The outer layer of teeth is the enamel , which is mainly composed of hydroxyapatite, a mineral composed of calcium and phosphate ions.
Enamel is the hardest material in the human body and provides the strength needed to bite and chew.
It is important to have a strong enamel in order to protect the inner layers of the teeth, where the softer dentine is, which contains the blood vessels and nerves. If enamel loses some of its minerals (calcium and phosphate ions) , it becomes softer and plaque bacteria may get into the inner layers of the teeth, potentially causing caries. Moreover, the teeth can get more sensitive to heat, cold and sweetness.
Teeth are subject to acid attacks from food and beverages, and by the acids produced by plaque bacteria. Thereby, the enamel is demineralized (it loses minerals) and weakened every day and Calcium and Phosphate ions are lost. The weakened enamel makes teeth more susceptible to caries which is a major health concern worldwide.