in all significant findings, therefore the enamel knot placement and inhibitory zone for this cusp seem to have the greatest influence on ultimate crown morphology in mandibular premolars. Generally, 2D and 3D analyses yielded similar results, but the strength of relationships was greater for 3D measurements across P3 cusps with significant height disparities.

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