Enamel done
- 1. ENAMEL CONTENTS Introduction Development of Enamel Chemical Properties of Enamel Physical Properties Of Enamel Structure Of Enamel Conclusion References DEFINIION The white, calcified portion, which covers the anatomic part of the teeth is called enamel. -sturdevant’s INTRODUCTION Hardest calcified tissue in human body Color: yellowish white to grayish white depends on translucency Acts as semipermeable membrane. Forms a protective covering (2 mm – knife edge). It is very brittle but the underlying dentin provides some resilience It formed by ameloblast cells, which originate from embryonic germ layer- Ectoderm Once it get worn off it cannot be regenerated It thickness is maximum at cusps and incisal region which reduces towards CEJ. • Incisal edges=2mm • Premolar cusps= 2.3-2.5mm • Molar= 2.5-3mm LIFE CYCLES OF AMELOBLAST According to their function, can be divided into six stages: 1. Morphogenic stage.
- 2. 2. Organizing stage. 3. Formative stage. 4. Maturative stage. 5. Protective stage. 6. Desmolytic stage. Morphogenic Stage Before ameloblast get matures it interact with mesenchymal cells and decide the shape of DEJ and Crown Pulpal layer adjacent to the basal lamina is a cell free zone At cervical region – cell is relatively undifferentiated Organizing stage Inner enamel epithelium interact with the cells of dental papilla which differentiate into odontoblast Cells become elongated Proximal part contain nuclei Distal end is nucleus free zone Dentin formation begins at the end of this stage Cell free zone disappear
- 3. Formative stage Formative stage starts after the first layer of dentine form. Change in the organization and number of cytoplasmic organelles and inclusions are related to initiation of Enamel matrix formation. Development of blunt cell process on the ameloblast surface which penetrate the basal lamina and enter the predentin As dentine is formed nutrition supply of the inner enamel epithelium changes from dental papilla to the capillaries that surround the outer enamel epithelium- Reversal of nutritional stream Reduction and gradual disappearance of the stellate reticulum Maturative stage Starts after most thickness of enamel matrix form in occlusal and incisal area. Ameloblast reduce in length
- 4. Cells of stratum intermedium takes spindle shape Ameloblast display microvilli at distal extremities these structure indicate an absorptive function of these cells Protective stage After enamel get completely calcified the ameloblast can no longer be differentiated from stratum intermedium and outer enamel epithelium These layer forms reduced enamel epithelium It Protect by seperating it from CT until the tooth erupts, if it contacts then anomalies develop. In such case enamel may be resorbed or cover by a layer of cementum.(afibrillar cementum) Desmolytic stage. Reduced enamel epithelium induces atrophy of CT separating it with oral epithelium thus fusion of the two epithelia can occur. Premature degeneration of the reduced enamel epithelium may prevent the eruption of he tooth. Organic Matrix Formation Amelodentinal membrane Development of Tome’s processes Distal terminal bars. Ameloblasts covering maturing enamel.
- 5. Enamel matrix Secretory activity of ameloblast starts after small dentin layer form Ameloblast lose their projections separating them from predentin Islands of enamel matrix deposit along the dentin This layer is known as dentino enamel membrane Tomes process Surface of ameloblast facing the enamel is not smooth The projection of ameloblast into the enamel matrix is tomes process. Interdigitation - long axis of rods and ameloblast are not parallel Picket fence arrangements 2 ameloblasts involved in the synthesis of each enamel rod Distal terminal bars Appear at the distal end of the ameloblast Separate the tomes process from the cell proper They are localized condensation of cytoplasmic substance
- 6. Ameloblasts covering maturing enamel Are shorter than the ameloblast covering incompletely formed enamel During enamel maturation 90% initially secreted protein is lost Organic content and water is lost in mineralization CHEMICAL PROPERTIES In volume the organic matter and water are nearly equal to the inorganic contents. Amelogenesis- proline, histidine, glutamine, lucine Non-amelogenin- enamelin, tuftlin, ameloblastin Physical characteristics Properties:- Hard, brittle, totally acellular , highly mineralized Secreted by stratified squamous epithelium The specific gravity is 2.8. KHN-343 Density:- Decreases from surface to the DEJ CHEMICAL PROPERTIES ORGANIC 4% AMELOGENINS 90% NON-AMELOGENINS 10% INORGANIC 96% HYDROXYAPPITITE CRYSTALS
- 7. Thickness:- On cusps- 2.5 mm & incisal edges-2.0 mm. STRUCTURES OF ENAMEL ENAMEL RODS Basic unit of enamel Cylindrical in longitudinal section named so. CROSS SECTION Shows the key hole pattern Head represents the rod and key shows the inter rod region Head -occlusal aspect ; tail- cervical regioN Each rod is formed by 4 ameloblast
- 8. Enamel rod – 5-12 million/tooth Appatite crystal is hexagonal Enamel initially starts with a high protein content, but these are removed and the voids backfilled with HAP as the tooth matures Characteristics Length: greater than the thickness. Diameter average: 4 µm near DEJ and 8µm near surface Deviate about 65° from the tails. Crystals length: 0.05 – 1 µm. Thickness: about 300 A°. Average width: about 900 A°. Cross sections: somewhat irregular.
- 9. Striations Light and dark lines Cross sections in light microscope is suggested to be due to diurnal rhythm in the enamel formation and that in these areas rods shows variations in composition. Segment length: about 4 µm. DIRECTION OF ENAMEL RODS • 90º to DEJ and tooth surface, cervical region of permanent teeth- outward and apically directed; of deciduous- horizontally directed • At the cusps or incisal edges rods changes gradually to an oblique direction. • Rods converge in their outward course and forms developmental fissures and pits
- 10. THE CLINICAL SIGNIFICANCE OF ENAMEL RODS In cavity preparation In acid etching of enamel. In preparing cavities, it is important that unsupported enamel rods are not left at the cavity margins because they would soon break and produce leakage. Bacteria would lodge in these spaces producing secondary dental caries The operator should create all enamel walls so that all rods forming the prepared enamel wall, have their inner ends resting on sound dentin All enamel walls must consist of either : Full length enamel rods on sound dentin. OR Full length enamel rods on sound dentin supported on preparation side by shortened rods also on sound dentin ROLE OF ENAMEL RODS IN ACID ETCHING The dissolution occurs more in the head region, tail and periphery of the head are resistant to acid attack. Etching produces -irregular and pitted surface, microscopic undercuts Composite or pit and fissure sealants is bonded to the enamel surface by resin tags formed by etching The standard treatment protocol for acid etching of enamel is 37% phosphoric acid for 15-30 seconds. ENAMEL BONDING SYSTEM Its an unfilled liquid acrylic monomer mixture which flows between enamel rods. Enamel bonding depends upon resin tags becoming interlocked with surface irregularities created by etching. The microtags and macrotags are the basis for enamel micromechanical bonding
- 11. Gnarled enamel Rods appear more irregularly Makes enamel stronger Seen in the incisal or cuspal region This is hypermineralized. Hunterschrager bands Alternate dark and light strips. Originate- DEJ The Dark bands- Parazones Light bands- Diazones Angle btw diazones and parazones-40 degree It minimize the risk of cleavage in the axial direction under the occlusal masticatory forces They are form due to slight difference in permeability and a different content of organic material. Strae of retzius Incremental lines of growth Brownish bands in ground sections Form due to variation in structure and mineralization Daily rate of enamel formation- 3.5 microns
- 12. Increase inner to outer and decreases from occlusal to cervical Enamel formation is more rapid in the middle region of the tooth than the DEJ. They end as shallow furrows- perikymata Broadening of these lines occur in metabolic disturbances. Etiology 1. Periodic bending of Enamel rods. 2. Variation in organic structure. 3. Physiologic calcification rhythm. Neonatal Line It is the boundary between the enamel forms before and after the birth Seen in deciduous teeth and the 1st permanent molar It is usually the darkest and thickest stria of Retzius. Etiology Due to sudden change in the environment and nutrition. Enamel Lamellae Thin, leaf like structures, Develop in planes of tension, a short segments of rod may not fully calcified Extends from Enamel surface towards the DEJ. Confused with cracks caused by grinding (decalcification). Represent site of weakness in the tooth and may form a road of entry of bacteria that initiate caries
- 13. 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 E. Reach into the D. Reach into the D. Occurrence Less common Less common More common Enamel lamellae What do all three of these structures have in common? Answer: They are all hypocalcified. Legend: A, Enamel lamella; B, Enamel tuft; C, Neonatal line
- 14. Enamel tufts Forms in the formative stage of the enamel Arise from DEJ. Reach to 1/5 – 1/3 the thickness of Enamel In ground section: resemble tufts of grass. Consist of hypocalcified Enamel rods They are wavy due to the waviness of the adjacent rods. Dentinoa enamel junction Scalloped junction – the convexities towards Dentin. The outline of DEJ formed by the arrangement of the ameloblasts and basement membrane of dental papila More prominent before mineralization is complete Hypermineralized ; about 30µm thick
- 15. Enamel Spindles The odontoblasts processes cross DEJ and enters the Enamel More in the cuspal region Filled with organic matter. The direction of spindles and rods is divergent. They are only about one tenth the length of an enamel tuft SURFACE STRUCTURES a. Structureless layer (E. skin) b. Perikymata c. Rod ends d. Cracks e. Enamel cuticle STRUCTURELESS LAYER About 30 µm thick. In 70% permanent teeth and all deciduous teeth. Found least often over the cusp tips. Commonly in the cervical areas. Prism less enamel Apatite crystals area parallel to one another and perpendicular to the striae of Retzius. More mineralized than the bulk of Enamel beneath it.
- 16. PERIKYMATA External manifestation of the striae of Retzius. Lie parallel to each other and to CEJ 30 perik./mm at the CEJ. 10 perik./mm near the incisal edge. Powdered graphite demonstrates them. These are elevation not depression. Due to even development of enamel pre natal- Perikymata are absent in deciduous teeth ; present on cervical region of permanent teeth ROD ENDS Are concave and vary in depth and shape. Are shallow in the cervical regions. Deep near the incisal or occlusal edges. Enamel surface - pits of 1-1.5µm- ends of ameloblast - elevation of 10-15µm enamel cap, large enamel elevation called Enamel Brochs
- 17. CRACKS Narrow fissure like structure. Seen on almost all surfaces. The outer edges of lamellae. At right angles to DEJ. Long cracks are thicker than the short one. May reach the occlusal or incisal edge. e. Enamel cuticle 1. Primary E. cuticle (Nasmyth’s membrane). 2. Secondary E. cutile (afibrilar cementum). 3. Pellicle (a precipitate of salivary proteins. Primary enamel cuticle Covers the entire crown of newly erupted tooth. Thickness: 0.2 µm. Removed by mastication (remains intact in protective areas). It is basal lamina which is Secreted by amloblasts after completion of enamel formation EM: similar to basal lamina. Secondary enamel cuticle Cover the cervical area of the enamel. Thickness: 10 µm. Continuous with the A fibrillar Cementum. Mesodermal in origin Secreted after Enamel organ retracted from the cervical region during tooth development.
- 18. PELLICLE Precipitate of salivary protein Covers the crown Re-form within hours after mechanical cleaning. May be colonized by microorganisms to form a bacterial plaque. Plaque may be calcified forming calculus. What is Amelogenesis Imperfecta ? Amelogenesis Imperfecta represents a group of hereditary defects of enamel unassociated with any other generalized defects. It is entirely an ectodermal disturbance , since the mesodermal components of the teeth are basically normal Prevelance-1 in 700 to 1 in 15,000 Enamel in both hypo maturation and hypo calcified AI is not mineralized to normal level hence called- hypo mineralized. AI can be inherited as an x-linked, autosomal recessive (AR), or autosomal dominant (AD) condition. DEVELOPMENTAL DEFECTS 3 stages.. Formative stage deposition of organic matrix. Calcification stage matrix mineralization Maturation stage crystallites enlarge and mature Histological Features Hypoplastic type —disturbance in the differentiation or viability of ameloblasts. Hypocalcification type– defects in matrix structure and of mineral deposition. Hypomaturation type– alteration in enamel rod & rod sheath struc
- 19. CLASSIFICATION Based on clinical,histological,&genetic criteria-Witkop & Sauk Hypoplastic Pitted, AD Local, AD Smooth, AD Rough, AD Rough, AR Smooth, X-linked dominant Hypocalcified Diffuse AD Diffuse AR Hypomaturation Diffuse , X-Linked recessive Diffuse Pigmented, AR Snow-capped teeth, X-linked Combination Type Hypomaturation-hypoplastic with taurodontism,AD Hypoplastic-hypomaturation with taurodontism,AD Gaene coading AMLEX- associate with Amelogenin (enamel matrix) ENAM –associate with Enamelin MMP-20- codes for proteinase named Enamelysin KLK-4- codes for protease associate with Kalkrein-4 (mutatio of it involve in Hypomaturation) DLX3- group of gene coading for number of proteins critical for craniofacial, tooth, hair, brain, and neural development AMBN – coads for Ameloblastin
- 20. Hypoplastic Type Inadequate deposition of enamel matrix. Generalized pitted- Seen on buccal side Rows and columns of pitting Enamel between pitted area is normal Later get discoloured Localized pitted- Seen in middle 1/3rd of tooth Lateral bands of pitting Both dentitions are involved Smooth pattern- Translucent brown colour Enamel is smooth, glossy, thin, hard Interdental spacing Open bite Appear like tooth preparation Resorption of unerrupted tooth R/g- thin radio opaque covering Female with X linked- Vertical furrows of hypoplastic enamel
- 21. Rough pattern- Enamel is thin hard and rough surface Denser than seen in smooth pattern R/g- thin peripheral outline of radio dense enamel Enamel Agenesis- Total lack of enamel formation Shape and color of dentin Tapered incisally Open bite Rough surface Resorption of unerrupted teeth R/g- no peripheral enamel overlying dentin
- 22. Treatment Bonding procedures (protect caries and improve esthetics) Composite resin Porcelain veneers Orthodontic therapy- to partially close the interdental spaces before restoration Intracoronal restorations-amalgams and composite resins Full dental coverage with crowns Hypocalcified Type Enamel matrix laid down appropriately but NO proper mineralization occur • Color yellow brown or orage • Enamel is soft • Rapid calculus apposition. • Before eruption shape is normal and after function enamel is lost • Cervical portion which is mineralized better. • Open bite • R/g-density of enamel and dentin are similar • Autosomal recessive—more severe
- 23. Hypomaturation Type Enamel matrix laid down appropriately, begins to mineralize BUT defect in maturation of crystals. Types- Pigmented Pattern- Mottled and Agar brown color Fracture by underlying dentin Soft ; get punctured by dental explorer Open bite Extensive calculus deposition
- 24. Snow capped pattern- • Zone of white opaque enamel on the incisal or Occlusal third • Appear like denture dipped in white paint • Both dentitions are involved The hypomaturation and hypocalcified AI types- Conventional approaches If severely hypomineralized- full coverage restorations . SS crowns with composite inserts or composite (bonding can greatly reduce tooth sensitivity and provide reasonable esthetics)
- 25. Resin crowns on permanent incisors soon after they begin to erupt ( age 7 – 10 years)…. In adolescence or early adulthood when all the teeth are present Ultimately, PFM or other crowns can be used Amelogenesis imperfecta with Taurodontism In this both the hypomaturationand the hypoplastic features of enamel are seen Also associate with Taurodontism- Large pulp chambers So this is a combine variant of AI This pattern is also seen in some systemic disorders like- Trico-dento-osseous syndrome
- 26. Hypomaturation with hypoplastic Enamel is more hypomaturation and less hypoplastic Features- • Color- mottled yellow-white to yellow-brown • Pitting on buccal surface • R/g- enamel appears similar to dentin density WITH large pulp chambers • Seen In single rooted teeth with Taurodontism Hypoplastic with Hypomaturative Enamel is more hypoplastic and less Hypomaturative. Features- Enamel is thin(feature of hypoplasia) Pitting on buccal surface R/g- density of enamel is same as that of dentin WITH large pulp chambers- Taurodontism CONCLUSION Enamel is the non regenerative structure of tooth thus, the sound enamel, must be conserve as much as possible Moreover for laymen entire tooth means ENAMEL, so must preserve it and maintain it for good esthetic REFERENCES Orban’s oral histology and embryology (12th edition),enamel,page no. 45-79 A.R. Ten Cate,oral histology development,structure and function(5th edition),chapter 11 Neville, Damm, Allen,Bouquet,Oral and maxillofacial pathology (2nd edition) ,chapter 2, page no. 50-66 Theodore M. Roberson,Harald O. Heyman,Edward J. Swift ,sturdevent’s art and science of operative dentistry(5th edition) cahpter2,page no. 17,18