Hypomineralised structure of enamel

These are the presentation prepared by student of BPKIHS Batch 2015 BDS on observation of respective faculty of BPKIHS

1. HYPOMINERALIZED STRUCTURE OF ENAMEL Presented By : Kajal Mehta (680) Kritika Shrestha (681) Resource Faculty: Dr.Ashish Shrestha Dr.Sashi Keshwar

2. OBJECTIVES : Brief discussion of Enamel Hydroxyapatite Crystals Enamel Rod Hypocalcified Structure Striae of Retzius Neonatal Line Enamel Spindle Enamel Tuft Enamel Lamellae

3. ENAMEL : Most highly mineralized tissue Protective structure of crown Ectodermal in origin Hardest calcified structure of the body Components Organic-4% Inorganic-96% water

4. Contd….. Thickest over cusps and incisal edges and thinnest at the cervical margin Neither repair nor replacement Hardness and density decreases from surface towards interior and from cuspal/incisal tip towards cervical margin

5. HYDROXYAPATITE CRYSTALS : Inorganic material of enamel Hexagonal in shape Unite to form enamel rod or prism Chemical formula- Ca10(PO4)6(0H)2 Comprises- 88-90%of tissue by volume 95-96% by weight Present in form of cystallites 70nm in width 25nm thick

6. Contd.. Average conc. In dry wt % of human tooth enamel; Oxygen-43.4 Calcium-36.6 Phosphorous-17.7 Minor constituents for 2-3% Na-0.67 Carbon-0.64 Mg-0.35 Water is present as part of crystals between Rods & surrounding rods.

7. It has central core or C-axis of hydroxyl ion around which calcium & phosphorous ions are arranged in form of triangle During formation, Mg can replace Ca & Carbonate can replae hydroxyl ion Conc. Of ions increase from surface of enamel towards dentin whereas conc. Of fluoride decreases from surface of enamel towards dentin Structure of hydroxyapatite crystals

8. ENAMEL ROD : Key hole or paddle shaped Highly organized pattern of crystal orientation Cylindrical in longitudinal section Clear crystalline appearance Range- 5 million in lower lateral incisor to 12 million in upper first molars Separated by interrod substance

9. Contd…. 3 main patterns: Pattern I Appear circular found near DEJ and -near the enamel surface Pattern II Aligned in parallel rows Pattern III Key hole or paddle shaped Bodies are near occlusal and incisal surfaces Tails point cervically

10. DIRECTION OF RODS : Right Angle to the dentin surface. Vertical in the cuspal Region,more oblique as they go cervically . In Decidous teeth,it is Horizontal cervically . In Permanent teeth,it is directed more Gingivally

11. HYPOMINERALIZED STRUCTURE Mere decrease in mineral content of enamel. Severe enough to give tooth a translucent appearance. Leads to soft enamel.

12. STRIAE OF RETZIUS : Brownish bands in ground section Illustrates rhythmic deposition of successive layer of enamel matrix Broadening of these lines occur in metabolic disturbances Etiology: Periodic bending of enamel rods Variation in organic structure Fig : Ground section of striae of Retzius

13. Fig: T.S of striae of retzius * Concentric ring in TS. *Evenly spaced Retzius line indicates 6-11 day cycle of enamel formation .

14. NEONATAL LINE : Darkest & thickest striae of retzius Present in decidious & 1 st permanent molar Demarcates enamel formed before &after birth Developed due to abrupt change in environment & nutrition after birth

15. Schematic diagram showing Striae of Retzius and Neonatal Line

16. ENAMEL SPINDLES : Narrow, spindle shaped, short,thin,dark strucure Extension of odontoblatic process Pass through the DEJ into enamel Seen numerous near the cusp tips

17. ENAMEL TUFTS : Ribbon like structure Resembles tufts of grass: in ground section Represent protein rich areas in the enamel matrix Development abrupt change in the direcion of enamel rod which leads to the different ratio of inter-rod and rod enamel creates less mineralized and weakened planes

18. Enamel tufts and Enamel lamella

19. ENAMEL LAMELLAE : Thin leaf like structure Extend from the surface of enamel to DEJ to varying depth Develop as a result of failure of maturation process Represent site of weakness 3 types: *Type A *Type B *Type C

20. REFERENCES :