Enamel lamellae

Enamel lamellae are thin, leaf-like structures that extend from the enamel surface toward the dentinoenamel junction. They may extend to, and sometimes penetrate into, the dentin. They consist of organic material, with but little mineral content. In ground sections, these structures may be confused with cracks caused by grinding of the specimen. So, careful decalcification of ground sections of enamel is required to distinguish cracks and enamel lamellae. The former disappear, whereas the latter persist.

Lamellae may develop in planes of tension. Where rods cross such a plane, a short segment of the rod may not fully calcify. If the disturbance is more severe, a crack may develop that is filled either by surrounding cells, if the crack occurred in the unerupted tooth, or by organic substances from the oral cavity, if the crack developed after eruption.

Three types of lamellae can thus be differentiated:

• Type A: lamellae composed of poorly calcified rod segments.
• Type B: lamellae consisting of degenerated cells.
• Type C: lamellae arising in erupted teeth where the cracks are filled with organic matter, presumably originating from saliva.

The last type may be more common than formerly believed. Although lamellae of type A are restricted to the enamel, those of types B and C may reach into the dentin.

If cells from the enamel organ fill a crack in the enamel, those in the depth degenerate, whereas those close to the surface may remain vital for a time and produce a hornified cuticle in the cleft. In such cases the inner parts of the lamella consist of an organic cell detritus, the outer parts of a double layer of the cuticle. If connective tissue invades a crack in the enamel, cementum may be formed. In such cases lamellae consist entirely or partly of cementum.

Lamellae extend in the longitudinal and radial direction of the tooth, from the tip of the crown toward the cervical region. This arrangement explains why they can be observed better in horizontal sections. It has been suggested that enamel lamellae may be a site of weakness in a tooth and may form a road of entry for bacteria that initiate caries. Later it was shown that enamel cracks or lamellae showed uptake of dyes suggesting that these structures may act as pathways for caries producing bacteria.

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