LECTURE V 1 Learning Objective • At the end of this lecture, the students will be able to know about the; Ultrastructure of Enamel Rods Enamel Cuticle Enamel Lamellae Enamel Tufts Dentinoenamel Junction (DEJ) Enamel Spindles 2 ENAMEL CUTICLE • Primary enamel cuticle or the Nasmyth’s membrane • A typical basal lamina under electron microscope • Probably visible with the light microscope - wavy course • Apparently secreted by the ameloblasts 3 Enamel Cuticle Cont’d… • Function of the enamel cuticle • Afibrillar cementum • Pellicle 4 ENAMEL LAMELLAE • Thin, leaf-like structures • May extend to, and sometimes penetrate into, the dentin • Consist of organic material with little mineral content • May be confused with cracks 5 Enamel Lamellae Cont’d… • Types of Lamellae Type A: composed of poorly calcified rod segments Type B: consisting of degenerated cells Type C: filled with organic matter, presumably originating from saliva • Lamellae can be observed better in horizontal sections 6 Enamel Lamellae Cont’d… • 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 Unerupted tooth: filled by surrounding cells After eruption: filled by organic substances from the oral cavity 7 ENAMEL TUFTS • Arise at the dentinoenamel junction and reach into the enamel to about one fifth to one third of its thickness • Resemble tufts of grass - erroneous • Does not spring from a single small area but is a narrow, ribbon-like structure • Consist of hypocalcified enamel rods and interprismatic substance 8 Enamel Tufts Cont’d… • SEM studies Revealed enamel tufts to be tubular structure with cross striations • TEM studies Showed plate-like structures in the center of the tufts • In another study Needle-like crystals and granular or amorphous material was found partially occluding the channels or the voids These studies concluded that the tufts were hypomineralized structures 9 DENTINO ENAMEL JUNCTION (DEJ) • The surface of the dentin at the DEJ is pitted • Into the shallow depressions of the dentin fit rounded projections of the enamel • appears not as a straight but as a scalloped line • convexities of the scallops are directed toward the dentin 10 DEJ Cont’d… • The pitted DEJ is preformed even before the development of hard tissues • In the DEJ, the crystals of dentin and enamel mix with each other • Is more pronounced in the occlusal area • A hypermineralized zone about 30 μm thick 11 ODONTOBLAST PROCESSES AND ENAMEL SPINDLES • Occasionally odontoblast processes pass across the DEJ into the enamel • Many are thickened at their end termed enamel spindles • Direction corresponds to the original direction of the ameloblasts—at right angles to the surface of the dentin 12 Enamel Spindles Cont’d… • In ground sections of dried teeth The organic content of the spindles disintegrates and is replaced by air The spaces appear dark in transmitted light • TEM studies Showed spindles to be channels containing small needle-like crystals or granular and/ or amorphous material They are found mainly in the cusp tip regions 13 For Questions & Queries: [email protected] .