Histology, Pathology, and Embrology: The Clinical Importance of Enamel and Dentin and their Composition

Enamel

Located: above the anatomical crown
Physical characteristics

• Origin: ectoderm
• Hardness: hardest tissue in the body
• dentin and bone come from the mesenchyme
• Permeability: allows for exhange of ions- flouride application
• Non-Vital: not a living tissue, it has chemical reactions (mineralization vrs demineralization), contains no cells, no blood vessels or nerves, no power of growth and repair, any inperfections during development is permanent, no more enamel is laid down after the tooth has eurrupted.
• Thickness: like the sharp part of a knife; 2-2.5mm
• Color: yellowish white to gray white, translucent, tends to look whiter then it actually is becuase of the colors surrounding the tooth.
• it also reflects underlying dentin
• Chemica compostion: 96% hydroyaplite, yeah I dont know what that meanas either. (inorganic), 2.3% water, 1.7% organic collagen
• Microscoaclly enamel looks hard, shiny and translucent.

- In baby teeth there is only enamel present (little dentin and little cementum) therefore the teeth are whiter due to less dentin

Atttition is worn away biting surfaces making changes in dentin where the enamel worn

you can see how the tooth has been worn away, and the brown part showing is actually the dentin being exposed. This is caused by excessive grinding of the teeth.

Under a microscope you can see tiny rods/prisms ectending prependicular from the deno-enamel junction (where the dentin and enamel meet) to outer surface, they are made by ameloblasts and those cells determine the shape. The rods can have curvatures, and there is about 5-12 million rods on each tooth. They fit together like a key hole shape

Development of Enamel

• Bell Stage
• ameloblasts lay down a gel matrix
• they move away from the DEJ towards the OEE
• Mineralization Stage
• occurs after the matrix has been deposited
• emeoloblasts deposit minerals of calcium and phosphrous into the matrix and crystalization occurs
• occurs at the cusp tip (center) and moves outward
• Maturation Stage
• minerals increase in size, and are tightly packed together
• if lack of growth of packing, hypocalcification can occur or hyoplasa.

In development incemental lines of Retzius are created. They represent the metabolic changes during enamel formation. They curve our and away from the DEJ (looks like rings on a tree). This is a normal occurance, beacuse there are periods of metabolic disturbances during amelogensis. The importance of these lines are that decay (cavities) follow the lines of enamel rods to the dentin, and then the decay increases rapidly when it reaches the dentin.

Enamel Lamellae are microspoic separations or crack left between ename rods, they are cuased by developmental problems or stress on the tooth. They may be more suseptable to decay. If the cracks are severe they can extend to the surface, appearing as a visable crack in enamel.

Enamel Tuffs look like "clumps of grass" at the DEJ and extending shortly to the enamel

Enamel Spindles are an odonotblast that us trapped between an emeolobloast in early devlopment and that odonotblast process is caught in the enamel. This is a living tissue that has a thin corkscrew shape.

A= Enamel Lamellae

B= Enamel Tuffs

C= Enamel Spindles