Close up of a girl's mouth with braces on her teeth smiling Set of dental braces elements Portait of a smiling young woman showing her perfect white teeth with braces. Cementum Teen girl braces mouth open tongue as hard as bone but not as hard as enamel, which enables the tooth to withstand the pressure of chewing and protects it from harmful bacteria and changes in temperature from hot and cold foods. A bundle of Teen girl braces mouth open tongue extends from the floor of the mouth to form the tongue. Between ages 10 and 12, the first and second premolars, as well as the canines, erupt. Each type of tooth serves a different function in the chewing process. The phase during which permanent teeth develop usually lasts for about 15 years as the jaw steadily grows into its adult form.