The outside white part of teeth is called the "enamel". The enamel is made of calcium phosphate and is very hard. Under the enamel is the dentine. The dentine is softer than the hard enamel. So it is hurt more by tooth decay (cavities). Under the dentine is the "pulp" which has the nerves and blood vessels that go to the tooth. This is the part that causes the pain of a toothache. "Cementum" is outside the dentine where there is no enamel. Cementum holds the tooth to the bone of the jaw.