Dr. Shahzadi Tayyaba Hashmi HISTOLOGY OF ENAMEL Dr. Shahzadi Tayyaba Hashmi

introduction Enamel is a highly mineralized structure covering the anatomic crown of tooth It is the only tissue that is totally acellular PHYSICAL PROPERTIES: Colour: Appears bluish white or grayish at the thick opaque areas & yellow-white at the thin areas reflecting underlying dentin Thickness: Thickness over the cusps of the molars where it measures 2.5 mm & incisal edges of incisors where it is 2.0 mm

introduction Hardness: Enamel is the hardest calcified tissue in the body because of its high content of minerals Enamel can withstand load of mastication and resist wear process

introduction CHEMICAL PROPERTIES: Enamel is composed of organic & inorganic substances Organic --------4% (Mainly non collagenous proteins) Amelogenins ameloblastins ii. Inorganic--------96% Mainly calcium phosphate crystals (hydroxyapatite crystals) iii. Water

MICROSCOPIC STRUCTURE Enamel rods(prisms) Rod sheaths Cementing inter-rod substance

1) Enamel rods Course Number Transverse striation Direction Gnarled enamel

1. course The enamel rod starts straight at dentino- enamel junction (D.E.J.) for about 30 µ then has a wavy course till near the outer surface of enamel where it become straight once more

2. Number The number of the enamel rods varies from 5 millions in lower lateral incisor to 12 millions in the upper first premolars The number of the rods equals the number of the ameloblasts

Direction of rods Permanent teeth Deciduous teeth

Gnarled enamel Gnarled enamel Twisted course of enamel rods Gnarled enamel is twisted and intertwined rod structure associated with increase strength of the enamel Present mainly in the incisal edges and tip of the cusps D Twisted course of enamel rods Gnarled enamel

Gnarled enamel

2) Rod sheath A thin peripheral layer Darker than the rod Relatively acid-resistant Less calcified and contains more organic matter than the rod itself Electron Microscope :often incomplete

3) Interprismatic substance Cementing E. rods together More calcified than the rod sheath Less calcified than the rod itself Appears to be minimum in human teeth