Molars are the large, flat teeth at the back of your mouth, designed for grinding and crushing food. Most adults have 12 molars: three on each side of the upper jaw and three on each side of the lower jaw. They sit behind the narrower premolars and are the furthest teeth back in your dental arch.
Which Teeth Are Molars
Your molars fall into three groups based on their position, and each group has a common nickname tied to when it appears.
- First molars (the “6-year molars”): These erupt between ages 6 and 7. They’re the first permanent teeth most children get, and they arrive behind the baby teeth rather than replacing them. In dental numbering, they’re teeth 3, 14, 19, and 30.
- Second molars (the “12-year molars”): These come in between ages 11 and 13, filling in just behind the first molars. They’re teeth 2, 15, 18, and 31.
- Third molars (wisdom teeth): The last to arrive, typically between ages 17 and 21, if they come in at all. They’re teeth 1, 16, 17, and 32, occupying the very back corners of the mouth.
Dentists number permanent teeth 1 through 32, starting at the upper right wisdom tooth and sweeping around to the upper left, then dropping to the lower left and continuing to the lower right. Every molar sits at the ends of that sequence, which is why your molars carry the lowest and highest numbers in each row.
How Molars Differ From Premolars
Premolars (sometimes called bicuspids) sit directly in front of your molars and can look similar at first glance. But molars are larger, with broader chewing surfaces and more cusps. Premolars typically have two cusps, while molars have four or five. Molars also have more roots to anchor their bigger crowns into the jawbone.
There’s a developmental difference too. Premolars replace baby teeth that fall out, so they have a “milk” predecessor. Molars don’t replace anything. They emerge into empty space behind the existing teeth, which is why your first molars can arrive years before you lose your last baby tooth.
Molar Anatomy Up Close
Upper (maxillary) first molars are the largest teeth in the upper jaw. They typically have four major cusps, each with a different shape and size. The largest cusp sits on the tongue side toward the front of the tooth, with a rounded, blunt tip suited for crushing. The cusp on the cheek side toward the front is sharper and the second largest. The remaining two cusps are progressively smaller. About a third of people also have a fifth, smaller cusp on the tongue side called the cusp of Carabelli, bringing the total to five.
Lower molars have a similar multi-cusped design but tend to have two roots instead of three. Upper molars generally have three roots, which gives them exceptional anchorage in the bone. That broad, multi-cusped surface is what makes molars so effective at grinding food into small, digestible pieces, working like a mortar and pestle every time you chew.
Baby Molars Come First
Children develop two sets of primary (baby) molars on each side of both jaws, for a total of eight. The first primary molars typically break through around 15 to 16 months of age, though the range can stretch from about 9 to 23 months. The second primary molars follow at roughly 23 to 25 months, with some children getting them as late as 30 months.
These baby molars serve as placeholders and chewing surfaces for years. They’re eventually replaced not by permanent molars but by permanent premolars, usually between ages 9 and 12. Meanwhile, the permanent first molars have already erupted behind them by age 6 or 7, filling brand-new space at the back of the jaw.
Why Wisdom Teeth Cause Problems
Third molars are the most variable teeth in the human mouth. Some people develop all four, some develop fewer, and some never develop them at all. Even when they do form, they frequently lack the room to emerge properly. A large meta-analysis found that about 37% of people have at least one impacted wisdom tooth, meaning it’s stuck fully or partially beneath the gum or bone. Looking at individual teeth, nearly half of all third molars are impacted.
When a wisdom tooth is partially erupted, the flap of gum tissue over it can trap bacteria and lead to infection or decay. Fully impacted teeth can press against neighboring molars or develop cysts. Whether to remove symptom-free wisdom teeth remains one of the more debated questions in dentistry: some practitioners favor early removal to prevent future complications, while others argue that extracting a tooth causing no problems carries its own risks.
Molars Are Especially Cavity-Prone
The same grooves and pits that help molars grind food also make them the teeth most vulnerable to cavities. Food particles and bacteria settle into those deep fissures, and toothbrush bristles often can’t reach the bottom. This is why the chewing surfaces of molars account for a disproportionate share of cavities, especially in children and teenagers whose brushing habits are still developing.
Dental sealants, a thin protective coating painted into those grooves, can significantly reduce that risk. Studies on children’s first permanent molars have shown a 37% to 44% reduction in cavities over a three-year period compared to unsealed teeth. Sealants are most effective when applied soon after the molars erupt, before decay has a chance to start.
Why Molars Look the Way They Do
Molar shape is closely tied to diet, and human molars tell a long evolutionary story. Our early ancestors, the australopithecines, had large, flat molars with blunt cusps and thick enamel. That design was well suited for processing hard, brittle foods like seeds and nuts but poor at handling tough, fibrous material like leaves or raw meat. The thick enamel likely served a dual purpose: resisting fracture under heavy bite forces and lasting longer against an abrasive diet of gritty, unprocessed plant foods.
Modern human molars are smaller than those of our ancestors, reflecting a long dietary shift toward softer, cooked foods. But the fundamental design remains the same: broad, multi-cusped surfaces built for grinding rather than tearing or cutting. That’s the core job of every molar in your mouth, from the first ones that arrive at age 6 to the wisdom teeth that may or may not show up more than a decade later.