HYPOCALCIFIED STRUTURES OF ENAMEL.pptx

hypocalcified stages

1. ENAMEL HYPOCALCIFIED STRUCTURES DEPARTMENT OF ORAL AND MAXILLOFACIAL PATHOLOGY AND MICROBIOLOGY BDS I YEAR 25/11/2023 Dr. Shefali MDS SENIOR LECTURER ORAL PATHOLOGY

2. CONTENTS Introduction Structure of enamel Hypo calcified structures of enamel Summary and Conclusion FAQs MCQs Video link References Suggested readings

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

4. HYDROXYAPATITE CRYSTALS Inorganic material of enamel Hexagonal in shape Unite to form enamel rods or prisms Chemical formula- Ca10(PO4)6(0H)2 Comprises- 88-90%of tissue by volume 95-96% by weight Present in form of crystallites

5. Formation, mineralization, and maturation of some mineralized tissues.

6. HYPOCALCIFIED STRUCTURES OF ENAMEL Rod sheath Incremental lines ( straie ) of Retzius Neonatal line Cross striations Enamel lamellae Enamel tufts Enamel spindles cracks Dentino enamel junction

7. SURFACE STRUCTURES Aprismatic enamel Perikymata Enamel cuticle Rod ends Pits, caps and brochs Pellicle

8. ENAMEL LAMELLAE Thin leaf like structures From enamel surface towards DEJ, sometimes penetrate into dentin. Consist of organic material with little mineral content Develop in plane of tension, where rod cross such plane, a short segment may not calcify If more severe a crack develop that is filled either by cells or organic substances

9. Enamel Lamellae

10. ENAMEL LAMELLA Enamel lamella extend for varying depths from surface of enamel & consist of linear, longitudinally oriented defects filled with organic material It is formed as a result of local failure of maturation process . Best seen in transverse section Can be seen in decalcified section because of protein content. It may arise developmentally due to incomplete maturation of a groups of prisms (in which case they would contain protein) or after eruption as cracks during function (containing saliva & oral debris).

11. 3 TYPES-

12. Enamel Lamellae Type A Type B Type C Consistency Poorly calcified rod seg . Degenerated cells Organic matter from saliva Tooth Unerupted Unerupted Erupted Location Restricted to the Enamel. Reach into the Dentin. Reach into the Dentin. Occurrence Less common Less common More common

13. ENAMEL CRACKS The term cracks was used to describe the narrow, fissure-like structures that are seen on almost all surfaces. They are actually the outer edges of lamellae. In decalcification of ground sections of enamel , cracks usually disappear whereas the enamel lamellae still persist because they contain greater concentrations of organic material.

14. ENAMEL CRACKS Narrow fissure like structure. Seen on almost all surfaces. They are the outer edges of lamellae. Extend for varying distance along the surface. At right angles to D EJ. Long cracks are thicker than the short one. May reach the occlusal or incisal edge.

15. Careful decalcification of ground sections of enamel makes possible the distinction between cracks and lamellae. The former disappear whereas the latter persist. Cracks don’t contain organic material and lamellae has higher protein content.

16. Enamel Tufts Arise from DEJ. Reach to 1 / 5 – 1 / 3 the thickness of Enamel In ground section: resemble tufts of grass The inner end arises at the dentin. Consist of hypocalcified E. rods and interprismatic substance. The extend in the direction of the long axis of the crown (best seen in horizontal sections).

17. Enamel tufts consist of several unconnected "leaves" of hypo-calcified enamel. They display a wavy twisted appearance A, Enamel spindle; B, Enamel tuft

18. BERKOVITZ

19. Transverse ground section of enamel Enamel lamella Enamel tufts ENAMEL LAMELLA & TUFTS

20. ENAMEL SPINDLES The odontoblasts processes may cross DEJ (before the hard substance is formed) to the E. and ends as E. spindles. Odontoblasts process trapped in the enamel More in the cuspal region They are filled with organic matter. The processes and spindles are at right angle to the surface of the dentin. The direction of spindles and rods is divergent. Spindles appear dark in ground sections under transmitted light.

21. ENAMEL SPINDLES

22. ENAMEL SPINDLES Before the formation of enamel certain odontoblastic processes project & get trapped b/w the adjacent ameloblast to form enamel spindles. They do not follow the direction of enamel rods. Spindles are more prominent in the cuspal region & generally oriented in a direction perpendicular to the DEJ.

23. ENAMEL SPINDLES Enamel spindles LONGITUDINAL SECTION SHOWING ENAMEL SPINDLES

24. DENTINOENAMEL JUNCTION Scalloped Convexity towards dentin Firm locking More pronounced occlusally

25. DENTINO-ENAMEL JUNCTION

26. STRIAE OF RETZIUS The incremental lines of Retzius appear as brownish bands in ground sections of the enamel. They illustrate the incremental pattern of the enamel, that is, the successive apposition of layers of enamel during formation of the crown . In longitudinal sections, they surround the tip of the dentin. In the cervical parts of the crown, they run obliquely. From the DE junction to the surface, they deviate occlusally.

27. STRIAE OF RETZIUS

28. CROSS STRIATIONS They demarcate rod segments and become more visible by the action of mild acids . The rods are segmented because the enamel matrix is formed in a rhythmic manner . In humans, these segments seem to be a uniform length of about 4 µm. The cross-striations seen in light microscope is suggested to be due to a diurnal rhythm in the enamel formation and that in these areas rods show varicosities and variation in composition.

29. NEONATAL LINE The neonatal line is due to the abrupt change in the environment and nutrition of the newborn infant. The prenatal enamel usually is better developed than the postnatal enamel. The neonatal line is an accentuated incremental line, denoting the prolonged rest period of enamel formation that occurs at the time of birth.

30. ROD SHEATH 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.

31. SURFACE STRUCTURES Perikymata Rod ends Cracks Pits, caps and brochs Enamel cuticle

32. SURFACE APRISMATIC ENAMEL 30um Rodless , aprismatic More mineralized Crystals parallel to each other & perpendicular to striae of Retzius

33. STRUCTURE OF ENAMEL… Striae of retzius extend from the DEJ to the outer surface of enamel , where they end in shallow furrows known as Perikymata . Perikymata grooves- seen as wave like concentric surface rings. Perikymata ridges- grooves are separated from each other by ridges. PERIKYMATA

34. A-PERIKYMATA GROOVES,B-PERIKYMATA RIDGES High power view of surface enamel with perikymata grooves separated by perikymata ridges (SEM ) Perikymata grooves Perikymata ridges

35. SURFACE PITS , CAPS AND BROCHS Pits of about 1–1.5 μm in diameter and small elevations of about 10–15 μm called enamel caps are seen. The surface pits are said to represent the ends of ameloblast and the caps are due to enamel deposition on nonmineralizable debris. Larger enamel elevations are termed enamel brochs .

36. ENAMEL CUTICLE Primary Enamel cuticle ( Nasmyth’s membrane). Secondary Enamel cutile ( afibrilar cementum ). Pellicle (a precipitate of salivary proteins.

37. PRIMARY ENAMEL CUTICLE Covers the entire crown of newly erupted tooth. Thickness: 0.2 µm. Removed by mastication (remains intact in protective areas). Secreted by postameloblasts . EM: similar to basal lamina. Prevent resorption of surface enamel before eruption

38. SECONDARY ENAMEL CUTICLE Covered the cervical area of the enamel. Thickness: up to 10 µm. Continuous with the cementum . Probably of mesodermal origin or may be elaborated by the attachment epithelium.

39. HUNTER SCHREGER BANDS Change in the direction of rods is responsible for the appearance of the Hunter– Schreger bands . Alternate Dark ( Diazones ) and light ( parazones ) bands Longitudinal section ( diazones ) Transverse( parazones ) Oblique light Change in rod direction

40. HUNTER SCHREGER BANDS

41. Seen due to: Change in the direction of Enamel rods- Most accepted Variation in calcification of the Enamel Alternate zones having different permeability and organic material. Hunter schreger bands

42. When enamel is cut parallel to the long axis of the tooth, individual crystals will be oriented differently in the groups of prism cut more transversely or longitudinally . Angulation is 40°. This complex pattern of prisms makes enamel resistant to fracture.

43. SEM of longitudinally sectioned enamel lightly etched to show alternating bands of transversely sectioned(diazones) & longitudinally sectioned(parazones) prism. Diazones Parazones

44. GNARLED ENAMEL In the region of the cusps or incisal edges, the rod arrangement appears to be further complicated—the bundles of rods seem to intertwine more irregularly. This optical appearance of enamel is called gnarled enamel. Due to change in rod direction

45. SUMMARY and CONCLUSION Enamel is about 96% inorganic mineral in the form of hydroxyapatite and 4% water and organic matter. Hydroxyapatite is a crystalline calcium phosphate that is also found in bone, dentin, and Cementum. Hypo mineralized zones of Enamel are the weak areas from where percolation of dental caries takes place.

46. QUESTIONS Long Answer Questions: Discuss Hypocalcified structures of enamel Short notes: Incremental lines of Retzius Neonatal line Enamel lamellae

47. MCQs Hypocalcified structure include all except: Incremental line Neonatal line Enamel lamellae Hunter shreger bands Hypocalcified structure of dentinal origin seen in enamel are: Enamel lamellae Enamel spindle Enamel tufts Neonatal line

48. Video Link https://youtu.be/Gxy6f0BKgk0

49. REFERENCES Orban's Oral Histology and Embryology- 15 th ed. SUGGESTED READING Ten Cate's Oral Histology, Development, Structure, and Function- 9th Edition. Provenza Text book of Oral Histology.