Role of the mandibular first molar in the development of the supraorbital region in apes and humans.
Our previous studies in apes and humans have demonstrated that the development of the supraorbital ridge is a direct consequence of masticatory forces. The smaller the power arm/load arm ratio of the mandible, the greater the force exerted by the temporalis muscle and the larger the supraorbital ridge. The purpose of the present study is to further elucidate the role of the masticatory apparatus, in particular the role of the first mandibular molar. Measurements of the size of the supraorbital ridges in ape skulls and in human skulls from Tuscany, Italy and St. Lawrence Island, Alaska, were determined using parasagittal CAT scans as in our previous studies. For the purpose of this study, the mesio-distal and buccolingual dimensions of the first molar were measured from the actual tooth in all cases. Statistical analysis shows a positive correlation between the mesio-distal dimension of the mandibular first molar and the size of the ridge in humans (r = 0.61, p < 0.005) and in apes (r = 0.79, p < 0.01), which explains much of the variation in the size of the supraorbital ridge, 37% (0.61(2)) in humans and 62% (0.79(2)) in apes. The role of the mandibular first molar differs in humans versus apes because of differences in masticatory mechanics.
Hilloowala
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Department of Anatomy, West Virginia University, Morgantown.
Trent
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R
Dal Pozzo
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G
D000328:Adult; D000818:Animals; D002508:Cephalometry; D005260:Female; D006071:Gorilla gorilla; D006801:Humans; D008297:Male; D008334:Mandible / Q000254:growth & development*; D008409:Mastication / Q000502:physiology; D008445:Maxillofacial Development / Q000502:physiology*; D008963:Molar / Q000254:growth & development*; D009915:Orbit / Q000254:growth & development*; D002679:Pan troglodytes; D011148:Pongo pygmaeus; D013045:Species Specificity