Dr Jamal Naim PhD in Orthodontics

1. Dr Jamal Naim PhD in Orthodontics Development of the Dento-gingival junction

2. Histogenesis After accomplishing of amelogenesis (Protective stage), the ameloblasts secrete or leave structure less material on enamel surface, known as primary enamel cuticle. The dental organ becomes reduced in thickness (reduced enamel epithelium) and functions as a protection against contact with connective tissue to inhibit cementum deposition or enamel resorption.

3. Histogenesis The reduced enamel epithelium consists of two layers: reduced ameloblasts Remnants of the dental organ The ameloblasts develop hemidesmosomes to attach the reduced enamel epithelium to the surface of the enamel.

5. Histogenesis At the time of eruption the reduced enamel epithelium secrete desmolytic enzymes causing degeneration of the C.T. present between it and the oral mucosa (desmolytic stage of ameloblasts). The outer layer of the reduced enamel epithelium and the cells of the oral epithelium proliferate into the degenerated C.T. to form a mass of cells over the erupting tooth, the epithelial plug.

6. Histogenesis epithelial plug

7. Histogenesis Cell death in the middle of the epithelial plug leads to the formation of epithelial lined canal through which tooth will erupt without hemorrhage.

8. Histogenesis Once the tip of the crown appears in the oral cavity enamel epithelium will be called primary attached epithelium, and the shallow groove present between the tooth and the gingiva is called gingival sulcus with epithelial attachment.

9. Histogenesis When the tooth first erupts; the enamel is almost covered by reduced enamel epithelium. By further eruption (active eruption) and gingival recession (passive eruption) the more the tooth will be exposed in the oral cavity.

10. Primary versus secondary attachment epithelium The cells of the primary attachment epithelium (PAE) originated from reduced dental epithelium and attached to the tooth surface by primary enamel cuticle. When primary attachment epithelium is replaced by oral epithelium, it is called secondary attached epithelium and attached to the tooth by secondary enamel cuticle.

11. Primary versus secondary attachment epithelium The junctional epithelium lies till now at enamel and the bottom of it is at the CEJ. With age the JE migrates apically, thus it passes on to the cementum and gain attachment to it by hemidesmosomes (cemental cuticle). Both secondary and cemental cuticle are referred to dental cuticle.

12. Shift of the dento-gingival junction • With time the gingiva change its position apically: • by eruption most of the anatomical crown is covered through the epithelium. • when the tooth reaches the occlusion plane, third or fourth of the anatomical crown is covered through the epithelium. • further recession exposing the cementum may occur by age.

13. Passive eruption • Passive eruption has been described in 4 stages where the first and the second stages considered normal and third and fourth stages may be normal or pathologic. • First Stage: • Occur in the primary teeth till one year before shedding, in the permanent teeth till 20-30 years. • The bottom of the sulcus present on the enamel and the apical end of the AE on the cemento-enamel junction. • The clinical crown is less than the anatomical crown.

14. Passive eruption First Stage

15. Passive eruption

16. Passive eruption • Second stage: • Occur till the age of 40 years or even later. • The bottom of the sulcus still present on the enamel and the apical end of the AE on the cementum. • The clinical crown is less than the anatomical crown. -

17. Passive eruption

18. Passive eruption • Third stage: • It is a transient stage. • The bottom of the sulcus present at the CEJ and the apical end of the AE on the cementum. • The clinical crown equal to the anatomical crown.

19. Passive eruption

20. Passive eruption • Fourth stage: • From 60 years later. • The bottom of the sulcus and the apical end of the AE present on the cementum. • The clinical crown is longer than the anatomical crown.

21. Passive eruption

22. Passive eruption • The downgrowth of the attachment epithelium entails: • dissolution of the fiber bundels • apical shift of the gingival and transeptal fibers. • Causes for these destruction are: • Collagenolysis • Toxic or inflammatory products • Immunologically component • Mechanical irritation