Deciduous teeth are also called milk teeth, baby teeth, or temporary teeth. All mammals have a set of deciduous teeth that erupt in infancy and are later replaced by permanent teeth. In humans, there are 20 deciduous teeth that generally come in by the age of three. These teeth fall out over the course of several years during childhood, to be replaced by a set of 28 permanent teeth and in most cases, four wisdom teeth.
Deciduous teeth begin forming in the jaw before a baby is born. By four months of gestation, the buds of all 20 teeth are starting to calcify. The first teeth begin to erupt at around six months of age, starting with the lower central incisors. Top incisors usually appear next, and over the next three years teeth grow in, with the molars appearing last. This period, called “teething,” is often quite painful for babies, causing drooling, irritability, decreased appetite, and increased waking.
By the time a child is three years old, all of the deciduous teeth should have appeared. Although these teeth are temporary, they need to be taken care of as carefully as permanent teeth because they play a role in how permanent teeth are spaced and aligned. If a baby tooth falls out prematurely, particularly a molar, a dentist or orthodontist may place a false spacer tooth so that the hole doesn’t affect the development of permanent teeth.
Deciduous teeth generally start to fall out when a child is five or six years old and they are replaced by permanent teeth, also called succedaneous teeth. The growth of the new teeth follows more or less the same pattern as the growth of baby teeth, starting with the incisors and moving back to the molars, with an added set of molars appearing around seven or eight years of age. In most children, all of the 28 permanent teeth should have appeared by age twelve or thirteen. Most people grow four more molars in late adolescence or early adulthood, called wisdom teeth.
Deciduous teeth differ from permanent teeth in that they are smaller with thinner, whiter enamel, and rounded crowns. The roots of the front baby teeth are longer and more slender than the roots of permanent teeth. On deciduous molars, the roots are also long and narrow, and they are widely flared while the roots on permanent teeth grow more closely together.