Humans have four types of teeth: incisors, canines, premolars, and molars. Each type has a distinct shape designed for a specific job in breaking down food. Adults have 32 permanent teeth in a full set, while children have 20 baby teeth that are gradually replaced starting around age six.
Incisors: Your Front Cutting Teeth
Incisors are the eight flat, thin teeth at the very front of your mouth, four on top and four on the bottom. Their sharp, chisel-like edges are built for biting into food and slicing it into smaller pieces. When you take a bite of an apple, your incisors do the work.
The two teeth right in the center are called central incisors, and the ones flanking them on each side are lateral incisors. These are the first permanent teeth most children get. Lower central incisors typically appear between ages six and seven, followed by upper central incisors between seven and eight. Lateral incisors fill in shortly after, usually by age nine.
Canines: The Pointed Tearing Teeth
Canines are the four pointed, slightly longer teeth sitting just outside your incisors. You have one in each corner of your mouth. Their shape, a single sharp cusp, makes them ideal for gripping and tearing tougher foods like meat. Canines also help guide your jaw into position when you close your mouth, which is why dentists consider them important anchors for your bite.
Permanent canines come in at different times depending on location. Lower canines typically erupt between ages nine and ten, while upper canines appear later, around eleven to twelve. Because they arrive after the incisors and first premolars, canines sometimes emerge crowded or out of alignment if there isn’t enough room.
Premolars: A Bridge Between Tearing and Grinding
Premolars (also called bicuspids) are the eight teeth positioned between your canines and molars. They serve a dual role: they can tear food like canines and grind it like molars. Their crowns are rounder than canine crowns but smaller than molar crowns, with two raised points (cusps) on top that create a surface for crushing.
First premolars tend to look more angular, with a prominent outer cusp that resembles a canine. Second premolars are more molar-like, with cusps that are closer in size to each other, giving them a broader grinding surface. Despite being bulkier than your front teeth, most premolars have only a single root. Premolars don’t exist in the baby tooth set at all. They’re unique to the permanent set and typically erupt between ages ten and twelve, replacing the baby molars that sat in those positions.
Molars: Your Heavy-Duty Grinding Teeth
Molars are the largest teeth in your mouth, sitting at the back of each row. Adults can have up to twelve molars: three on each side of the upper and lower jaws. Their broad, flat surfaces with multiple cusps are designed for grinding food down into small, swallowable pieces. Molars handle the heaviest chewing forces in your mouth.
First molars are actually among the earliest permanent teeth to arrive, erupting between ages five and seven, often before a child has lost many baby teeth. Second molars follow between ages eleven and thirteen. Third molars, commonly known as wisdom teeth, are the last to come in, typically between seventeen and twenty-one.
Wisdom Teeth
Third molars deserve special mention because they’re the teeth most likely to cause problems. They become partially or fully impacted when there isn’t enough space in the jaw for them to emerge properly. Modern diets tend to be softer than those of our ancestors, which may contribute to smaller jaws and more frequent impaction.
When a wisdom tooth is partially impacted, a flap of gum tissue can trap bacteria and food debris, leading to a painful infection called pericoronitis. Symptoms include pain, swelling of the gum and face, a bad taste, and difficulty opening your mouth fully. Wisdom teeth can also damage the neighboring second molar by causing cavities or bone loss. Removing symptomatic or diseased wisdom teeth is standard practice, though whether to extract healthy, problem-free wisdom teeth remains debated.
Baby Teeth vs. Adult Teeth
Children develop 20 baby (deciduous) teeth, ten in the upper jaw and ten in the lower. All 20 are already forming beneath the gums at birth. The first baby tooth, usually a lower central incisor, breaks through between six and twelve months of age. From there, roughly one new tooth appears per month, and most children have their full set by age three. Upper teeth generally erupt one to two months after the matching lower tooth.
The baby set includes incisors, canines, and molars, but no premolars. As children grow, these teeth are gradually pushed out by the 32 permanent teeth developing beneath them. The transition starts around age six and continues into the early twenties when the wisdom teeth finish the process.
What Every Tooth Is Made Of
Despite their different shapes, all four types of teeth share the same layered structure. The outermost layer on the visible crown is enamel, the hardest substance in the human body. Enamel acts as a shield against cavity-causing bacteria. Beneath the enamel sits dentin, a softer layer that becomes vulnerable to decay if the enamel above it wears away or cracks.
At the center of each tooth is the pulp, a soft tissue containing nerves and blood vessels. The pulp is what makes a damaged tooth hurt. Below the gumline, the root is covered in a material called cementum instead of enamel. Cementum works with the surrounding tissues to anchor the tooth firmly in the jawbone. The root itself isn’t fully formed at the time a tooth erupts; it continues growing and doesn’t reach full maturity until some time after the crown appears in the mouth.
When the Count Is Off
Not everyone ends up with exactly 20 baby teeth or 32 permanent teeth. A condition called hyperdontia produces extra teeth beyond the normal number. Studies across different populations put the prevalence at roughly 1.2% to 3%, with males slightly more affected than females. These extra teeth can appear anywhere in the mouth and sometimes need to be removed if they crowd or displace normal teeth. On the other end, some people are congenitally missing one or more teeth, with the wisdom teeth and upper lateral incisors being the most commonly absent.