tooth enamel 

Tooth enamel is one of the four major tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are dentin, cementum, and dental pulp. It is a very hard, white to off-white, highly mineralised substance that acts as a barrier to protect the tooth but can become susceptible to degradation, especially by acids from food and drink.

Tooth enamel is the hardest substance in the human body and contains the highest percentage of minerals, 96%, with water and organic material composing the rest.

tooth enamel by OveralldPlumber May 10, 2017