Patient-friendly definition from the DentistsDirectory.org dental glossary.
Deciduous teeth — commonly called baby teeth, milk teeth, or primary teeth — are the first set of 20 teeth that develop and erupt in childhood. The first tooth typically appears around 6 months of age, and the full set of 20 is usually in place by age 3. They begin to fall out and be replaced by permanent teeth from around age 6, with the process usually complete by the early teenage years.
A common and harmful misconception is that baby teeth do not need care because they will fall out anyway. In reality, deciduous teeth serve critical functions: they allow children to chew and eat a varied diet properly; they play a significant role in the development of speech sounds; and — most importantly — they hold space in the jaw for the permanent teeth developing beneath them. If a baby tooth is lost too early due to decay or injury, the neighbouring teeth can drift into the gap, blocking the permanent tooth from erupting in its correct position and often creating the need for orthodontic treatment.
The American Academy of Pediatric Dentistry recommends a child's first dental visit by age one or within six months of the first tooth erupting. Decay in baby teeth can spread rapidly — partly because their enamel is thinner than adult enamel — and can affect the developing permanent tooth beneath. Brush with a rice-grain-sized smear of fluoride toothpaste from the first tooth's appearance, increasing to a pea-sized amount around age 3. Avoid prolonged bottle feeding at night, which pools milk or juice against the teeth and is a primary cause of early childhood tooth decay.