The primary dentition contains 20 teeth. These baby teeth, also called deciduous teeth, are divided evenly between the upper and lower jaws, with 10 teeth in each. That’s fewer than the 32 teeth in a full set of adult teeth, partly because children’s jaws are too small to accommodate premolars or third molars (wisdom teeth).
Types of Primary Teeth
The 20 primary teeth are organized into four quadrants: upper right, upper left, lower right, and lower left. Each quadrant holds five teeth in the same arrangement:
- 2 incisors (one central, one lateral): the flat front teeth used for biting
- 1 canine: the pointed tooth next to the incisors, used for tearing food
- 2 molars (first and second): the wider back teeth used for grinding
Across all four quadrants, that gives a child 8 incisors, 4 canines, and 8 molars. Notably, there are no premolars in the primary set. The spaces where premolars will eventually sit are occupied by the primary molars, which are later replaced by the permanent premolars and molars.
When Primary Teeth Come In
The first baby tooth typically appears around 7 months of age, though it can show up as early as 3 months or as late as 13 months. The lower central incisors are usually first, followed closely by the upper central incisors around 9 months. From there, the teeth follow a fairly predictable sequence over the next year and a half.
Lateral incisors arrive between roughly 10 and 12 months. The first molars come in around 15 to 16 months, followed by the canines at about 17 to 18 months. The second molars are the last to appear, typically breaking through between 23 and 25 months. Most children have their full set of 20 primary teeth by age 2 to 2½.
If no teeth have appeared by 10 months of age (40 weeks), pediatric dentists generally consider this delayed eruption. In many cases the teeth simply arrive on a slower schedule, but delayed eruption can occasionally signal an underlying issue worth checking.
How Primary Teeth Are Labeled
Unlike permanent teeth, which are numbered 1 through 32, primary teeth are identified by letters. In the Universal Numbering System used in the United States, the 20 baby teeth are labeled A through T. The lettering starts with the upper right second molar (A) and moves across the top to the upper left second molar (J), then drops to the lower left second molar (K) and continues across to the lower right second molar (T).
When Primary Teeth Fall Out
Children begin losing their baby teeth around age 6, and the process stretches until about age 12. The order of shedding roughly mirrors the order of eruption: the teeth that came in first tend to fall out first.
The central incisors (upper and lower) are shed between ages 6 and 7. Lateral incisors follow at 7 to 8. The canines and molars take longer, with first molars falling out between 9 and 11 and canines and second molars between 10 and 12. Lower teeth generally shed slightly earlier than their upper counterparts, though the difference is small.
Why Primary Teeth Matter for Development
Baby teeth do more than chew food. They hold space in the jaw for the permanent teeth developing beneath them. When a primary tooth is lost too early, whether from decay, injury, or extraction, the neighboring teeth can drift into the gap. That drift reduces the space available for the adult tooth, which can lead to crowding, impacted teeth, or misalignment that may require orthodontic treatment later.
Primary teeth also play a role in speech development. The front teeth help children form certain sounds correctly, and gaps from early tooth loss can affect pronunciation during a critical learning window. For all these reasons, dentists often place a space maintainer if a baby tooth is lost well before its replacement is ready to come in. The device simply keeps the surrounding teeth from shifting until the permanent tooth erupts on its own.
Both the American Academy of Pediatric Dentistry and the American Dental Association recommend that a child’s first dental visit happen within 6 months of the first tooth appearing, and no later than 12 months of age.
Can Children Have Fewer or More Than 20?
Variations in the primary dentition are uncommon. Congenitally missing baby teeth (hypodontia) affect fewer than 1% of children in most populations. Studies of British children found the prevalence below 1% with no difference between boys and girls. A higher rate of about 5% has been reported in Japanese children, but across most groups the condition is rare enough that the vast majority of children will develop all 20 teeth on schedule.
Extra primary teeth (supernumerary teeth) are even less common. When they do occur, they most often appear near the upper front teeth. Both missing and extra teeth can usually be identified on a dental X-ray and managed early if needed.