Enamel

Enamel is a glassy substance used to coat metal, pottery, and glass, or the hard, protective outer layer of a tooth. As a coating, it's created by fusing powdered glass to a surface, resulting in a durable, glossy finish often used for things like cookware (enamelware), paint, and jewelry. In dentistry, it is the hardest substance in the human body, protecting teeth from decay.

Alvaro Mata : New gel restores dental enamel and could revolutionise tooth repair - https://www.nottingham.ac.uk/news/new-gel-restores-dental-enamel-and-could-revolutionise-tooth-repair