Bonding agents/ invisible aligners

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Bonding agents/ invisible aligners

  1. 1. BONDING AGENTSBONDING AGENTS Seminar on INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.comwww.indiandentalacademy.com
  2. 2. CONTENTSCONTENTS  INTRODUCTIONINTRODUCTION  HISTORICAL BACK GROUNDHISTORICAL BACK GROUND  PRINCIPLES OF ADHESIONPRINCIPLES OF ADHESION  REQUIREMENTS FOR ADHESIONREQUIREMENTS FOR ADHESION  MECHANISMS OF ADHESIONMECHANISMS OF ADHESION  COMPOSITION AND MICROMORPHOLOGYCOMPOSITION AND MICROMORPHOLOGY OF ENAMELOF ENAMEL  ENAMEL ADHESIONENAMEL ADHESION  ENAMEL BONDING AGENTSENAMEL BONDING AGENTS  COMPOSITION AND MICROMORPHOLOGYCOMPOSITION AND MICROMORPHOLOGY OF DENTINOF DENTIN  DENTIN ADHESIONDENTIN ADHESION www.indiandentalacademy.comwww.indiandentalacademy.com
  3. 3.  FACTORS AFFECTING ADHESIONFACTORS AFFECTING ADHESION  DENTIN SMEAR LAYERDENTIN SMEAR LAYER  DENTIN CONDITIONERSDENTIN CONDITIONERS  PRIMERSPRIMERS  ROLE OF HYBRID LAYERROLE OF HYBRID LAYER  REQUIREMENTS OF BONDING AGENTSREQUIREMENTS OF BONDING AGENTS  CLASSIFICATION OF BONDING AGENTSCLASSIFICATION OF BONDING AGENTS  MODREN CLASSIFICATION OF ADHESIVESMODREN CLASSIFICATION OF ADHESIVES  MOIST VERSUS DRY DENTIN BONDINGMOIST VERSUS DRY DENTIN BONDING  ROLE OF PROTIENS IN DENTIN BONDINGROLE OF PROTIENS IN DENTIN BONDING  MICROLEAKAGEMICROLEAKAGE  BIOCOMPATIBILITYBIOCOMPATIBILITY  CONCLUSIONCONCLUSION  BIBLOGRAPHYBIBLOGRAPHY www.indiandentalacademy.comwww.indiandentalacademy.com
  4. 4. CLINICAL FACTORS AFFECTINGCLINICAL FACTORS AFFECTING ADHESION:ADHESION: 1.1. Salivary and / or blood contaminationSalivary and / or blood contamination: -: - Difficulty in controlling saliva or blood whileDifficulty in controlling saliva or blood while accomplishing restorative therapy is aaccomplishing restorative therapy is a significant challenge, these contaminants cansignificant challenge, these contaminants can influence some adhesion concepts in ainfluence some adhesion concepts in a negative manner. Although dentin is wetnegative manner. Although dentin is wet substance, the constituents of saliva and bloodsubstance, the constituents of saliva and blood create an environment that can destroy dentincreate an environment that can destroy dentin bonding.bonding. www.indiandentalacademy.comwww.indiandentalacademy.com
  5. 5. Thus for years both textbooks ofThus for years both textbooks of operative dentistry and many adhesiveoperative dentistry and many adhesive manufacturers have recommended themanufacturers have recommended the use of rubber dam for proper isolationuse of rubber dam for proper isolation and prevention of cavity contamination.and prevention of cavity contamination. www.indiandentalacademy.comwww.indiandentalacademy.com
  6. 6.  Fritz et alFritz et al studied the effect of salivarystudied the effect of salivary contamination during bonding procedures,contamination during bonding procedures, on the bond strength. They stated thaton the bond strength. They stated that any kind of contamination of the bondingany kind of contamination of the bonding area should be avoided which is still bestarea should be avoided which is still best accomplished with rubber dam. Oneaccomplished with rubber dam. One bottle bonding agents have the advantagebottle bonding agents have the advantage that in contrast to previous generationthat in contrast to previous generation adhesives; they are less sensitive toadhesives; they are less sensitive to salivary contamination of etched enamelsalivary contamination of etched enamel and dentin.and dentin. www.indiandentalacademy.comwww.indiandentalacademy.com
  7. 7. They concluded that:They concluded that:  Air-drying of the contaminated area mustAir-drying of the contaminated area must strictly be avoided.strictly be avoided.  Contamination of the uncured adhesive isContamination of the uncured adhesive is not critical because saliva and adhesive arenot critical because saliva and adhesive are simply cleaned and the adhesive is reapplied.simply cleaned and the adhesive is reapplied.  Any contamination of already cured adhesiveAny contamination of already cured adhesive layer seriously compromises the bond, nolayer seriously compromises the bond, no matter how carefully the contaminant ismatter how carefully the contaminant is rinsed; this situation calls for resurfacing ofrinsed; this situation calls for resurfacing of the cavity and repetition of the entirethe cavity and repetition of the entire bonding procedure.bonding procedure. www.indiandentalacademy.comwww.indiandentalacademy.com
  8. 8.  T Kaneshima et al, in 2001, conducted aT Kaneshima et al, in 2001, conducted a study to evaluate the influence of bloodstudy to evaluate the influence of blood contamination on bond strengths. Thecontamination on bond strengths. The results obtained may be summarized asresults obtained may be summarized as follows:follows: If blood contamination occurred beforeIf blood contamination occurred before collagen fibers were exposed by eithercollagen fibers were exposed by either phosphoric acid etching or self-etchingphosphoric acid etching or self-etching primer application, the contaminationprimer application, the contamination had almost no influence on bondhad almost no influence on bond strength.strength. www.indiandentalacademy.comwww.indiandentalacademy.com
  9. 9.  Blood contamination of the dentin surfaceBlood contamination of the dentin surface where collagen fibers had been exposedwhere collagen fibers had been exposed decreased the bond strength even if thedecreased the bond strength even if the blood was washed away with a stream ofblood was washed away with a stream of water and air dried. However, when thewater and air dried. However, when the contaminated collagen fibers werecontaminated collagen fibers were dissolved or when blood contaminationdissolved or when blood contamination occurred after the exposed collagen fibersoccurred after the exposed collagen fibers were dissolved, the bond strength couldwere dissolved, the bond strength could be maintained by rinsing the blood awaybe maintained by rinsing the blood away and applying the self-etching dentinand applying the self-etching dentin primer.primer. www.indiandentalacademy.comwww.indiandentalacademy.com
  10. 10. The bond strength markedly decreasedThe bond strength markedly decreased when blood contamination occurred afterwhen blood contamination occurred after the self-etching primer application, butthe self-etching primer application, but was restored by reapplying the primer.was restored by reapplying the primer.  Based on these results, it is suggestedBased on these results, it is suggested that if the contamination occurred on thethat if the contamination occurred on the dentin where the self-etching dentin primerdentin where the self-etching dentin primer had already been applied, thehad already been applied, the contaminated surface should be rinsedcontaminated surface should be rinsed with water, air dried, and recoated with thewith water, air dried, and recoated with the dentin primer to restore the bond strengthdentin primer to restore the bond strength potential.potential. www.indiandentalacademy.comwww.indiandentalacademy.com
  11. 11. Moisture Contamination from AirMoisture Contamination from Air syringessyringes::  An unrecognized problem in most dentalAn unrecognized problem in most dental offices is water leakage from air wateroffices is water leakage from air water syringes. The source of leakage can besyringes. The source of leakage can be lack of drying devices on airlines leadinglack of drying devices on airlines leading from compressor, allowing wet air hasfrom compressor, allowing wet air has carried to the syringe.carried to the syringe. www.indiandentalacademy.comwww.indiandentalacademy.com
  12. 12. Oil contamination of hand piece or AirOil contamination of hand piece or Air water syringewater syringe: -: -  Adhesives combined with oilAdhesives combined with oil contamination provided an unpredictablecontamination provided an unpredictable clinical result and potential clinical failure.clinical result and potential clinical failure. Observation of oil present in the airlines isObservation of oil present in the airlines is not difficult.not difficult. www.indiandentalacademy.comwww.indiandentalacademy.com
  13. 13.  A simple test may be conducted byA simple test may be conducted by blowing air from air syringe or hand pieceblowing air from air syringe or hand piece on to a dry impermeable surface such ason to a dry impermeable surface such as glass slab or dry rubber glove andglass slab or dry rubber glove and observing any residue that is present. Oilobserving any residue that is present. Oil appears similar to water on dry surface butappears similar to water on dry surface but will not evaporate. Water will evaporatewill not evaporate. Water will evaporate from the test surface. Removing all oilfrom the test surface. Removing all oil from dental airlines should be thefrom dental airlines should be the immediate objective. Oil filters should beimmediate objective. Oil filters should be placed after the air compressor and beforeplaced after the air compressor and before the air syringe or hand piece.the air syringe or hand piece. www.indiandentalacademy.comwww.indiandentalacademy.com
  14. 14.  However, Bruno T. Rosa et al conducted aHowever, Bruno T. Rosa et al conducted a study to evaluate resin bond strength tostudy to evaluate resin bond strength to enamel contaminated with handpiece oil.enamel contaminated with handpiece oil. The result of this study showed that- allThe result of this study showed that- all bonding systems tested in this study havebonding systems tested in this study have a mean shear bond strength of at least 20a mean shear bond strength of at least 20 Mpa to dry, uncontaminated etchedMpa to dry, uncontaminated etched enamel. In both situations ofenamel. In both situations of contamination with oil, before or aftercontamination with oil, before or after etching, the mean shear bond strengthetching, the mean shear bond strength was atleast 18 MPa for all adhesives,was atleast 18 MPa for all adhesives, which indicates that oil contamination hadwhich indicates that oil contamination had little effect on bondinglittle effect on bonding www.indiandentalacademy.comwww.indiandentalacademy.com
  15. 15. Surface roughness of tooth surfaceSurface roughness of tooth surface:: --  Use of diamonds for tooth preparation isUse of diamonds for tooth preparation is most common in clinical dentistry.most common in clinical dentistry. Diamonds create irregularities in toothDiamonds create irregularities in tooth structure that is related directly to the size ofstructure that is related directly to the size of the diamond particles used on the diamondthe diamond particles used on the diamond abrasive instrument. Increased surface areaabrasive instrument. Increased surface area created by surface roughness explains thecreated by surface roughness explains the slight better bonds. It is possible thatslight better bonds. It is possible that mechanical retention may be increasedmechanical retention may be increased slightly by the microscopic roughnessslightly by the microscopic roughness produced on dentin or enamel by cuttingproduced on dentin or enamel by cutting instruments .instruments . www.indiandentalacademy.comwww.indiandentalacademy.com
  16. 16. Mechanical under cuts in toothMechanical under cuts in tooth preparationpreparation: -: -  Since, the beginning of dentistry, mechanicalSince, the beginning of dentistry, mechanical under cuts has been placed in toothunder cuts has been placed in tooth preparation to provide retention forpreparation to provide retention for subsequently used restorative materials. Ifsubsequently used restorative materials. If undercuts are present in tooth structure, theyundercuts are present in tooth structure, they hold restorative materials from bodilyhold restorative materials from bodily dislodgment from the preparations, and theydislodgment from the preparations, and they may also resist some microscopic movementmay also resist some microscopic movement of the restorative material caused by thermalof the restorative material caused by thermal or polymerization influences.or polymerization influences. www.indiandentalacademy.comwww.indiandentalacademy.com
  17. 17.  Therefore, restorations with traditional dentinTherefore, restorations with traditional dentin undercuts as well as chemical bonding, mayundercuts as well as chemical bonding, may produce better results, such as less leakageproduce better results, such as less leakage than those depending on adhesive alone.than those depending on adhesive alone. (Clim 1990). Whereas in a recent review of(Clim 1990). Whereas in a recent review of literature, Gordon J. Christensen hasliterature, Gordon J. Christensen has suggested “It seems logical to bondsuggested “It seems logical to bond restorative materials to tooth structures,restorative materials to tooth structures, reducing or eliminating the need to cut awayreducing or eliminating the need to cut away enamel or dentin to produce retentiveenamel or dentin to produce retentive grooves and undercuts, and reducinggrooves and undercuts, and reducing leakage around restorations.”leakage around restorations.” www.indiandentalacademy.comwww.indiandentalacademy.com
  18. 18. 6.6. Presence of plaque, calculus, andPresence of plaque, calculus, and extrinsic stains / debrisextrinsic stains / debris:: --  Any enamel / dentin surface that requiresAny enamel / dentin surface that requires bonding must be cleaned thoroughly beforebonding must be cleaned thoroughly before the bonding procedure begins. Plaquethe bonding procedure begins. Plaque present on the tooth surface preventspresent on the tooth surface prevents etching with 37% phosphoric acid. Toothetching with 37% phosphoric acid. Tooth surface stains and dental calculus if notsurface stains and dental calculus if not removed will not permit bonding. The toothremoved will not permit bonding. The tooth surface should be cleaned thoroughly beforesurface should be cleaned thoroughly before bonding either by use of scalers, abrasivebonding either by use of scalers, abrasive prophylactic pastes, rubber cups or evenprophylactic pastes, rubber cups or even abrasive rotary instruments.abrasive rotary instruments. www.indiandentalacademy.comwww.indiandentalacademy.com
  19. 19. TOOTH RELATED FACTORS AFFECTINGTOOTH RELATED FACTORS AFFECTING ADHESIONADHESION  1.1. Physico chemical properties of dentin thatPhysico chemical properties of dentin that complicate dentinal adhesioncomplicate dentinal adhesion: -: - www.indiandentalacademy.comwww.indiandentalacademy.com
  20. 20.  Mineralized dentin is relatively stiff whichMineralized dentin is relatively stiff which varies with dentinal depth. Following acidvaries with dentinal depth. Following acid etching the de-mineralized dentin matrixetching the de-mineralized dentin matrix becomes very soft and elastic. Infact, thebecomes very soft and elastic. Infact, the modulus of elasticity of demineralizedmodulus of elasticity of demineralized dentinal matrix is only about 5Mpadentinal matrix is only about 5Mpa (Macid(Macid et al 1996et al 1996), which is 100 times lower than), which is 100 times lower than that of mineralized dentin. The clinicalthat of mineralized dentin. The clinical implication of this low stiffness is that theimplication of this low stiffness is that the fibril network can easily collapse when air-fibril network can easily collapse when air- dried, there by interfering with the up takedried, there by interfering with the up take of adhesive monomers.of adhesive monomers. www.indiandentalacademy.comwww.indiandentalacademy.com
  21. 21.  Further the permeability of bondingFurther the permeability of bonding substrates to monomers and monomersubstrates to monomers and monomer diffusability in to the substrates are essentialdiffusability in to the substrates are essential factors for the hybridization of resins infactors for the hybridization of resins in dental substrates. Mineralized dentinaldental substrates. Mineralized dentinal matrix is relatively impermeable.matrix is relatively impermeable. Permeability refers the ability of substance toPermeability refers the ability of substance to move across diffusion Barrier (i.e. amove across diffusion Barrier (i.e. a substrate). Two types of dentinalsubstrate). Two types of dentinal permeability must be considered. Thepermeability must be considered. The diffusion of substances through tubulesdiffusion of substances through tubules filled with dentinal fluid to reach the pulp isfilled with dentinal fluid to reach the pulp is intratubular dentinal permeability (Hansen etintratubular dentinal permeability (Hansen et al. 1992; Hanks et al. 1994).al. 1992; Hanks et al. 1994). www.indiandentalacademy.comwww.indiandentalacademy.com
  22. 22.  The second important type of dentinalThe second important type of dentinal permeability is the diffusion of monomer intopermeability is the diffusion of monomer into demineralized intertubular dentin, the dentindemineralized intertubular dentin, the dentin between the tubules. This is referred to asbetween the tubules. This is referred to as intertubular dentinal permeability. After theintertubular dentinal permeability. After the surface is acid etched and rinsed with water,surface is acid etched and rinsed with water, these spaces are filled with water. It isthese spaces are filled with water. It is through these spaces that adhesivethrough these spaces that adhesive monomer must diffuse if it has to infiltratemonomer must diffuse if it has to infiltrate the demineralized dentinal matrix. Boththe demineralized dentinal matrix. Both intratubular and intertubular dentinalintratubular and intertubular dentinal permeability are important in dentin bonding.permeability are important in dentin bonding. www.indiandentalacademy.comwww.indiandentalacademy.com
  23. 23.  Along with this dentinal permeability andAlong with this dentinal permeability and consequent internal dentinal wetness,consequent internal dentinal wetness, these depend on several factors like thethese depend on several factors like the diameter and the length of the tubule, thediameter and the length of the tubule, the viscosity of the dentinal fluid,the surfaceviscosity of the dentinal fluid,the surface area available for diffusion, the patency ofarea available for diffusion, the patency of the tubules and rate of removal ofthe tubules and rate of removal of substances. The variability in dentinalsubstances. The variability in dentinal permeability makes it a more difficultpermeability makes it a more difficult substrate for bonding.substrate for bonding. www.indiandentalacademy.comwww.indiandentalacademy.com
  24. 24.  Dentinal tubules permit adhesiveDentinal tubules permit adhesive monomer to go down to the tubules formonomer to go down to the tubules for varying distances. Most tubules containvarying distances. Most tubules contain multiple lateral branches that radiate 2 to 6multiple lateral branches that radiate 2 to 6 um from the lumen and they provideum from the lumen and they provide another route for monomer infiltration ofanother route for monomer infiltration of hybrid layerhybrid layer (Mjor and Nardaul .1996.)(Mjor and Nardaul .1996.) www.indiandentalacademy.comwww.indiandentalacademy.com
  25. 25.  The resin monomers penetrate acid etchedThe resin monomers penetrate acid etched collagen fibrils through the spaces that cancollagen fibrils through the spaces that can swell or shrink depending on the bondingswell or shrink depending on the bonding conditions. Under some conditions (highconditions. Under some conditions (high water concentration, acidic pH) the collagenwater concentration, acidic pH) the collagen fibrils might swell slightly and reduce thefibrils might swell slightly and reduce the width of the peri fibrillar spaces making itwidth of the peri fibrillar spaces making it more difficult for primer monomers tomore difficult for primer monomers to infiltrate the collagen network. Under otherinfiltrate the collagen network. Under other conditions (air drying, dehydration by waterconditions (air drying, dehydration by water miscible organic solvents) the collagenmiscible organic solvents) the collagen fibrils may shrink (decreasing their diameter)fibrils may shrink (decreasing their diameter) there by bringing the adjacent fibrils in to anthere by bringing the adjacent fibrils in to an intimate contact with each other.intimate contact with each other. www.indiandentalacademy.comwww.indiandentalacademy.com
  26. 26.  As a result the collagen peptides mayAs a result the collagen peptides may form inter molecular hydrogen bonds withform inter molecular hydrogen bonds with the nearest neighboring collagen peptides,the nearest neighboring collagen peptides, which may contribute to further collapse ofwhich may contribute to further collapse of the network by causing shortening of thethe network by causing shortening of the fibrils and an increase in stiffnessfibrils and an increase in stiffness (Maciel(Maciel et at 1996et at 1996). So over drying of collagen). So over drying of collagen fibrils should be avoided.fibrils should be avoided. www.indiandentalacademy.comwww.indiandentalacademy.com
  27. 27. 2.2. Fluoride content of teethFluoride content of teeth  Increased fluoride content of enamel hasIncreased fluoride content of enamel has been shown to resist acid etching. Thisbeen shown to resist acid etching. This reduction is not significant clinically if thereduction is not significant clinically if the etching time is increased to allow moreetching time is increased to allow more time for the acid to etch the enameltime for the acid to etch the enamel surface and produce more roughness.surface and produce more roughness. Clinicians are now etching apparentlyClinicians are now etching apparently normal enamel for 15 sec and enamel thatnormal enamel for 15 sec and enamel that shows signs of fluoridation for double thatshows signs of fluoridation for double that time or more.time or more. www.indiandentalacademy.comwww.indiandentalacademy.com
  28. 28. 3.3. Dentinal canal characteristics: -Dentinal canal characteristics: -  Dentinal canals at the external surface ofDentinal canals at the external surface of roots or near the dentino enamel junctionroots or near the dentino enamel junction have small diameters. Whereas dentinalhave small diameters. Whereas dentinal canals close to the pulp are larger incanals close to the pulp are larger in diameter. Old dentin has smaller dentinaldiameter. Old dentin has smaller dentinal canals, while new dentin has largercanals, while new dentin has larger dentinal canalsdentinal canals (pashley 1990).(pashley 1990). www.indiandentalacademy.comwww.indiandentalacademy.com
  29. 29. 4.4. Transformed dentin surface due toTransformed dentin surface due to physiological and pathologicalphysiological and pathological process: -process: -  Structural changes can occur in theStructural changes can occur in the dentinal tubule due to carious, erosive anddentinal tubule due to carious, erosive and abrasive processes and physiologicalabrasive processes and physiological aging. In carious instances the lumen ofaging. In carious instances the lumen of the dentinal tubules are very narrow orthe dentinal tubules are very narrow or may even be obliterated by deposition ofmay even be obliterated by deposition of intratubular crystals and apposition ofintratubular crystals and apposition of irregular sclerotic dentin. Even repairativeirregular sclerotic dentin. Even repairative dentin forms at the pulpal aspect of thedentin forms at the pulpal aspect of the lesion.lesion. www.indiandentalacademy.comwww.indiandentalacademy.com
  30. 30.  In the normal dentin the odontoblasticIn the normal dentin the odontoblastic process extend through out the entireprocess extend through out the entire thickness of dentin but in the case ofthickness of dentin but in the case of carious dentin, they disappear at thecarious dentin, they disappear at the bottom of the carious lesions, collapsingbottom of the carious lesions, collapsing with fringe like ends.with fringe like ends.  This results in reduction of dentinThis results in reduction of dentin permeability. Further permeability ispermeability. Further permeability is reduced in aged sound dentin due toreduced in aged sound dentin due to progressive deposition of peritubularprogressive deposition of peritubular dentin and crystal formation in the tubules.dentin and crystal formation in the tubules. www.indiandentalacademy.comwww.indiandentalacademy.com
  31. 31.  AR Yazici et al conducted a study in 2004AR Yazici et al conducted a study in 2004 to evaluate the bond strengths of soundto evaluate the bond strengths of sound versus caries-effected dentin using a self-versus caries-effected dentin using a self- etching adhesive system, Clearfil SEetching adhesive system, Clearfil SE Bond. The results of this in vitro studyBond. The results of this in vitro study indicated that the bond strength of theindicated that the bond strength of the self-etching adhesive system, Clearfil SEself-etching adhesive system, Clearfil SE Bond to sound dentin was greater than toBond to sound dentin was greater than to caries affected dentin.caries affected dentin. www.indiandentalacademy.comwww.indiandentalacademy.com
  32. 32.  Whereas a recent study by A. Sengun etWhereas a recent study by A. Sengun et al has shown that the bond strengths ofal has shown that the bond strengths of Clearfil SE was similar to both cariesClearfil SE was similar to both caries affected and normal dentinaffected and normal dentin  S. M. Kwong et al conducted a study toS. M. Kwong et al conducted a study to evaluate the bond strengths to scleroticevaluate the bond strengths to sclerotic dentin using a self-etching and a total-dentin using a self-etching and a total- etching technique and they concluded thatetching technique and they concluded that removal of the surface layers of scleroticremoval of the surface layers of sclerotic dentin and/or conditioning with strongerdentin and/or conditioning with stronger acids may be beneficial to obtain strongeracids may be beneficial to obtain stronger bonding to sclerotic dentin.bonding to sclerotic dentin. www.indiandentalacademy.comwww.indiandentalacademy.com
  33. 33. The dentin smear layer and permeability:The dentin smear layer and permeability:  When the tooth surface is instrumentedWhen the tooth surface is instrumented with rotary and manual instruments duringwith rotary and manual instruments during cavity preparation, cutting debris iscavity preparation, cutting debris is smeared over the enamel and dentinalsmeared over the enamel and dentinal surfaces what is termed the smear layer.surfaces what is termed the smear layer. www.indiandentalacademy.comwww.indiandentalacademy.com
  34. 34.  The burnishing action of cuttingThe burnishing action of cutting instruments generate a considerableinstruments generate a considerable amount of frictional heat locally, so thatamount of frictional heat locally, so that the smear layer gets attached to thethe smear layer gets attached to the underlying surface in a manner thatunderlying surface in a manner that prevents it from being rinsed off orprevents it from being rinsed off or scrubbed away. This smear debrisscrubbed away. This smear debris occludes the dentinal tubules with theoccludes the dentinal tubules with the formation of smear plugs which affect theformation of smear plugs which affect the bonding negatively.bonding negatively. www.indiandentalacademy.comwww.indiandentalacademy.com
  35. 35. DENTIN SMEAR LAYERDENTIN SMEAR LAYER  Smear layerSmear layer - It is tenacious deposit of- It is tenacious deposit of microscopic debris that covers enamelmicroscopic debris that covers enamel and dentin surfaces and that have beenand dentin surfaces and that have been created during the preparation of enamelcreated during the preparation of enamel and dentin and its presence complicatesand dentin and its presence complicates resin bonding.resin bonding. Eick and othersEick and others (1970)(1970) first described this smear layer.first described this smear layer. www.indiandentalacademy.comwww.indiandentalacademy.com
  36. 36.  When viewed under scanning electronWhen viewed under scanning electron microscope the smear layer has anmicroscope the smear layer has an amorphous, irregular and granularamorphous, irregular and granular appearance that represents dentinalappearance that represents dentinal shavings, hydroxy apatite, tissue debris,shavings, hydroxy apatite, tissue debris, odontoblastic processes, obliteratedodontoblastic processes, obliterated tubule orifices, bacteria, denaturedtubule orifices, bacteria, denatured collagen etc.collagen etc. www.indiandentalacademy.comwww.indiandentalacademy.com
  37. 37. Composition:Composition:  The composition of smear layer reflects theThe composition of smear layer reflects the composition of the dentin from which it iscomposition of the dentin from which it is formed (Eick et al 1970). Thus the smearformed (Eick et al 1970). Thus the smear layer in superficial normal dentin may have alayer in superficial normal dentin may have a composition close to that of intertubularcomposition close to that of intertubular dentin where as the composition of smeardentin where as the composition of smear layer in deep dentin would reflect its degreelayer in deep dentin would reflect its degree of mineralization. However smear layer foundof mineralization. However smear layer found on deep dentin contains more organicon deep dentin contains more organic component than those found on thecomponent than those found on the superficial dentin.superficial dentin. www.indiandentalacademy.comwww.indiandentalacademy.com
  38. 38.  Scanning electron microscopicScanning electron microscopic examination has disclosed that itsexamination has disclosed that its composition is both organic and inorganic.composition is both organic and inorganic. The inorganic material in the smear layerThe inorganic material in the smear layer is made up of tooth structures and someis made up of tooth structures and some non specific inorganic contaminants. Thenon specific inorganic contaminants. The organic components may consists oforganic components may consists of heated coagulated proteins, odontoblastsheated coagulated proteins, odontoblasts plus saliva, blood cells andplus saliva, blood cells and microorganism.microorganism. www.indiandentalacademy.comwww.indiandentalacademy.com
  39. 39. Morphology:Morphology:  The smear layer consists of two separateThe smear layer consists of two separate layers, a superficial layer, and a layerlayers, a superficial layer, and a layer loosely attached to the underlying dentin.loosely attached to the underlying dentin.  Dentin debris enters the orifice of theDentin debris enters the orifice of the dentinal tubules and acts as smear plugs,dentinal tubules and acts as smear plugs, which can decrease the dentinwhich can decrease the dentin permeability by up to 86% (Meryon et al,permeability by up to 86% (Meryon et al, 1987).1987). www.indiandentalacademy.comwww.indiandentalacademy.com
  40. 40. www.indiandentalacademy.comwww.indiandentalacademy.com
  41. 41.  The smear layer is neither always firmlyThe smear layer is neither always firmly attached nor it is continuous over theattached nor it is continuous over the substrate. Clinically produced smear layersubstrate. Clinically produced smear layer have an average depth of 1-5 µmhave an average depth of 1-5 µm (Goldman et at 1981, Madder et at 1984).(Goldman et at 1981, Madder et at 1984). The depth entering the dentinal tubuleThe depth entering the dentinal tubule may vary from a few um up to 40 µm.may vary from a few um up to 40 µm. www.indiandentalacademy.comwww.indiandentalacademy.com
  42. 42.  Cengiz et at 1970 proposed that theCengiz et at 1970 proposed that the penetration of smear layer into dentinalpenetration of smear layer into dentinal tubules could be caused by capillarytubules could be caused by capillary action as a result of adhesive forcesaction as a result of adhesive forces between the dentinal tubules and thebetween the dentinal tubules and the smear material. One can conclude that asmear material. One can conclude that a smear layer is present on all tooth that aresmear layer is present on all tooth that are prepared for restorative purpose unlessprepared for restorative purpose unless the dentin surface was treated with anthe dentin surface was treated with an acid or a chelating agent.acid or a chelating agent. www.indiandentalacademy.comwww.indiandentalacademy.com
  43. 43. Several factors may cause the depth ofSeveral factors may cause the depth of smear layer to varysmear layer to vary::  dry or wet cutting of dentindry or wet cutting of dentin  type of instrument usedtype of instrument used  area and composition of dentinarea and composition of dentin www.indiandentalacademy.comwww.indiandentalacademy.com
  44. 44.  Cutting the tooth without a water spray willCutting the tooth without a water spray will produce a thicker layer of dentin debrisproduce a thicker layer of dentin debris and the use of coarse diamond bursand the use of coarse diamond burs produce a thicker smear layer than theproduce a thicker smear layer than the use of carbide burs.use of carbide burs.  Both steel and tungsten carbide burs showBoth steel and tungsten carbide burs show a rapid detoriation of the cutting edges,a rapid detoriation of the cutting edges, which significantly diminishes the cuttingwhich significantly diminishes the cutting efficiency of the bur, probably increasesefficiency of the bur, probably increases frictional heat and causes smearing.frictional heat and causes smearing. www.indiandentalacademy.comwww.indiandentalacademy.com
  45. 45.  A significant difference exits when theA significant difference exits when the burs are used with or without a coolant ofburs are used with or without a coolant of water spray. In the absence of coolantwater spray. In the absence of coolant smeared debris can be found commonlysmeared debris can be found commonly on the surface. The smeared debris doeson the surface. The smeared debris does not form a continuous layer but exists asnot form a continuous layer but exists as localized islands with discontinuitieslocalized islands with discontinuities exposing the underlying dentin. Coolant ofexposing the underlying dentin. Coolant of water spray does not prevent smearingwater spray does not prevent smearing but appears to significantly reduce thebut appears to significantly reduce the amount and distribution of it.amount and distribution of it. www.indiandentalacademy.comwww.indiandentalacademy.com
  46. 46.  In addition, its composition is influencedIn addition, its composition is influenced by the area of dentin where it isby the area of dentin where it is generated, because of varying organic togenerated, because of varying organic to inorganic component ratios andinorganic component ratios and percentage of dentinal tubules. All ofpercentage of dentinal tubules. All of these variables can affect the integrity,these variables can affect the integrity, morphology and composition of the smearmorphology and composition of the smear layer and perhaps its potential to bondlayer and perhaps its potential to bond with a dentin bonding agent.with a dentin bonding agent. www.indiandentalacademy.comwww.indiandentalacademy.com
  47. 47. REMOVAL OF SMEAR LAYERREMOVAL OF SMEAR LAYER  There are two divergent opinions aboutThere are two divergent opinions about smear layer treatment. Some believe thatsmear layer treatment. Some believe that the smear layer acts as an effectivethe smear layer acts as an effective natural cavity liner that seals the dentinalnatural cavity liner that seals the dentinal tubules and reduces permeability, makingtubules and reduces permeability, making the smear a clinical asset. Other arguesthe smear a clinical asset. Other argues that the smear layer interferes withthat the smear layer interferes with adhesion of restorative materials, servingadhesion of restorative materials, serving as focus of bacteria, and therefore itas focus of bacteria, and therefore it should be removed.should be removed. www.indiandentalacademy.comwww.indiandentalacademy.com
  48. 48.  Brannstrom et al reported that the smearBrannstrom et al reported that the smear layer, which was firmly attached to thelayer, which was firmly attached to the dentin initially, became loose and wasdentin initially, became loose and was largely replaced by bacteria and fluid withlargely replaced by bacteria and fluid with in a few weeks.in a few weeks. PashleyPashley and othersand others found that smear layer was effective infound that smear layer was effective in restricting dentin permeability. In addition,restricting dentin permeability. In addition, they found that shear bond strength tothey found that shear bond strength to dentin with smear layer intact were higherdentin with smear layer intact were higher than to dentin with smear layer removed.than to dentin with smear layer removed. www.indiandentalacademy.comwww.indiandentalacademy.com
  49. 49.  The removal of smear layer andThe removal of smear layer and demineralization of the dentin matrixdemineralization of the dentin matrix may facilitate bonding through amay facilitate bonding through a number of mechanisms.number of mechanisms. 1.1. The exposed collagen may provideThe exposed collagen may provide reactive groups that can chemicallyreactive groups that can chemically interact with bonding primers.interact with bonding primers. 2.2. Exposure of collagen fibrils and theirExposure of collagen fibrils and their epsilon-amino groups, which mayepsilon-amino groups, which may catalyze HEMA polymerization.catalyze HEMA polymerization. 3.3. Exposure of intact collagen thatExposure of intact collagen that serves as a scaffold for the creationserves as a scaffold for the creation of resin collagen hybrid layer.of resin collagen hybrid layer. www.indiandentalacademy.comwww.indiandentalacademy.com
  50. 50.  The retention of smear layer not onlyThe retention of smear layer not only lowers dentin permeability but also maylowers dentin permeability but also may prevent the decrease in bond strengthprevent the decrease in bond strength seen with some bonding systems, asseen with some bonding systems, as deeper dentin is prepared. It also greatlydeeper dentin is prepared. It also greatly lowers the effects of pulpal pressure onlowers the effects of pulpal pressure on bond strengths.bond strengths. www.indiandentalacademy.comwww.indiandentalacademy.com
  51. 51.  Another approach to avoiding the intrinsicAnother approach to avoiding the intrinsic weakness of the smear layer is to removeweakness of the smear layer is to remove it, but use some of the mineral in theit, but use some of the mineral in the smear layer to react with ions in thesmear layer to react with ions in the etching to form insoluble precipitates thatetching to form insoluble precipitates that adhere to each other and to underlyingadhere to each other and to underlying dentin matrix more firmly than did thedentin matrix more firmly than did the original smear layer particles.original smear layer particles. Bowen et alBowen et al used ferric oxalate in 2.5% nitric acid forused ferric oxalate in 2.5% nitric acid for this purpose.this purpose. www.indiandentalacademy.comwww.indiandentalacademy.com
  52. 52.  In order to chemically attach a restorativeIn order to chemically attach a restorative system to tooth structure, one of thesystem to tooth structure, one of the several options must be considered for theseveral options must be considered for the smear layer. For the currently availablesmear layer. For the currently available dentin bonding agents, the smear layer isdentin bonding agents, the smear layer is managed in one of the five ways:managed in one of the five ways: www.indiandentalacademy.comwww.indiandentalacademy.com
  53. 53. 1.1. No treatment at allNo treatment at all: The smear layer is left: The smear layer is left in places with out modification, and thein places with out modification, and the dentin bonding agent applied directly to it.dentin bonding agent applied directly to it. 2.2. Dissolution of smear layerDissolution of smear layer: The dissolved: The dissolved smear layer plays a part in chemicalsmear layer plays a part in chemical attachment of dentin bonding agent toattachment of dentin bonding agent to dentin.dentin. 3.3. The smear layer is removedThe smear layer is removed: The dentin: The dentin bonding agent develops chemicalbonding agent develops chemical attachment directly to intact dentin.attachment directly to intact dentin. 4.4. The modification of the smear layerThe modification of the smear layer: This: This process theoretically improves theprocess theoretically improves the attachment of smear layer to dentin.attachment of smear layer to dentin. 5.5. Smear layer removal and its replacementSmear layer removal and its replacement byby another mediating agent.another mediating agent. www.indiandentalacademy.comwww.indiandentalacademy.com
  54. 54. System that work by removing the smearSystem that work by removing the smear layer:layer:  All bond all etch technique.All bond all etch technique.  Gluma bond system.Gluma bond system.  Denthesive.Denthesive.  Clear fill liner bond system.Clear fill liner bond system.  Scotch bond 2.Scotch bond 2.  Syntac.Syntac.  Tenure.Tenure.  X-R bond.X-R bond. www.indiandentalacademy.comwww.indiandentalacademy.com
  55. 55.  Systems that work by preserve the smearSystems that work by preserve the smear layerlayer  All bond 2All bond 2  Prisma universal Bond 3Prisma universal Bond 3  Tripton,Tripton,  Tokuso light bond.Tokuso light bond.  Systems that work by dissolve the smearSystems that work by dissolve the smear layerlayer  XR – BondXR – Bond  Imperva BondImperva Bond  Systems that work by modification of theSystems that work by modification of the smear layersmear layer  All bondAll bond  Prisma universal Bond - 2.Prisma universal Bond - 2. www.indiandentalacademy.comwww.indiandentalacademy.com
  56. 56. Methods of Removal of Smear LayerMethods of Removal of Smear Layer  Brannstrom’s group has publishedBrannstrom’s group has published several articles describing the use ofseveral articles describing the use of water, hydrogen peroxide,water, hydrogen peroxide, benzalkonuim chloride, EDTA(Ethylenebenzalkonuim chloride, EDTA(Ethylene Diamine TetraAcetic Acid) and otherDiamine TetraAcetic Acid) and other agents to remove the smear layer.agents to remove the smear layer. www.indiandentalacademy.comwww.indiandentalacademy.com
  57. 57.  He has formulated severalHe has formulated several commercially available products likecommercially available products like Tublicid, that are designed to removeTublicid, that are designed to remove most smear layer without removingmost smear layer without removing smear debris that has fallen intosmear debris that has fallen into orifices of the tubules of the dentin.orifices of the tubules of the dentin. Though this concept is ideal, it isThough this concept is ideal, it is difficult to achieve clinically because ofdifficult to achieve clinically because of complex geometry of many cavitiescomplex geometry of many cavities and difficulty in obtaining adequateand difficulty in obtaining adequate access.access. www.indiandentalacademy.comwww.indiandentalacademy.com
  58. 58. 1.1. Remove the smear layer by etchingRemove the smear layer by etching with acid.with acid.  Etching dentin with 6% citric acid forEtching dentin with 6% citric acid for 60 sec removes the entire smear layer60 sec removes the entire smear layer as does 15 sec of etching with 37%as does 15 sec of etching with 37% phosphoric acid.phosphoric acid. www.indiandentalacademy.comwww.indiandentalacademy.com
  59. 59.  The advantages are:The advantages are:  The smear layer is essentially removedThe smear layer is essentially removed  The tubules are open and available forThe tubules are open and available for retentionretention  The surface collagen is exposed for possibleThe surface collagen is exposed for possible covalent linkages with new experimentalcovalent linkages with new experimental primers.primers.  When smear layer is removed, one does notWhen smear layer is removed, one does not have to worry about its slow dissolutionhave to worry about its slow dissolution under a restoration leaving a void betweenunder a restoration leaving a void between the cavity wall and the restoration, whichthe cavity wall and the restoration, which might permit bacterial colonization.might permit bacterial colonization. www.indiandentalacademy.comwww.indiandentalacademy.com
  60. 60.  The disadvantage is:The disadvantage is:  In the absence of smear layer there isIn the absence of smear layer there is no physical barrier to bacterialno physical barrier to bacterial penetration of dentinal tubules.penetration of dentinal tubules. 2. Another entirely different approach2. Another entirely different approach would lie to use a resin that wouldwould lie to use a resin that would infiltrate through the entire thicknessinfiltrate through the entire thickness of smear layer and either bond toof smear layer and either bond to underlying matrix or penetrate intounderlying matrix or penetrate into the tubules.the tubules. www.indiandentalacademy.comwww.indiandentalacademy.com
  61. 61. 3.To try to fix the smear layer by3.To try to fix the smear layer by gluteraldehyde or tanning agents such asgluteraldehyde or tanning agents such as tannic acids or ferric chloride.tannic acids or ferric chloride. The idea is toThe idea is to increase the cross linking of exposedincrease the cross linking of exposed collagen within the smear layer and betweencollagen within the smear layer and between it and the matrix of the underlying dentin toit and the matrix of the underlying dentin to improve its cohesion.improve its cohesion. 4.A fourth and most recent approach4.A fourth and most recent approach to theto the problem is to remove the smear layer byproblem is to remove the smear layer by etching with acid and replace it with anetching with acid and replace it with an artificial smear layer composed by aartificial smear layer composed by a crystaline precipitate.crystaline precipitate.  Bowen has used this approach by treatingBowen has used this approach by treating dentin with 5% ferric oxalate which replaceddentin with 5% ferric oxalate which replaced the original smear layers.the original smear layers. www.indiandentalacademy.comwww.indiandentalacademy.com
  62. 62. DENTIN CONDITIONERS: -DENTIN CONDITIONERS: -  There is confusion regarding two terms –There is confusion regarding two terms – etchants and conditioners. Acids such asetchants and conditioners. Acids such as phosphoric, maleic, nitric, or citric are usedphosphoric, maleic, nitric, or citric are used for partial or total removal of the smear layerfor partial or total removal of the smear layer and superficial demineralization of theand superficial demineralization of the underlying dentin. Such liquids or gels areunderlying dentin. Such liquids or gels are termed etchants and may also be calledtermed etchants and may also be called conditioners by some dental manufacturers.conditioners by some dental manufacturers. Etching implies the dissolution of theEtching implies the dissolution of the substrate, whereas conditioning involvessubstrate, whereas conditioning involves cleaning structural alteration, and increasingcleaning structural alteration, and increasing the adhesiveness of the substratethe adhesiveness of the substrate ( Jendresen and Glantz, 1981).( Jendresen and Glantz, 1981).www.indiandentalacademy.comwww.indiandentalacademy.com
  63. 63.  Conditioning of the dentin will be definedConditioning of the dentin will be defined as any alteration of dentin done after theas any alteration of dentin done after the creation of dentin cutting debris, termedcreation of dentin cutting debris, termed the smear layer. The objective of dentinthe smear layer. The objective of dentin conditioning is to create a surface capableconditioning is to create a surface capable of micro mechanical and possibleof micro mechanical and possible chemical bonding to a dentin bondingchemical bonding to a dentin bonding agent. The principal effects ofagent. The principal effects of conditioning of dentin may be classifiedconditioning of dentin may be classified as:as:  Physical changes.Physical changes.  Chemical changes.Chemical changes. www.indiandentalacademy.comwww.indiandentalacademy.com
  64. 64.  Physical changesPhysical changes:: 1. Increase or decrease in the thickness and1. Increase or decrease in the thickness and morphology of the smear layer.morphology of the smear layer. 2. Changes in the shape of the dentinal2. Changes in the shape of the dentinal tubules.tubules.  Chemical changesChemical changes:: 1. Modifications of organic matter.1. Modifications of organic matter. 2. Decalcification of the inorganic matter.2. Decalcification of the inorganic matter. www.indiandentalacademy.comwww.indiandentalacademy.com
  65. 65.  Conditioning of dentin may be done inConditioning of dentin may be done in several means.several means.  1) Chemical:1) Chemical: a) Acidsa) Acids  2) Thermal:2) Thermal: a) Lasersa) Lasers  3) Mechanical:3) Mechanical: a) Abrasiona) Abrasion www.indiandentalacademy.comwww.indiandentalacademy.com
  66. 66. CHEMICALCHEMICAL  Acid conditionersAcid conditioners:: These acidic conditioners demineralizeThese acidic conditioners demineralize dentin to a depth of at least 2-5dentin to a depth of at least 2-5 µµm. Them. The factors that limit the depth offactors that limit the depth of demineralization are:demineralization are:  Type of acidType of acid  Etching timeEtching time  Strengthening of acidStrengthening of acid  Buffering capacity of the dentin.Buffering capacity of the dentin. www.indiandentalacademy.comwww.indiandentalacademy.com
  67. 67.  Historically several acids have beenHistorically several acids have been researched as dentin conditioners. Theseresearched as dentin conditioners. These include hydrochloric acid, oxalic acid,include hydrochloric acid, oxalic acid, pyruvic acid, maleic acid, phosphoric acid,pyruvic acid, maleic acid, phosphoric acid, 10% citric acid, and 10% citric acid with10% citric acid, and 10% citric acid with 3% ferric chloride, 10% citric acid with3% ferric chloride, 10% citric acid with 20% calcium chloride, 2.5% nitric acid and20% calcium chloride, 2.5% nitric acid and chelators like EDTA.chelators like EDTA. www.indiandentalacademy.comwww.indiandentalacademy.com
  68. 68. Phosphoric acid: -Phosphoric acid: -  It was the first dentin conditioner that wasIt was the first dentin conditioner that was successfully used to remove the smearsuccessfully used to remove the smear layer, etch the dentin and restore it withlayer, etch the dentin and restore it with adhesive composite resin (adhesive composite resin (Fusayama andFusayama and other, 1979other, 1979)) www.indiandentalacademy.comwww.indiandentalacademy.com
  69. 69. Scanning electron micrograph of etched dentin showing exposed collagen fibers. www.indiandentalacademy.comwww.indiandentalacademy.com
  70. 70.  This helps by removing the surface dentin,This helps by removing the surface dentin, leaving a clean, well-defined etchingleaving a clean, well-defined etching pattern where the tubules are enlargedpattern where the tubules are enlarged into funnel shape. Phosphoric acid is theinto funnel shape. Phosphoric acid is the acid of choice currently for the etchingacid of choice currently for the etching purpose.purpose.  However, controversy remains about theHowever, controversy remains about the optimal concentration of H3PO4. Theoptimal concentration of H3PO4. The most widely used concentrations used inmost widely used concentrations used in clinical practice exceed 30% phosphoricclinical practice exceed 30% phosphoric acid.acid. www.indiandentalacademy.comwww.indiandentalacademy.com
  71. 71. Total etch/all etch technique:Total etch/all etch technique:  FusayamaFusayama pioneered the research of totalpioneered the research of total etching establishing the protocol foretching establishing the protocol for simultaneous etching of dentin andsimultaneous etching of dentin and enamel with phosphoric acid in 1979.enamel with phosphoric acid in 1979.  Kuraray’s original clearfil new bondKuraray’s original clearfil new bond system accomplishes the total etch usingsystem accomplishes the total etch using 37% phosphoric acid for 60 seconds.37% phosphoric acid for 60 seconds. Bisco system uses 10% phosphoric acidBisco system uses 10% phosphoric acid for 15sec in all etch technique.for 15sec in all etch technique. www.indiandentalacademy.comwww.indiandentalacademy.com
  72. 72. THERMAL MODIFICATIONSTHERMAL MODIFICATIONS  Lasers: -Lasers: -  Hard tissue lasers in dentistry are anHard tissue lasers in dentistry are an emerging technology. A pulsed Nd-YAGemerging technology. A pulsed Nd-YAG laser will not disturb the pulp, even whenlaser will not disturb the pulp, even when the approach is as close as 1the approach is as close as 1µµm. Most ofm. Most of the research has been conducted on drythe research has been conducted on dry dentin, but laser will operate on dentindentin, but laser will operate on dentin immersed in saliva/water.immersed in saliva/water. www.indiandentalacademy.comwww.indiandentalacademy.com
  73. 73.  The mechanism of dentin removal is throughThe mechanism of dentin removal is through microscopic explosions caused by themicroscopic explosions caused by the thermal transients. The carbonized, blackthermal transients. The carbonized, black soot that results is easily washed off withsoot that results is easily washed off with water. The laser treatment results inwater. The laser treatment results in desensitized dentin, presumably bydesensitized dentin, presumably by occlusion of the open and permeableocclusion of the open and permeable dentinal tubules. Microorganisms anddentinal tubules. Microorganisms and organic debris are eliminated from the lasedorganic debris are eliminated from the lased surfaces. The laser decreases the organicsurfaces. The laser decreases the organic fraction and increases the inorganic fractionfraction and increases the inorganic fraction of the dentin surface.of the dentin surface.  The bond strength increased by 60% whenThe bond strength increased by 60% when this was done presumably by increasing thethis was done presumably by increasing the bondable inorganic fraction of the dentinbondable inorganic fraction of the dentin surface. The laser may create microsurface. The laser may create micro mechanical retention (white and othersmechanical retention (white and otherswww.indiandentalacademy.comwww.indiandentalacademy.com
  74. 74. MECHANICAL MODIFICATIONSMECHANICAL MODIFICATIONS  Micro-abrasionsMicro-abrasions It is a mechanical means of modification ofIt is a mechanical means of modification of dentin. Aluminum oxide is used for the purposedentin. Aluminum oxide is used for the purpose of micro abrasion. It removes healthy as well asof micro abrasion. It removes healthy as well as diseased dentin and results in a smear layer. Itsdiseased dentin and results in a smear layer. Its abrasion action depends on the particle size asabrasion action depends on the particle size as well as the velocity. The 0.5-micron or largerwell as the velocity. The 0.5-micron or larger particles create a smear on the dentin andparticles create a smear on the dentin and increase the surface area (Blake 1991). Theincrease the surface area (Blake 1991). The smear layer formed might be used to enhancesmear layer formed might be used to enhance the bond strengths of smear-mediated dentinthe bond strengths of smear-mediated dentin bonding agents.bonding agents. www.indiandentalacademy.comwww.indiandentalacademy.com
  75. 75.  An in vitro investigation of a comparison ofAn in vitro investigation of a comparison of bond strengths of composite to etchedbond strengths of composite to etched and air abraded human enamel surfacesand air abraded human enamel surfaces was done by G.B. Gray et al in 2006. Theywas done by G.B. Gray et al in 2006. They concluded composite resin applied toconcluded composite resin applied to enamel surfaces prepared using an acidenamel surfaces prepared using an acid etch procedure exhibited higher bondetch procedure exhibited higher bond strengths than those prepared with airstrengths than those prepared with air abrasion technology.abrasion technology. www.indiandentalacademy.comwww.indiandentalacademy.com
  76. 76. PRIMERS:PRIMERS:  Primer is a hydrophilic, low-viscocityPrimer is a hydrophilic, low-viscocity monomer dissolved in solvents such asmonomer dissolved in solvents such as water, acetone, or alcohol – are applied towater, acetone, or alcohol – are applied to the etched or conditioned dentin substratethe etched or conditioned dentin substrate but are not rinsed off.but are not rinsed off. www.indiandentalacademy.comwww.indiandentalacademy.com
  77. 77.  Nowadays major advances have beenNowadays major advances have been achieved in adhesion by the introduction ofachieved in adhesion by the introduction of primers, which promote wetting of the dentinprimers, which promote wetting of the dentin with the bonding agent, and penetration ofwith the bonding agent, and penetration of the bonding agent into the dentin. Primerthe bonding agent into the dentin. Primer monomers are amphiphilic i.e. they containmonomers are amphiphilic i.e. they contain hydrophilic groups. E.g.: -OH, -COOH forhydrophilic groups. E.g.: -OH, -COOH for better compatibility of the resin monomersbetter compatibility of the resin monomers with the moist dentin, and hydrophobicwith the moist dentin, and hydrophobic methacrylate groups for the co-methacrylate groups for the co- polymerization with the bonding resin. Thepolymerization with the bonding resin. The objective of this step is to transform theobjective of this step is to transform the hydrophilic dentin surface in to ahydrophilic dentin surface in to a hydrophobic and spongy state. Nakabayashihydrophobic and spongy state. Nakabayashi and Pashley summarized the function ofand Pashley summarized the function of dentin primer as “to maintain or recover thedentin primer as “to maintain or recover the porosity of the demineralized dentin”.porosity of the demineralized dentin”. www.indiandentalacademy.comwww.indiandentalacademy.com
  78. 78.  Primers are monomers dissolved inPrimers are monomers dissolved in solvents . Organic solvents aid insolvents . Organic solvents aid in displacing water, expanding or re-displacing water, expanding or re- expanding the collagen fiber network andexpanding the collagen fiber network and thus promoting the infiltration of thethus promoting the infiltration of the monomer into the sub-micron ormonomer into the sub-micron or nanometer sized spaces within thenanometer sized spaces within the collagen fiber network.collagen fiber network.  Besides HEMA, most of the primersBesides HEMA, most of the primers contain other monomers such as NPG-contain other monomers such as NPG- GMA, PMDM, BPDM and PENTA. MoreGMA, PMDM, BPDM and PENTA. More recent primers also include a chemical /recent primers also include a chemical / photo polymerization initiator so that theirphoto polymerization initiator so that their monomers can be polymerized inside.monomers can be polymerized inside.www.indiandentalacademy.comwww.indiandentalacademy.com
  79. 79. WET VERSUS DRY BONDING:WET VERSUS DRY BONDING:  The concept of ‘Moist’ or ‘Wet’ bondingThe concept of ‘Moist’ or ‘Wet’ bonding technique was proposed by Dr. Johntechnique was proposed by Dr. John Kanka (1990). Vital dentin is inherentlyKanka (1990). Vital dentin is inherently wet; therefore complete drying of dentin iswet; therefore complete drying of dentin is difficult to achieve clinically. Water hasdifficult to achieve clinically. Water has been considered an obstacle for attainingbeen considered an obstacle for attaining an effective adhesion of resins to dentin.an effective adhesion of resins to dentin. With that in mind, research has shiftedWith that in mind, research has shifted towards development of dentin adhesivestowards development of dentin adhesives compatible with humid environments.compatible with humid environments. www.indiandentalacademy.comwww.indiandentalacademy.com
  80. 80.  Most newer adhesives combineMost newer adhesives combine hydrophilic and hydrophobic monomers inhydrophilic and hydrophobic monomers in the same bottle, dissolved in an organicthe same bottle, dissolved in an organic solvent such as ethanol or acetone. Thesolvent such as ethanol or acetone. The “wet – bonding” technique prevents the“wet – bonding” technique prevents the spatial alternations (i.e. collagen collapse)spatial alternations (i.e. collagen collapse) that occur upon drying demineralizedthat occur upon drying demineralized dentin, such alterations may prevent thedentin, such alterations may prevent the monomers from penetrating labyrinth ofmonomers from penetrating labyrinth of nano channels formed by dissolution ofnano channels formed by dissolution of hydroxyapatite crystals between collagenhydroxyapatite crystals between collagen fibers (Maciel KT et al 1996).fibers (Maciel KT et al 1996). www.indiandentalacademy.comwww.indiandentalacademy.com
  81. 81. www.indiandentalacademy.comwww.indiandentalacademy.com
  82. 82.  The use of adhesive systems on moist dentin isThe use of adhesive systems on moist dentin is made possible by incorporation of the organicmade possible by incorporation of the organic solvents acetone or ethanol in primers orsolvents acetone or ethanol in primers or adhesives. Because the solvent can displaceadhesives. Because the solvent can displace water from both the dentin surface and the moistwater from both the dentin surface and the moist collagen network, it promotes the infiltration ofcollagen network, it promotes the infiltration of resin monomers throughout the nano spaces ofresin monomers throughout the nano spaces of the dense collagen web. The “Wet bonding”the dense collagen web. The “Wet bonding” technique has been shown repeatedly totechnique has been shown repeatedly to enhance bond strengths because waterenhance bond strengths because water preserves the porosity of collagen networkpreserves the porosity of collagen network available for monomer inter diffusion (Kanca Javailable for monomer inter diffusion (Kanca J 1992).1992). www.indiandentalacademy.comwww.indiandentalacademy.com
  83. 83.  If the dentin surface is dried with air, theIf the dentin surface is dried with air, the collagen undergoes immediate collapsecollagen undergoes immediate collapse and prevents resin monomers fromand prevents resin monomers from penetrating (Carvalho RM et al 1996).penetrating (Carvalho RM et al 1996). Kanca and Gwinnett (1992) recommendedKanca and Gwinnett (1992) recommended that etched dentin should not be driedthat etched dentin should not be dried before application of the bonding primer.before application of the bonding primer. www.indiandentalacademy.comwww.indiandentalacademy.com
  84. 84.  The clinician must be aware that pooledThe clinician must be aware that pooled moisture should not remain on the tooth,moisture should not remain on the tooth, because excess water can dilute thebecause excess water can dilute the primer and render it less effective. (Tay etprimer and render it less effective. (Tay et al 1996). A glistening hydrated surface isal 1996). A glistening hydrated surface is preferred. Many clinicians, however, stillpreferred. Many clinicians, however, still dry the tooth preparation after rinsingdry the tooth preparation after rinsing away the etching gel to check for theaway the etching gel to check for the classic etched enamel appearance.classic etched enamel appearance. www.indiandentalacademy.comwww.indiandentalacademy.com
  85. 85.  Because it is clinically impossible to dry enamelBecause it is clinically impossible to dry enamel without simultaneously drying dentin, the dentinwithout simultaneously drying dentin, the dentin collagen collapses easily upon air dryingcollagen collapses easily upon air drying resulting in the closing of the micropores in theresulting in the closing of the micropores in the exposed intertubular collagen (Tay FR andexposed intertubular collagen (Tay FR and Gwinett AJ 1996) For acetone based water –Gwinett AJ 1996) For acetone based water – free dentin bonding systems, the etched dentinfree dentin bonding systems, the etched dentin surface must be rewetted before applying thesurface must be rewetted before applying the adhesives. Rewetting the dried etched dentinadhesives. Rewetting the dried etched dentin with water or with aqueous rewetting agents haswith water or with aqueous rewetting agents has been demonstrated to restore bond strengthbeen demonstrated to restore bond strength values and to raise the collapsed collagenvalues and to raise the collapsed collagen network to a level similar to a “wet bondingnetwork to a level similar to a “wet bonding technique” (Gwinett AJ 1994).technique” (Gwinett AJ 1994). www.indiandentalacademy.comwww.indiandentalacademy.com
  86. 86.  Some authors have suggested that theSome authors have suggested that the inclusion of water in the composition ofinclusion of water in the composition of some adhesives may result in rewettingsome adhesives may result in rewetting the collagen fibers in areas that are notthe collagen fibers in areas that are not fully moist, thus opening the interfibrillarfully moist, thus opening the interfibrillar spaces to the infiltration of the primingspaces to the infiltration of the priming resin. Therefore the simultaneousresin. Therefore the simultaneous inclusion of both an organic solvent andinclusion of both an organic solvent and water may be fundamental for the bestwater may be fundamental for the best infiltration of some adhesives intoinfiltration of some adhesives into demineralized dentin. This could result indemineralized dentin. This could result in a less technique-sensitive procedure.a less technique-sensitive procedure. www.indiandentalacademy.comwww.indiandentalacademy.com
  87. 87.  A review of literature has showed that moistA review of literature has showed that moist bonding is only essential for particular bondingbonding is only essential for particular bonding systems with low water content of primer suchsystems with low water content of primer such as all bond 2. The primer of all bond 2 containsas all bond 2. The primer of all bond 2 contains acetone as solvent with only 5% of water. Inacetone as solvent with only 5% of water. In contrast with water content of 20% or more (e.g.contrast with water content of 20% or more (e.g. opti -bond FL, scotch bond multipurpose) areopti -bond FL, scotch bond multipurpose) are able to re-expand the collapsed collagen due toable to re-expand the collapsed collagen due to their intrinsic rewetting capacity. Acetone basedtheir intrinsic rewetting capacity. Acetone based primers adhesive (e.g. prime and bond 2.1, one-primers adhesive (e.g. prime and bond 2.1, one- step) have shown higher bond strengths andstep) have shown higher bond strengths and reduced micro-leakage when a moist bondingreduced micro-leakage when a moist bonding protocol is followed.protocol is followed. www.indiandentalacademy.comwww.indiandentalacademy.com
  88. 88.  So, moist bonding is only mandatory inSo, moist bonding is only mandatory in bonding system with minimal waterbonding system with minimal water content of the primer / primer adhesives,content of the primer / primer adhesives, while water based primers / primerwhile water based primers / primer adhesives have shown to be less sensitiveadhesives have shown to be less sensitive to variations in the moisture of the etchedto variations in the moisture of the etched dentin surface.dentin surface.  When etched dentin is dried using an airWhen etched dentin is dried using an air syringe bond strength decreasesyringe bond strength decrease substantially, especially for acetone andsubstantially, especially for acetone and ethanol – based dentin adhesive systemsethanol – based dentin adhesive systems (Kanca J 1992).(Kanca J 1992). www.indiandentalacademy.comwww.indiandentalacademy.com
  89. 89.  When water is removed the elasticWhen water is removed the elastic characteristics of collagen may be lost. Thecharacteristics of collagen may be lost. The collapse of the collagen fibers upon drying maycollapse of the collagen fibers upon drying may therefore be a result of the changes in thetherefore be a result of the changes in the molecular arrangement. While in a wet state,molecular arrangement. While in a wet state, wide gaps separate the collagen molecules fromwide gaps separate the collagen molecules from each other, in a dry state, the molecules areeach other, in a dry state, the molecules are arranged more compactly like a heap of cookedarranged more compactly like a heap of cooked noodles. This is because extrafibrillar space innoodles. This is because extrafibrillar space in hydrated Type I collagen are filled with water,hydrated Type I collagen are filled with water, while dried collagen has fewer extrafibrillarwhile dried collagen has fewer extrafibrillar spaces open for the penetration of thespaces open for the penetration of the monomers included in the adhesive systems.monomers included in the adhesive systems. www.indiandentalacademy.comwww.indiandentalacademy.com
  90. 90.  Water removal also may permit additionalWater removal also may permit additional hydrogen bonds to form between collagenhydrogen bonds to form between collagen molecules that were previously bonded to watermolecules that were previously bonded to water molecules, leaving no interfibrillar space. Duringmolecules, leaving no interfibrillar space. During air drying, water that occupies the interfibrillarair drying, water that occupies the interfibrillar spaces previously filled with hydroxyapatitespaces previously filled with hydroxyapatite crystals is lost by evaporation, resulting in acrystals is lost by evaporation, resulting in a decrease of the volume of a collagen network todecrease of the volume of a collagen network to approximately one third of its original volume.approximately one third of its original volume. When air -dried demineralized dentin is rewetWhen air -dried demineralized dentin is rewet with water, the collagen matrix may re – expandwith water, the collagen matrix may re – expand and recover its primary dimensions to the levelsand recover its primary dimensions to the levels of the original hydrated state (Maciel et al 1996).of the original hydrated state (Maciel et al 1996). www.indiandentalacademy.comwww.indiandentalacademy.com
  91. 91.  This spatial re – expansion occurs because theThis spatial re – expansion occurs because the spaces between fibers are refilled with water andspaces between fibers are refilled with water and because Type I collagen itself is capable tobecause Type I collagen itself is capable to undergoing expansion upon rehydration. Theundergoing expansion upon rehydration. The stiffness of decalcified dentin increases whenstiffness of decalcified dentin increases when the tissue is dehydrated either chemically inthe tissue is dehydrated either chemically in water – miscible solvents or physically in air. Thewater – miscible solvents or physically in air. The increase in stiffness is reversed whenincrease in stiffness is reversed when specimens are rehydrated in water. Thereforespecimens are rehydrated in water. Therefore rewetting dentin after air – drying to check forrewetting dentin after air – drying to check for the enamel frosty aspect may be an acceptablethe enamel frosty aspect may be an acceptable clinical procedure.clinical procedure. www.indiandentalacademy.comwww.indiandentalacademy.com
  92. 92.  Clinically, it is very difficult to either assess orClinically, it is very difficult to either assess or standardize the ideal amount of moisture thatstandardize the ideal amount of moisture that should be left on the dentin surface before theshould be left on the dentin surface before the application of the adhesive system. The idealapplication of the adhesive system. The ideal dentin surface for moist bonding is visibly moistdentin surface for moist bonding is visibly moist but without an excess of water leading to abut without an excess of water leading to a meniscus on the surface. Ideally, water shouldmeniscus on the surface. Ideally, water should form a uniform layer with out pooling (over wet)form a uniform layer with out pooling (over wet) and with our dry areas (over dried). Therefore airand with our dry areas (over dried). Therefore air drying with an air – water syringe after rinsing offdrying with an air – water syringe after rinsing off the etching gel is not recommended because itthe etching gel is not recommended because it cannot produce a uniform layer of water on thecannot produce a uniform layer of water on the surface.surface. www.indiandentalacademy.comwww.indiandentalacademy.com
  93. 93.  A recent study demonstrated that the excessA recent study demonstrated that the excess water after rinsing the etching gel can bewater after rinsing the etching gel can be removed with a damp cotton pellet, a disposableremoved with a damp cotton pellet, a disposable brush, or a tissue paper without adverselybrush, or a tissue paper without adversely affecting bond strengths.affecting bond strengths.  Research has demonstrated that moist bondingResearch has demonstrated that moist bonding increases the bond strengths of many bondingincreases the bond strengths of many bonding systems. However the water present in betweensystems. However the water present in between the fibrils should be displaced completely and ifthe fibrils should be displaced completely and if too much water is present, the resin monomerstoo much water is present, the resin monomers may not be able to successfully compete for themay not be able to successfully compete for the collages fibril surface there by leaving a void.collages fibril surface there by leaving a void. www.indiandentalacademy.comwww.indiandentalacademy.com
  94. 94.  Jorge Perdigao et al conducted a study toJorge Perdigao et al conducted a study to determine the effect of solvent anddetermine the effect of solvent and rewetting time on dentin adhesion. Theyrewetting time on dentin adhesion. They concluded that:concluded that: www.indiandentalacademy.comwww.indiandentalacademy.com
  95. 95.  When dentin is left moist, all DBSs resultWhen dentin is left moist, all DBSs result in similar bond strengths regardless ofin similar bond strengths regardless of their solvent.their solvent.  water-based adhesives are less sensitivewater-based adhesives are less sensitive to variations in surface moisture thanto variations in surface moisture than ethanol or acetone-based DBSs.ethanol or acetone-based DBSs.  Rewetting dentin after air drying restoresRewetting dentin after air drying restores the bond strengths to the level obtainedthe bond strengths to the level obtained on moist dentin, if rewetting is performedon moist dentin, if rewetting is performed for twice as long as the air drying.for twice as long as the air drying. www.indiandentalacademy.comwww.indiandentalacademy.com
  96. 96.  L Hitme et al, in 2002, conducted a study toL Hitme et al, in 2002, conducted a study to evaluate the influence of drying and HEMAevaluate the influence of drying and HEMA treatment on dentin wettability. They havetreatment on dentin wettability. They have concluded that air-drying acid-etched dentinconcluded that air-drying acid-etched dentin significantly decreased the spreading/infiltrationsignificantly decreased the spreading/infiltration of water in comparison with blot drying. Re-of water in comparison with blot drying. Re- wetting with water only partly restores thewetting with water only partly restores the spreading/infiltration on etched and air-driedspreading/infiltration on etched and air-dried dentin. However, HEMA primer prevents thedentin. However, HEMA primer prevents the collagen collapse and restores the collapsedcollagen collapse and restores the collapsed collagen network. Although multi-step dentincollagen network. Although multi-step dentin bonding systems can be routinely used inbonding systems can be routinely used in clinical practice because of their primers, the soclinical practice because of their primers, the so called “one bottle” systems must be used onlycalled “one bottle” systems must be used only on blot-dried dentin surfaces.on blot-dried dentin surfaces. www.indiandentalacademy.comwww.indiandentalacademy.com
  97. 97. www.indiandentalacademy.comwww.indiandentalacademy.com
  98. 98. Application of primerApplication of primer  Bonding can be carried out by applying primer toBonding can be carried out by applying primer to a collapsed matrix followed by application ofa collapsed matrix followed by application of bonding agent or else a primer and bondingbonding agent or else a primer and bonding agent may be directly applied to a non-collapsedagent may be directly applied to a non-collapsed demineralized dentin without the intermediatedemineralized dentin without the intermediate step of primer application. In Prime and bondstep of primer application. In Prime and bond and Bisco one step dental adhesive theyand Bisco one step dental adhesive they combine the priming and bonding step.combine the priming and bonding step.  www.indiandentalacademy.comwww.indiandentalacademy.com
  99. 99.  Bonding to the smear layer covered dentinBonding to the smear layer covered dentin was not very successful before 1990 aswas not very successful before 1990 as the resins did not penetrate through thethe resins did not penetrate through the smear layer and the smear layer was verysmear layer and the smear layer was very weakweak (Tao et al 1988).(Tao et al 1988). This led mostThis led most manufactures to use acidic conditioners.manufactures to use acidic conditioners. How ever the resulting soft collagen richHow ever the resulting soft collagen rich surface can collapse and interfere withsurface can collapse and interfere with monomer infiltration.monomer infiltration. www.indiandentalacademy.comwww.indiandentalacademy.com
  100. 100.  So in order to prevent this and to simplifySo in order to prevent this and to simplify the number of bonding steps,the number of bonding steps, WatanabeWatanabe (1990(1990) developed a new bonding system) developed a new bonding system which was an aqueous solution of 20%which was an aqueous solution of 20% phenyl-p in 30% HEMA. This self-etchingphenyl-p in 30% HEMA. This self-etching and self-priming system providedand self-priming system provided important new information on smear layerimportant new information on smear layer as bonding substrates. The ideal self-as bonding substrates. The ideal self- etching, self-priming bonding system isetching, self-priming bonding system is one that can penetrate 2.0one that can penetrate 2.0µµm of smearm of smear layer and engage underlying of dentin to alayer and engage underlying of dentin to a depth of 1depth of 1 µµm.m. www.indiandentalacademy.comwww.indiandentalacademy.com
  101. 101. Microscopic examination of attachmentsMicroscopic examination of attachments produced by primer has shownproduced by primer has shown deficiencies like:deficiencies like:  Incomplete surface coverageIncomplete surface coverage  Incomplete inter-fibrillar saturation with inIncomplete inter-fibrillar saturation with in the hybrid zone.the hybrid zone.  Incomplete penetration to the full depth ofIncomplete penetration to the full depth of demineralized dentin.demineralized dentin. www.indiandentalacademy.comwww.indiandentalacademy.com
  102. 102. Steps for effective priming: -Steps for effective priming: -  One method of improving surfaceOne method of improving surface coverage and diffusion of the primer is bycoverage and diffusion of the primer is by the application of multiple coats. Athe application of multiple coats. A second coat of primer has shown tosecond coat of primer has shown to increase the shear bond strengthincrease the shear bond strength significantly.significantly. JAJA Platt et al conducted a study in 2001, toPlatt et al conducted a study in 2001, to determine the effect of double adhesivedetermine the effect of double adhesive application on the shear bond strength toapplication on the shear bond strength to dentin using three one-bottle adhesivedentin using three one-bottle adhesive systems.systems. www.indiandentalacademy.comwww.indiandentalacademy.com
  103. 103. This study showed that:This study showed that:  The dentin shear bond strength of Prime &The dentin shear bond strength of Prime & Bond NT is improved by the use of a secondBond NT is improved by the use of a second application, when following manufacturer’sapplication, when following manufacturer’s instructions.instructions.  The dentin shear bond strength of One StepThe dentin shear bond strength of One Step and Optibond Solo are not improved by theand Optibond Solo are not improved by the use of a second application, when followinguse of a second application, when following manufacturer’s instructions.manufacturer’s instructions.  The surface of dentin should not be over driedThe surface of dentin should not be over dried or over-wet.or over-wet.  The etching time should not exceed the timeThe etching time should not exceed the time recommended by the manufacturers.recommended by the manufacturers. www.indiandentalacademy.comwww.indiandentalacademy.com
  104. 104. SOLVENTS:SOLVENTS: --  Three types of solvents are commonlyThree types of solvents are commonly used in dentin adhesives, they include:used in dentin adhesives, they include:  ACETONEACETONE  ETHANOL.ETHANOL.  WATER.WATER. www.indiandentalacademy.comwww.indiandentalacademy.com
  105. 105. Basic characteristic of solvents:Basic characteristic of solvents: -- ACETONEACETONE  Highly volatile, evaporates quicklyHighly volatile, evaporates quickly  Excellent water – chaserExcellent water – chaser  Strong drying agentStrong drying agent  Storage and dispensing problems presentStorage and dispensing problems present www.indiandentalacademy.comwww.indiandentalacademy.com
  106. 106. ETHANOLETHANOL  Excellent penetration capabilityExcellent penetration capability  Good comprise in respect of evaporationGood comprise in respect of evaporation  Good surface energy for wetting exposedGood surface energy for wetting exposed collagen fiber networkcollagen fiber network WATERWATER  Excellent penetration capabilityExcellent penetration capability  Enables self – etching capability of acidEnables self – etching capability of acid monomersmonomers  Evaporates slowly consequently more difficult toEvaporates slowly consequently more difficult to removeremove  Remaining water may hamper resinRemaining water may hamper resin penetration / polymerizationpenetration / polymerization www.indiandentalacademy.comwww.indiandentalacademy.com
  107. 107.  Organic solvents aid in displacing water,Organic solvents aid in displacing water, expanding or re-expanding the collagen network,expanding or re-expanding the collagen network, and thus promoting the infiltration of theand thus promoting the infiltration of the monomer into the submicron or nanometer sizedmonomer into the submicron or nanometer sized spaces within the collagen fiber network.spaces within the collagen fiber network.  AF Reis et al conducted a study to evaluate theAF Reis et al conducted a study to evaluate the effect of organic solvents on one-bottleeffect of organic solvents on one-bottle adhesives’ bond strength to enamel and dentin.adhesives’ bond strength to enamel and dentin. The result of this study demonstrated thatThe result of this study demonstrated that complete solvent elimination did not produce acomplete solvent elimination did not produce a statistical decrease in enamel bond strengths.statistical decrease in enamel bond strengths. However, the high viscocity adhesive solutionHowever, the high viscocity adhesive solution that resulted from solvent evaporationthat resulted from solvent evaporation significantly decreased bond strengths tosignificantly decreased bond strengths to demineralized, moist dentin substrate.demineralized, moist dentin substrate. www.indiandentalacademy.comwww.indiandentalacademy.com
  108. 108.  They concluded that this reductionThey concluded that this reduction probably occurred as a function of twoprobably occurred as a function of two factors : incomplete monomer infiltrationfactors : incomplete monomer infiltration and incomplete water displacement. Theand incomplete water displacement. The absence of a water-chaser monomer-absence of a water-chaser monomer- carrier resulted in difficult resin infiltration.carrier resulted in difficult resin infiltration. www.indiandentalacademy.comwww.indiandentalacademy.com
  109. 109. HYBRID LAYERHYBRID LAYER  Hybrid layer in dentin was first describedHybrid layer in dentin was first described in detail by Nakabayashi, 1992. A similarin detail by Nakabayashi, 1992. A similar phenomenon was first described in vitrophenomenon was first described in vitro for enamel by Gwinnett and Buonocore infor enamel by Gwinnett and Buonocore in 1965.1965. www.indiandentalacademy.comwww.indiandentalacademy.com
  110. 110.  Hybrid layer is an intermediate layer of resin,Hybrid layer is an intermediate layer of resin, collagen, and dentin produced by acid etching ofcollagen, and dentin produced by acid etching of dentin and resin infiltration into the conditioneddentin and resin infiltration into the conditioned dentin.dentin.  Basically it is a transitional zone of resinBasically it is a transitional zone of resin reinforced dentin sandwiched between curedreinforced dentin sandwiched between cured resin and unaltered dentinal substrate and isresin and unaltered dentinal substrate and is generated by monomer impregnation of thegenerated by monomer impregnation of the exposed collagen of demineralized superficialexposed collagen of demineralized superficial dentin, after removal and/or modification of thedentin, after removal and/or modification of the smear layer. The synonyms are “adhesionsmear layer. The synonyms are “adhesion interface”, resin dentin “inter diffusion zone”,interface”, resin dentin “inter diffusion zone”, inter penetration zone”.inter penetration zone”. www.indiandentalacademy.comwww.indiandentalacademy.com
  111. 111.  The formation of hybrid zone depends onThe formation of hybrid zone depends on several factorsseveral factors  1) Type of conditioners.1) Type of conditioners.  2) Depth of the cavity, hybrid layer appeared to2) Depth of the cavity, hybrid layer appeared to be thinner at the deeper parts of the dentinbe thinner at the deeper parts of the dentin compared with the middle and superficial parts.compared with the middle and superficial parts. In the superficial dentin most of the hybrid layerIn the superficial dentin most of the hybrid layer is composed of hybridized intertubular dentinis composed of hybridized intertubular dentin with only occasional resin tag penetrating in towith only occasional resin tag penetrating in to the tubules. In deep dentin the tubules are sothe tubules. In deep dentin the tubules are so numerous and so large that there is less amountnumerous and so large that there is less amount of hybridized intertubular dentin and large resinof hybridized intertubular dentin and large resin tags are seen.tags are seen. www.indiandentalacademy.comwww.indiandentalacademy.com
  112. 112.  3) Permeability of the dentin surface.3) Permeability of the dentin surface.  4) The conditioning and priming pre4) The conditioning and priming pre treatment procedures.treatment procedures.  5) Diffusability and wettability of monomer5) Diffusability and wettability of monomer resins.resins.  In order to obtain an intimate associationIn order to obtain an intimate association between the resin monomers and collagenbetween the resin monomers and collagen fibrils, the primers and bonding agentsfibrils, the primers and bonding agents must be able to wet the collagen fibrils.must be able to wet the collagen fibrils. www.indiandentalacademy.comwww.indiandentalacademy.com
  113. 113. Role of the Hybrid LayerRole of the Hybrid Layer  The role of the hybrid layer in dentinThe role of the hybrid layer in dentin bonding is somewhat controversial.bonding is somewhat controversial. Studies of various adhesive systemsStudies of various adhesive systems report different results. In order to obtainreport different results. In order to obtain proper adhesion, it is essential to create aproper adhesion, it is essential to create a hybrid layer at the resin-dentin interfacehybrid layer at the resin-dentin interface (Nakabayashi, 1985, Sugaizaki, 1991,(Nakabayashi, 1985, Sugaizaki, 1991, Vanmeerbeek and others, 1992, 1993).Vanmeerbeek and others, 1992, 1993). www.indiandentalacademy.comwww.indiandentalacademy.com
  114. 114.  A study with Prime & Bond (Dentsply) indicatedA study with Prime & Bond (Dentsply) indicated that the removal of collagen fibers may actuallythat the removal of collagen fibers may actually increase bond strengths of resin to dentin.increase bond strengths of resin to dentin. Studies with One-Step(Bisco) indicated that theStudies with One-Step(Bisco) indicated that the hybrid layer might not play any important role inhybrid layer might not play any important role in the establishment of bond strengths. For athe establishment of bond strengths. For a multibottle adhesive system, All-Bond 2(Bisco),multibottle adhesive system, All-Bond 2(Bisco), one study reported that the presence or absenceone study reported that the presence or absence of the hybrid layer did not affect fractureof the hybrid layer did not affect fracture toughness of resin-dentin interfaces. Thereforetoughness of resin-dentin interfaces. Therefore the presence of the collagen layer wouldthe presence of the collagen layer would presumably allow for the establishment of apresumably allow for the establishment of a stress-relieving layer at the interface.stress-relieving layer at the interface. www.indiandentalacademy.comwww.indiandentalacademy.com
  115. 115.  A study using a self-etching primerA study using a self-etching primer demonstrated that dentin bond strengths did notdemonstrated that dentin bond strengths did not vary from 1 day to 6 months to 1 year in teethvary from 1 day to 6 months to 1 year in teeth subjected to occlusal function. It also showedsubjected to occlusal function. It also showed that porosity in the hybrid layer increasedthat porosity in the hybrid layer increased significantly at 1 year, due to loss of resinsignificantly at 1 year, due to loss of resin between the collagen fibers. Since these resultsbetween the collagen fibers. Since these results were obtained with a hybrid layer being createdwere obtained with a hybrid layer being created by a self-etching primer, they cannot beby a self-etching primer, they cannot be generalized to total-etch adhesives. However,generalized to total-etch adhesives. However, they do support the theory that collagen maythey do support the theory that collagen may play an important role in the strength of theplay an important role in the strength of the resin-dentin interface.resin-dentin interface. www.indiandentalacademy.comwww.indiandentalacademy.com
  116. 116.  For most dentin adhesives, theFor most dentin adhesives, the ultramorphological characterization of theultramorphological characterization of the transition between the hybrid layer and thetransition between the hybrid layer and the unaffected dentin suggests that there is anunaffected dentin suggests that there is an abrupt shift from hybrid tissue toabrupt shift from hybrid tissue to mineralized tissue, without any emptymineralized tissue, without any empty space or pathway that could result inspace or pathway that could result in leakage. The demarcation line seems toleakage. The demarcation line seems to consist of hydroxyapatite crystalsconsist of hydroxyapatite crystals embedded in the resin from the hybridembedded in the resin from the hybrid layer.layer. www.indiandentalacademy.comwww.indiandentalacademy.com
  117. 117.  According to Kanka, acid etched dentin cannotAccording to Kanka, acid etched dentin cannot be dried without shrinking. It is literally floatingbe dried without shrinking. It is literally floating in the rinsing water. If the water is evaporatedin the rinsing water. If the water is evaporated by air-dryng, the collagen fibrillar networkby air-dryng, the collagen fibrillar network collapses into a relatively impermeable organiccollapses into a relatively impermeable organic film that interfares with resin infiltration. Resinfilm that interfares with resin infiltration. Resin tags could still be formed and gave some resintags could still be formed and gave some resin retention, but hybridization of the dentin betweenretention, but hybridization of the dentin between tubules could not occur. This left much nakedtubules could not occur. This left much naked collagen fibrils in the acid etched layer that couldcollagen fibrils in the acid etched layer that could slowly hydrolyze and leads to gap formationslowly hydrolyze and leads to gap formation between resin and dentin.between resin and dentin. www.indiandentalacademy.comwww.indiandentalacademy.com
  118. 118.  Kanka discovered that if one left some residualKanka discovered that if one left some residual water in acid etched dentin, bond strength couldwater in acid etched dentin, bond strength could be doubled. Also it creates thicker hybrid layersbe doubled. Also it creates thicker hybrid layers (i.e., more resin uptake in etched surfaces) than(i.e., more resin uptake in etched surfaces) than did dry bonding.did dry bonding.  Most adhesive interface studies by SEMMost adhesive interface studies by SEM (Scanning Electron Microscope) have(Scanning Electron Microscope) have demonstrated creation of hybrid layers. Medinademonstrated creation of hybrid layers. Medina et al, in 2001, in his study had shown that acidet al, in 2001, in his study had shown that acid etching of dentin and the application of Prime &etching of dentin and the application of Prime & Bond are required for the formation of a distinctBond are required for the formation of a distinct hybrid layer and resin tags. However, there washybrid layer and resin tags. However, there was no significant correlation between shear bondno significant correlation between shear bond strength and the thickness of the hybrid layer.strength and the thickness of the hybrid layer. www.indiandentalacademy.comwww.indiandentalacademy.com
  119. 119. REQUIREMENTS OF A BONDINGREQUIREMENTS OF A BONDING AGENT:AGENT: A bonding agent is usually an unfilledA bonding agent is usually an unfilled resin that consists of hydrophobicresin that consists of hydrophobic monomers (such as Bis-GMA, TEGDMA,monomers (such as Bis-GMA, TEGDMA, UDMA, and hydrophilic monomers, suchUDMA, and hydrophilic monomers, such as HEMA).as HEMA).  Criteria for an “ideal” dentin bondingCriteria for an “ideal” dentin bonding system were enumerated in 1961 at asystem were enumerated in 1961 at a workshop held at the University of Indianaworkshop held at the University of Indiana Dental School.Dental School. www.indiandentalacademy.comwww.indiandentalacademy.com
  120. 120. These criteria were:These criteria were: 1.1. Provide a high bond strength to dentinProvide a high bond strength to dentin that should be present immediately afterthat should be present immediately after placement and that should beplacement and that should be permanent.permanent. 2.2. Provide a bond strength to dentin similarProvide a bond strength to dentin similar to that to enamel.to that to enamel. 3.3. Show good biocompatibility to dentalShow good biocompatibility to dental tissue, including the pulp.tissue, including the pulp. www.indiandentalacademy.comwww.indiandentalacademy.com
  121. 121. 4. Minimize microleakage at the margins of4. Minimize microleakage at the margins of restorations.restorations. 5. Prevent recurrent caries and marginal staining.5. Prevent recurrent caries and marginal staining. 6. Be easy to use and minimally technique6. Be easy to use and minimally technique sensitive.sensitive. 7. Possess a good shelf life.7. Possess a good shelf life. 8. Be compatible with a wide range of resins.8. Be compatible with a wide range of resins.  In a current review of literature, J. D. Eick et alIn a current review of literature, J. D. Eick et al had proposed to add the criterion that thehad proposed to add the criterion that the systems should not be toxic or sensitizing tosystems should not be toxic or sensitizing to the operators or patients. And, finally, Bondingthe operators or patients. And, finally, Bonding agents should seal tooth surfaces from oralagents should seal tooth surfaces from oral fluids.fluids. www.indiandentalacademy.comwww.indiandentalacademy.com
  122. 122. CLASSIFICATION OF DENTIN BONDINGCLASSIFICATION OF DENTIN BONDING AGENTS:AGENTS:  The BeginningThe Beginning : During the 1950s, the first: During the 1950s, the first attempt to develop an adhesive system forattempt to develop an adhesive system for bonding to dentin was made by Hagger, abonding to dentin was made by Hagger, a Swiss researcher working forSwiss researcher working for Amalgamated Dental Company, London.Amalgamated Dental Company, London. www.indiandentalacademy.comwww.indiandentalacademy.com

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