The word "牙齿" is formed through a compounding process where two independent, semantically related characters are combined to create a single, more comprehensive concept. The first character, "牙" (yá), specifically refers to the front teeth, like incisors and canines, used for biting. The second character, "齿" (chǐ), historically refers to the back molars used for chewing and can also represent the general idea of teeth or a tooth-like object. By joining them, the compound word "牙齿" encompasses the entire set of teeth in the mouth, merging the specific functions and images of both front and back teeth into one general term for "tooth" or "teeth".