Dental Anatomy: Morphology, Tissues and the Arches

Each tooth type has a form specific to its function. Incisors are blade-shaped for cutting. Canines carry a single conical cusp for piercing and tearing. Premolars add a second cusp for crushing. Molars present three to five cusps across a broad occlusal table for grinding.

• Incisors (8 total, 4 upper, 4 lower): Flat crowns with a sharp incisal edge. Central incisors are wider than laterals. The maxillary central incisors are the most variable in size across populations. Shovel-shaped incisors, a deep fossa on the lingual surface, appear at high frequency in East Asian and Indigenous American populations and are a notable morphological marker.
• Canines (4 total): Single pointed cusp, longest root in the permanent dentition. The maxillary canine root is often the last to resorb in fire cases because of its mass. The canine is frequently the last tooth standing in severely decomposed or burned remains.
• Premolars (8 total, permanent dentition only): Two main cusps (buccal and lingual) with a central groove. The maxillary first premolar often has two roots; all others are single-rooted. There are no premolars in the deciduous dentition, so mixed dentition radiographs show premolar development in the alveolar bone while deciduous molars still occupy the surface.
• Molars (12 total, including third molars): Broad multi-cusped crowns with multiple roots. Maxillary molars have three roots; mandibular molars have two. Third molars vary enormously: impacted, congenitally absent, or fully erupted. Their development timeline from formation to root completion spans adolescence to early adulthood and is routinely used in age estimation.

The morphological variation within each type is considerable. The Dahlberg Arizona State University (ASU) dental anthropology system catalogues 45 separate crown and root traits, each scored on a standardised plaque reference, that vary by population and by individual. For an odontologist, these traits become part of the individualising picture when ante-mortem records are absent and biological profiling is the goal.

A longitudinal section exposes four distinct tissues arranged concentrically from the outer crown to the central canal, each with a specific composition, a specific response to heat and acid, and a specific forensic role.

Secondary dentine has direct forensic significance. Odontoblasts, the cells lining the pulp chamber, continue depositing dentine throughout life in response to wear, caries, and thermal insult. This secondary dentine gradually reduces the pulp chamber volume. Kvaal and colleagues (1995) showed that pulp-to-tooth area ratios measured on radiographs correlate with chronological age and can be used to estimate age in adults, a method that requires no physical destruction of the tooth.

Teeth sit in two curved bony ridges: the maxillary (upper) arch in the maxilla and the mandibular (lower) arch in the mandible. Both arches describe a roughly parabolic curve, though the exact form varies by individual and population. The maxillary arch is slightly wider, so upper teeth slightly overlap lower teeth at the front and the buccal cusps of upper molars sit outside their mandibular counterparts. This offset is called Angle's Class I occlusion and is the normal reference point.

Within each arch, position is described by quadrant (upper right, upper left, lower right, lower left) and by designation within the quadrant. Each arch holds eight teeth in a complete dentition: two incisors, one canine, two premolars, and three molars. The midline separates the two halves. Teeth distal to the midline are posterior; teeth toward the midline are anterior.

The human dentition goes through two sets. The deciduous dentition consists of 20 teeth distributed evenly across the four quadrants: two incisors, one canine, and two molars per quadrant (no premolars). They begin to erupt around six months of age, with the mandibular central incisors usually first. By about age three the full deciduous set is in place.

From approximately age six the permanent dentition erupts and the deciduous teeth are progressively resorbed and shed. During the mixed dentition phase, roughly six to twelve years, a child has a combination of both sets. The eruption sequence is relatively predictable: the mandibular first molar and central incisor usually lead, followed by the maxillary central incisor, and then a cascade through the premolars and second molars. Third molars, if they erupt at all, appear from age seventeen onward and are often impacted.

In forensic age estimation the eruption sequence and root formation stages are read from dental radiographs against standard atlases. Demirjian's 1973 system, still widely referenced, assigns a maturity score to each of seven mandibular teeth based on the stage of crown and root completion visible on a panoramic radiograph, then converts the total to an estimated age. In paediatric remains, this is often the most accurate biological age indicator available.

The forensic value of dental identification rests on the accumulation of biological and treatment-related features over time. Developmental markers dominate in younger individuals; in adults with restorative histories the combination of features approaches individual uniqueness.

• Restorations: Amalgam, composite, and gold restorations are individually placed and shaped. Their outline, surface texture, and radiographic density are recorded in ante-mortem records and survive most postmortem conditions intact.
• Missing and supernumerary teeth: Congenital absence (most commonly of maxillary lateral incisors or mandibular second premolars) and extra teeth (mesiodens, distomolars) are traits that narrow identification immediately.
• Rotations and tilt: Teeth that are rotated about their long axis or tilted mesially or distally create characteristic radiographic appearances that are reproduced faithfully in ante-mortem periapical films.
• Wear facets: Attrition from tooth-to-tooth contact and abrasion from dietary or occupational grit create facets whose location on specific cusps reflects occlusal contact patterns unique to each individual.
• Root morphology: Root curvature, bifurcation points, and accessory canals visible on radiographs are genetically determined and do not change after eruption, making them stable identifiers even when crown tissue is damaged.
• Pathological and developmental anomalies: Peg laterals, enamel pearls, dens in dente, taurodontism, and gemination all produce characteristic radiographic silhouettes. A single anomaly on a specific tooth in the correct arch position can produce a match.

The persistence of teeth as identifiers follows directly from enamel's mineral composition and the low organic content of dentine and cementum. Soft tissue, bone, and hair are all destroyed or rendered unreliable by decomposition, immersion, and fire within timescales of months to years depending on conditions. Enamel operates on a different scale. Teeth have been recovered from archaeological sites thousands of years old with crown morphology and root form intact.

In mass-casualty events such as aircraft disasters, the combination of fire, impact, and fragmentation destroys many tissue samples. Dental evidence has provided identifications in cases where fingerprints were consumed, DNA was degraded by heat or water, and visual identification was impossible. The Lockerbie bombing of 1988 and the Bali bombings of 2002 both relied heavily on dental comparison as the primary identification method for a significant fraction of victims.

For an examiner, this durability shifts a fundamental question. The question is not whether teeth will survive; it is whether ante-mortem records exist in a form that allows comparison. A dentition is only as useful for identification as the records against which it is compared. The anatomy covered in this topic is the grammar both the ante-mortem record and the postmortem chart must speak in common.