The physical stock, mode of life—sedentary or nomadic—and food complex are all major factors basic to dental health. Incidence of caries varies directly with the ratio of carbohydrate, especially finely prepared cereals and nuts, to protein and fat intake ; the contrast between the Sioux and sub-Suian groups (below) is a significant example. Preservation of the anatomy and physiology of the masticating mechanism is the sine qua non of dental health, i.e., mutilation through attrition to a large degree in primitive races—through decay and loss in modern stocks—accelerates a vicious cycle of which caries is the center. The natural history of Homo sapiens shows that the mode of preparation of food is frequently the major factor in caries causation. Society, in every human culture, is both homogeneous and conservative, and especially so with the entrenched mechanized economy of Western civilization. Hence both individual and group are quite helpless in changing the food-habit pattern. Therefore, the human dentition will tend to greater pathosis, degeneracy and involution, as few, if any, geographical areas are untouched by deleterious Western processed foods.
Data compiled from a uniform examination of 7,942 males—average age 18 —well representative of a cross-section of American youth, showed that individual teeth differ markedly in susceptibility to caries. First molars are most susceptible —the mandibular being 2.36 times that of the maxillary. At this age, the affections of mandibular first molars are more numerous than the combined total lesions in all other teeth-17.7 percent of M1 were lost. The eight mandibular anterior teeth are highly resistant to caries, their average susceptibility compared with the most susceptible tooth being as 1 to 39. The resistance of the maxillary cuspid to caries is high, its susceptibility compared with that of the mandibular first molar being as 1 to 29. Occurrence of caries is bilaterally symmetrical, owing to similarity in intrinsic factors (morphology) as well as in extrinsic factors (physiology and environment). Remnants of enamel cuticle serve as nidi and supporting membrane for proliferation of heavy microbiotic blankets on the surfaces of teeth. Culsdesac of the cuticle are invaginated into every pit and fissure ; some remnants remain throughout the life of the individual. When intact, cuticle is resistant to both acid and alkali. On approximal surfaces, the initial carious lesion is at the cervical border of the physiologically produced facet—at the margin of the cuticle ; in sulci and pits, the lesion begins most often at the peripheral border of the culdesac and proceeds alongside the invaginated sac. Microorganisms are first in intimate relation with the enamel surface ; then breaches occur, V-shaped etchings are produced in the enamel, and bacteria adhere in the depressions as superficial layers are continuously decalcified and removed. Bacteria do not penetrate deeply into the inter-columnar interstices produced by their fermentation acid. A short bacillary form may be seen ” under 2000 diameters ” in fracture lines. Dentinal tubuli are invaded by anerobes before decalcification of dentin matrix. There is strong correlation between incidence of caries in different teeth and their respective surfaces, and intricacy of structure of the teeth, with which structural faults are constantly associated. The role of food debris—removed neither physiologically nor artificially—in enzymic (fermentative) destruction of enamel is demonstrated clinically on the plain buccal surfaces of upper second and third molars. Studies of the incidence and distribution of caries, in homogeneous races stabilized in definite habitats, and with immutable food habits and mode of life for countless generations, gave findings summarized below :
Eskimo. In group of 324 Eskimo crania, in National Museum, incidence of caries approximately 1 percent.
California. In 300 crania of pre-Spanish, or early post-Spanish California aborigines, in Museum of Anthropology of University of California (138 from Santa Barbara archipelago and mainland ; 104 from San Francisco Bay and central coast ; 50 from Great Valley ; 8 from Nevada slope of Sierra), there was peculiarly close adaptation to native habitat ; food complex omnivorous ; acorn meal most widely used staple, technique of preparation extending to that of seeds and flesh. (a) Of Santa Barbara group, 30 percent afflicted with caries ; (b) over 50 percent of lesions occurred on approximo-cervical areas, in persons of midlife or older and in teeth worn beyond contact points, which induced food impaction ; (c) exhibited uniformly larger carious lesions than other sub-groups ; sedentary people ; diet consisted mainly of sea-food, also mountain sheep, seeds, acorns, and edible roots. (d) San Francisco Bay people comparatively free from caries ; 14 percent of persons affected—approximo-cervical locus ; (e) staple food, mollusks; attrition in fourth degree, with pernicious sequelae, characterizes pathology of teeth. (f) In Great Valley group incidence of caries highest-36 percent ; (g) in contrast with other sub-groups, 46 percent of lesions on occlusal surfaces ; only two cases of caries—in all California crania in individuals under twenty-five—found in this group ; (h) group too small for definite conclusions, but causative agent of caries acted earlier, occurred in higher percent of individuals, localized chiefly on occlusal surfaces, and ratio of plant to animal food highest. (i) Nevada skulls free from caries.
North America. Crania, of four representative North American stocks, in National Museum. Sioux had most superb osseous and dental systems ; as true nomads, followed buffalo and subsisted on its flesh; incidence of caries about 8 percent. Arikara, sub-Suian group ; sedentary life on banks of Missouri River and tributaries ; raised maize, squash; intake of vegetal food much higher than of protein. Incidence of caries above 40 percent. Comparison of Sioux and Arikara very important matter in study of basic cause of caries. A pre-Columbian Algonquin tribe, living in Kentucky, subsisted on mollusks and game; teeth exhibited universal and extensive attrition, which is adverse to caries until teeth are worn beyond contact points ; incidence of caries low. Zuni, sedentary agricultural people, living in communal houses in villages; subsisted largely on crops of maize and squash, with wild turkey ; closely inbred, very conservative group ; physically not very vigorous ; dentition evidences involution, not a few teeth diminutive, aberrant, or hypoplastic; caries 75 percent. Zuni now live in their pueblos as in the time of Coronado (1540).
South America. In group of 329 pre-Spanish Peruvian skulls, in Museum of Anthropology, University of California, 35 percent have one or more carious teeth. Youth and young adults relatively free from caries ; in middle and old ages, incidence increased directly with age ; locus predominantly approximo-cervical ; anterior teeth practically free from caries ; whole kernels of parched maize main staple diet of masses.
Micronesia. In a group of 106 ancient Micronesian crania from Guam, in Bishop Museum, Honolulu, 18 percent evidence caries. Habitat tropical, insular, and isolated. Indigenous diet exclusively vegetal and fish. Of forty-two carious teeth, 60 percent of senile type—caries du collet; 40 percent localized in pits. Defectively formed or hypoplastic teeth not symptomatic of caries. Specific exciting environmental cause existed before either sound or hypoplastic tooth succumbed to carious decalcifying process. Children and youth free from caries.
Polynesia. Crania of ancient Polynesians (Hawaiians), in Bishop Museum, Honolulu, indicated Hawaiians comparatively immune to caries until middle life. Distribution of caries and food habits analogous to those of people of ancient Guam, though of entirely different racial stock.
Ancient Egypt. Examination of skeletal collection from Egypt, in the Museum of Anthropology, University of California. In predynastic times, widespread attrition of teeth, but negative evidence of caries. Predynastic man, in Nile valley, subsisted on coarse cereals, tubers, fish ; in later epochs, incidence of 12 percent or more of caries only in persons past midlife; 60 percent of lesions initiated at proximo-cervix—after teeth had been worn beyond contact points, or after slight migration, both of which conditions permitted approximal food impaction ; only few pit cavities ; only postcuspid teeth affected. Caries prevalent in upper social strata in later epochs ; with flowering of civilization, diet became varied, luxuriant, refined, for upper classes especially ; teeth functioned less in Byzantine and Coptic eras.
References: numerous, since 1923, in the leading American journals in dentistry and anthropology.