Dental Anthropology

Dental Anthropology is the subdiscipline of biological anthropology, paleoanthropology, and bioarchaeology that investigates the morphology, histology, development, wear, pathology, and biomolecular composition of human and non-human primate teeth. Because dental enamel is the hardest and most heavily mineralized tissue in the vertebrate body—composed of ~96% inorganic calcium phosphate hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) by weight, with only ~1% organic protein (amelogenin, ameloblastin, enamelin) and ~3% water, and zero post-eruptive cellular remodeling—teeth survive in the paleontological and archaeological record far more frequently and in better chemical integrity than porous bone. Furthermore, because tooth crown and root morphology is under polygenic, neutral genetic control (h² ≈ 0.60–0.85) and is locked permanently into place before a tooth erupts into the oral cavity, teeth serve simultaneously as taxonomic "fingerprints" for hominin systematics, neutral genetic proxies for human population migrations (biodistance), circadian kymographs of childhood ontogeny, and time capsules of ancient diets and oral microbiomes.

In placental mammals, the heterodont dentition is partitioned into four functional tooth classes across four quadrants (upper/maxillary left and right; lower/mandibular left and right): chisel-like incisors (I) for nipping, conical canines (C) for puncturing and social display, bicuspid premolars (P, specifically evolutionary P₃ and P₄) for crushing, and multi-cusped molars (M) for grinding.

All catarrhine primates—Old World monkeys (Cercopithecoidea), lesser and great apes, and humans (Hominoidea)—share an identical 2.1.2.3 / 2.1.2.3 adult permanent dental formula (2 incisors, 1 canine, 2 premolars, and 3 molars per quadrant = 32 permanent teeth, preceded in childhood by a 2.1.2 / 2.1.2 deciduous ["milk"] dentition of 20 teeth). However, hominoids (apes and humans) are distinguished from Old World monkeys by their lower molar occlusal crown pattern:

• Bilophodont Molars (Old World Monkeys): Possess four cusps arranged in two parallel transverse ridges (lophs) for leaf-shearing.
• The Dryopithecus Y-5 Pattern (Apes and Humans): First described by William King Gregory (1916) in the Miocene ape Dryopithecus, the lower first molar (M₁) bears five distinct cusps—three on the buccal (cheek) side (protoconid, hypoconid, and hypoconulid) and two on the lingual (tongue) side (metaconid and entoconid)—separated by occlusal fissures that form a "Y" open toward the lingual side where the metaconid (cusp 2) and hypoconid (cusp 3) make direct contact. In modern humans, while M₁ typically retains the ancestral Y-5 pattern, evolutionary postcanine reduction frequently simplifies M₂ and M₃ to a four-cusped cruciform (+4) pattern and causes congenital agenesis of the third molars ("wisdom teeth") in 10–35% of individuals.

To standardize the scoring of heritable, non-metric crown and root variations across archaeological skeletons and fossil hominins, Christy G. Turner II, Christian Nichol, and G. Richard Scott developed the Arizona State University Dental Anthropology System (ASUDAS) in 1991—a set of 24 three-dimensional bronze/epoxy reference plaques scoring over 36 discrete crown and root traits on ordinal scales:

1. Maxillary Central Incisor Shoveling (UI¹): Pronounced mesial and distal lingual marginal ridges enclosing a deep lingual fossa, giving the incisor the profile of a coal shovel (first systematically classified by Aleš Hrdlička in 1920). High-grade shoveling and double-shoveling occur in 70–95% of Northeast Asians and Native Americans (driven in part by positive selection on the EDAR V370A ectodysplasin receptor allele during the Last Glacial Maximum in Beringia/East Asia) and are also diagnostic of classic Homo erectus and Neanderthals.
2. Carabelli's Trait (Cusp of Carabelli on UM¹): An accessory fifth tubercle or cusp located on the mesiolingual surface (protocone) of the upper first molar; occurs in highest frequencies (20–30% full cusp expression) in Western Eurasian (Eurodont) populations.
3. Three-Rooted Lower First Molar (3RM₁): Addition of a supernumerary distolingual root (radix entomolaris) on LM₁; rare in Europe and Africa (<1–2%) but reaches 20–40% in Northeast Asian, Arctic Inuit/Aleut, and Na-Dene Native American populations (and was recently discovered in the 160,000-year-old Xiahe Denisovan mandible from the Tibetan Plateau).
4. Middle Trigonid Crest and Cusp 7: A continuous enamel bridge connecting the protoconid and metaconid on lower molars—present in >90% of Neanderthals and Sima de los Huesos Homo heidelbergensis, making it a primary diagnostic marker for the Neanderthal clade.

Using multivariate Mean Measure of Divergence (MMD) statistics across ASUDAS traits, Christy Turner and Richard Scott partitioned modern global populations into five major dental complexes: Afridont (sub-Saharan Africa: ancestral high cusp numbers, Bushman canine, Y-groove retention), Eurodont (Western Eurasia: simplified two-cusped lower premolars, Carabelli's cusp, 4-cusped LM₂), Sundadont (Southeast Asia, Polynesia, and Jōmon Japan: intermediate shoveling and root retention), Sinodont (Northeast Asia and all Indigenous Native Americans: intensified shoveling, single-rooted UP¹, three-rooted LM₁, and odontomes), and Sahulodont (Australia and Melanesia: large megadont crowns).

During childhood tooth crown formation (amelogenesis), secretory ameloblasts lay down enamel matrix outward from the dentin–enamel junction (DEJ) toward the outer crown surface in strict biological rhythms (discovered by Gustaf Retzius in 1837 and calibrated experimentally via fluorescent tetracycline labeling in primates by Alan Boyde, Christopher Dean, and Tanya Smith):

• Daily Cross-Striations (~24-Hour Circadian Rhythm): Fine microscopic varicosities (~3 to 5 μm apart) along individual enamel prisms formed every 24 hours by the circadian metabolic rhythm of the ameloblast.
• Striae of Retzius (~7 to 10-Day Circaseptan Rhythm) and Surface Perikymata: Darker incremental growth lines formed at a regular multi-day periodicity (the repeat interval, typically 6–7 days in chimpanzees, 7–8 days in Australopithecus, and 7–11 days in Homo). Where striae of Retzius reach the outer labial surface of the tooth crown, they form wave-like horizontal ridges and troughs visible under a hand lens or scanning electron microscope called perikymata.
• The Neonatal Line (Birth Marker): In all deciduous teeth and the cusps of the permanent first molars (M₁, which begin mineralizing just before birth), the physiological trauma of birth and the transition from placental nutrition to neonatal nursing imprint an accentuated, dark Retzius line—the neonatal line. In forensic anthropology and bioarchaeology, the presence of a neonatal line proves that an infant survived birth (live birth vs. stillbirth), and counting the daily cross-striations beyond the neonatal line yields the specific postnatal age at death to the day!

By imaging internal cross-striation repeat intervals via non-destructive phase-contrast synchrotron X-ray microtomography (at the European Synchrotron Radiation Facility in Grenoble) and counting external perikymata on fossil hominin teeth, Christopher Dean and Tanya Smith reconstructed the evolution of human prolonged childhood life history:

• Whereas modern humans erupt their first permanent molar (M₁) at ~6.0 years of age, the Taung Child (Australopithecus africanus) and DIK-1-1 (A. afarensis) erupted M₁ at ~3.2–3.5 years, KNM-WT 15000 ("Turkana Boy", Homo erectus) died at ~8.5 years of age (despite already standing 160 cm tall, equivalent to a 13-year-old modern adolescent!), and Neanderthal juveniles (such as Scladina and El Sidrón) exhibited slightly faster molar crown formation than Homo sapiens, proving that the slow, extended modern human childhood evolved comparatively recently within the genus Homo.

During life, the oral biofilm (dental plaque) on tooth surfaces undergoes continuous mineralization by salivary calcium phosphate ions, forming rock-hard layers of dental calculus (tartar) that entomb food micro-debris, host proteins, and oral bacteria inside a crystalline hydroxyapatite vault impervious to postmortem soil contamination:

• Microbotanical & Dietary Residues: Dissolving small flakes of dental calculus in weak EDTA releases preserved starch grains and phytoliths—proving that Neanderthals at Spy Cave (Belgium) and Shanidar Cave (Iraq) cooked barley and tubers, and that Neanderthals at El Sidrón (Spain) self-medicated a painful dental abscess using salicylic-acid-bearing poplar bark and Penicillium mold (Weyrich et al., 2017).
• Milk Proteins and Dairying Origins: Tandem mass spectrometry (paleoproteomics) of Neolithic and Bronze Age human dental calculus (Warinner et al., 2014) directly detects β-lactoglobulin (BLG) whey peptides specific to cattle, sheep, or goat milk, mapping the spread of prehistoric dairy consumption even in individuals who lacked the genetic lactase-persistence mutation.

1. Turner, C. G., II, Nichol, C. R., & Scott, G. R. (1991). Scoring procedures for key morphological traits of the permanent dentition: The Arizona State University dental anthropology system. In M. A. Kelley & C. S. Larsen (Eds.), Advances in Dental Anthropology (pp. 13–31). New York: Wiley-Liss. https://doi.org/10.1017/9781316156629
2. Dean, C., Leakey, M. G., Reid, D., Schrenk, F., Schwartz, G. T., Stringer, C., & Walker, A. (2001). Growth processes in teeth distinguish modern humans from Homo erectus and earlier hominins. Nature, 414(6864), 628–631. https://doi.org/10.1038/414628a
3. Smith, T. M., Tafforeau, P., Reid, D. J., Pouech, J., Lazzari, V., Zermeno, J. P., ... & Hublin, J.-J. (2010). Dental evidence for ontogenetic differences between modern humans and Neanderthals. Proceedings of the National Academy of Sciences, 107(49), 20923–20928. https://doi.org/10.1073/pnas.1010906107
4. Warinner, C., Rodrigues, J. F. M., Vyas, R., Trachsel, C., Shved, N., Grossmann, J., ... & Cappellini, E. (2014). Pathogens and host immunity in the ancient human oral cavity. Nature Genetics, 46(4), 336–344. https://doi.org/10.1038/ng.2906