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Since the 1890s oral biological researchers have been interested in the idea that strenuous mastication of unprocessed food will stimulate proper oral-facial growth and occlusal relationships. Conversely, lack of such function due to consumption of refined food is one hypothesis among many for the etiology of malocclusion in industrialized humans. Adequately controlled experimental testing of the idea has been limited to rats. To investigate the "disuse" theory in a larger-bodied and more occlusally relevant animal model, we raised four Yucatan minipigs from weaning on hard diet (HD) and another four on softened but equivalent diet (SD). The animals were monitored for eight months, sacrificed, and then occlusal and osteometric data collected. Variations due to dietary regime are pervasive and not due to caries, periodontitis, or attrition differences. Whereas HD body weight is 10% greater than SD, the deep masseter is 25% greater, with similar disproportion in superficial masseter and temporalis weight. Facial prognathism, arch narrowness, tooth crowding/maleruption and posterior cranial tapering are markedly different in the two groups. A curious posterior torsional difference in the mandibular rami, as well as broadness and flatness of the mandibular symphysis, also occur in SD. We performed a Q-mode principal coordinates analysis of the 19 logged variables for the specimens, bootstrapping the variable list, to demonstrate a statistically significant (P < .01) overall pattern of dramatic differences. Having controlled other celebrated orthodontic etiologies (genetic background, respiratory mode, infectious degeneration and interproximal attrition), these results support the proposition that dietary consistency relates directly to human craniofacial growth.

Of a sample of 40 baboons, 24 were given soft experimental diet, removing masticatory stress, for a 2-year period during growth. In oral-facial and dental occlusal structures, the experimental animals showed significantly elevated variability, reduced correlations, and some disruption of normal occlusion.

Among 43 squirrel monkeys (Saimiri sciureus) raised either on naturally tough or on artificially soft foods, there are significant differences in occlusal features. Animals raised on soft foods show more rotated and displaced teeth, crowded premolars, and absolutely and relatively narrower dental arches. Dietary consistency may be a determinant of occlusal health.

Moderate differences in the hardness of diet are related to significant differences in maxillary width and other measures of facial size. Probably even more important is a relationship to the coordination of growth of different parts of the dentofacial complex. Muscular stimulation mediated through occlusal function seems to play a significant role in the coordinated development of facial structures.

Forty-three squirrel monkeys were raised on either naturally tough or artificially softened foods. Significant differences were found in craniofacial and occlusal development between hard and soft diet animals: The latter exhibit maxillary arch narrowing, palatal arching, rotated and displaced teeth, crowded premolars, and retarded cranial bone mineralization. The correlates in results between soft diet squirrel monkeys and American children suggest that dietary consistency may be an important factor in human craniofacial growth.

The infratemporal fossa grows allomorphically in primates at a faster rate than general cranial and inferred body size. The coefficient of allometry approximates 1.5 across most primate groups, suggesting direct scaling of the muscsulus temporalis cross-sectional area to body mass. This coefficient is larger than 1.5 in Lorisoidea and Ceboidea. Mediolateral relative growth of the infratemporal passage that accommodates m. temporalis rather than antero-posterior growth absorbs a disproportionate amount of this expansion. Likewise, infratemporal fossa breath is positively allometric to tooth size, especially in insectivorous, frugivorous and folivorous primate samples that are homogeneous with respect tok diet. The seemingly growth-related positive relations between tooth size and distal placement of the zygomatic root that is consistent over the cumulative sample is erased by controlling for diet. Increased relative amounts of m. temporalis per unit of dental occlusal area is indicated in larger-bodied forms; increasing crown height may be a mechanism to adjust for this.