Humans have eight incisors in their permanent (adult) set of teeth. Four sit along the upper jaw and four along the lower jaw. Children also have eight incisors in their baby teeth, which eventually fall out and are replaced by the adult set.
How the Eight Incisors Are Arranged
Your incisors are the front teeth, the ones most visible when you smile. Each jaw holds four, split into two types:
- Central incisors: The two teeth right at the center of each jaw. Your upper central incisors are the widest, most prominent teeth in your mouth.
- Lateral incisors: One on each side of the central incisors, slightly smaller in size.
That gives you two central and two lateral incisors on top, and the same arrangement on the bottom, for a total of eight. They’re part of your full set of 32 permanent teeth.
When Incisors Come In
Baby incisors are typically the first teeth to appear. The lower central incisors usually emerge between 6 and 10 months of age, making them most babies’ very first teeth. The upper central incisors follow at around 8 to 12 months. Lateral incisors fill in shortly after: 9 to 13 months on top, 10 to 16 months on the bottom.
Children keep these eight baby incisors until around age 6 or 7, when they begin to loosen and fall out. The permanent incisors grow in to replace them, generally following the same order: lower centrals first, upper centrals next, then the laterals.
What Incisors Do
Incisors have sharp, flat edges built for cutting. Their job is to bite off a manageable piece of food from a larger one, like when you take a bite of an apple or tear bread. Once the incisors cut the food, your back teeth (premolars and molars) take over the grinding work.
Beyond chewing, incisors play a major role in how your face looks. They’re the most visible teeth when you talk or smile, and the way your upper and lower incisors line up affects both the function of your bite and the overall shape of your lower face.
Upper vs. Lower Incisors
Your upper and lower incisors look different from each other. Upper incisors, especially the central pair, are noticeably wider from side to side. They’re the largest incisors in your mouth. Lower incisors are narrower from side to side but slightly thicker from front to back, making them more compact overall.
The cutting edges sit in different positions, too. On upper incisors, the biting edge lines up with or slightly in front of the center of the root. On lower incisors, the edge sits slightly behind that center line. This offset is what allows the upper teeth to close just in front of the lower teeth, creating the slight overlap most people have in a normal bite. Over time, the two sets wear against each other in complementary patterns: the upper incisors develop wear on their back surfaces, while the lower incisors wear on their front surfaces.
Missing or Extra Incisors
Not everyone ends up with exactly eight. The most common variation is a congenitally missing upper lateral incisor, meaning the permanent tooth simply never develops. This affects roughly 1 to 3 percent of the population and can occur on one side or both. When it happens, the baby lateral incisor may hang on longer than usual since there’s no permanent tooth pushing it out, or a visible gap may develop.
On the other end of the spectrum, some people develop supernumerary (extra) incisors. An extra tooth can grow in behind or between the normal incisors, sometimes staying buried in the bone and sometimes partially emerging. Dentists spot these on routine X-rays and decide whether they need to be removed based on whether they’re crowding or displacing the other teeth.
How Dentists Identify Each Incisor
If you’ve ever looked at a dental chart and wondered what the numbers mean, each incisor has its own designation in the Universal Tooth Numbering System used in the United States. The upper incisors are numbered 7 through 10, counting from right to left as the dentist faces you. The lower incisors are numbered 23 through 26, again right to left. Baby incisors use letters instead: D through G for the upper jaw, and N through Q for the lower. Knowing these numbers can help you make sense of treatment plans or insurance documents that reference specific teeth.