Deciduous teeth, otherwise known as milk teeth, baby teeth, temporary teeth and now more commonly primary teeth, are the first set of teeth in the growth development of humans, which is called teething. They develop during the embryonic stage of development and erupt—that is, they become visible in the mouth—during infancy. They are usually lost and replaced by permanent teeth, but in the absence of permanent replacements, they can remain functional for many years.
Primary teeth are smaller, whiter, and prone to wear than permanent teeth. Around six months after birth, the first teeth erupt, and the primary dentition is complete by two and a half years old. Shedding starts around age five or six and is done by age thirteen. The primary teeth are gone when the roots of the permanent teeth grow toward the mouth cavity.
In humans, each jaw has four incisors, two canines, and four molars, totaling 20 teeth in the primary dentition. The premolars, also known as bicuspid teeth, take the place of the primary molars in the adult dentition. There are 32 teeth in the permanent dentition. The 12 adult molars erupt behind the primary teeth and do not replace any of these.