LECTURE VII

1 Learning Objective

• At the end of this lecture, the students will be able to know about the;  Development of Enamel  Epithelial Enamel Organ  Outer Enamel Epithelium  Stellate Reticulum  Stratum Intermedium  Inner Enamel Epithelium  Cervical Loop

2 EPITHELIAL ENAMEL ORGAN

• Stage preceding the formation of hard structures (dentin and enamel) • Originate from the stratified epithelium of the primitive oral cavity • Consists of four distinct layers;  Outer enamel epithelium  Stellate reticulum  Stratum intermedium  Inner enamel epithelium (ameloblastic layer)

3 Epithelial Enamel Organ Cont’d…

4 Epithelial Enamel Organ Cont’d…

• The borderline is the subsequent dentinoenamel junction • Its outline determines the pattern of the occlusal or incisal part of the crown

5 Epithelial Enamel Organ Cont’d…

• At the border of the wide basal opening of the enamel organ, the inner enamel epithelium reflects onto the outer enamel epithelium • This is the cervical loop

6 Epithelial Enamel Organ Cont’d…

• The inner and outer enamel epithelia are elsewhere separated from each other by a large mass of cells differentiated into two distinct layers

7 Epithelial Enamel Organ Cont’d… • The layer that is close to the inner enamel epithelium consists of two or three rows of flat polyhedral cells—the stratum intermedium • The other layer, which is more loosely arranged, constitutes the stellate reticulum

8 OUTER ENAMEL EPITHELIUM (OEE)

• Consists of a single layer of cuboid cells • Separated by a delicate basement membrane

9 Outer Enamel Epithelium Cont’d…

• At the highest convexity of the organ the cells of the outer enamel epithelium become irregular in shape

10 Outer Enamel Epithelium Cont’d…

• The capillaries proliferate and protrude toward OEE  May even indent the stellate reticulum

11 Outer Enamel Epithelium Cont’d…

• OEE develop villi, cytoplasmic vesicles and large numbers of mitochondria • The capillaries in contact with the outer enamel epithelium show areas with very thin walls

12 STELLATE RETICULUM

13 Stellate Reticulum Cont’d…

14 Stellate Reticulum Cont’d…

• Forms the middle part of the enamel organ • The neighboring cells are separated by wide intercellular spaces • Filled by a large amount of intercellular substance • Star shaped, with long processes reaching in all directions from a central body • Desmosomes • Structure renders it resistant and elastic  Acts as a buffer  Permit only a limited flow of nutritional elements from the outlying blood vessels to the formative cells

15 STRATUM INTERMEDIUM

• Location • Flat to cuboid in shape • Arranged in one to three layers

16 Stratum Intermedium Cont’d…

• Desmosomes • The function of the stratum intermedium is not understood • May play a role in production of the enamel itself;  Either through control of fluid diffusion into and out of the ameloblasts or  By the actual contribution of necessary formative elements or enzymes. • Show mitotic division even after the cells of the inner enamel epithelium cease to divide.

17 INNER ENAMEL EPITHELIUM

• Derived from the basal cell layer of the oral epithelium. • Assume a columnar form and differentiate into ameloblasts that produce the enamel matrix

18 CERVICAL LOOP • At the free border of the enamel organ the outer and inner enamel epithelial layers are continuous and reflected into one another • The cuboid cells gradually gain in length

19 Cervical Loop Cont’d…

• When the crown has been formed, the cells of this portion give rise to Hertwig’s epithelial root sheath

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