OPTION 2

Structure of Enamel Rods

•            The crystals are grouped into enamel prisms or rods. The number of enamel prisms in a tooth like permanent maxillary first molar is estimated to be around 12 million and the average thickness of each rod is 4 μm.

•            The enamel prisms appear as segmental rods in longitudinal section and in cross-section they appear as oval, fish scale or keyhole shaped.

•            The prisms are covered by prism sheath or rod sheath and interprismatic substance is said to be present between prisms. These areas are rich in organic matter. In longitudinal Sections cross-striations, demarcate the prisms and they represent secretion of enamel in a time interval.

 

Key concept:

•            Drawing of keyhole pattern of human enamel indicating orientation of apatite crystals within individual rods.

•            Crystals are oriented parallel to long axes of ‘bodies’ of rods and fan out at an angle of approximately 65 degrees in ‘tails’ of rods.