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Stresses in adhesive restorations / dental courses

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Stresses in adhesive restorations / dental courses

  1. 1. www.indiandentalacademy.com •INDIAN DENTAL ACADEMY •Leader in continuing Dental Education
  2. 2. CONTENTS…. • Basic polymer chemistry • The fundamentals of polymerization • Reaction kinetics in photopolymerised networks • The effects of polymerization shrinkage • Factors influencing shrinkage and stress • Measurement of shrinkage and stress • Counteracting polymerization shrinkage and stress • Conclusion www.indiandentalacademy.com
  3. 3. BASIC POLYMER CHEMISTRY Inter atomic induction forces Chain configuration www.indiandentalacademy.com
  4. 4. POLYMERISATION • A repetitive intermolecular reaction…… • Types…… • Addition and Condensation Polymerization • Co polymerization…. www.indiandentalacademy.com
  5. 5. R – R External energy 2 R ¤ C = C R C – C ¤ C = C R C – C – C – C ¤ R C – (C – C) n – C ¤ C = C R C – (C – C) n = C + HC – C ¤ R C – (C – C) m – C ¤ R C – (C – C) n – C –C – (C – C) m – C R (or) R C – (C – C )n – CH3 + R C – (C – C) m – CH3 INDUCTION PROPAGATION CHAIN TRANSFER TERMINATION www.indiandentalacademy.com
  6. 6. Inducing and inhibiting polymerization Chemicals  peroxide - amine  peroxide – sulfinic acid  xylidine – diethanolamine  Ascorbic acid – peroxide  Sulfinic acid – lauryl mercaptan  Tri alkyl boranes Light  Ultraviolet light  visible light Thermal systems  peroxides  azo compounds Inhibitors of polymerization • methyl ether of hydroquinone • oxygen (Chandler – 1973 ; Bowen – 1974; Stansbury and Ge – 2003; Watts – 2005)www.indiandentalacademy.com
  7. 7. CONDENSATION POLYMERISATION • Production of a “non macromolecular structure” • Formation of by products….. • STEP GROWTH polymerization……. • Vs addition polymerization :  Simultaneous activation  Non macro molecular product  By products  Kinetics of the reaction www.indiandentalacademy.com
  8. 8. CO POLYMERISATION • What is a co polymer???? • The need for copolymeric structures….. • n H2C = CHA + m H2C = CHB --(H2C – CHA – H2C – CHB) m+n • n H2C = CHA + m H2C = CHB - (H2C – CHA)n + (H2C – CHB)m • Types : • Random - ABBAABBAAABBBBAAB • Block - AAAABBBBAAAABBBB • Graft / Branched – AAAAAAAA B B www.indiandentalacademy.com
  9. 9. WHAT EXACTLY HAPPENS ?? • Why does volumetric shrinkage occur ? • Monomeric factors  Bis GMA – 5.2 %  TEGDMA – 12.5 % (Thompson – 1979 ; Versluis – 1996 ; Ferracane – 2005 ;Braga – 2005) www.indiandentalacademy.com
  10. 10. Kinetic landmarks….. • Gel point – formation of a continuous network structure - conversion dependent • Visco elastic flow • Auto acceleration : viscosity – macroradical termination – inhibition of monomer mobility • Vitrefication stage : glass transition temperature reaches cure temperature • Residual unsaturation : mixture of pendant reactive groups and free monomers (Carvalho – 1996 ; Russo – 1999; Ferracane – 2005, 2006 ; Pereira – 2005) www.indiandentalacademy.com
  11. 11. www.indiandentalacademy.com
  12. 12. Effects of shrinkage and stress…. (York and Arthur – 1973; Hancox – 1998) (Sekiya – 1989; Sano – 2000) (Willems – 1990; Tanaka – 2001) Cuspal deflection; cusp crack ; enamel fracture Adhesive failure - Secondary caries Micro cracks www.indiandentalacademy.com
  13. 13. Factors influencing shrinkage and stress….. Cavity Technique Material Reaction kinetics www.indiandentalacademy.com
  14. 14. Cavity configuration C=C= BONDED WALLSBONDED WALLS UNBONDED WALLSUNBONDED WALLS C-FACTORC-FACTOR (Feilzer, Davidson and De Gee – 1987) www.indiandentalacademy.com
  15. 15. www.indiandentalacademy.com
  16. 16. (Davidson‘ s modification) www.indiandentalacademy.com
  17. 17. Curing LightCuring Light 0 mm0 mm 11 22 33 44 DEPTH OF CUREDEPTH OF CURE DEGREE OFDEGREE OF CONVERSIONCONVERSION 65%65% 25%25% 45%45% www.indiandentalacademy.com
  18. 18. Curing EquipmentCuring Equipment FactorsFactors ProceduralProcedural FactorsFactors RestorationRestoration FactorsFactors • Bulb frosting or degradationBulb frosting or degradation • Light reflector degradationLight reflector degradation • Optical filter degradationOptical filter degradation • Fiber-optic bundle breakageFiber-optic bundle breakage • Light-guide fractureLight-guide fracture • Tip contamination by resin buildupTip contamination by resin buildup • Line voltage inconsistenciesLine voltage inconsistencies • Infection control barriersInfection control barriers • Light tip directionLight tip direction • Access to restorationAccess to restoration • DISTANCE from surfaceDISTANCE from surface • Size of tipSize of tip • Tip movementTip movement • TIME of exposureTIME of exposure • Restoration thicknessRestoration thickness • Cavity designCavity design • Filler - amount and sizeFiller - amount and size • Restoration shadeRestoration shade • Monomer ratiosMonomer ratios FACTORS AFFECTING CUREFACTORS AFFECTING CURE www.indiandentalacademy.com
  19. 19. 0 25 50 75 100 0 2 3 4 5 CONVERSION (%) SHRINKAGE(%) 1 65%65% ConversionConversion 15-25% =15-25% = GelationGelation 50% Filler 25% Bis-GMA 25% TEGDMA Flow Bond Stretching (External Contraction) Micro cracks (Internal Contraction) The Shrinkage – Conversion RelationshipThe Shrinkage – Conversion Relationship Revisited….Revisited…. A physico chemical explanation (Fogleman – 2002 ;Boutry and Deveaux – 2006) www.indiandentalacademy.com
  20. 20. Post-gel Phase Possibility No. 1Possibility No. 1 Gap FormationGap Formation If stress exceeds bond strengthIf stress exceeds bond strength Post Curing High C factor restoration www.indiandentalacademy.com
  21. 21. Possibility No. 2Possibility No. 2 DistortionDistortion If bond strength exceeds stressIf bond strength exceeds stress (Davidson, Feilzer and De Gee – 1984)(Davidson, Feilzer and De Gee – 1984) Post-gel Phase www.indiandentalacademy.com
  22. 22. C -FACTOR IN THE ROOT CANAL…. • The advent of resin based sealers…. • The importance of canal geometry and resin film thickness • The lack of shrinkage stress relief in narrow canals…. • Possible parameters influencing stress relief – Resin sealer volumetric shrinkage – Voids in sealer – Polymerization rate • The monobloc concept…..mission impossible???? (Tay and Pashley – 2005) www.indiandentalacademy.com
  23. 23. MATERIAL BASED FACTORS - Theoretical Considerations • Filler content : shrinkage α polymer matrix • Filler size – relationship between surface are – volume ratio …. (Spahl et al – 1994) • Filler distribution / dispersion…… (Stansbury – 1999) • CTE mismatch….. FILLERS www.indiandentalacademy.com
  24. 24. Elastic modulus • Higher the elastic modulus and shrinkage, higher the contraction stress • Hooke’s Law…… www.indiandentalacademy.com
  25. 25. • Conversion kinetics of dimethacrylate monomers…. • Influence of co monomer concentrations…. (Cook et al – 1992 ; Lovell et al – 1999) • Role of TEGDMA and its stereochemistry…. (Krejsci – 2000 ; Truffier – 2001;Ferracane – 2001; Braga – 2003) • Reaction diffusion termination…. • The role of inhibitor (BHT)….. Chemistry of Co monomers www.indiandentalacademy.com
  26. 26. Self cure Vs Light cure • The magnitude of polymerization…. (Kato – 1993 ; Kinomoto – 1999) • Marginal adaptation…. • Manipulation – voids – porosity…. (De Gee – 1979 ; Alster – 1992 ; Feilzer – 1993) • Layer thickness Vs stress generation www.indiandentalacademy.com
  27. 27. ADHESIVE THICKNESS…. • Importance of bond strength… • The reason behind…..stress absorption • Low stiffness of adhesive…. • Drawbacks…… (Asmussen – 1975; Ferracane et al – 2000 ; Davidson et al – 1990) www.indiandentalacademy.com
  28. 28. PRE HEATED COMPOSITES – Pre heating to 54 – 60 º C ; 45 – 60 seconds - rapid photo polymerization – Increased molecular mobility and collision frequency…. – Increased degree of conversion and physico mechanical properties….yet….. (Daronch and Rueggeberg – 2005, 2006) www.indiandentalacademy.com
  29. 29. Influence of Photo activation methods…. • Achieving adequate polymerization…. • Increase in temperature – increased shrinkage • Increased light intensity – increase in temperature – increased shrinkage strain • Why ???? (Contraction stress = Power Density x Time) (Rueggeberg – 1994 ; Bennett – 2004 ; Elhejazi- 2006) www.indiandentalacademy.com
  30. 30. Contraction stress relaxation by hygroscopic expansion • Main cause for mechanical stress in adhesive restorations….. • Expansion by water diffusion up to equilibrium…. • Relaxation of shear stresses parallel to adhesive interface. • Influencing factors….. – Cavity configuration – Chemistry of the monomer – Nature of fillers (Feilzer, Gee and Davidson – 1990) www.indiandentalacademy.com
  31. 31. C-Factor 0.5 HOW DOES IT SHRINK ????? (Hansen – 1982; Versluis and Douglas – 1998 ; Sagakuchi – 1998) Challenging the traditional view…. www.indiandentalacademy.com
  32. 32. Measuring shrinkage and stress - A review of literature…. www.indiandentalacademy.com
  33. 33. • Direct measurement – Tensilometer (Bowen – 1967; Feilzer – 1987 ; Ferracane – 1998) – Strain gauge (Kinomoto – 1998; Torii – 1999) – Force transducer (Bowen – 1967; Shono – 1999; Manahart – 2001) – Ring slitting method (Ferracane – 2003) – Dilatometry (Cash – 1991 ; Braga – 2002) – Interferometry (Davidson – 1984; Hoffman – 2003) • Finite Element Analysis (Versluis -1999; Ausiello – 2002) • Photoelastic analysis (Kinomoto – 1998 ; Torii – 1999) • Indirect measurements – Microleakage analysis (Anseth – 1996; Morgan – 1998) – Cuspal deflection measurement by LVDT (Linear Variable Displacement Transducer) – WATT’S METHOD (Rueggeberg – 1989; Braga – 1999) – Degree of conversion • Direct chemical analysis (Sagakuchi – 1999; Ferracane – 2002; Chen – 2004) • Mid IR spectroscopy (Dusek – 2004) • FTIR spectroscopy (Elliott – 2002; Hilton – 2003) • Photo differential scanning calorimetry (Labella – 1999; Lovell – 2002) www.indiandentalacademy.com
  34. 34. Strategies To Counteract Shrinkage And Stress…. Controlled stress reduction Natural mechanisms www.indiandentalacademy.com
  35. 35. Incremental layering Weaver and Blank technique / Deliperi and Bardwell technique (1988) (Wedge layering / oblique stratification) Bertolotti technique (1991) (The Three site layering technique / Directed Shrinkage technique) www.indiandentalacademy.com
  36. 36. • Vertical layering / facio lingual layering • Horizontal layering / gingivo occlusal layering • Centripetal build up / Bichacho tecnique (1994) • Successive Cusp Build up / Axial bevel technique / Liebenberg technique (1996) Other stratification techniques…….. www.indiandentalacademy.com
  37. 37.  The conventional view….  If each increment were to shrink and exhibit stress…. (Morin – 1988 ; Sakaguchi – 1991; Hassan – 2005)  Hypothesis – cavity deformation Vs no deformation The incremental layering approach….. Controversies exist !!!! www.indiandentalacademy.com
  38. 38. Split increment horizontal layering / Hassan Technique (2005) Uncured increment Diagonal increment 3 4 www.indiandentalacademy.com
  39. 39. Stress absorbers…. • Low elastic modulus liners…. (Alster – 1992; Ferracane – 1999; Ausiello – 2002) • Parameters : – Elastic modulus – Thickness • Flowable composites as liners…. (Braga – 2003) www.indiandentalacademy.com
  40. 40. Bi Layered restoration • Mc Lean and Prosser (1985) • The advantages of using glass ionomer…. • Types – Open – Closed – Centripetal approach www.indiandentalacademy.com
  41. 41. Auto-cure GIC Fuji 2 LCFuji 2 LC LiningLining consistencyconsistency Pack composite alongPack composite along the fissure patternthe fissure pattern Melichez technique – modified sandwich approach www.indiandentalacademy.com
  42. 42. CURING PROTOCOLS….. Initial low radiant exposure (290 mW/cm2 for 2 seconds) ; delay of 5 minutes ; radiant exposure of 330mW/cm2 for 60 second Vs Single continuous exposure ( 330 mW/cm2 for 60 seconds) (Lim et al – 2002)Pulse Delay Stepped Ramped Standard Intensity Pulsed High Intensity Time (seconds) Irradiance The duty cycles • Full power • Two staged • Ramped • Custom • oscillating www.indiandentalacademy.com
  43. 43. FILLERS • Non bonded silica nanofillers : • size of the filler…. • why NON bonded ????? • High density polyethylene spheres • size of the filler…. • how does it reduce stress ?? www.indiandentalacademy.comwww.indiandentalacademy.com
  44. 44. OTHER REINFORCING FILLERS……OTHER REINFORCING FILLERS……  Silicate glass and glass ceramic fillers (Antonucci – 1991 ; Bowen – 1992 ; Bayne – 1999)  Chopped glass fillers (glass inserts) and branched fiber fillers (Bayne and Thompson – 1996)  Nano porous fillers ; cooled composite inserts (Luo – 1999)  Ceramic whiskers…. (Antonucci and Eichmiller – 1999) www.indiandentalacademy.com
  45. 45. Fiber reinforcementFiber reinforcement  Reinforcing mechanisms….Reinforcing mechanisms….  Transitional boundary layer (the crack shieldingTransitional boundary layer (the crack shielding effect)effect)  Load – crack formation – crack deflection – absorbedLoad – crack formation – crack deflection – absorbed by layer - tougheningby layer - toughening  Silane coupling agentSilane coupling agent – increases particle / matrix bond– increases particle / matrix bond  Rod like particlesRod like particles – bridges across the advancing crack– bridges across the advancing crack ( the crack blocking effect)( the crack blocking effect) (Bausch et al – 1997; Breschi – 1999) www.indiandentalacademy.com
  46. 46. Alternative monomer formulations…. www.indiandentalacademy.comwww.indiandentalacademy.com
  47. 47. CYCLOPOLYMERIZABLE MONOMERS • Monofunctional acrylate monomers + paraformaldehyde = difunctional monomers (Stansbury – 1990) • Chemistry : oxy bis – methacrylate + α hydroxy methyl acrylate + Isobutyronitrile initiator • Expanding monomer + diepoxide monomer + PTHF (polyol) (Krenkel et al – 1999) • Polymer backbone with cyclic ether structure • High degree of conversion (30 % more that conventional dimethacrylate monomers) (Stansbury – 1990, 1992; Ruyter – 1996) • Yet………….decreased shrinkage….????? ( 40% decrease ) (BUTLER’S HYPOTHESIS – 1975) • Disadvantage…. www.indiandentalacademy.com
  48. 48. OXASPIRO MONOMERS • Chemistry : 2,3- Bis (methylene) Spiro orthocarbonates • “Double ring opening” polymerization….. (Zindan – 1987; Feilzer – 1990) • Shrinkage values 50 % lesser than conventional dimethacrylates…. (Thompson – 1990; Stansbury and Bailey – 1991) • Requirements…….difficulties not addressed so far:  reactivity with dimethacrylates  effective utilization of “ring opening” mechanism  glass transition temperature  drawbacks of symmetrical orthocarbonates…. www.indiandentalacademy.com
  49. 49. THIOL ENE OLIGOMERS • Posner – 1905 ; Bowman - 1990 • Step growth addition reaction with free radical chain transfer (Jacobine – 1993 ; Cramer – 2002) • Drawbacks of spiro orthocarbonates… (Carioscia – 2005) • Chemistry : Triallyl- 1,3,5 – Triazine- 2,4,6 – trione + Pentaerythritol tetra ( 3- mercaptopropionate) + CQ + ethyl 4-dimethylaminobenzoate. • Stepwise, yet rapid…. • Not inhibited by oxygen…. (Cramer – 2002) • Increased depth of cure. • Complete conversion…….no longer a dream. • Shrinkage 3.3 % as compared to 5 % of Bis GMA/TEGDMA • STRESS 0.3 MPa ( 2.8 Mpa for BisGMA/TEGDMA) (Bowman – 2003, 2005 ; Stansbury – 2005) www.indiandentalacademy.com
  50. 50. Also tried…….and forgotten !! • Vinyl Cyclo Propanes (VCP) – replaces TEGDMA (Miyazaki et al – 1997) • Poly butadiene rubber polymer (20 µm aggregates) + fumed silica + Bis GMA – TEGDMA (Lee et al – 1999; Mozner - 1999) • Liquid crystal monomers - 1,4 [4,6 – acryloyloxy hexane – 1, oxy] benzoyloxy – 2 t butyl benzene + silica - OX 50 (Rawls – 1997; Norling et al – 1999) • Methacrylated derivative of styrene allyl alcohol (MSAA)…. (Culbertson et al – 1997; Ferracane – 2000) • Reaction between branches of Bis GMA (Holter and Frey – 1997; Mulhaupt – 1997) www.indiandentalacademy.com
  51. 51. EPOXY RESIN BASED COMPOSITES • Chemistry : 3,4 – epoxy cyclo hexyl methyl – (3,4 – epoxy) cyclohexane carboxylate + nanosilica fillers (55 %) + photo initiator ( 4 – octyl phenyl) phenlidonium hexafluoroantimonate (OPIA) +CQ • Surface treatment of fillers – γ glycidoxy propyl trimethoxysilane • Light absorption at 240 – 250 nm… UV light…disadvantage….. • 75 % degree of conversion • Shrinkage 35 % less than conventional monomers……WHY?? • Shrinkage stress of 0.8 Mpa (Craig – 1998;Chen – 2006; Brinker – 2006) www.indiandentalacademy.com
  52. 52. SILORANES • Chemistry : Siloxanes + Oxiranes (ethylene oxide – an epoxide) • Siloxane – hydrophobic • Cationic ring opening polymerization – acidic carbo cation based • Weinman and Christopher – 2005 : Shrinkage values  Silorane (3M ESPE) – 1 %  Tetric Ceram – 2.5 %  Spectrum TPH – 3%  Solitaire – 4 % www.indiandentalacademy.com
  53. 53. Resins with enhanced cure….Resins with enhanced cure….  Multi ethylene glycol dimethacrylates– diethylene glycolMulti ethylene glycol dimethacrylates– diethylene glycol dimethacrylate + polyethylene glycoldimethacrylate + polyethylene glycol (Anseth – 1996)(Anseth – 1996)  Esterified multi methacrylate oligomers of poly isopropylideneEsterified multi methacrylate oligomers of poly isopropylidene diphenoldiphenol (Wan and Culbertson – 1997)(Wan and Culbertson – 1997)  DiBenzylidene Sorbitol in bioactive composites withDiBenzylidene Sorbitol in bioactive composites with ethoxylated Bis GMA - decreased shrinkage; enhancedethoxylated Bis GMA - decreased shrinkage; enhanced propertiesproperties (Antonucci, Wilson and Wilder – 2005)(Antonucci, Wilson and Wilder – 2005) www.indiandentalacademy.com
  54. 54.  Ormocers…..multifunctional urethane + thioether methacrylate alkoxysilanes (Wolter and Storch – 1994)  Organosilsesquioxane (RSi01.5)n – condensation reaction of siloxanes and silanes (Antonucci – 1997; Laine – 1998) ORGANIC – INORGANIC HYBRIDS www.indiandentalacademy.com
  55. 55. Indirect composites • The need for indirect composite restorations….. • Microfilled, small particle, hybrid and Ceromer (CERamic Optimized polyMER) • Main differences : – Increased filler loading ( > 60 %) – Multi functional methacrylates and bi functional monomers – Shrinkage < 1.2 % (Braga – 2004; Rueggeberg – 2005)www.indiandentalacademy.com
  56. 56. Modes Of Curing Indirect Composites • Superficial - temperature and pressure Eg., SR Isosit, Coltene Brilliant, Visio Gem, Clearfil CR • Conventional – only light curing Eg., EOS • Secondary curing – initial light curing, additional heat and light curing Eg., True Vitality, Dentacolor, Adoro, Herculite XRV, ArtGlass, BelleGlass) www.indiandentalacademy.com
  57. 57. TECHNIQUE MATERIAL • Forget GV Black for adhesive restorations ! • Stratification technique (?) • Stress absorbers; Bilayered restorations ; Melichez approach • Modified curing protocol • Indirect composite restorations • Reinforcing fillers • Increasing inhibitor concentration • Alternative monomer formulations (SOC; thiol ene; siloranes; epoxy resins) • Ormocers www.indiandentalacademy.com
  58. 58. To conclude…..To conclude….. • Understanding the physics of polymerization – notUnderstanding the physics of polymerization – not just a theoretical expanse of knowledge……just a theoretical expanse of knowledge…… • The target …..The target ….. www.indiandentalacademy.comwww.indiandentalacademy.com
  59. 59. THANK YOU !!THANK YOU !! www.indiandentalacademy.comwww.indiandentalacademy.com

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