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Tooth, also known as teeth, are hard, calcified structures that are attached to the jawbone and play a crucial role in the digestion and mastication of food. Teeth are present in both humans and many other animal species, with the number of teeth varying depending on the individual and their genetics.

Teeth are made up of four main layers: the enamel, the dentin, the cementum, and the pulp. The enamel is the outermost layer, a hard, translucent substance that protects the tooth from decay and wear. The dentin is the second layer, a dense, bony tissue beneath the enamel. The cementum is a thin layer of bone-like tissue that covers the root of the tooth, helping to anchor it to the jawbone. The pulp is the innermost layer, containing blood vessels, nerves, and connective tissue that supply the tooth with nutrients and facilitate sensation.

In humans, teeth are typically divided into two categories: deciduous teeth, which are temporary and begin to erupt when a child is around six months old, and permanent teeth, which begin to erupt when a child is around six years old. A typical adult human has 32 teeth, including incisors, canines, premolars, and molars, with the first molars usually being the first teeth to erupt.

The loss of teeth, known as tooth loss, is a common occurrence in humans, often resulting from tooth decay, gum disease, or injury. Prosthetic teeth, such as dentures or crowns, are commonly used to replace missing teeth and maintain oral health.