Tooth enamel is one of the four major tissues that make up the tooth in humans and many other animals. It makes up the visible part of the tooth covering the crown. The other major tissues are dentin, cementum and dental pulp. It protects the teeth but can be easily decayed and destroyed. It is the hardest substance in the human body and contains the highest percentage of minerals 96% . This mineral is hydroxyapetite which is crystalline calcium phosphate. In humans enamel varies in thickness over the surface of the tooth thickest at the cusps and thinnest at the border.