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Enamel significance in operative dentistry  /certified fixed orthodontic courses by Indian dental academy
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Enamel significance in operative dentistry /certified fixed orthodontic courses by Indian dental academy

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  • 1. ENAMEL :CLINICALSIGNIFICANCE INOPERATIVEDENTISTRY INDIAN DENTAL ACADEMYLeader in Continuing Dental Education www.indiandentalacademy.com www.indiandentalacademy.com
  • 2. INTRODUCTION• Enamel provides a hard durable shape for the functions of teeth and a protective cap for the vital tissues of dentin and pulp.Both colour and form contribute to esthetic appearance of enamel.• Much of the art of restorative dentistry comes from efforts to stimate the color,texture,translucency and contours of enamel with synthetic dental materials such as resin composite or porcelain. www.indiandentalacademy.com
  • 3. • Nevertheless, the lifelong preservation of the patient’s own enamel is one of the defining goals of the dentist.• Although enamel is capable of lifelong service,its crystallised mineral makeup and rigidity as well as stress from occlusion,make it vulnerable to acid demineralization(caries),attrition(wear) and fracture.• Compared to other tissue mature enamel is unique in that except for alterations in the dynamics of mineralization repair or replacement is only possible through dental therapy. www.indiandentalacademy.com
  • 5. • Bulk of the organic material consists of Tyrosine rich amelogenin polypeptide tightly bound to the hydroxyapatite crystals as well as nonameloginin proteins.• Proteins in enamel contains high percentages of serine,glutamic acid and glycine. www.indiandentalacademy.com
  • 6. • DEVELOPMENT (AMELOGENESIS)• Enamel is a ectodermally derived tissueEPITHELIAL ENAMEL ORGAN• Enamel organ originating from stratified epithelium of the primitive oral cavity consists of 4 distinct layers.1.Outer enamel epithelium2.Stellate reticulum3.Stratum intermedium4.Inner enamel epithelium(ameloblastic layer) www.indiandentalacademy.com
  • 7. • Inner enamel epithelium differentiates into ameloblasts to produce enamel matrix• The borderline between the inner enamel epithelium and connective tissue of the dental papilla is the subsequent DeninoEnamel junction.Its outline determines the pattern of the occlusal or incisal part of the crown. www.indiandentalacademy.com
  • 8. • Enamel formation occurs in three stages1.Formative stage:deposition of enamel matrix.2.Calcification or Mineralization stage: The laid matrix is mineralised along with removal of organic material and water.3.Maturation stage: crystallites enlarge and gradual completion of mineralisation. www.indiandentalacademy.com
  • 9. www.indiandentalacademy.com
  • 10. DEVELOPMENTAL DEFECTS• AMELOGENESIS IMPERFECTA It represents a group of hereditary defects of enamel unassociated with any other generralised defects.• It is entirely an ectodermal disturbance and the mesodermal components of the tooth are normal. www.indiandentalacademy.com
  • 11. • According to the 3 stages in the development of normal enamel,three basic types of AI are recognised.• 1.Hypoplastic type-there is defective matrix formation. cl.f:Enamel has not formed to full normal thickness on newly erupted teeth 2.Hypocalcification type-defective mineralisation of formed matrix. cl.f:enamel is so soft that it can be removed by a prophylaxis instument. www.indiandentalacademy.com
  • 12. 3)Hypomaturation type:Enamel crystallites remain immature cl.f:defective enamel can be pierced by an explorer point under firm pressure and can be lost by chipping away from the dentin. www.indiandentalacademy.com
  • 13. Hypoplasticwww.indiandentalacademy.com
  • 14. Hypomaturative www.indiandentalacademy.com
  • 15. Hypocalcified www.indiandentalacademy.com
  • 16. • GENERAL FEATURES *crowns of affected teeth may show discoration ranging from yellow to dark brown. *chalky texture or cheesy consistency *surface may be smooth or with numerous parallel vertical wrinkles or grooves *chipped or show depressions in the base of which dentin may be exposed. www.indiandentalacademy.com
  • 17. * Contact points between teeth are often open and occlusal surfaces and incisal edges are severely abraded. www.indiandentalacademy.com
  • 18. ROENTGENOGRAPHIC FEATURESEnamel may be totally absent orAppear as thin layer,chiefly over the tips of the cusps and the interproximal surfaces.When the calcification of enamel is so affected,it appears to have same radiodensity as the dentin,making diffentiation between the two difficult www.indiandentalacademy.com
  • 19. ENVIRONMENTAL ENAMEL HYPOPLASIA Possible factors capable of producing injury to the ameloblasts are Nutritional deficiency (vit A, C, D) Exanthematous diseases (measles, chicken pox) Congenital syphilis Hypocalcemia Birth injury,Rh hemolytic disease Local infection/trauma Ingestion of fluoride www.indiandentalacademy.com
  • 20. Effects of flouride on enamel► Anti cariogenic property1.Increased enamel resistance or reduction in enamel solubility.2.Increased rate of post eruptive maturation3.Remineralisation of incipient lesion4.Inhibition of demineralisation5.Interference with microorganisms6.Modification of tooth morphology www.indiandentalacademy.com
  • 21. Flourosis► Caused by excessive systemic flouride during enamel matrix formation and calcification.► Mild intermittent white spotting► Chalky or opaque areas► Surface pitting► Marked wear of enamel surface► Brown stains► Severe cases-corroded appearance www.indiandentalacademy.com
  • 22. STRUCTURE OF ENAMELENAMEL RODS The basic structural unit of enamel,the rods owes its existence to the highly organised pattern of crystal orientation. The rods are cylindrical in shape and are made of crystals with their long axes running for the most part parallel to the longitudinal axis of the rods. The rods vary in number from 5 million for a mandibular incisor to about 12 million for a maxillary molar. www.indiandentalacademy.com
  • 23. www.indiandentalacademy.com
  • 24.  From the DEJ the rods run in a tortuous course to the surface of the tooth Rods located in the cusps,the thickest part of the enamel are longer than those at the cervical areas off the tooth. Diameter of rods increases from DEJ towards the surface of the enamel at the ratio of about 1:2 Enamel contain rods surrounded by rod sheaths and separated by the inter-rod substances. The inter rod region is an area surrounding each rod,in which crystals are oriented in a different direction from those making up the rod www.indiandentalacademy.com
  • 25. The boundary where crystals of the rod meet those of inter-rod region at sharp angles is known as the rod sheath.Rod sheath contain more enamel protein than other regions.The consistent arrangement of rod sheaths with their greater protein content, account for fish scale appearance of enamel matrix. www.indiandentalacademy.com
  • 26. ROD INTERRELATIONSHIP Rods in each row run in a direction nearly perpendicular to the surface of dentin,with a slight inclination towards the cusps as they pass outward. In deciduous tooth the rods run horizontally at the central and cervical part of the crown,becoming increasingly oblique to almost vertical at the tip of cusps and incisal edges In permanent tooth the rod arrangement is similar in occlusal 2/3 of the crown,but deviating from horizontal to a more apical direction in the cervical region. www.indiandentalacademy.com
  • 27. Submicroscopic strcture of enamel rod In transverse section the rods are shaped with a rounded head or body section and a tail section. Generally the head position is oriented in the incisal or occlusal direction,the tail section is oriented cervically. www.indiandentalacademy.com
  • 28. ENAMEL PRISMThe structural components of the enamel prism are millions of small, elongated apatite crystallitesThe crystallites are tightly packed in a distinct pattern of orientation that gives strength and structural identity to the enamel prisms.The long axis of the apatite crystallites within the central region of the head(body) is aligned almost parallel to the rod long axis www.indiandentalacademy.com
  • 29. The crystallites incline with increasing angles (upto 65 degree)to the prism axis in the tail regionThe susceptibility of these crystallites to acid, either from an etching procedure or caries,appears to be correlated with their orientation.whereas the dissolution process occurs in the head regions of the rod,the tail regions and the periphery of the head regions are relatively resistant to acid attack. www.indiandentalacademy.com
  • 30. GNARLED ENAMELEnamel rods follow a way,spiralingcourse,progresing from the dentin towardthe enamel surface where they end a fewmicrometers short of the tooth surface.There are groups of enamel rods that mayentwine with adjacent groups of rods andthey follow a curving irregular path towardthe tooth surface,comprising of gnarledenamel. www.indiandentalacademy.com
  • 31. Gnarled enamel occurs near thecervical regions and the incisaland occlusal areas. It is notsubject to cleavage as is theregular enamel. This type ofenamel formation does not yieldreadily to the pressure of bladed,hand cutting instruments in toothpreparation. www.indiandentalacademy.com
  • 32. HUNTER SCHREGER BANDSThese are optical phenomenon produced bychange in enamel rod directionThey are most clearly seen in longitudinalground sections viewed by reflected light .These bands appear as alternate dark and lightzones of varying width with differentpermeability and organic content.,originating atthe dentine enamel border and pass outwardending at some distance from the outer enamelsurface www.indiandentalacademy.com
  • 33. www.indiandentalacademy.com
  • 34. They are regarded as functionaladaptation ,minimising the risk of cleavagein the axial direction under the influence ofocclusal masticating forces. www.indiandentalacademy.com
  • 35. ENAMEL TUFTS www.indiandentalacademy.com
  • 36. ENAMEL TUFTS They are hypo-mineralised structures of enamel rods and inter-prismatc substance arising at the DEJ and reach into the enamel to about 1/5th to 1/3rd of its thickness. They extend into the enamel in the direction of the long axis of the crown may be involved in the spread of dental caries. www.indiandentalacademy.com
  • 37. www.indiandentalacademy.com
  • 38. ENAMEL LAMELLAE They are thin,leaf life faults between enamel rod groups that extend from the enamel surface toward the DEJ.they extend to and sometimes penetrate the dentin. They consist mostly of organic material which is a weak area predisposing a tooth to entry of bacteria and dental caries. www.indiandentalacademy.com
  • 39. Enamel lamellae www.indiandentalacademy.com
  • 40. ENAMEL SPINDLE Occasionally odontoblast processes pass across the DEJ into the enamel.Their ends are thickened and are termed as enamel spindles. They seem to originate from processes of odontoblasts that extended into the enamel epithelium before hard substances were firmed. They may serve as pain receptors, thereby explaining the enamel sensitivity experienced by some patients during tooth preparation. www.indiandentalacademy.com
  • 41. www.indiandentalacademy.com
  • 42. INCREMENTAL LINES OF RETZIUS Enamel rods are formed linearly by successive apposition of enamel in discrete increments. The resulting variations in structure and mineralisation are called the Incremental striae of Retzius. In horizontal sections they appear as concentric circles and in longitudinal sections.the lines traverse the cuspal and incisal areas in symmetric arc pattern. When these circles are incomplete at the enamel surface, a series of alternaing grooves called,the imbrication lines of pickerill are formed. www.indiandentalacademy.com
  • 43. The elevations between the gooves are called perikymata.They are continuous around a tooth and usually lie parallel to each other and to the CEJ www.indiandentalacademy.com
  • 44. STRUCTURELESS OUTER LAYER OFENAMELIt is about 30µm thick structureless outer layer of enamel,most commonly toward the cervical area and less often on cusp tips.There are no prism outlines visible,and apatite crystals are parallel to one another and perpendicular to striae of retzius.Layer is heavily mineralisd. www.indiandentalacademy.com
  • 45.  Microscopically,the enamel surface initially has circular depressions indicating where the enamel rods end. These concavities vary in depth and shape and they may contribute to the adherence of plaque material, with a resultant caries attack. www.indiandentalacademy.com
  • 46. DENTINOENAMEL JUNCTION Theinterface of the enamel and dentin is established as these 2 hard tissues begin to form and is scalloped in outline. The convexities of the scallops are directed toward the dentin Scanning electron microscope shows it to be a series of ridges that increase the surface area and probably enhance the adhesion between enamel and dentin. www.indiandentalacademy.com
  • 47.  Itis hyper mineralised and 30µm thick and the interdigitation contributes to a firm attachment between dentin and enamel www.indiandentalacademy.com
  • 48. CEMENTOENAMEL JUNCTION The relation between enamel and cementum at the cervical region of the tooth is variable. In 30% of all teeth,cementum meets the cervical end of enamel in a relatively sharp line. In about 10% of teeth,enamel and cementum do not meet. In 60% of the teeth,cementum overlaps the cervical end of enamel for a short distance. www.indiandentalacademy.com
  • 49.  Thisoccurs when the enamel epithelium degenerates at its cervical termination, permitting connective tissue to come in direct contact with the enamel surface. Electron microscopic evidence indicates that when connective tissue cells, cementoblasts come in contact with enamel the produce a laminated, electron dense ,reticular material termed afibrillar cementum. www.indiandentalacademy.com
  • 50. FISSURES AND GROOVES They are formed at the junction of the developmental lobes of the enamel.Sound coaleacence of the lobes results in grooves,faulty coalescence results in fissures. Fissures act as food and bacterial traps that may predispose tooth to dental caries. Occlusal grooves,which are sound,sserve an important function as an escape path for the movement of food to the facial and lingual surfaces during mastication. The resulting narrow clefts provide a protected niche for acidogenic bacteria and the organic nutrients they require. www.indiandentalacademy.com
  • 51. PRIMARY ENAMEL CUTICLE OR NASMYTH MEMBRANE Ameloblast cell degenerates following formation of enamel rod. The final act of ameloblast cell is the secretion of a membrane covering the end of the enamel rod. This membrane covers the entire crown of newly erupted tooth but is probably soon removed by mastication and cleaning www.indiandentalacademy.com
  • 52. PELLICLE An organic deposit called pellicle covers the erupted enamel. It is a precipitate of salivary proteins. The pellicle reforms within hours after an enamel surface is mechanically cleaned. Microorganisms may invade the pellicle to form bacterial plaque,a potential precursor of dental caries www.indiandentalacademy.com
  • 53. PROPERTIES OF ENAMEL HARDNESS: The haardest substance of the human body is enamel. Its Knoop Hardness number is 343 (68 for dentin) Hardness vary over the external tooth surface according to the location. It decreases inward with hardness lowest at the DEJ www.indiandentalacademy.com
  • 54.  Density of enamel also decreases from the surface to DEJ. Enamel is very brittle structure with a high elastic modulus and low tensile strength, which indicates a rigid structure Enamel will wear because of attrition or frictional contact opposing enamel or harder restorative materials, such as porcelain, Normal physiological wear of enamel is 29µm/year. www.indiandentalacademy.com
  • 55.  However dentin is a highly compressive tissue that acts as a cushion for the enamel.Enamel requires a base of dentin to withstand masticatory forces. Enamel rods that fail to possess a dentin base because of caries or improper cavity preparation design are easily fractured away from neighbouring rods.For maximum strength in tooth preparation,all enamel rods should be supported by dentin www.indiandentalacademy.com
  • 56. PERMEABILITY The organic matrix and water contained in the enamel is in a network of micropores opening to the external surface. The micropores form a dynamic connection between the oral cavity and the systemic, pulpal and dentinal tubules fluids. Various fluids,ions and low molecular weight substances,whether deleterious,physiologic or therapeutic can difusse through the semipermeable enamel. The dynamics of acid demineralisation,caries reprcipitation or remineralisation,flouride uptake are therefore not limited to the surfac but are active in 3 dimensions www.indiandentalacademy.com
  • 57. COLOUR AND TRANSLUCENCY Enamel is mostly gray and semitranslucent. Its colour is primarily a function of its thickness and the colour of the underlying dentin. From approximately 2.5mm at the cusp tips and 2mm at the incisal edges, enamel thickness decreases significantly below deep occlusal fissures and tapers to a negligible thickness cervically at the junction with the cementum or dentin of the root. www.indiandentalacademy.com
  • 58.  The young anterior tooth has a translucent gray or slightly bluish enamel tint at the thick incisal edge. A more chromatic yellow orange shade predominates cervically where dentin shows through thinner enamel. Caries and demineralisation, anomalies of development, extrinsic stains,antibiotic therapy and excessive fluorides can alter the natural colour of the teeth www.indiandentalacademy.com
  • 59.  Enamel becomes temporarily whiter within minutes when a tooth is isolated from the moist oral environment. (temporary loss of loosely bound water) Shade must be determined before isolation and the preparation of a tooth for a tooth colored restoration. www.indiandentalacademy.com
  • 60. RESILIENCE Although enamel is vulnerable and incapable of self repair,its protective and functional adaptation is noteworthy.Carious demineralisation to the point of cavitation generally takes 3-4 years.Demineralisation of enamel is impeded because the apatite crystals 10 times larger than those in dentin. Enamel apatite crystals offer les surface to volume exposure and little space for acid penetration between the crystals www.indiandentalacademy.com
  • 61.  With preventive measures and exogenous or salivary renewal of calcium,phosphate and especially fluoride,the dynamics of demineralisation can be stopped or therapeutically reversed Enamel thickness and degree of mineralisation are greatest at the occlusal and incisal surfaces where masticatory contacts occurs.If enamel were uniformly crystalline,it would shatter with occlusal forces. www.indiandentalacademy.com
  • 62.  A substructure, organised into discrete parallel rods with the scalloped DEJ, minimises the transfer of occlusal stress laterally and directs it anisotropically or unidirectionally to the resilient dentinal foundation. The interwoven paths and interlocked key-hole morphology of the enamel rods help control lateral cleavage.As a functional adaptation to occlusal stress, spiraling weave of rod direction is so pronounced at the cusp tips of posterior teeth i.e. refered to as Gnarled Enamel. Further subdivision of enamel rods into distinct crystals separated by a thin organic matrix provides additional relief to help prevent fracture. www.indiandentalacademy.com
  • 63. ACID ETCHING Because there are 30,000 to 40,000 enamel rods/sq mm and the etch penetration increases the bondable surface area 10 to 20 fold, micromechanical bonding of resin restorative materials to enamel is significant.Acid etch modification of enamel for restoration retention provides a conservative, reliable alternative to traditional surgical methods of tooth preparation and restoration. www.indiandentalacademy.com
  • 64.  The enamel rod boundaries form natural cleavage lines through which longitudinal fracture may occur. The fracture resistance between enamel rods is especially imperiled if the underlying dentinal support is pathologically destroyed or mechanically removed by dental instrument. Loss of enamel rods that form the cavity walls or cavo margin of a dental restoration creates a gap defect similar to an occlusal fissure. Leakage or ingress of bacteria or their products may lead to secondary caries. Therefore, a basic tenet of cavity wall preparation is to bevel or parallel the direction of enamel rods and to avoid www.indiandentalacademy.com undercutting them.
  • 65.  A common precept, that cavity preparation should always be cut perpendicular to the external coronal surface, is not supported histologically. Each successive row of enamel rods runs slightly different course in a wave pattern, both horizontally and vertically, through the inner half of the thickness. And then continues in a relative straight parallel course to the surface. However ,on axial surfaces and cuspal slopes,the path of each row terminates a an oblique angle to the surface rather than at a perpendicular tangentt of 90 degrees. www.indiandentalacademy.com
  • 66.  Starting at 1 mm from the CEJ,the rods on the vertical surfaces run occlusally or incisally at approximately a 60 degree inclination and progressively incline approaching the marginal ridges and cusp tips,where the rods are essentially parallel to the long axis of the crown. The rods beneath the occlusal fissures are also parallel to the long axis,but rods on each side of the fissure vary upto 20 degrees from the long axis. Therefore if cut perpendicular to the external surface, occlusal walls of preparations on axial surfaces might incorporate compromised enamel.An obtuse enamel cavosurface angle would more parallel the rod direction and preserve the integrity of the enamel margin. www.indiandentalacademy.com
  • 67. www.indiandentalacademy.com
  • 68. ADHESION TO ENAMEL Adhesion to enamel is achievd through acid etching of this highly mineralised substrate,which substantially enlarges its surface area for bonding. This enamel bonding technique known as the acid etching technique,was the invention of Buonocore in 1955. Research into the underlying mechanism of the bond suggested that tag like resin extensions were formed and micromechanically interlocked with the enamel micro porosities created by etching www.indiandentalacademy.com
  • 69.  Enamel etching transforms the smooth enamel surface into an irregular surface with a high surface –free energy (about 72 dynescm). Acid etching removes about 10µm of the enamel surface and creates a micro porous layer from 5 to 50 µm deep. www.indiandentalacademy.com
  • 70.  3 enamel etching patterns have been described. Type 1:there is predominant dissolution of the prism cores. Type 2:there is predominant dissolution of the prism peripheries. Type 3:no prism structures are evident. Microtags are formed circularly between enamel prism peripheries;microtags are formed at the cores of enamel prisms.Microtags probably contribute most to the bond sterngth because of their greater quantity and large surface area www.indiandentalacademy.com
  • 71.  PHOSPHORIC ACID ETCHANTS Generally use of a phosphoric acid concentration between 30% and 40%,an etching time of not less than 15seconds and washing times of 5-10 seconds are recommended to achieve the most receptive enamel surface with bonding. www.indiandentalacademy.com
  • 72.  UNIVERSAL ENAMEL DENTIN CONDITIONING The selective enamel etchings technique is replaced by a total etch concept in which the conditioner or acid etchant is applied simultaneously to enamel and dentin. As a result 2 different micro retentive surfaces are exposed in which the adhesive resin will become micro mechanically inter-locked. Less concentrated phosphoric acids or weaker acids in variant concentrations such as citric,maleic,nitric and oxalic acid are used. www.indiandentalacademy.com
  • 73.  The objective of such universal enamel dentin conditioning agents is to find the best compromisd between etching enamel sufficiently to create a micro-retentive etched pattern and etching dentin mildly,avoiding exposure of collagen to a depth that is inaccessible for complete infiltration by resin. www.indiandentalacademy.com
  • 75. • The configuration of enamel walls is the shape, dimension, location, and angulation of enamel components in final tooth preparation.• The correlation is the relationship of the enamel configuration to surrounding tooth preparation and restoration details. www.indiandentalacademy.com
  • 76. • Whenever enamel is stressed, it tends to split along the length of the rods. This splitting is easier when the enamel rods is parallel to each other and will be somewhat difficult if the rods are interlaced and twisted together.• For an ideal enamel wall,Noy devised certain structural requirements. These requirements tend to take full advantage of the enamel’s hardness and strength and avoid the disadvantages of the enamel’s splitting characteristics. www.indiandentalacademy.com
  • 77. • STRUCTURAL REQUIREMENTS The enamel wall must rest upon some dentin. All carious dentin must be removed and the enamel cut back until it is supported by sound tooth structure. Otherwise there would be some portion of the enamel left standing that has been weakened by the dissolution of its minerals in backward caries. This enamel would most likely break down under the stress of mastication. www.indiandentalacademy.com
  • 78.  The enamel rods which form the cavosurface angle must have the inner ends resting on sound dentin. When this condition is established the dentin which is elastic gives the enamel which is brittle a certain degree of elasticity which is very important at the margins of restoration www.indiandentalacademy.com
  • 79. The cavosurface angle must be so trimmed or bevelled that the margins will not be exposed to injury in condensing the restorative material against it. www.indiandentalacademy.com
  • 80.  GENERAL PRINCIPLES FOR FORMULATION OF ENAMEL WALLS The enamel portion of a wall should be the smoothest portion of the preparation anatomy. Any roughness besides interfering with the proximity of tooth with the restorative material, will increase possibility of frail, loosely attached enamel rods, which will be detached during function increasing the leakage space in the critical marginal area. www.indiandentalacademy.com
  • 81.  Junction between different enamel walls should be rounded.This will improve adaptability of the restorative material at the preparation corners,in addition to decreasing sress concentration there. If inclining a preparation wall to follow the direction of enamel rods will nullify its resistance and retention capabilities,different planes for that walls should be established. www.indiandentalacademy.com
  • 82. • When the enamel preparation margins come to an area of abrupt directional changes of enamel walls,this area should be included in the preparation and the margins placed in areas of a more predictable rod pattern. www.indiandentalacademy.com
  • 83. ENAMEL CARIESHISTOLOGY : The striae of Retzius are regions characterised by reltively higher organic contents.Both the striae and the inherent spaces in prism boundaries provide sufficient porosity to allow movement of water and ions. Movement of ions though carious enamel can result in acid solution of the underlying dentin before actual cavitation of enamel surface. www.indiandentalacademy.com
  • 84. • Because the striae form horizontal lines of greater permeability in the enamel,they probably contribute to the lateral spread of the smooth surface lesions. www.indiandentalacademy.com
  • 85. • THE CLINICAL CHARACTERISTICS : On clean dry tooth earliest evidence of caries is a white spot which are chalky white and opaque and they are revealed only when the tooth surface is dry.This is incipient caries where the surface texture is unaltered and these areas of enamel loose their translucency because of the extensive surface porosity caused by demineralisation. Care must be taken to distinguish white spots of incipient caries from developmental white spot hypocalcification of enamel. www.indiandentalacademy.com
  • 86. • Incipient caries will partially or totally disappear visually when the enamel is hydrated(wet),while hypocalcified enamel is unaffected by drying and wetting. A more advanced lesion develops a rough surface i.e. softer than the unaffected normal enamel.Softened chalky enamel that can be chipped away with an explorer is a sign of active caries. Incipient caries of enamel can reminieralise. Non cavitated lesions retain most of the original crystalline framework of the enamel rods and the etched crystallites serve as nucleating agents for remineralisation. www.indiandentalacademy.com
  • 87. • Calcium and phosphate ions from the saliva can then penetrate the enamel surface and precipitate on the highly reactive crystalline surface.The supersaturationof saliva with calcium and phosphate ions serves as the driving force for the mineralisation process. Pesence of trace amounts of flouride ions during this process greatly enhances precipitation of calcium and phosphate ions resulting in the enamel becoming more resistant to subsequent caries attacks, because of the incorporation of more acid resistant flurophosphate. www.indiandentalacademy.com
  • 88. • Remineralised[arrested]lesions is observed clinically as intact, discolored, usually brown or black spots. The change in color is due to trapped organic debris and metallic ions within the enamel.These remineralised caries are more resistant to caries attack. They are not restored unless they are esthetically objectionable.. www.indiandentalacademy.com
  • 89. ZONES OF INCIPIENT LESION• The four regularly observed zones in a sectioned incipient lesion are• The translucent zone• The dark zone• The body of lesion• The surface zone www.indiandentalacademy.com
  • 90. • TRANSLUCENT ZONE• Deepest zone• The pores or voids form along the enamel prism boundaries due to hydrogen ion penetration.• Pore volume is 1%, 10 times greater than normal enamel.• DARK ZONE• Does not transmit polarised light.• Pore volume is 2-4%.• Loss of crystalline structure suggestive of demineralisation www.indiandentalacademy.com
  • 91. • BODY OF LESION• Largest portion in demineralising phase.• Largest pore volume from 5% at the periphery to 25% at the centre.• Striae of retzius are well marked indicating preferential dissolution along the areas of relatively higher porosity.• SURFACE ZONE• Relatively unaffected by caries attack.• Lower pore volume than the body of lesion. www.indiandentalacademy.com
  • 92. Minimal intervention dentistry• ART It is a procedure based on excavating carious cavities in teeth using hand instrument only and restoring with adhesive filling material like GIC. www.indiandentalacademy.com
  • 93. Chemo mechanical system• Carisolv A gel that selectively attacks denatured collagen in carious dentin.thus making the carious dentin softer.A set of specially designed instrument used for removal of softened material. www.indiandentalacademy.com
  • 94. Air Abrasion (Kinetic System)• It uses a concentrated stream of air and fine powder to remove decay without drilling.• Uses finely graded 27.5µm aluminium oxide powder aministerd under compressed air through a fine tip. www.indiandentalacademy.com
  • 95. Ozone treatment• Powerful biocide• Rapidly penetrate the bacteria and kill them in their niche.• Alters metabolic products of bacteria that inhibits mineralization www.indiandentalacademy.com
  • 98. PHYSICAL CHARACTERISTICS• Because of high mineral content, enamel is extremely hard, a property that enables it to withstand the mechanical forces during mastication• Enamel forms a protective covering of variable thickness over the entire surface of the crown.• It is approx.2-2.5 mm near the cusps thinning to knife edge at the neck of the tooth. This variation in thickness influences the color of enamel, since the underlying dentin is seen through the thinner regions.• It is translucent and varies in colour from light yellow to grayish white www.indiandentalacademy.com
  • 99. • Translucency can be attributed to variation in degree of calcification and homogenicity.• Yellowish teeth has a thin, translucent enamel through which the yellow colour of the dentin is visible, and grayish teeth has a more opaque enamel. Grayish teeth frequently show a slighty yellow colour at the cervical area, presumably because the thinness of the enamel permits the light to strike the underlying yellow dentin and be reflected. Incisal areas has bluish tinge where the thin edge consists only of a double layer of enamel. www.indiandentalacademy.com
  • 100. CHEMICAL CHARACTERSITICS• It is highly mineralized tissue with 96% mineral and 4% organic material and water.• Inorganic content of enamel is crystalline calcium phosphate.• Various ions such as Sr, Mg, Pb a F, if present during enamel formation may be adsorbed or incorporated by the hydroxapatite crystals.• The entire volume of enamel is occupied by the densely packed hydroxyapatite crystals.• The organic material consists of tyrosine rich amelogin polypeptide.• Proteins in enamel contains high percentages of Serine, Glutamic acid and Glycine. www.indiandentalacademy.com
  • 101. • Roentgen-ray diffraction studies reveal that the molecular structure in typical of the group of proteins called cross-beta-proteins.• In addition, histochemcial reactions have suggested that the enamel forming cells of developing teeth also contain a polysaccharide- protein complex and that an acid mucopolysaccharide enters the enamel itself at the time when calcification becomes a prominent feature. www.indiandentalacademy.com
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  • 103. AGE CHANGES• Enamel is a non-vital tissue that is incapable of regeneration.• With age, it becomes progressively worn away in the regions of masticatory area.• Wear facets are increasingly pronounced in older people• Other age changes seen are discoloration and reduced permeability• Linked to these changes there is an apparent reduction in incidence if caries.• Water content of enamel also decreases.• Teeth darken with age. It may be due to addition of organic material to enamel from the environment or may be due to the deepening of dentin colour seen through the progressively thinning layer of transclucent enamel. www.indiandentalacademy.com
  • 104. OUTER ENAMEL EPITHELIUM• In early stages of development the outer enamel epithelium consists of single layer of cuboidal cells separated from the surrounding connective issue of denial sac by a delicate basement membrane.• During enamel formation the cells of outer enamel epithelium develop villi, cytoplasmic vesicles and increase in number of mitochondria all indicating cell specialization for active transport of materials. www.indiandentalacademy.com
  • 105. STELLATE RETICULUM• it forms the middle part of the enamel organ, the neighboring cells are separated by the wide intercellular spaces filled by a large amount of intercellular substances.• They are flat to cuboidal in shape and are arranged in one to three layers.• They are connected with each other with the neighboring cells of stellate reticulum and the inner enamel epithelium by desmosomes.• It is believed that stratum intermedium is involved in production of enamel itself. www.indiandentalacademy.com
  • 106. INNER ENAMEL EPITHELIUM• The cells of the inner enamel epithelium are derived from the basal cell layer of oral epithelium.• Before enamel formation begins, these cells assume a columnar form and differentiate into ameloblast that produce the enamel matrix.• The cell differentiation occurs earlier in the region of the incisal edge or cusps than in the area of cervical loop. www.indiandentalacademy.com
  • 107. AMELOGENESIS• Enamel formation occurs in 2 steps• First step produces a partially mineralized (30%) of enamel once the full width of the enamel has been depicted.• The second step involves significant influx of mineral along with removal of organic materials and water.• Enamel formation begins at the early crown stage of tooth development and involves the differentiation of cells of the tips of the cusps.• Secretory phase of amelogenesis• This phase involves secretion and synthesis of the organic matrix of the enamel. www.indiandentalacademy.com
  • 108. • The organic matrix consists of enamel protein, a number of enzymes including serine proteases, metallo proteases, phosphates and traces of other protein analogous to glycerolated phosphorylated and sulphated non-collagenous proteins.• 90% of enamel proteins are amelogenin• 10% are tuftelin and amelin www.indiandentalacademy.com
  • 109. MINERALIZATION OF ENAMEL• It takes places in IV stages• I stage involves immediate partial mineralization in the matrix segments and the interprismatic substances as they are laid down.• 30% of mineralization is achieved during I stage.• In the II stage (maturation) there is greater completion of mineralization.• The II stage begins with a secondary increase in mineralization that starts at the surface of the enamel and sweeps rapidly into the deeper layer until reaches the innermost 8 micron layer.• A tertiary increase in mineral rebounding from the innermost layer outward the enamel surface forms the III stage.• A surface layer of 15 microns wide can be distinguished during this phase and it mineralizes slowly. www.indiandentalacademy.com
  • 110. • As the IV stage commences the outer layer mineralizes rapidly and heavily and becomes the most mineralized part of the enamel.• Enamel is most highly mineralized at its surface with the degree of mineralization decreasing toward the DEJ until the inner most layer is reached where there is increased mineralization.• Throughout amelogenesis this complicated process in under cellular control and associated cells undergo significant morphologic changes. www.indiandentalacademy.com
  • 111. CLINICAL CONSIDERATIONDevelopment of caries in enamel• Dental caries is a microbial disease of the calcified tissue of the teeth, characterized by demineralization of inorganic portion and destruction of organic substance of tooth.• Clinical characteristics• Patients with dental caries usually have extensive deposits of plaque on the tooth which must be removed before clinical examination.• On clean dry tooth the earliest evidence of caries is a white spot which are chalky white and opaque and they are revealed only when the tooth surface is dry. This is incipient caries where the surface texture is unaltered and these areas of enamel lose their translucency because of the extensive subsurface porosity caused by demineralization. www.indiandentalacademy.com
  • 112. • Care must be exercised to distinguish white spots of incipient caries from developmental white spot hypocalcification of enamel. Incipient caries will partially or totally disappear visually when the enamel is hydrated (wet), while hypocalcified enamel is unaffected by drying and wetting.• A more advanced lesion develops a rough surface that is softer than the unaffected normal enamel. Softened chalky enamel that can be chipped away with an explorer is a sign of active caries.• Incipient caries of enamel can remineralize. Non- Cavitated lesions retain most of the original crystalline framework of the enamel rods and the etched crystallites serve as nucleating agents for remineralization, Calcium and phosphate ions from the saliva can then penetrate the enamel surface and precipitate on the highly reactive crystalline surfaces in the enamel lesion. The super saturation of saliva with the Calcium and Phosphate ions serves as the driving force for the remineralization process. www.indiandentalacademy.com
  • 113. • Presence of trace amounts of Fluoride ions during this remineralization process greatly enhances the precipitation of Calcium and Phosphate ions, resulting in the remineralized enamel becoming more resistant to subsequent caries attacks, because of the incorporation of more acid- resistant Flouorophosphate.• Remineralized (arrested) lesions is observed clinically as intact, discolored, usually brown or black spots. The change in colour is due to trapped organic debris and metallic ions within the enamel. These remineralized caries are more resistant to caries attack than the adjacent unaffected enamel. They shouldnt be restored unless they are esthetically objectionable. www.indiandentalacademy.com
  • 114. • Hicks reported the effect of caries-like lesions and progression in sound enamel after argon laser irradiation. Surface melting and sealing (fusing) of enamel and dentinal surfaces occurred. The resulting surfaces lost a significant amount of organic, water and carbonate content, resulting in a marked resistance to demineralization. The threshold pH for enamel dissolution was lowered from 5.5 to 4.78. The hard tooth structure was four times more resistant to acid dissolution. This increased resistance resulted in a significant reduction in carious lesions depth. The mircropores of lased enamel may trap the released ions (calcium, phosphate, fluoride) that become dissolved during caries formation. Lased enamel has a greater affinity for calcium, phosphate and fluoride ions, with resulting reprecipitation of the mineral phase. Laser treatment is an important treatment in the prevention of caries sound enamel. www.indiandentalacademy.com
  • 115. • Irradiation of dental enamel by specific wavelengths and fluences of CO2 laser light beneficially alters the chemical composition of the crystals, decomposing the carbonate component, markedly reducing the acid relativity of the mineral. Efficient conversion of light to heat in the outer few micrometers of enamel increases the resistance of the mineral to acid if a critical threshold temperature is reached. This surface alteration has a marked effect on inhibition of subsurface caries progression. www.indiandentalacademy.com
  • 116. Cavity Preparation• Although enamel is the hardest tissue in human body, it comprises one of the weakest points in a preparation wall especially when it looses its dentinal support.• Enamel rods are stronger than interprismatic enamel. So whenever enamel is stressed it tends to split along the length of rods.• This splitting is easier when the rods are parallel to each other. If rods are interlaced and twisted together then spitting will be difficult.• Enamel must rest on sound dentine• Enamel rod which forms the cavosurface angle must be supported or be resting on sound dentine and their outer end must be covered by the restorative material. www.indiandentalacademy.com
  • 117. • The Enamel rod which forms the cavorsurface angle must have their inner end resting on sound dentine.• The vcavosurface angle must be so beveled that the margins will not be exposed to injury in condensing the restorative material. www.indiandentalacademy.com
  • 118. Enameloplasty• It is grinding away a shallow developmental enamel fissure or pit to create a smooth saucer shaped surface which is self cleansing or easily cleaned.• This procedure does not require external outline form nor does it equire any restorative material. www.indiandentalacademy.com
  • 119. Prepartions of enamel wall before acid conditioning• Partial bevel: This should involve 1/3 to 1/2 of the enamel wall at 45-70 degrees to the cavity walls. It is always used when the cavity preparations internal anatomy and walls can adequately retain the restoration, and acid- conditioning is used only to reduce marginal leakage. It is also to be used with restorative resins exhibiting minimal setting shrinkage.• Long bevel: In this design feature, the entire enamel wall is beveled at 45-70 degrees to the cavity wall. It is used when the cavity preparations details are not retaining enough for the resinous restoration, or when the resinous material used exhibits considerable shrinkage during polymerization. This design will also decrease microleakage. www.indiandentalacademy.com
  • 120. • Hollow ground bevel:In this design feature, about two-thirds of the enamel wall thickness is ground in a concave manner so the cavity margin will have a right-angled cavo-surface angle, with butt joint between the restorative material and the marginal enamel. This combines the advantage of the retaining, sealing and acid- conditioning of the enamel with the strong butt- joint and definite junction of tooth structure and restorative material. The hollow ground bevel is used for inaccessible areas, e.g., gingival walls to avoid possible overhangs which could occur with either partial bevel or long bevel finish lines. It is also indicated for areas of direct loading, to accommodate the maximum bulk of restorative material. www.indiandentalacademy.com
  • 121. • Scalloping the margins:This feature is used in conjunction with a partial or long bevel, in order to further increase the surface area and irregularities of the enamel that is to be conditioned. It is used when conditioned enamel will play a major role in the retention of the restoration. Scalloping has the disadvantage of greater possibilities of flash and overhangs. Under no circumstances should scalloping be used for gingival walls or inaccessible portions of any wall margin. www.indiandentalacademy.com
  • 122. • Skirting:This feature is used if conditioned enamel will be the main retentive mode for resinous material. In restoring a wide and shallow defect, it is essential to involve enamel from the surrounding surfaces of the tooth. The involved enamel surface should be atleast double the surface area of the defect to be restored or minimally 1mm in width. Also, the involved enamel surface should be distributed around the defect so that principal, auxillary and reciprocating retaining areas are in accordance with the magnitude, location and direction of loading forces, both in static and dynamic occlusal contacts. Such surface involvement is called a Skirt. www.indiandentalacademy.com
  • 123. Etching Time• An etching time of 60 secs was originally recommended for permanent enamel using 37% phosphoric acid. But studies using scanning electron microscopy (SEM) showed that a 15 sec etch enamel resulted in a similar surface roughness as that provided by a 60 sec etch. Clinically, reduced etching time do not appear to diminish the retention of pit & fissure sealants. Acids should be applied on enamel with a soft sponge or cotton Pellet, using light patting touches with no rubbing at all. Acid conditioned enamel should be washed for one minute using a copious stream of water. It should then be air- dried before applying the components of the restoration. After drying a characteristic whitish or chalkish appearance is the sign for proper enamel conditioning. www.indiandentalacademy.com
  • 124. • Co2 laser can cause changes in enamel comparable to acid etching. laser will not cause any damage to dentin or pulp as the intensity is controlled. The surface treated by laser is resistant to caries attack and harder. This may be considered comparable to acid etching procedure and may be used as an adjuvant.• Nd: YAG Laser absorption enamel can be enhanced by placement of an initiator (a dark organic substance) on the area of the enamelin which etching is desired. By this technique, the procedure time is saved by 50% and the need to protect gingiva and dentinal tissue is eliminated. www.indiandentalacademy.com
  • 125. Enamel Microabrasion• Enamel microabrasion is not a bleaching technique but a selective erosion process that removes stained enamel. Currently microabrassion is recommended for the removal of stains that are superficial and localized in enamel. It is the primary treatment of choice for superficial fluorosis stain, removal, small white stains and some multicolored stains, but not deep internal stains.• The generic use of 18% hydrochloric acid and pumice can be used for enamel microabrasion. Only one commercially developed system currently exists for enamel microabrasion. The PREMA system (Premier enamel micro abrasion) compound contains an abrasive mixed with hydrochloric acid of approximately 10%. This system offers a unique, easy and safe approach to enamel microabrassion. www.indiandentalacademy.com
  • 126. Macroabrasion• An alternative technique for the removal of localized superficial white spots (not subject to conservative, remineralization therapy) and other surface stains or defects is called macroabrasion. macroabrasion simply utilizes a 12-fluted composite finishing bur or a micron finishing diamond in a high speed handpiece to remove the defect. Care must be taken to use light intermittent pressure and to carefully monitor removal of tooth structure in order to avoid irreversible damage to the tooth. www.indiandentalacademy.com
  • 127. • Air-water spray is recommended not only as a coolant, but also to maintain the tooth in a hydrated state to facilitate assessment of defect removal. Teeth that possess white spot defects are particularly susceptible to dehydration resulting in other apparent white spots that are normally seen when the tooth is hydrated. Dehydration exaggerates the appearance of white spots and make defect removal difficult to assess. www.indiandentalacademy.com
  • 128. • Microabrasion is recommended over macroabrasion for the treatment of superficial defects in children because of better operator control and superior patient acceptance.To accelerate the process, a combination of macroabrasion and microabrasion also may be considered. Gross removal of the defects accomplished with macroabrasion followed by finer treatment with microabrasion. www.indiandentalacademy.com
  • 129. Bleaching• The lightening of the color of a tooth through the application of a chemical agent to oxidize the organic pigmentation of the tooth is referred to as bleaching. Most bleaching techniques use some form or derivative of hydrogen peroxide in different concentrations and application techniques. The mechanism of action of bleaching teeth with hydrogen peroxide is considered to be oxidation of organic pigments. With all bleaching techniques, there is a transtitory decrease in the potential bond strength of composite when it is applied to bleached, etched enamel. This reduction in bond strength results in bond strength results from residual oxygen or peroxide residue in the tooth which inhibits set of the bonding resin, Precluding enamel tag formation in the tched enamel. However no loss of bond strength is noted if the composite restorative treatment is delayed at least 1 week after www.indiandentalacademy.com cessation of any bleaching.
  • 130. Types of Bleaching1. Non-Vital bleaching 1. in-Office Thermocatalytic technique 2.Out of the office technique-Walking Bleach2. Vital Bleaching 1.In Office technique-Power bleaching. 2.Dentist Prescribed home applied technique (Nightguard vital bleaching) www.indiandentalacademy.com
  • 131. Laser tooth whitening• The whitening effect of the laser is achieved by a chemical oxidation process. Once the laser energy is applied, the hydrogen peroxide breaks down to water and a free oxygen radical, which combines with and thus removes the stain molecule.• Laser tooth whitening was officially started in Feb 1996 with the approval of ion laser technology (ILT) argon and Co2 lasers to be used wit a patented system of chemicals. Argon laser energy, in the form of a blue light, with the wavelength of about 480 nm in the visible part of the spectrum, is absorbed by dark colour. It seems to be the ideal instrument to be used in tooth whitening when used together with hydrogen peroxide and a patented catalyst. This affinity to dark stains ensures that the yellow brown colors can be easily removed. www.indiandentalacademy.com
  • 132. Recent Advances• As with other structured of the head and face, the teeth are formed under the control of many genes. Scientists at NIDCR and NIDCR supported institutions have identified several of the genes that go into making a tooth - from the dentin that the lines the pulp cavity and root canals, to the exterior enamel, the hardest substance in the human body. Mature enamel is unique in that it is practically pure mineral, a mix of calcium and phosphate, with little of the protein component that is present in bone. During enamel formation, however, proteins are essential in laying down a structural framework and serving as catalytic sites for building enamel crystals. Recently, researchers have made great strides in testing out the roles of the various enamel proteins in normal and abnormal tooth development www.indiandentalacademy.com
  • 133. • Tuftelin is an important enamel protein whose gene was recently located on chromosome 1. Tuftelin is thought to bind mineral and acts as a focal point for initial crystal formation. This gene is a candidate for autosomal amelogenesis imperfecta.Amelogenin, the most abundant enamel protein, was found to have genes on both the X and Y chromosomes. The genes produce slightly different proteins, a fortuitous event that now allows forensic scientists of determine the sex of an individual from a mere tooth fragment. Amelogenin is also thought to regulate the size and orientation of the calcium hydroxyapatite crystals during enamel formation. www.indiandentalacademy.com
  • 134. • Not long ago, a deletion in the amelogenin gene was found to be the cause of X-linked amelogenesis imperfecta. This condition, which occurs in about 1:14,000 individuals in the U.S., produces a weakened tooth enamel.Scientists at NIDCRs laboratories in Bethesda, Marryland have identifies a new protein that looks like another key player in enamel formation. The protein, named ameloblastin, was discovered through the NIDCRs cranio facial, oral, dental genome project. This ambitious undertaking has identified over 400 genes that are active in rodent tooth development 60 ler cent of them previously unknown genes. The gene for ameloblastin is particularly intriguing because it is active in enamel forming cells. The human equivalent of this gene is located on a region of choromosome 4 that is linked to several tooth disorders. www.indiandentalacademy.com
  • 135. Reference1. Oral history - Ten Cate.2. Orbans histology and embryology3. Operative dentistry - Clifford M. Sturdevant4. Operative dentistry - Marzouk.5. Contemporary Esthetic dentistry; Practice fundamentals -Bruce J.Crispin.6. Dental Clinics of North America - Esthetic Dentistry-October 1998.7. Dental Clinics of North America -Laser Dentistry -October 20008. Federation of Operative Dentistry -Volume I - December, 1990. www.indiandentalacademy.com
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