While babies only have primary teeth visible in the mouth, the foundation for their permanent teeth is already established. Humans develop two sets of teeth during their lifetime: the 20 primary, or deciduous, teeth, and the 32 permanent, or adult, teeth. At birth, a baby’s jaw already holds the developing structures for both sets of teeth. The primary teeth are the first to emerge, serving the child’s needs for chewing and speech throughout early childhood.
The Hidden Development of Permanent Teeth
The journey of the permanent teeth begins deep within the jawbone, nestled beneath the primary teeth. These teeth start forming as early as five weeks into gestation, with the foundation for some developing even before the baby is born. They exist as tooth buds, or tooth germs, which are clusters of cells that mature into a complete tooth structure. These permanent tooth buds are positioned directly underneath their corresponding primary predecessors.
This anatomical arrangement coordinates the process of losing baby teeth later in life. The developing permanent teeth are separated from the primary tooth’s root by a thin layer of bone. As the child grows, the permanent tooth structure matures and begins its upward movement toward the surface. This development ensures the adult teeth are ready to erupt when replacement is needed.
Timeline for Primary Tooth Eruption and Shedding
A child will eventually have 20 primary teeth, consisting of incisors, canines, and molars, with 10 teeth in the upper jaw and 10 in the lower. The process of teeth breaking through the gumline, known as eruption, starts around six months of age, though the timing can vary widely. The lower central incisors are usually the first to appear, followed by the upper central incisors. The entire set of primary teeth is often completed by the age of three years.
The primary teeth remain in place for several years, holding space in the jaw for the larger permanent teeth. Shedding, or exfoliation, of these primary teeth begins around age six, though it can be earlier or later. The loss of the baby teeth usually follows the same order in which they erupted, starting with the front incisors. This phase continues until around age 12, when the last primary teeth are lost.
The Arrival of Permanent Teeth
The transition from the primary dentition to the permanent dentition is a coordinated biological event. As the permanent tooth begins to move upward, it exerts pressure against the root of the baby tooth above it. This pressure stimulates specialized cells called odontoclasts, which begin physiological root resorption. The odontoclasts dissolve the primary tooth’s root structure, causing the tooth to loosen.
As the root of the primary tooth is reabsorbed, the tooth becomes loose and eventually falls out, leaving space for the permanent successor to emerge. The first permanent teeth to appear are often the “six-year molars,” which erupt behind the last primary molars, rather than replacing a baby tooth. These four first molars establish the correct bite and jaw alignment for the rest of the permanent teeth. The full set of 32 permanent teeth, including the third molars (wisdom teeth), can take until the late teens or early twenties to completely erupt.