“Crossing the street, rats are universally despised.” People hate rats because they either steal food or chew through clothing, damage boxes, cabinets, tables, chairs, and other furniture. Some also transmit diseases, which is why they are a primary target for pest control.
Why do rats frequently chew things? To understand this question, we first need to know the structure of their teeth.
Teeth consist of three parts: the crown, neck, and root. The roots are embedded in the grooves of the upper and lower dental beds, while the neck and crown are exposed outside the dental bed. The outermost layer of the tooth is hard enamel, with a thicker layer of dentin underneath. In the middle is a cavity called the pulp cavity, which contains pulp that aids in tooth growth. In some animals, pulp exists throughout their lives, while in others, it disappears after teeth mature. However, in rats, the pulp inside the incisors on the upper and lower dental beds not only exists throughout their lives but also continuously grows. To prevent the incisors from growing too long and hindering eating, rats must regularly grind their incisors against hard objects.
An experiment demonstrated this: placing a rat in a ventilated metal box and feeding it only soft food without any hard objects to grind its teeth resulted in the incisors growing much longer over time.