Tooth enamel is the hardest substance in the human body.
It consists mainly of calcium phosphate and calcium carbonate.
Tooth enamel covers the crown of each tooth and is important because its hard structure protects the tooth from mechanical wear e.g. due to chewing food. Tooth enamel also protects the structure of the tooth from chemical attack by acids that might otherwise dissolve the dentin part of the tooth.
Certain acids are found naturally in some foods, even in "healthy" foods, e.g. citric acid in lemons and limes (as well as carbonated soft drinks and other food products).
See also info about other parts of the mouth.
The topics of digestion and teeth are included in some school e.g. GCSE and/or A-Level courses in subjects such as biology and human biology and in other courses that include human anatomy & physiology, diet, nutrition, and other health sciences.