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smear layer /certified fixed orthodontic courses by Indian dental academy


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smear layer /certified fixed orthodontic courses by Indian dental academy

  1. 1. SMEAR LAYER INDIAN DENTAL ACADEMYLeader in Continuing Dental Education
  2. 2. Contents Introduction History What is smear layer? Morphology of the smear layer Physiological considerations Pathological considerations Smear layer in Restorative dentistry Smear layer in Endodontics Role of Bonding Methods of removal Advantages and Disadvantages conclusion
  3. 3. Introduction The term Smear layer is used most often to describe the grinding debris left on dentin by cavity preparation. Any debris produced iatrogenically by the cutting, not only of coronal dentin, but also of enamel, cementum and even the dentin of the root canal.
  4. 4. History Smear layer -17th century – Leeuwenhock. Boyde,Switsur and Stewart,1963 - Grinding debris – referred to as the smear layer. Eick and others,1970-Smeared layer. Mc Comb and Smith,1975 - Presence of smear layer- instrumented root canals. Goldman and others 1982 - Smear layer after the use of endodontic instruments.
  5. 5. What is Smear layer ? When tooth structure is cut ,instead of being uniformly sheared, the mineralized matrix shatters. Considerable quantities of cutting debris , made up of very small particles of mineralized collagen matrix, are produced. At the strategic interface of restorative materials and the dentin matrix, most of the debris is scattered –enamel and dentin surface.
  6. 6. Definition Any debris ,calcific in nature, produced by the reduction or instrumentation of dentin, enamel or cementum or as a contaminant which precludes interaction with the underlying pure tooth structure. - Eick
  7. 7. Morphology of the Smear LayerFormation Exact mechanism- incompletely understood. Boyde et al (1963)- Frictional heat during cavity preparation –important factor. Frictional heat may be 600ºC below the melting point of apatite -1800ºC to 2500ºC. Physiochemical phenomenon.
  8. 8.  Gwinett A.J. (1984) –Dentin richer source of protein than enamel, so the dentin matrix may contribute to the smear layer formed on enamel. Smear layer-by cutting when energy was expended.
  9. 9. Structure of smear layer SEM - Amorphous, irregular and granular appearance. Eick et al (1970) - tooth particles – less than 0.5µm to 15 µm. Pashley et al (1988) - Globular subunits ,0.05 -0.1 µm -originated from mineralized fibers.
  10. 10.  Light microscope-Smear layer is absent. SEM - undemineralized –low magnification-amorphous apperance & dentinal tubules are obscured. Higher magnification-granular substructure.
  11. 11. Composition SEM : Organic and inorganic Organic : heated coagulated proteins (gelatin formed by the deterioration of collagen heated by cutting temperatures ) Necrotic or viable pulp tissue Odontoblastic processes Saliva Blood cells and microorganisms. Inorganic Minerals from the dentinal structures Some non specific inorganic contaminants
  12. 12. Layers of the smear layer Cameron (1983) & Mader et al (1984)- 2 parts Superficial smear layer Smear plugs Extension of the packed material into dentinal tubules- 40µm Tubular packing phenomena- action of burs & endodontic instruments (Brannstrom and Johnson 1974) Penetration of smear material in to dentinal tubules-caused by capillary action – Cengiz et al (1990)
  13. 13. Thickness –Smear layer Goldman et al & Mader et al – 1-5µm Thickness depends on Type and sharpness of the cutting instruments Dry or wet cutting of the dentin Size and shape of the cavity or root canal Amount & chemical make up of irrigant used Thickest smear layer-10-15µm –coarse diamond blade (Pashley)
  14. 14. Attachment to the dentin Gwinnet- smear layer is variable. Pashley – smear layer lying over the dentin is analogous to wood being covered by wet saw dust. It is very tenacious but it is still permeable.
  15. 15. Smear layer after use of steel and tungsten burs It produce an undulating pattern ,the troughs of which run perpendicular with the direction of movement of the handpiece. Fine grooves can be seen running perpendicular to the undulations and parallel with the direction of rotation of the bur - “Galling” Frictional humps represent a “rebound effect” of the bur against the tooth surface. Galling phenomena - more marked with tungsten carbide burs. Fine grooves can be related to small facets found on cutting flutes of the bur.
  16. 16. Smear Layer– Carbide bur
  17. 17. Diamond burs Diamond points unlike carbide burs remove the dentinal structure by abrading action. Fine diamond burs- thin & dense smear layer Coarse diamond burs-thicker &looser smear layer
  18. 18.  Absence of coolant- smeared debris can be found commonly on the surface. It does not form a continuous layer but exists rather as localized islands with discontinuities exposing the underlying dentin. Coolant of water spray- reduce the amount and distribution of smeared debris.
  19. 19. Smear layer after the use of rotary instrumentsHero 642-Snowy appearence ProFile-Shiny & burnishedEngine Reamers –thinner & Profile -Muddy Appearance less compressed
  20. 20. PHYSIOLOGICAL CONSIDERATIONSINFLUENCE ON PERMEABILITY OF DENTINSubstances diffuse across dentin at a rate that is proportional Concentration gradient Surface area available for diffusion.The area available for diffusion in dentin is determined by Density of the tubules Diameter of the tubules.Theoretical area of diffusional surface varies from about 1% at DEJto 22% at the pulp.
  21. 21. Pashley distinguished between fluid movement inwardsfrom the dentin surface and outwards from the dentinal tubules. ‘Diffusion ’ as the movement of fluid from a high to lowconcentration. The rate of such movements varies with squareof radius (r 2 ). ‘ Convection’ as the pressure gradient in the tubules whichresults in a tendency for fluid outflow from the tubules ends.This varies with fourth power of radius (r 4 ).
  22. 22. (d4) (2π) (∆P)Fluid flow = ----------------- = 16 x (n) (L)
  23. 23. The presence of smear layer - effect on the resistanceto movement of fluid across dentin by modifying tubuleradius. Pashley & Others in 1978 - 86% of the totalresistance to flow of fluid. After etching with acid, the rate of flow of fluid increased-15 fold and (Reeder and Others 1978) 32 fold. Pashley - smear layer is removed Diffusion - ↑ 5 – 6 times. Convection - ↑ 25 – 26 times
  24. 24. INFLUENCE ON SENSITIVITY OF DENTIN Dentin sensitivity-open tubules in exposeddentin (Brannstrom 1982 ). Pashley et al- Movement of fluid in dentinal tubules –Dentin sensitivity. Etching dentin greatly increases the ease with which fluid can move across dentin. ↑ sensitivity of dentin to osmotic, thermal and tactile stimuli.
  25. 25.  If dentin is sensitive, then according to hydrodynamic theory of dentin sensitivity, the dentinal tubules must be patent and must allow movement of fluid across dentin. The presence of smear layer will prevent bacterial penetration of the tubules but will permit bacterial products to diffuse slowly into pulp.
  26. 26. PATHOLOGICAL CONSIDERATIONS a) Bacteria in the smear layer under restorations: Brannstrom and Nyborg, 1971- growth of bacteria undersilicate restorations.17 of the water cleaned cavities, withsmear layer remaining, numerous bacteria were present.Antiseptically cleaned & restored cavities-bacteria present. Bacteria may multiply on cavity walls even if there is noappreciable communication to the oral cavity seems to indicatethat certain microorganisms get sufficient nourishment fromthe smear layer and dentinal fluid.
  27. 27.     b) Smear layer on dentin exposed to oral cavityWhen a smear layer is produced experimentally on human dentin,and left exposed, it disappears after a couple of days and isreplaced by bacteria and after a week all most all tubules areopened and some even widened.The consequence is the invasion of bacteria.
  28. 28. c)The protective effect of smear plug in tubuleapertures and the consequences of removing theplugs Vojinovic, Nyborg and Brannstrom, 1973 - Etching thecavity prior to the placement of composite resin -massive invasion ofbacteria into dentinal tubules.The corresponding cavities cleaned by water and with the smear layerleft, had a bacterial layer on cavity walls but practically no invasioninto dentinal tubules.Smear plugs in the aperture of the tubules -prevented bacterialinvasion.
  29. 29.  Pashley (1984) - smear plugs reduced the permeability of dentin. Etching and removal of smear plugs and peritubular dentin - area of wet tubules may increase from about 10% to 25% - Garberoglio and Brannstrom, 1976 Difficult to dry the dentin.
  30. 30. d) Pulpal irritation due to removal of smear layerCut dentin should not be treated with acid or EDTA -tubules becomeopen and widened. e) Smear layer in root canals after reaming Carlson. L. Mader, J. Craig Baumgartner . Root canals- instrumented with k-type files and irrigated with 5.25% NaOClsolution. The smeared material -2 componentsSmeared layer on canal walls (1-2 µ m )Depth of tubule packing -few µ m to 40 µ m
  31. 31. Smear layer in restorative dentistry Operative cutting process-smear layer. Before restoration the layer Left in place Dissolved Can be replaced Modified or impregnated. Various studies-bacteria entrapped in the smear layer may survive and multiply under restorations.
  32. 32. Composite resin restorations Early bonding agents utilizing the smear layer. Bond strength-un satisfactory. Newer bonding system –partially or totally removed or impregnate the smear layer. Cements Glass ionomer and polycarboxylate-removal of smear layer. 10 % polyacrylic acid,30 %citric acid or hydrogen peroxide and distilled water.
  33. 33. Dahl (1978) - pumicing the dentin - three foldincrease in the tensile strength of the bond . When cements are applied to dentin covered with asmear layer and then tested for tensile strengthThe failure - either adhesive (between cement & smear layer)or cohesive (between constituents of smear layer)
  34. 34. Tensile strength of a cement-dentin interface, Remove the smear layer by etching with acid. Use a resin that would infiltrate through the entirethickness of the smear layer. To fix smear layer with glutaraldehyde (Hoppenbrouwers , Driessens & stadhouders, 1974) or tanning agents such astannic acid or Ferric chloride (Powis & other ,1982). To remove the smear layer by etching with acid and replaceit with an artificial smear layer composed of crystallineprecipitate(causton & Johnson,1982). Bowen used 5% ferric oxalate….
  35. 35.
  36. 36. Cast restorations While cementing cast restorations- pressure generated onand inside the casting .Since the cement is an incompressible liquid, it will transfer thispressure of fluid on and in dentin.Displacement of fluid in dentinal tubules.Thus it may be movements of fluid rather than the acidity of thecement, produces pain and pulpal irritation. The ease with which fluid can be forced across dentin isformalized by a term called “Hydraulic conductance ”. Volume of fluid transported across a known area of surfaceper unit time under a gradient of unit pressure (Reeder &Others, 1978).
  37. 37. SMEAR LAYER IN ENDODONTICSIf a smear layer containing bacteria or bacterial products-allowed to remain within pulp chamber or root canals,it mightprovide a reservoir of potential irritants.Apical Leakage Kennedy-absence of smear layer-less apical leakage. Removal of smear layer would improve gutta percha seals ifmaster cones are softened with chloroform and used withsealer and lateral condensation. Plasticized gutta percha –dentinal tubules-smear layer isabsent –mechanical lock between the guttapercha and thecanal wall.
  38. 38. B.Sealers Endodontic sealers acts as a glue to -good adaptation ofgutta percha to the canal walls. If the smear layer is not removed, the gutta percha may partlybe glued to dentin in the smear layer as well as to the exposedparts of the canal wall. Removing the smear layer from the root canals permitsincreased tensile strength of plastic posts(Goldman &others,1984).
  39. 39. ROLE OF SMEAR LAYER IN BONDING Smear layer-removed or altered-strong adhesive bond. Acid etching of the dentin Pka of the acid PH Chemical concentration& Viscosity.
  40. 40. Adhesive Strategies-A ScientificClassification of Modern Adhesives. 3 Adhesion strategies-interact with the smear layer.1.modify the smear layer &incorporate it in the bonding processes.One and two step2. removes the smear layer .Two-step and three-step3. Dissolves the smear layer. One and two step
  41. 41. Smear layer –Modifying Adhesive Smear layer –natural barrier to the pulp. Protecting it against bacterial invasion. Limiting the outflow of pulpal fluid. Effective wetting and in situ polymerization of monomers- micromechanical +chemical bond.
  42. 42. Smear layer –Removing Adhesives Removal of smear layer-total-etch concept. Three-step smear layer –removing adhesives. With the newest generationof one- bottle or single-bottle adhesives -3 step smear layer removing systems-reduced to two steps.
  43. 43. Smear Layer-Dissolving Adhesives Self-etching adhesives. Self-etching primers partially demineralize the smear layer & the underlying dentin –with out removing dissolved smear layer remnants or unplugging the tubule orifices.
  44. 44. Smear Layer Treatment and Dentin Bonding Agents To chemically attach a restorative system to tooth structure one of several options must be considered for the smear layer. Smear layer is managed- 5 ways (John et al). 1. No treatment at all. Smear layer is left intact. Eg. Scotch Bond 2 and prisma.
  45. 45.  Dissolution : Dissolved smear layer plays a part in the chemical attachment of dentin bonding agent. Eg: Scotch bond 2 and Mirage bond.Treatment agent :SB-2 -Maleic acid. Mirage Bond-HEMA Removal: Gluma Treatment agent-EDTA.
  46. 46. Modification Eg: XR Bond, All bond Treatment agent: XR Bond-ethyl alcohol,po4 ester. All bond- Succinic acid &HEMARemoval & Replacement Eg-Tenure –replaces the smear Layer with oxalate crystals which are deposited in the dentinal tubules. Treatment agent –Nitric acid, Aluminium oxalate.
  47. 47. AdvantagesSmear layer-Acts as a Biological Bandaid.It affords a drier surface for adhesion.Dentinal fluid flow rate –reduced in the presence of smearlayer.Bacterial penetration –dentinal tubules is prevented.DisadvantagesIt do not afford adequate bonding of material to dentin throughthem.It affect the physiologic status of the odontoblastic process inthe underlying dentin.
  48. 48.  25-30 % porous –cant produce totally effective sealing. Failure of retrograde filling following apical surgery. Avenue for leakage of microorganisms & a source of substrate for bacterial growth. Viable bacteria-remain in dentinal tubules use the smear layer –sustained growth &activity.
  49. 49. Methods of removal-smear layer Smear layer removal is a controversy –fluctuateswith the various modalities of restorative dentistry. Pashley-removing most of the smear layer over thetubules is difficult to achieve clinically - complex geometry ofmany cavities .Irrigating solutions - used during and after instrumentation toincrease cutting efficacy of root canal instruments and toflush away debris.
  50. 50. The efficacy of the irrigating solution is dependent on :Chemical nature of solutionQuantity and temperatureContact timeDepth of penetration of irrigation needleType and gauge of needleSurface tension of irrigating solutionAge of solution (Ingle 1985).
  51. 51.   SODIUM HYPOCHLORITE NaOCl -organic tissue dissolving capacity.Use of NaOCl during or after instrumentation - superficiallyclean canal walls with smear layer present (Baken et al1975, Goldman et al 1981). Alternating use of hydrogen peroxide and NaOClMc Combe and Smith (1975) - combination was not moreeffective in removing smear layer than NaOCl aloneproduced.
  52. 52. CHELATING AGENTSEthylene – Diamine tetra acetic acid(EDTA) which reacts with calcium ionsin dentin -soluble calcium chelates(Grossman et al 1988). Fehr and Nygaard-Ostby (1963) -Decalcified dentin to a depth of 20 – 30µm in 5 mins. Fraser (1974) - chelating effect-negligible in apical third of root canals. EDTA for 5 mins In a combination, urea peroxide wasadded (Rc-Prep) to float the dentinaldebris -root canal (Stevard et al 1969).
  53. 53. A quarternary ammonium bromide (Cetrimide) -added toEDTA (Fehr and Nygaard – Ostby 1983). Mc Combe and Smith,1975 -when this combination (REDTA)was used -no smear layer except in apical part of canal.EDTAC – Circumpulpal surface had a smooth structure;Dentinaltubules-regular circular appearence. 15 mins-working time(Goldberg and Spielbers, 1982).-Salvisol - based on Aminoquinaldinum diacetate .combined action of chelation and organic debridement .Better cleansing properties than EDTA-C (Frenstiller et al 1988).
  54. 54. ORGANIC ACIDS Citric acid -effective root canalirrigant (coel 1975) and even moreeffective than Naocl alone inremoving the smear layers(Baumgartner et al 1984). 50% Citric acid Citric acid removed smearlayer better -polyacrylic acid , lacticacid and phosphoric acid exceptEDTA .Disadvantage -leaves precipitatedcrystals. Crystals of Ca & P
  55. 55. 50% lactic acid , Canal walls -clean, but theopenings of dentinal tubules didnot appear to be completelypatent . Bitter (1989)- 25 % tannicacid-canals were cleaner & lactic acidsmoother than the walls treated –H2O2 and NaOCl. McComb et al (1976) - 5% and 10 % polyacrylic acid-remove the smear layer –accessible regions. polyacrylic acid
  56. 56. SODIUM HYPOCHLORITE AND EDTA Smear layer - organic and inorganic components . Combination - NaOCl and acids such as citric ,tannic,polyacrylic or chelating agents such as EDTA. Most effective working solution -5.25% NaOCl and themost effective final flush was 10ml. of 17% EDTA followed by10ml. of 5.25% NaOCl (Goldman et al.1982).
  57. 57. 1% NaoCl & EDTA 5
  58. 58. MTAD and NaOCl MTAD-mixture of tetracycline isomer Acid (citric acid ) detergent (Tween -80)PH-2.15- removing inorganic substances.NaOCl- removes organic portion.EGTA and NaOClEthylene glycol-bis (B-amino-ethyl ether)-N,N,N,N-Tetra acetic acid.No erosion –intertubular and peritubular dentin.
  59. 59. SUGGESTED METHODS FOR REMOVING SMEAR LAYERAuthor Amount SolutionGoldman etal. (1981) REDTA 17% 20mlGoldman etal. (1982) REDTA 17% 10ml Naocl 5.25% 10mlYamada etal (1983) REDTA 17% 10ml Naocl 5.25% 10mlWhite etal (1984) REDTA 17% 10ml Naocl 5.25 10mlCiucchi etal (1989) Naocl 3% 1ml EDTA 15% 2mlGettleman etal (1991) EDTA 17% -
  60. 60. Ultrasonic removal A small file activated ultrasonically-fluid movement called Acoustic streaming . Cameron (1988) - 2 % to 4 % NaOCl +ultrasonic energy- removal of smear layer. Cameron (1983) -3-5 min irrigation-effective. Guerisoli et al- 15 % EDTAC +Distilled water or 1 % Naocl.
  61. 61.   Acoustic streaming
  62. 62. LASERS Weichman & Johnson (1971) first  applied a laser to the root canals -toseal the apical foramen in vitro -highpower CO2 laser. Middle thirdpashley et al (1992)- Co2 laser- dentinpermeability; melting smear layer. Apical third
  63. 63. Nd:YAG laser- debris & smear layerbeing removed or melted,fused andrecrystallized .(Harashima et al1997). Argon laser - efficient cleaningactivity on instrumented root canals Middle third(Harashima et al 1997)Er : YAG laser -more effective - Aror Nd:YAG laser (Takalashi et. al.1996) Apical third
  64. 64. Potassium Titanyl phosphate (KTP) laser -wavelength of 532µm - remove smear layer and debris from rootcanal. (Tenfik et. al 1998 ) Nano second-pulsed, frequency-doubled Nd:YAGlaser - smear layer removal (Arrastia-Jitosho et. al. 1998)
  65. 65. xenon chlorine (xecl) laser - 308 µm can melt dentine andseal exposed dentinal tubules. (pini et. al. 1989, stabholz et.Al)Ar-fluoride (F) excimer laser–removal of peritubular dentineat relatively high fluency (10 ~13 J/cm2) with melting andresolidification of the dentinal smear layer (stabholz et. Al).
  66. 66. MICRO BRUSHES Rotary and ultrasonic endobrushes - ISO lengthcontain 16mm. of bristles, - bristle diameters of 0.40, 0.50 ,0.60 and 0.80mm. Rotary activated micro brushes -300 RPM, helicalbristle pattern effectively -residual debris out of the canal in acoronal direction. Micro brushes designed for ultrasonic use- activateNaOCl and 17% EDTA -produced cleaned canals. Regardless of rotary versus ultrasonic activation,microbrush can finish the preparation -17% EDTA for 1 min. toclean the root canal system.
  67. 67.
  68. 68. Conclusion Smear layer is seen as a part of our daily clinical practice. Though its dimensions are in micrometers, it is of strategic importance in restorative dentistry and endodontics. To prevent the infection into the dentinal tubules, microleakage, and for proper adhesion , it is advised to remove the smear layer and smear plugs.
  69. 69. Thank