The human mouth undergoes a significant transformation, evolving from a set of temporary teeth to a full complement of permanent ones. This process involves the loss of the primary dentition (20 teeth) and their replacement by a second, more robust set (32 teeth). Understanding which teeth are shed and which remain for life is key to grasping how the mouth develops.
The Deciduous Set: Which Teeth Fall Out
The 20 primary teeth are naturally lost during childhood. This set includes incisors, canines, and molars, but notably, it contains no premolars. The primary dentition consists of five teeth in each quadrant: a central incisor, a lateral incisor, a canine, a first molar, and a second molar.
Eruption typically begins around six months of age, with the full set usually present by two and a half years old. The shedding process, called exfoliation, generally starts around age six and continues until about age twelve. The lower central incisors, which are often the first to erupt, are usually the first ones lost.
The primary first and second molars are shed to make way for the permanent premolars, a tooth type not present in the deciduous set. This replacement ensures the child’s jaw has adequate space for the larger, permanent teeth.
The Permanent Set and the New Arrivals
The permanent dentition is a set of 32 teeth, including those that replace the primary set and “new arrivals” that erupt into empty jaw space. The teeth that replace the baby teeth are called successional teeth, and they include the eight incisors, four canines, and eight premolars. These 20 teeth take the former positions of their primary counterparts.
The remaining 12 teeth in the permanent set never fall out because they never had a predecessor. These include the eight permanent molars and the four wisdom teeth. The permanent molars erupt directly behind the primary teeth. The first permanent molars are often the first adult teeth to erupt, typically around age six.
The third molars, commonly known as wisdom teeth, are the last teeth to emerge, often between the late teens and early twenties. These four teeth complete the full set, but they frequently lack enough space to fully erupt. This lack of space is why many adults have only 28 teeth.
The Mechanics of Tooth Replacement
The process of a primary tooth falling out is known as root resorption, which is the physiological breakdown and dissolution of the primary tooth’s root structure. The developing permanent tooth below is the primary trigger for this process.
As the permanent tooth grows toward the surface, the dental follicle secretes chemical signals that activate specialized cells called odontoclasts. These odontoclasts progressively dissolve the dentin and cementum of the primary tooth’s root. The root is absorbed, causing the tooth to lose its anchor and become loose.
This replacement mechanism is timed by genetic and hormonal factors. Once the root is sufficiently resorbed, the primary tooth is held only by the surrounding gum tissue, allowing it to be easily exfoliated. The space is then clear for the permanent tooth to erupt into its correct position.
Why Caring for Primary Teeth is Essential
Although primary teeth are temporary, their health is essential for the proper development of the permanent teeth. They act as natural space maintainers, holding the necessary width and depth in the jawbone for the adult teeth to erupt correctly. Premature loss of a primary tooth, often due to decay, can disrupt this alignment.
When a baby tooth is lost too early, adjacent primary teeth can drift into the empty space. This shifting can block the path of the underlying permanent tooth, potentially causing it to erupt misaligned or become impacted. Maintaining the integrity of primary teeth is important for preventing future orthodontic problems, such as crowding or malocclusion.
Healthy primary teeth also play a role in proper chewing, which promotes jawbone and muscle development. Furthermore, they are necessary for clear speech development during early childhood. Protecting these temporary teeth from infection also safeguards the developing permanent tooth bud beneath the gums from potential damage.