Humans are diphyodonts, meaning they develop two successive sets of teeth over a lifetime. The number of teeth a person loses during childhood is a direct result of replacing the temporary set with a permanent one. This transition requires the complete shedding of the first set to make way for the final, larger set, fundamentally shaping the structure of the adult mouth.
Deciduous Teeth: The Initial Count
The first set of teeth, known as deciduous, primary, or baby teeth, consists of exactly 20 teeth. This set is typically fully present by the time a child reaches about three years of age, split evenly with 10 teeth in the upper jaw and 10 in the lower jaw.
These 20 teeth are composed of three distinct types: incisors, canines, and molars. The primary set lacks premolars, which are teeth found only in adult dentition. Primary teeth function as placeholders, maintaining necessary space in the jawbone for the larger, permanent teeth developing beneath them.
Understanding Tooth Shedding
The process by which the primary teeth are lost is called exfoliation, and it typically begins around the age of six years. This biological mechanism is driven by the developing permanent tooth positioned directly beneath the baby tooth. The erupting permanent tooth exerts pressure that triggers the roots of the primary tooth to dissolve.
Specialized cells called odontoclasts are responsible for this physiological root resorption. These cells systematically break down the hard tissues of the primary tooth’s root and the surrounding periodontal ligament. This resorption occurs in intermittent periods of activity and rest.
As the root structure is gradually absorbed, the primary tooth loses its anchorage, causing it to become loose and eventually fall out. The general sequence of shedding usually mirrors the order of eruption, starting with the central incisors. The process continues until approximately age 12, when the last of the 20 primary teeth are typically replaced.
The Complete Set of Permanent Teeth
The permanent dentition is the second and final set of teeth, designed to last throughout adulthood. A complete set of adult teeth totals 32, which is 12 more teeth than the primary set. This set includes incisors, canines, premolars, and molars, split evenly with 16 teeth in the upper jaw and 16 in the lower jaw.
The increase in count comes from the addition of premolars and extra molars. The permanent set introduces eight premolars, which replace the primary molars, and four extra molars in each jaw (first, second, and third molars). This results in a total of 12 molars in the adult mouth.
The third molars, commonly called wisdom teeth, are the last to emerge, typically between the ages of 17 and 21. Because they may not always have enough room to fully erupt, they are often removed. Consequently, many adults have a functional count of 28 teeth if their wisdom teeth are absent or surgically removed.