Deciduous teeth Deciduous teeth Deciduous teeth, commonly known as milk teeth, baby teeth and temporary teeth, are the first set of teeth in the growth development of humans and other diphyodont mammals. 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 start to form during the embryo phase of human life. The development of primary teeth starts at the sixth week of tooth development as the dental lamina.
Dentition animals with two successions of teeth (deciduous, permanent) is referred to as "diphyodont", while the dentition of animals with only one set of teeth throughout life is "monophyodont". The dentition of animals in which the teeth are continuously discarded and replaced throughout life is termed "polyphyodont". The evolutionary origin of the vertebrate dentition remains contentious. Current theories suggest either an "outside-in" or "inside-out" evolutionary origin to teeth, with the dentition arising from odontodes on the skin surface moving into the mouth, or vice versa. Despite this debate, it is accepted that vertebrate teeth are homologous to the dermal denticles found