Size and shape variability in human molars during odontogenesis.

Area of Science:

• Developmental biology
• Paleontology
• Anthropology

Background:

• The patterning cascade model (PCM) proposes variability in cusp development based on formation timing.
• Understanding cusp variability aids in reconstructing evolutionary and developmental processes.

Purpose of the Study:

• To test the PCM's predictions regarding cusp size and shape variability in human molars.
• To investigate if variability differences among cusps align with their developmental timing.

Main Methods:

• Utilized micro-computed tomography (µCT) scanning of human maxillary permanent first molars (UM1) and deciduous second molars (um2).
• Reconstructed 3D models of the enamel-dentin junction (EDJ) and outer enamel surface (OES).
• Performed landmark-based 3D geometric morphometric analyses to assess size and shape variability.

Main Results:

• Size variability generally supported the PCM, with later-formed cusps showing less variation, especially in later developmental stages.
• Shape variability did not consistently support the PCM, with UM1 and um2 exhibiting different patterns.
• Differences in size variation were smaller for crown components formed later in odontogenesis.

Conclusions:

• Temporal factors, like cusp initiation order and mineralization duration, influence molar size variability.
• Both topographic and temporal factors likely affect molar shape variability.
• The PCM partially explains size variability but requires refinement to account for shape variability patterns in human molars.