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Correction: Ko et al. Timing of Mouse Molar Formation Is Independent of Jaw Length Including Retromolar Space. <i>J. Dev. Biol.</i> 2021, <i>9</i>, 8.

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Unexpected variation of human molar size patterns.

Julia C Boughner1, Denver F Marchiori1, Garnet V Packota2

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Journal of Human Evolution
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Summary

The Inhibitory Cascade Model

Keywords:
Anatomically modern Homo sapiensDental evolutionInhibitory cascade modelTooth developmentTooth eruptionWisdom teeth

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Area of Science:

  • Paleoanthropology
  • Dental Anthropology
  • Evolutionary Biology

Background:

  • The Inhibitory Cascade Model posits that first molar (M1) size predicts second (M2) and third (M3) molar size and development.
  • This model is applied to understand dental evolution in fossil Homo.
  • Its applicability to contemporary humans (Homo sapiens) regarding molar development and eruption is not fully understood.

Purpose of the Study:

  • To investigate the validity of the Inhibitory Cascade Model in modern Homo sapiens.
  • To determine if M1 size predicts M2 and M3 size, initiation, development, and eruption in contemporary humans.
  • To explore the factors influencing human molar size variation.

Main Methods:

  • Radiographic analysis of 323 oral quadrants from contemporary humans.
  • Measurement of mesiodistal crown lengths for M1, M2, and M3.
  • Statistical analysis of molar size ratios and patterns.

Main Results:

  • Observed molar size patterns showed a central tendency around parity (M1=M2=M3) with 13 distinct ratio patterns.
  • Molar size patterns varied between maxilla and mandible and included linear and nonlinear progressions.
  • M1 size alone does not predict M3 size or eruption; M2 size is crucial for predicting M3 size.

Conclusions:

  • Human molar size is genetically influenced but sensitive to localized factors (maxilla vs. mandible).
  • The Inhibitory Cascade Model's predictions for fossil Homo should be approached with caution due to modern human molar variability.
  • A single, stereotypical molar size ratio is not characteristic of contemporary Homo sapiens.