In the last two posts, we learned interesting facts about incisors and canine teeth in humans and animals. Now it is time to learn about molars and how they work with the other teeth. They are one of the most diverse types of teeth, and while some animals have smaller, sharp molars others have huge flat molars. They need to be strong enough to withstand the massive pressure of biting down. A hyena’s bite force is 1100 pounds per square inch and their molars are strong enough to grind bone!
Hyena’s have one of the strongest bites of all animals, so their teeth need to be very strong.
Adult humans have 32 teeth and 20 of these are premolars or molars. We have so many because they do most of the work of tearing, grinding and crushing food to prepare it to be digested and used by the body.
Human molars can be separated into three categories: premolars, molars and wisdom teeth. Primary (baby) teeth have two sets of molars which usually appear between the first and third birthdays, and we don’t have any premolars or molars until they grow in as permanent teeth. The first permanent molars arrive behind the baby molars around the age of six, but the baby molars don’t start to come out until age nine. The two sets of primary molars are then replaced by two sets of premolars.
Humans do not have any premolars in their baby (primary) teeth. Premolars only appear as permanent teeth.
Premolars are also called bicuspids. Although next to the pointy canine teeth, premolars have a flatter biting surface with two smaller points which are called cusps. The flatter surface allows the teeth to crush food, while the points help the canines and incisors do the work of tearing. Correct alignment creates the most efficient chewing and allows the premolars to pass food back to the molars.
Another important job the premolars do is to help shape the face and, although you can’t see them, roots help with this shaping. The first upper (maxillary) premolars have two roots, while the second upper premolars usually have one, and all the lower premolars each have one.
Molars are the teeth furthest back in the mouth, and their main job is to chew, grind and crush food. They also work with the tongue to help you swallow food. It is important that food be broken down to tiny pieces before it is swallowed so that your stomach and the rest of your digestive tract can finish breaking it down and extract the nutrients that fuel your body. Our molars have a large flat surface and multiple cusps creating jagged edges which make their important job easy. However, they also have to withstand a lot of force. If you bite down, you can feel that most of the force of your bite is concentrated on your molars, and their design enables them to handle this force every time you bite down.
Upper molars have three roots while lower molars only have two roots. Interestingly, it is common for roots in molars to have more than one canal. So, if an upper molar has three roots, it may have three, four or more root canals!
Wisdom teeth are simply the molars furthest back in the mouth. They are the last to appear, usually in the late teens or early twenties. Wisdom teeth are often removed because they are impacted or will cause overcrowding which leads to oral health problems. If the wisdom teeth are positioned correctly and allowed to grow in, a teenager or young adult may still be teething as they surface!
Premolars, molars and wisdom teeth have the largest surfaces of all the teeth and are often positioned close together. Add the fact that they spend the most time chewing and touching food and it makes sense that these teeth would be prone to cavities. You can contribute to the health of your whole mouth by paying special attention to cleaning and flossing these teeth.
What about molars in animals? Carnivores do not do much chewing and grinding, so their few molars are usually relatively small with many sharp points. Their molars help the canine teeth tear off chunks of meat which are swallowed whole. Often a carnivore has more premolars than molars. Lions, which have ten premolars and only four molars, are a great example of this.
Herbivores need a lot of large, strong, flat molars to grind leaves and other plant parts. Many herbivores have jaws that can move side to side, not just up and down, for even more effective grinding. Giraffes are an interesting herbivore which usually have a total of 24 premolars and molars with jaws that move this way to help grind the leaves and fruit from the trees they like to eat.
Giraffe skull with many molars and a long space between the molars and incisors.
Omnivores molars greatly vary in size, shape and number depending on the diet of their species. Although adult humans have eight premolars and twelve molars, other omnivore species, like the mouse, have zero premolars and twelve molars. The opossum, another omnivorous species, has twelve premolars and another sixteen molars.
Bears are amazing omnivores that will eat whatever is available. Although they are huge and able to kill easily, only a small portion of their diet is meat. Bears will eat bugs, seeds, nuts, flowers, grass, and of course they will go through human trash that is left out. With such a wide variety in their diet they need teeth to match. Their incisors are small and great for biting grasses and young plants, while their canines are long, sharp and useful for the times they eat meat. More often though, they use their canines for tearing apart logs to reach the tasty bugs hiding in them. Their molars are very interesting for an animal that looks like a ferocious carnivore, because they look a lot like ours! Bears use their molars to crush and grind food like we do, which is important preparation for digesting all the plants they eat.
Bears are omnivores with molars similar to human molars.
Molars are remarkable because of all the different sizes, shapes and functions that they have. They show whether an animal is a carnivore, herbivore or omnivore, and are strong enough to hold up under enormous amounts of pressure.
Did you know that even a few types of birds have something similar to teeth? In the next post we will discuss this and other unusual teeth situations in humans and animals, as well as other types of teeth that animals can have.
At Jungle Roots Children’s Dentistry & Orthodontics, we strive to provide the highest comprehensive pediatric and orthodontic dental care in a unique, fun-filled environment staffed by a team of caring, energetic professionals. We believe the establishment of a “dental home” at an early age is the key to a lifetime of positive visits to the dentist.