The back teeth are called molars and premolars. Premolars (also known as bicuspids) sit just behind your canine teeth, and molars fill in the rest of the row all the way to the back corners of your mouth. Together, these teeth handle the heavy work of crushing and grinding food so you can swallow it.
Types of Back Teeth
Adults have three distinct types of back teeth on each side of both the upper and lower jaw:
- Premolars (bicuspids): You have eight total, two on each side of each jaw. They sit between your pointed canine teeth and your molars. Premolars are slightly smaller and simpler in shape than molars, with two raised points (cusps) on top, which is why they’re called bicuspids. Their job is to crush and grind food into smaller pieces before the molars finish the work.
- First and second molars: These are the large, broad teeth at the very back of your mouth. You have eight of them. They’re your most powerful chewing teeth, with wide, flat surfaces featuring four or five cusps. Upper molars typically have three roots anchoring them into the jawbone, while lower molars usually have two.
- Third molars (wisdom teeth): The four teeth at the very back corners of your mouth, two on top and two on the bottom. They’re the last to come in and the ones most likely to cause problems.
In total, a full adult mouth contains 20 back teeth: 8 premolars, 8 first and second molars, and 4 wisdom teeth. That’s more than half of your 32 permanent teeth.
What Your Dentist’s Numbers Mean
When your dentist says something like “number 19 has a cavity,” they’re using the Universal Numbering System. Teeth are numbered 1 through 32 starting from the upper right wisdom tooth. Your back teeth occupy the highest and lowest numbers on the chart: 1 through 5 and 12 through 16 on top, 17 through 21 and 28 through 32 on the bottom. Knowing this can help you follow along at your next appointment.
When Back Teeth Come In
Back teeth arrive in stages over the course of childhood and young adulthood. In baby teeth, the first molars break through around 15 to 16 months of age, with the second baby molars following around 23 to 25 months. Children don’t get premolars in their baby set. Those only appear as permanent teeth.
The permanent first molars are often called “six-year molars” because they typically erupt between ages 5 and 7. They come in behind the baby teeth rather than replacing them, so parents sometimes miss them. Second molars arrive between ages 11 and 13, and wisdom teeth come in much later, usually between 17 and 25, though the timing varies widely from person to person.
Why Back Teeth Do the Heavy Lifting
Your front teeth cut and tear food, but it’s your premolars and molars that actually break it down enough to swallow. These teeth can generate hundreds of pounds of vertical force. Their broad, bumpy surfaces are designed to grind food the way a mortar and pestle works, mixing and crushing it until your tongue can shape it into a ball to swallow.
The cusps on your back teeth fit together like interlocking gears when you close your jaw. This design channels force straight down through the tooth and into the jawbone, which protects the teeth from sideways stress that could crack them.
Why Back Teeth Get More Cavities
The same grooves and pits that make your back teeth so good at grinding food also make them the most cavity-prone teeth in your mouth. Those tiny fissures on the chewing surface can be extremely narrow and deep, shaped like hourglasses or branching Y-patterns that a toothbrush bristle simply can’t reach. Bacteria settle into these grooves, build up plaque, and produce acid that eats into the enamel.
To make matters worse, the enamel in these grooves gets less benefit from fluoride in toothpaste and drinking water compared to the smooth, flat surfaces of your front teeth. This is why dentists often recommend dental sealants for children’s molars shortly after they erupt. Sealants are a thin coating painted over the chewing surface that fills in the grooves and blocks bacteria from settling in.
The Wisdom Tooth Problem
Wisdom teeth are the back teeth most likely to need attention. Many people’s jaws simply don’t have enough room for them. When a wisdom tooth can’t fully break through the gum, it becomes impacted. Impacted wisdom teeth can cause pain, trap food and bacteria behind them, damage neighboring teeth, lead to gum infection, or develop fluid-filled cysts. They can also interfere with orthodontic treatment. Partially erupted wisdom teeth are especially prone to decay because they’re nearly impossible to keep clean. Not everyone needs their wisdom teeth removed, but those experiencing any of these issues typically do.