Word Wednesday: Teeth

One of the key characteristics of mammals are their teeth. Unlike fish, reptiles and amphibians, mammals have different types of specialized teeth. This is why dinosaurs and sharks regrow their teeth, but humans only get two sets. There are four different types: incisors, canines, premolars, and molars.

incisor

Incisor comes from the Latin word ‘incisusmeaning cutting. These are your front teeth and, like the name suggests, they work like scissors to cut through food.

canine

Canine comes from the Latin word ‘caninus‘ which means like a dog. Canines, or eye teeth, are longer, pointier teeth. They are used to hold food to tear it apart.

molar

Molar comes from the Latin phrase ‘molaris dens‘ which means grinding tooth. Molars are your back teeth and are used to grind up food. Premolars are between your canines and your molars and are used in chewing to transition from the cutting of the incisors to the grinding of the molars.

Front view of the skull of Tasmanian Devil (Sarcophilus ursinus), showing Polyprotodont and carnivorous dentition. The modern accepted name is Sarcophilus harrisii. (Cambridge Natural History, Mammalia)

When studying teeth, scientists often use a dental formula. This is a simple way of showing the number of each type of tooth in one half of the jaw. To determine the total number of teeth, just double each part of the dental formula. For example, humans have four incisors, two canines, four premolars, and six molars in both the upper and lower jaws. That can be written either as (I2C1P2M3)/(I2C1P2M3) where the superscript numbers represent the upper jaw and the subscript numbers represent the lower jaw, or 2.1.2.3/2.1.2.3 where the numbers on the top represent the upper jaw and the numbers on the bottom represent the lower jaw.

While humans have all four types of teeth and have the same number of teeth in our upper jaws as we do in our lower, that is not the case for all mammals. Cows have no upper incisors or canines, so their dental formula is 0.0.3.3/3.1.3.3 . Dogs have more incisors than we do, as well as more premolars and fewer molars in their upper jaw than the lower: 3.1.4.2/3.1.4.3 .

Despite there only being four different types of teeth, animals have greatly modified both their appearance and number. However, that is a topic for another day.

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