Enamel

• Enamel is the hardest (Rank 5 on Mohs Hardness Scale whereas dentine ranks 3 to 4) and most highly mineralized (96% versus 70% for Dentine) substance in the human body and is composed primarily of Calcium phosphate (hydroxyapatite)
• It is the visible part of a tooth – the others being dentine , cementum , and pulp
• Unlike the pulp and dentine enamel has no cells or nerve endings and so long as the tooth is covered by it does not become Sensitive
• Because enamel has no cells it cannot be regenerated. If the acidic environment is removed though enamel can remineralization with calcium and Fluoride . The critical pH is 5.5 anything below this and enamel dissolves
• Enamels high mineral content also makes it brittle (Young’s Elastic Modulus of 83Gpa whereas dentine is more flexible at around 18Gpa) so to avoid Fractures enamel must have dentine under it for support
• Enamel varies in thickness from 2.5 mm at the tip and thinnest or non existent at the gum line -- this is where teeth are usually sensitive
• As enamel is semitranslucent, the Colour of dentin and any material underneath the enamel strongly affects the appearance of a tooth. Teeth with thinner enamel tend to appear more yellow due to the greater influence of the yellowish dentine
• Enamel on baby or milk teeth has a more opaque crystalline form and thus appears whiter than permanent teeth.