Teeth eruption is the movement of a tooth from the jawbone to its functional place in the mouth, breaking through the gum tissue. Humans develop two distinct sets of teeth over a lifespan: the 20 primary (baby) teeth and the 32 permanent (adult) teeth. The entire timeline for this process spans from infancy through early adulthood. This article provides the typical timeline for when these teeth emerge, which helps track normal growth and development.
The Standard Timeline for Primary Teeth
The eruption of the 20 primary teeth typically begins around six months of age following a generally predictable sequence. The first teeth to appear are usually the lower central incisors, the bottom two front teeth, emerging between six and ten months. These are quickly followed by the upper central incisors (eight to twelve months) and then the lateral incisors.
The sequence continues with the first molars, which are positioned further back in the mouth, appearing between 13 and 19 months. Next, the canine teeth fill the space between the lateral incisors and the first molars, emerging between 16 and 23 months. The full set is completed by the eruption of the second molars, which generally appear between 25 and 33 months. By age three, all 20 primary teeth are usually present and functional.
Factors Affecting Eruption Timing
The timeline for primary tooth eruption is an average, and significant individual variation is considered normal, with a difference of six months on either side of the average being common. Genetic predisposition is the strongest predictor of eruption timing; children often follow the patterns of their parents regarding early or late teething. The timing of the first tooth can vary widely, appearing as early as four months or not until after the first birthday.
Factors related to overall health and development can influence delayed eruption. Low birth weight, prematurity, and inadequate nutritional status in early life are associated with delayed eruption of primary teeth. Infants with a gestational age of less than 37 weeks or a birth weight under 2,500 grams tend to have a significant delay in the emergence of the first tooth. Less commonly, hormonal imbalances or systemic diseases can also cause teeth to emerge later than the typical range.
Transitioning to Permanent Teeth
The transition from primary to permanent dentition marks the next major phase of the eruption timeline, typically starting around age six. This phase begins with the exfoliation, or shedding, of the primary teeth. Shedding occurs as the developing permanent tooth pushes against and dissolves the root of the baby tooth. The lower central incisors are usually the first baby teeth to be lost.
Simultaneously, the first permanent molars erupt directly behind the last primary molars, without replacing any existing tooth. These large teeth appear around ages six to seven and are important for establishing the adult bite. Following this, the permanent incisors erupt, replacing their primary counterparts between ages six and eight.
The mixed dentition phase, where a child has both primary and permanent teeth, lasts until all 20 primary teeth are shed. The canines and premolars (which replace the primary molars) erupt between ages nine and twelve. The second permanent molars emerge behind the first molars between ages eleven and thirteen, bringing the full permanent set, excluding wisdom teeth, to 28 teeth. Most individuals have this full complement of permanent teeth by ages 12 to 14.