Rodents have two incisors in the upper as well as in the lower jaw which grow continuously and must be kept worn down by gnawing ; this is the origin of the name , from the Latin rodere , to gnaw .

They have four incisors that keep growing , and must be kept worn down by gnawing -LRB- eroding teeth by grinding them on something hard -RRB- ; this is the origin of the name , from the Latin rodere , `` to gnaw '' , and dent , `` tooth '' .
