Dental Anatomy

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DENTAL ANATOMY

MAXILLARY TEETH

Maxillary central incisor

Maxillary lateral incisor

Maxillary canine

Maxillary first premolar

Maxillary second premolar

Maxillary first molar

Maxillary second molar

MANDIBULAR TEETH

Mandibular central incisor

Mandibular lateral incisor

Mandibular canine

Mandibular first premolar

Mandibular second premolar

Mandibular first molar

Mandibular second molar

Third molars

ENAMEL

Enamel composition: 96% mineral (inorganic), 4% organic (protein). Enamel is derived from the ectoderm and formed by ameloblasts which differentiate from the inner enamel epithelium. When protein and water are removed from the secreted matrix, hydroxyapatite crystals are formed, tightly stacked into enamel rods/prisms. At the cusp tips the crystalline structure becomes irregular, termed gnarled enamel.

Enamel is not considered a viable tissue and cannot heal itself, but can undergo remineralization provided the damage is not extensive. Enamel does not have any nerve innervation on nutrient supply. The incremental lines formed by changes in daily apposition are called daily periodic bands. More pronounced weekly bands are called lines/striae of Retzius. Perikymata are lines of Retzius that reach the surface of enamel and are visible externally. A distinct line is formed around the time of birth called the neonatal line. Hunter–Schreger bands are alternating light and dark zones produced as an optical phenomenon (not structural) during light microscopy of longitudinal cut sections.

DENTIN

Dentin has a lower mineral (70%) and a higher organic (30%) composition compared to enamel, making it harder than bone but softer than enamel. It is derived from the ectomesenchyme (neural crest tissue), and is formed by odontoblasts which differentiate from the dental papilla. Dentin is considered a viable structure, innervated by cellular extensions (odontoblast process or Tomes’s fibers) that interface with neurons and retain the ability to repair itself. The incremental lines formed by changes in the daily apposition are called lines/striae of von Ebner (lines of Owen). A distinct line is formed around the time of birth called the neonatal line.

The initial 150 microns of dentin formed is called mantle dentin. A nidus starts the mineralization process, leading to “globules” of mineralized dentin that eventually fuse together into circumpulpal dentin (majority of dentin). Most of the circumpulpal dentin that forms in between dentin tubules is termed intertubular dentin. If these globules fail to fuse they can leave hypomineralized interglobular dentin between them. The odontoblastic processes shrink away leaving space for hypermineralized peritubular dentin. When the tubules completely occlude with peritubular dentine it’s called sclerotic dentin. Sclerotic dentin increases with age, leading to less dentin sensitivity. Dentin sclerosis will slow down caries progression. Reparative dentine is formed by odontoblast-like cells from the pulpal tissue in response to pulpal injury.

Dentin can also be classified according to the time it was formed. Primary dentin is formed up to the completion of root development. Secondary dentin refers to any dentin formed after root completion that’s not a result of trauma. Tertiary dentin forms in response to some insult (caries, restoration, attrition, abrasions, erosion etc.).

Dentin sensitivity

The most widely accepted mechanism for dental pain is explained by the hydrodynamic theory: pain is perceived when fluid moves inside dentin tubules triggering mechanoreceptors near the predentin. Temperature changes, air movement, and osmotic pressure can push and pull fluid through the tubular system. Dentin sensitivity is very common. Only a small area of dentin needs to be exposed to the environment to initiate a response.

Any treatment that can reduce this fluid movement by occluding the tubules may help reduce sensitivity. Many treatments have been proposed for dentin sensitivity including topical fluoride, fluoride rinses, silver diamine fluoride, oxalate solutions, dentin bonding agents, sealants, iontophoresis, and desensitizing toothpastes.

CEMENTUM

Cementum has the lowest proportion of inorganic matrix (50:50) and is therefore the least resistant to acidic dissolution. It is derived from the ectomesenchyme (neural crest tissue), formed by cementoblasts which differentiate from the dental follicle. Like dentine, cementum is considered a viable structure able to undergo repair. The incremental lines formed by changes in the daily apposition are called resting lines. Mature cementum is only about 10 microns thick and covers radicular (root surface) dentin. It provides attachment for the Sharpey’s fibers of the PDL, protects the root from resorption, and apical deposition of cementum allows for eruptive movements.

EMBRASURES AND CONTACTS

Embrasures are triangle shaped spaces located interproximally all round the contact point between two adjacent teeth. There are 4 embrasures for each contact area. Gingival tissue generally fills the cervical embrasure and is “col” shaped when viewed in a faciolingual cross section. The embrasures function to make a spillway for food and to protect the gingiva from trauma. The height of contour, the thickest portion of the tooth forms the contact area on the mesial and distal surfaces. These stabilize the dental arch and prevent food from pushing into the interproximal areas, protecting the periodontal tissues. Loss of optimal contacts can lead to periodontal disease, food impaction, and drifting of teeth.

SALIVA

Saliva is the body’s main protection against caries. If there is a hindrance in the saliva quality or quantity it can cause prolonged pH depression, decreased antibacterial effects, decreased clearing of bacteria, and decreased availability of ions. Saliva stimulants like gums and paraffin waxes or a saliva substitute can be of some benefit. The mechanism by which it guards the teeth:

Bacterial clearance – bacteria become stuck to glycoproteins in saliva and are swallowed.

Buffering – saliva contains urea and other buffers to raise pH.

Antimicrobial proteins and antibodies – lysozyme, lactoferrin, lactoperoxidase, secretory IgA.

Remineralization – calcium, phosphate, potassium and fluoride ions are readily available.

Xylitol is a natural sugar from birch trees that keeps sucrose from binding with strep mutans, and the bacterial cell cannot ferment the xylitol.