1. Cell-free components: continuous loss and inability to regenerate 2. Non-vascular: Limited nutritional source 3. Low organic content: compressive resistance, toughness 4. The hardest tissue: 296KHN, wear-resistant

1. Distribution and thickness: edge: 2mm; tip: 2.5mm; neck: thin, blade-shaped 2. Color: Milky white or light yellow, depending on the thickness of the enamel and the degree of mineralization 3. Hardness: 296KHN (Knoop hardness number) - wear-resistant! quartz (1) Resist friction and protect deep tissue (2) The content of inorganic substances is high, so it is highly brittle and easy to break - it is impossible to get a beer bottle (3) Observation with grinding slices-slicing will demineralize, and tissue with high inorganic content will be removed 4. Composition: Inorganic substances: 96% (W/W) 86% (V/V) Organic substances: 1% (W/W) 2% (V/V) Water: 3% (W/W) 12% (V/V) 5. Inorganic substances: calcium (Ca2), phosphorus (P3-) ionic apatite crystals—90% Other phosphate crystals are a small amount 6. Organic substances: Less than 1%, composed of protein and lipids: protein: Types: three major categories, including amylogenin, non-enamel and protease Function: The function of guiding the growth of enamel crystals, bonding crystals and glaze columns 7. Water in the enamel: >Binding water: surround the crystal (mainly present form), and form a crystal hydration layer with the help of OH and CO32 on the crystal surface: >Free water 8. Metabolism of enamel > Have metabolic ability >When the pulp is necrotic, the enamel metabolism is affected. The enamel loses its luster, becomes black and brittle

(I) The basic structure of enamel - glaze column (Enamel Rod)

(II) Enamel dentin boundary and structures related to the initial formation of enamel