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A tooth consists of three main regions: the crown (visible above the gums and covered by enamel), the neck (a constricted area connecting crown to root), and the root (anchored in the jawbone). The crown's shape varies by tooth type to enable cutting, tearing, or grinding. The root secures the tooth firmly in place within the jaw.

Root number varies by tooth type. Incisors, canines, and lower premolars have single roots. Upper premolars and the first two lower molars typically have two roots, while upper molars generally have three roots. This variation allows different teeth to perform specialized functions in food processing.

Enamel is the hardest substance in the human body, composed primarily of hydroxyapatite, a calcium phosphate compound. It covers the tooth crown and protects against decay and physical damage. Its translucent property allows the underlying dentin color to show through, giving teeth their characteristic appearance.

Dentin is a white-to-yellowish, bone-like substance that comprises most of the tooth's internal structure beneath the enamel. Though less hard than enamel, it resists wear effectively. Dentin contains radial striations called dentinal tubules that house odontoblast processes, which secrete and maintain dentin throughout life.

Nerves and blood vessels enter the tooth through the apical foramen, an opening at the root's tip. The trigeminal nerve supplies sensation, with the mandibular nerve serving lower teeth and the maxillary nerve serving upper teeth. The maxillary artery supplies upper teeth while the inferior alveolar artery supplies lower teeth, both branches of the external carotid artery.

The pulp cavity is a space within the tooth filled with soft connective tissue containing blood vessels and nerves. It extends into the root as the root canal, which connects to the apical foramen. Cementum, a calcified connective tissue, covers the root and anchors the tooth to the periodontal ligament.

Tooth sensitivity, or dentin hypersensitivity, occurs when enamel wears down or gum lines recede, exposing the underlying dentin layer. This exposure makes teeth painfully sensitive to cold, hot, sweet, or acidic stimuli. Unlike dental caries caused by bacteria, sensitivity results from physical enamel loss or gum recession.