The Patterning Cascade Model and Human Mandibular Premolar Variation

The patterning cascade model (PCM) provides a predictive framework for examining crown variation and posits that tooth size and enamel knot spacing, along with surrounding inhibitory fields, strongly influence crown morphology. The aim of this study is to determine if mandibular premolar variation aligns with predictions derived from the PCM.

Using three-dimensional (3D) scans and two-dimensional (2D) images of dental casts representing a contemporary human sample (n = 63), we collected crown area, cusp area, and intercusp distance measurements, including 3D distances to account for differential cusp height. After controlling for size variation, relative measurements were subjected to analyses of variance, t-tests, dichotomized generalized linear model regressions, and linear regressions to examine their relationship with lingual cusp number.

Relative intercusp distance between the mesiolingual cusp and its distal neighbor differs significantly between two and three lingual cusped premolars; those with two lingual cusps exhibit greater distance, on average. Two lingual cusped P₄s exhibit greater 2D distance between the buccal and mesiolingual cusps. Models involving the relative area of the mesiolingual cusp and its distal neighbor were significant, with three lingual cusped P₄s exhibiting smaller cusps.

These findings partially align with PCM-derived expectations. The mesiolingual cusp is involved in all significant findings, which suggests its precursory enamel knot placement and inhibitory zoning have the greatest influence on mandibular premolar morphology. Generally, 2D and 3D analyses yield similar results, but the strength of the relationship is greater for 3D measurements in P₃s, which are characterized by marked cusp height disparities.