Dentine Bonding Current Perspectives.pptx

A comprehensive review of dentine bonding systems ,history of dentine bonmding,self etch vs etch and rinxe systems,how to select your bonding systems, mechanism of action,short comings and future perspevctives

1. Bonding C urrent perspectives Dr. Josey Mathew

2. What comes in this? History The basics Components of Dental Adhesive Systems Enamel Bonding Dentine Bonding Generations of DBAs Today’s Adhesives Strategies to preserve bond stability Universal adhesives Future Conclusion 2

3. “Marriage is a sacred bond between two imperfect souls, which is made possible by God” Dave Willis “Bonding in dentistry may be a marriage between two imperfect surfaces (resin and tooth) made possible by the dentist” 3

4. HISTORY 1951 - Oscar Hagger - Developed an acidic GPADMA - permitted resin adhesion to dentin. 1955 - The foundation for adhesives Buonocore - A cid etching of enamel-Based on industrial use of 85% phosphoric acid for 30 seconds. 1957 - Bowen -bisphenol A-glycidyl methacrylate resin -first composite material. 1960-1970’s - 1 st and 2 nd Generation bonding agents 1963 - Boyde and Steward- first described Smear layer. 1970 - Eick et al Composition of smear layer and its role in Bonding. 1975 - Gwinnett and Silver stone - 3 patterns of etching in enamel 1979 – Fusayama - Total etch concept 4

5. 1980’s – 3 rd Generation Bonding agents 1982- Nakabayashi - Hybrid layer Early 1990’s – 4 th Generation Dentin bonding system 1992 - Kanca et al -Wet bonding technique 1999 - Prati and Pashley - Reverse Hybrid layer Mid 1990s - 5 th Generation Dentin Bonding Systems Early 2000’s - 6 th Generation Dentin Bonding Systems 2003 - 7 th Generation Dentin Bonding System 2010 - 8 th Generation Dentin Bonding System 2011- Universal adhesives 5

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7. ADHESION- THE BASICS ADHESIVE/ ADHERENT- A material, that joins two substrates together and solidifies and is able to transfer a load from one surface to the other. ADHEREND - M aterial to which an adhesive is applied ADHESION - I ntermolecular attraction that exists between molecules of two unlike substances when placed in intimate contact with each other. COHESION- Force with which molecules of the same kind are attracted. 7

8. PRIMARY MECHANISM OF ADHESION 8

9. WETTING OF A LIQUID Surface Energy-Intermolecular forces at the interface between two media Surface Tension-The force that holds liquid molecules together. 9

10. REQUIREMENTS FOR GOOD ADHESION Clean adherend Good wetting Intimate Contact Bonding Good polymerisation 10

11. CO-FACTORS FOR ADHESION Surface roughness Surface Energy of Substrate High for etched enamel Low for smear layer covered dentine Bond promoting effects Eg. Capillary forces-Etched enamel Hydrophilicity/ phobicity Interfacial pores(air/moisture) 11

12. SUBSTRATES Enamel / Dentin / Cementum Enamel Ideal Dry Mineral - 92 Vol % - Hydroxyapatite Dentin Complex Moist 45 Vol % Hydroxyapatite More Organic - 33 Vol % - Predominantly-Type I Collagen Approx 32%-Water Water content-increases 20 X from superficial to deep 12

13. Tubular structure Mean tubular volume Total in Coronal dentin-10% Near DEJ 4% Near pulp 28 % Dentinal tubular fluids- Outward pressure of 25-30 mm of Hg Odontoblastic processes Intratubular Collagen fibers Rods/ Prisms Major inorganic fraction Submicron crystallites distributed in key-hole pattern. 13

14. DIFFERENCES BETWEEN ENAMEL AND DENTINE HYDROXYAPATITE Larger More regular and parallel oriented Smaller Arranged criss cross pattern within organic matrix- Micro-mechanical interlocking difficult Chemical bonding facilitated 14

15. SMEAR LAYER-REMOVE OR RETAIN?? Remove… Tubules are open for good retention The exposed collagen network provides reactive groups that can chemically interact with primers. Exposed collagen promotes micro mechanical bonding to resin Retain…. Protective barrier. Lowers dentinal permeability. Lowers pulpal pressure Use of bonding agents that can penetrate the smear layer and incorporate into bonding layer 15

16. COMPONENTS OF DENTAL ADHESIVE SYSTEMS Etchant Primer Dentin adhesive / Bonding resin 16

17. E TCHANTS 30-40% Phosphoric acid Thickeners (Silica micro particles or Xanthum gums ) Colour dye Glycol for wettability and to decrease viscosity Organic Maleic acid Tartaric acid Citric acid EDTA A cidic monomers-SE systems Polymeric - Polyacrylic acid Mineral acids Hydrochloric acid Nitric acid Hydrofluoric acid 17

18. CALCIUM CHELATORS Remove smear layer without decalcification or significant physical changes in the underlying dentin substrate. EDTA pH - 7.4 Tublicid : 0.1% EDTA 0.15% Benzalkonium chloride Scrubbed on the surface for a few seconds, Smear layer removal, smear plug intact 18

19. LASERS & AIR ABRASION Nd: YAG lasers used at 10-30 pulses per second The surface is desensitized by occlusion of open and permeable dentinal tubules. Air abrasion: Aluminium oxide particles of particle size of 0.5 microns are used 19

20. PRIMERS Bifunctional monomer in a volatile solvent such as acetone or alcohol hydrophilic, low viscosity Adhesion promoting agents Displaces residual moisture in dentine Wets and envelops the exposed collagen fibrils. Carry monomers into interfibrillar channels Transforms hydrophilic dentine into hydrophobic Increases surface free energy SEs use acidic monomers as primers 20

21. COMMONLY USED PRIMERS 30-55% HEMA (Hydroxy ethyl methacrylate)- most commonly used 2-5% NTG-GMA (N- Tolyglycine - glycidyl methacrylate) 16% BPDM (Biphenyl dimethacrylate ) 6% PENTA( dipentaerythritol penta acrylate monophosphate) 10% PMDM (Pyromellitic acid diethyl methacrylate) 21

22. DENTIN ADHESIVES / BONDING RESIN Thin layer of resin applied between conditioned dentin and composite. Link between hydrophilic primer and hydrophobic composite C o polymerizes with the primer molecules and restorative resin Form resin tags to seal open dentinal tubules Stabilizes the formed hybrid layer and resin tags Commonly used Bis GMA, UDMA, TEGDMA, Methacrylated phosphates, PENTA . Act as a stress relaxation buffer - relieve polymerization stresses Usually unfilled but may contain fillers ( Optibond S olo, Prime and bond NT) 22

23. I nitiators and Accelerators: Light cured: - C amphoroquinone and organic amine Dual cured bonding agents : - Catalyst to promote self curing Fillers: Mostly unfilled Inorganic fillers 0.5% to 40% by wt. Microfillers or nanofillers Functions of nanofillers Prevents nanoleakage Causes uniform thickness of adhesive layer Better flexibility to adhesives Better dissipation of forces Scatter of light is prevented 23

24. SOLVENTS Acetone, Ethanol, Water Acetone evaporates fast- requires shortest drying time in mouth. Ethanol evaporates more slowly-moderate drying time Water evaporates very slowly-longest drying time. 24

25. ENAMEL BONDING Etching The objectives of enamel etching : Clean the enamel Remove enamel smear layer   Creates micropores( 5-10 µm ) Removal of prismatic and interprismatic mineral crystals Increase surface energy of enamel x 2000 25

26. ETCHING PATTERNS ( Silverstone et al 1975 ) Type I I nvolves dissolution of prism cores without dissolution of prism peripheries - HONEY COMB Type II T he peripheral enamel is dissolved, but the cores are left intact - COBBLESTONE 26

27. Type III M ixture of Type I & Type II configurations Type IV Shows a pitted enamel surface Random distribution of depressions with no preferential destruction of either cores or peripheries. These areas occasionally occur in little patches over enamel surface 27

28. Type V E xtremely flat and smooth L acking micro irregularities for penetration and retention of resins Similar to Type IV patterns N o evidence of prism outlines seen. 28

29. ENAMEL BONDING AGENTS Used in the past - Consists of bis-GMA or UDMA resins with diluents like TEGDMA. Flow easily into the microporosities of enamel. Now EBAs replaced by DBAs. Advantage Simultaneous bonding to both enamel and dentin possible 29

30. R ESIN TAGS Macro tags - space surrounding the enamel prisms   Micro tag s - result from resin infiltration / polymerization within the tiny etch-pits at the cores of the etched enamel prisms. Major contribution to retention to enamel . 30

31. DENTIN BONDING Etching dentine Changes in I ntertubular dentin Exposes longitudinally/obliquely oriented collagen fibers Changes in peritubular dentin Opens tubule orifices in typical funnel shape configuration Exposes circularly oriented collagen fibril arrangement Decrease surface energy Increase surface roughness Demineralization; 3-5µm Exposing a scaffold of Collagen fibers that is depleted of HAp 31

32. Dentine bonding…. Application of Primer Containing hydrophilic monomers like HEMA in Organic solvents Solvents displace water from dentine HEMA improves wettability Promotes re-expansion of Collagen network Make hydrophilic dentin hydrophobic 32

33. Dentine Bonding…. Application of adhesive Resin Adhesive resin applied on prepared surface Penetration of hydrophobic monomers into interfibrillar spaces of Collagen network & into dentinal tubules Monomers polymerized in situ- Hybrid layer 33

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35. Hybridization ( N akabayashi,1982) Structure formed in dental hard tissues by demineralization of the surface and subsurface, followed by infiltration of monomers and subsequent polymerization . 35

36. ZONES OF HYBRID LAYER (Perdiago 1996) Top layer : Amorphous electron dense phase consisting of denatured collagen. Middle layer : Collagen fibrils separated by electrolucent spaces of 10- 20 nm. Bottom layer : Gradual transition to underlying unaltered dentin partially demineralized containing HA crystals enveloped by resin . 36

37. ULTRAMORPHOLOGIC FEATURES OF HYBRIDISATION Shag carpet appearance Tubule wall hybridization Lateral tubule hybridization 37

38. SHAG CARPET APPEARANCE (Bradjdic et al 2008) Appears when acid etched dentin surface is actively scrubbed with an acidic primer solution. M echanical + Chemical action- Dissolves additional mineral salts Causes fluffing and separation of entangled collagen at the surface. Loose organization of collagen fibrils directed towards the adhesive resin often unraveled into their micro-fibrils. 38

39. TUBULE WALL HYBRIDIZATION Extension of the hybrid layer into tubule wall area. Hermetically seals the pulp dentinal complex against microleakage. Especially protective when bond fails at top or bottom of the hybrid layer Tubule wall hybridization ensures a leakage free seal of tubules 39

40. LATERAL TUBULE HYBRIDIZATION Formation of tiny hybrid layer into the walls of lateral tubule branches. This microversion of hybrid layer typically surrounds a central core of resin called microresin tag. 40

41. REVERSE HYBRID LAYER Prati et al 1999 A pplication of NaOCI after acid etching   R emoves exposed collagen - solubilizes the fibrils down into the underlying mineralized matrix -- creating sub micron porosities Cylindrical channels - available for resin infiltration within the mineralized matrix. Proposed as mineralized, hydrophilic alternatives to collagen rich, hydrophobic acid- demineralized dentin, possessing increased bond strengths Not recommended for clinical use. 41

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43. GHOST HYBRID LAYER In pre bonded dentine Aluminum oxide air abrasion (white arrows) results in partial removal of the original hybrid layer (HL) --new ghost-like hybrid layer (HL2). The adhesive layer interface (ALI) was also modified, causing incorporation of aluminum oxide powder even after cleaning. 43

44. DRY BONDING Drying dentine by blast of air C ollapse of collagen fibres – Ineffective penetration HYBRIDOID ZONE 44

45. WET BONDING WWBT (WATER WET BONDING TECHNIQUE) Acetone/ alcohol based primers applied to moist demineralized dentine, water diffuses from the wet dentine into the acetone, while the acetone diffuses into the demineralized dentine matrix. Substitution of water - chemical dehydration of the collagen network - also increases the modulus of elasticity of collagen. Solvents evaporate - resin monomers occupy the spaces around the collagen fibrils. Hybrid layer formation Kanca and Gwinnett et al, in 1990s 45

46. Disadvantages Acetone quickly evaporates S hould be quickly applied R atio of monomer & acetone changes Technique sensitive White frosted appearance of enamel that indicates proper etching cannot be observed. 46

47. DRY BONDING WITH WATER BASED PRIMERS Too much water -- dilute the monomer concentration Bonding in which acid etched dentin is dried U ses adhesive systems that use water based primers Water in these primers— Probably plasticized the stiffened, collapsed collagen network Re- expanded collagen network Increased permeability to primer resins. 35-50% HEMA in water - maximum bond strength 47

48. OVER WET PHENOMENA Some regions in complex cavity preparations (such as proximal boxes) may be too wet. When single bottle primer/adhesives are applied Solvent may diffuse into the water, instead of vice versa, A dhesive monomers undergo phase changes, forming blisters , resin globules 48

49. Generations of Dentin Bonding Agents First generation bonding agent Second generation bonding agents. Third generation bonding systems. Fourth generation bonding systems. Fifth generation bonding systems. Sixth generation bonding systems Seventh generation Eighth generation Historical Current 49

50. 1 ST GENERATION DENTIN ADHESIVES-1960s C ontained N-phenylglycine and glycidyl methacrylate (NPG-GMA) NPG-GMA is a bifunctional molecule O ne bonds to dentin through chelation with calcium on the tooth surface while the other bonds (polymerizes) to composite resin. Bond strength - 1 to 3 Mpa Eg. Cervident (S S white Co, PA) 50

51. 2 ND G ENERATION ADHESIVES - LATE 1970s Phosphate esters containing phenyl-P & HEMA in ethanol. M echanism of action – polar interactions between negatively charged phosphate groups in resin and positively charged Ca ion in the smear layer. Bond strength - 1- 5 Mpa Clearfil bond system F.(Kuraray)   Disadvantages: I & II Low bond strength Bonding obtained to the smear layer, not to the dentin itself. 51

52. 3 RD GENERATION - LATE 1980S Required either removal, modification or dissolution of the smear layer. Two component Primer / adhesive system PHOSPHATE BASED (HEMA+10 MDP) Bonding through Ca- Phosphate i nteraction Bond strength: 8-15 MPa Eg : Scotch bond 2 (3M Dental) 52

53. 4 TH GENERATION – EARLY 1990s Hybrid layer - Nakabayashi 1982 Total etch concept 3 Steps Etching Priming Bondi ng 53

54. Advantages Good Bond strength: 17-25 Mpa. No reduction in bond strength when applied to moist surface Can bond to mineralized tissue as well as metal, amalgam, composite and porcelain Disadvantages Multiple steps: Technique sensitive All bond 2( Bisco Dental) Scotch bond multipurpose( 3M Dental Optibond ( Kerr) 54

55. 5 TH GENERATION- MID 1990S 2 steps Etching Priming + Bonding Moist bonding Removes smear layer Total etch 55

56. Advantages Good Bond strength:20-25 Mpa. Time saving and simple to use Some agents have incorporated fluoride and elastomeric components - improve marginal integrity Disadvantages Two steps: Technique sensitive Lack many of the components to perform multisubstrate bonding Post operative sensitivity Eg. Prime and Bond (Dentsply) Optibond Solo(Kerr) Single Bond 3M 56

57. 6 TH GENERATION- EARLY 2000s E tchant and Primer are combined in one step. ( Self etching primers) Contains P hosphate derivatives of hydrophilic monomer such as P henyl-P (Acidic Monomer) 50% HEMA or other hydrophilic monomer -prime the dentin Type s TYPE 1 Light / Dual cure Applied in separate layers Liquid 1- acidic primer and Liquid 2- adhesive. Solvent used is water. Eg.Clearfil SE Bond 2(Kuraray) TYPE II Light cure type The self etch primer and adhesive are mixed outside and applied. Eg AdheSE One ( Ivoclar ) 57

58. Advantages No need to acid etch with phosphoric acid. No post conditioning rinsing required Reduced post operative sensitivity Simultaneous demineralization and resin infiltration. Less sensitive to degree of wetness and dryness. Low technique sensitivity Disadvantages Less effective bonding to enamel, Sclerotic and caries affected dentin Initial bond might deteriorate with aging May inhibit set of self cure or dual cure resin materials 58

59. 7 TH GENERATION ALL IN ONE SYSTEMS 2003 C ombine conditioning, priming & application of adhesive resin but unlike 6 th gen don’t require mixing Use smear layer as a bonding substrate. Bond strength to Enamel 19-32 Mpa Dentine 18-28 Mpa Eg. iBond ™ (Heraeus) Xeno® IV (Dentsply) G-Bond™ (GC) 59

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61. 8 TH GENERATION NANO FILLER CONTAINING Futurabond DC ( Voco America ) Increases penetration of resin monomers & Hybrid layer thickness Better enamel and dentine bond strengths Stress absorption Longer shelf life Decrease dimensional changes Draw backs Increased viscosity Accumulation of Fillers on top surface- Act as flaws and induce cracks Decrease bond strength E Sofan Etal 2017 61

62. WATER TREES All-in-one adhesives--very acidic and very hydrophilic. They attract and absorb water — L eaching of unpolymerized monomers or hydrolytic degradation products through water-filled channels Water trees These channels pass from the hybrid layers, through the adhesives, to the adhesive-composite interface. Lower bond strength Reduces Bond durability . 62

63. REVERSE WATER TREES Originate from water trapped at the interface between the adhesive and the overlying resin composite. During light curing ,t he heat generated by light curing reflect trapped water back into less polymerized subsurface They spread downward with their branches pointing toward the dentin. 63

64. TODAYS ADHESIVES Etch and rinse adhesives (E & R) Self Etch (SE) Mild/Ultra mild 64

65. ETCH AND RINSE ADHESIVES (E & R) Positives… Micromechanical bonding Complete smear layer removal Best approach for enamel, the bond is long lasting Long track record (>20 years) Proven long-term clinical bonding effectiveness (>10 years) Annual failure rate 3.1- 5.8 % Possibility to apply a thick film of hydrophobic adhesive resin --Stress absorbing potential. 65

66. Negatives…. Phosporic acid -Aggressive deep demineralization of dentin ( 4-5µm). Dentinal HAp -The natural protection of collagen is removed--Collagen is deeply exposed, Thick hybrid layers should be produced-Deep resin infiltration needed E&R hybrid layers are vulnerable to leakage and enzymatic degradation. Chemical interaction is weak and only secondary (Van der Waals forces Hydrogen bonding…) 66

67. E&R BONDING PROTOCOL-TOTAL ETCH Enamel Total removal of Smear layer -Deep pits in Enamel + dentin Rinse and Air dry White frosted appearance-Macro and Micro resin tags Enamel to appear white frosted Dentine Phosphoric acid- Never more than 15 sec WET Bonding –Mandatory for acetone based primers-technique sensitive Gentle air drying for Water/Alcohol based allowed Application of Water/Ethanol based primer will rewet partially collapsed Collagen fibers Dentine dull 67

68. Application of Primer or Primer + Bonding Resin To be applied for at least 15 sec Active Rubbing dentin surface with a microbrush using light finger pressure Intensify functional monomers interaction with dentin Massage resin into Collagen network Apply fresh primer out of dispensing well Gently air dry to evaporate primer solvent Glossy film should not move on airdrying Priming to be repeated /prolonged if dull spots are seen on primed dentine surface Primer containing photo initiator better Polymerization of primer in the Collagen meshwork 68

69. Adhesive resin application Adhesive resin should be in visible thick layers Always to be light cured To stabilize the adhesive interface Prevent water uptake from underlying dentin Flowable composite application on top of adhesive Thin film thickness Stabilize interface and stress absorption 69

70. SE ADHESIVES Depending on etching aggressiveness Strong pH< 1 Intermediate pH ≈ 1.5 Mild pH ≈ 2 Ultramild pH >2.5 70

71. SELF ETCHING OF ENAMEL Strong SE- Etching pattern similar to Phosphoric acid(PA) Micromechanical retention with resin Difference with Phosphoric Acid Dissolved calcium phosphate is not rinsed off These embedded Calcium phosphates –very unstable-weakening interfacial integrity Mild and ultra mild Demineralisation capacity is limited Bonding to enamel poor - particularly to unprepared enamel 71

72. WHY STRONG SE SYSTEMS ARE NOT FAVORED NOW? Eg . Adper Prompt –L –Pop -- strong SE adhesive(3M ESPE) Functional monomer - diHEMA Phosphate Ca-Salt of Phosphoric acid is formed Ca- Salt of Phosphoric acid is not very stable-dissociates into Phosphoric acid Too strong- Destabilizing dentin bonding 72

73. MILD & ULTRA MILD SEs Dentine surface is only partially demineralized – micro retention is produced within first superficial micro meter - micromechanical bonding Collagen remains surrounded and protected by Hap Abundantly available Ca bond with reactive functional monomer - Chemical bonding Mild preferred over ultra mild-Smear may interfere with bonding 73

74. BOND STRENGTH OF SEs TO ENAMEL To bur cut enamel Bond strength of SE adhesives significantly lower compared to E & R. To uncut enamel Outer surface of enamel-indistinct and abnormal prism structures or no prism - stronger resistance to acid Mild / ultramild SE - Poor bond strength - PA pre etching needed 74

75. Concern regarding pre etching with PA acid- PA can “over etch” the parallel prismatic enamel surface-weaker bonding Etching of parallel prismatic enamel surface-separate the apatite crystals and subsurface enamel prisms from deeper part of Enamel 75

76. MILD SELF - ETCH Positives…. Shallow hybridization (<1 µm) - easy for resin to diffuse Partial Demineralization – Sufficient micromechanical interlocking Limited collagen exposure – less vulnerable for enzymatic bio degradation Primary (ionic) chemical interaction- depends on functional monomer Long track record especially for 2 step self adhesives - >20 Yrs Proven long term clinical bonding effectiveness - > 10 Yrs Lowest annual failure rate – 2.5 to 3.8 % Possibility to apply thick film of hydrophobic adhesive resin - providing stress absorbing potential. 76

77. Negatives…. Enamel – Poor bond strength Potential smear layer interference (ultra mild/mild ) Functional monomers sensitive for hydrolytic degradation 77

78. ACID BASE RESISTANT ZONE - ABRZ “SUPER DENTIN” Tsuchiya et al ABRZ beneath hybrid layer of SEs-dentin interface after an acid challenge Important role in preventing recurrent caries by sealing restoration margins-promote restoration durability Dependent on adhesive material used Found with functional monomer 10 MDP but not with Phenyl P 78

79. PREFERRED BONDING TECHNIQUE SELECTIVE ETCHING - PROTOCOL Selectively etch enamel -30-50% Phosphoric acid- 15 Sec Thorough rinsing with water and air dry Actively rub 10 MDP based mild SE for at least 15 Sec Longer the better Continuously supply fresh primer onto the dentin Gentle air dry for solvent evaporation Apply adhesive resin in a visibly thick layer Stress absorption Light cure 79

80. 10-MDP Most effective functional monomer available now 1. Methacrylate functional groups at one end copolymerises with the adhesive 2. Hydrophilic phosphoric acid ester functional group at the other end ionically bonds to Ca of Hap 3. Longer Carbon spacer group prevents steric hindrance between methacrylate and phosphoric acid ester group provides hydrophobicity to reduce water sorption Enable parallel alignment of adjacent 10-MDP molecules during nanolayering 80

81. 4. Has substantial etching effects produces micromechanical interlocking releases Ca substantially from dentin-10-MDP nanolayering 10 MDP ionically react with Ca Producing CaRPO4 structure resistant to water and acids Nano layering results in stable 3D structures –contribute to bond durability 81

82. SHORTCOMINGS OF 10 MDP Sensitive to hydrolytic breakdown (SEs contain water) Degrade to hydrodecyl dihydrogen phosphate and methacrylate Attempts to overcome hydrolytic breakdown Analoges of 10-MDP Hydrloytically stable Phosphonate and acrylamide based monomers-Not effective as 10MDP Fluoro carbon functional monomers MF8P and MF10 P (Kuraray Noritake)-promising but very expensive 82

83. STRATEGIES TO PRESERVE BOND STABILITY 1. Non-Thermal Atmospheric Plasma Treatment (NTAP) Highly reactive particles-cross link rapidly to form various functional groups on the surface of the substrates NTAP of Dentine- Increased surface wettability, improved resin polymerization, deeper resin penetration Activates the dentin surface by depositing free radicals or peroxides, thereby intensifying the interaction between adhesive monomers and dentin collagen. Present status-No consistent results-not considered sufficiently effective 83

84. 2.Ethanol wet bonding-for E &R Strategy Gradual exchange of dentine surface water for ethanol Serving as better medium for infiltration of hydrophobic resin into the collagen-fibril network deeply exposed by Phosphoric acid. THEORETICALLY MOST EFFECTIVE STRATEGY Clinically impractical as successive ethanol applications requires at least several minutes 84

85. 3. Inhibition of enzymatic degradation MMPs along with cysteine cathepsin Linked to degradation of adhesive-dentine interfaces Present status MMPs are released by phosphoric acid etching in E & R mode Not always confirmed in SE adhesives Hydrolytic breakdown due to water sorption –Causes more relevant bond degradation. Doubtful role of MMPs in bond failure 85

86. Most common MMP inhibitor - Chlorhexidine gluconate i . incorporated into etchant ii. incorporated in adhesive iii. applied as a solution directly on dentin after etching Retards bond degradation Not detected beyond 1 year Present status-Does not harm bonding but beneficial effect not supported by evidence 86

87. 4.Dentin biomodification by collagen cross –linking Basic principle Inhibit MMPs Enhance intra and inter molecular cross linking of collagen- Collagen more resistant to biodegradation Natural – Proanthocyanidin ( appln time 10 min-40h), Riboflavin Synthetic – Gluteraldhehyde - reduce cell viability-not advised now Benefits not that substantiated but some evidence regarding improvement with 60 sec application also seen. 87

88. 5. Biomimetic repair of E &R hybrid layers by Remineralization Tay & Pashley 2008 Aim –To prevent degradation of denuded collagen within incompletely resin –infiltrated adhesive dentine interfaces produced by E& R adhesives Possible in lab-Intra and inter fibrillar remineralization after several months Applicability in clinical setting –doubtful, time consuming Defies logic –Why to demineralize first n then try remineralization when you have SE (Partial demineralization+ Most collagen surrounded/protected by mineral.) 88

89. 6.Effective Polymerization of adhesives General guideline Always light cure adhesive immediately, separately Blocks water uptake from underlying wet dentine through osmosis For direct restorations Apply adhesive in visibly thick layer For indirect restorations Thoroughly air thin until adhesive no longer moves and does not pool prior to light curing Use of warm air stream (60 degree) for solvent evaporation Increase the immediate and the six-month resin-dentin BS 89

90. Extend light curing time Higher energy density (produced by the longer exposure times) enhances the formation of free radicals, which initiates polymerization. Heat produced by light curing units mainly during prolonged exposure time, is likely to increase solvent evaporation rates . This may provide room for the formation of a high-molecular weight and cross-linked polymer Delayed light-curing protocol Can ensure better resin penetration and faster solvent evaporation . 90

91. 7.Extra Hydrophobic Resin Sealing Most clinically possible technique Placement of an extra adhesive layer results in 1.Higher hydrophobicity 2.Better polymerization efficiency 3.thicker film thickness Prevents water sorption from wet underlying dentine Alternate technique Apply flowable composite on top of low film thickness adhesive ELASTIC BONDING CONCEPT 91

92. Elastic bonding concept Thick resin layer -- Viscous Adhesive Stretching of this layer provides sufficient elasticity to relieve stress of resin composite . T hickness of 125um Reduce shrinkage stresses Distribute stresses from Occlusion n thermal changes 92

93. 8. Ionic Bonding of 10 MDP with HAP & 10 MDP – Ca salt nano layering For -Mild self etch n Universal adhesives Based on Adhesion-decalcification (AD) concept Bart Van Meerbeek et al 2020 93

94. ADHESION-DECALCIFICATION CONCEPT 10-MDP-acidic functional monomer Limited surface decalcification and etching effects on HAp -Micro retention Ionically interact through their phosphate group to Ca of HAp Calcium released causes 10-MDP to self assemble into 4 nm nanolayers stable 10-MDp salt formation Thus mild SEs & UAs bond to teeth chemically 94

95. Adhesion-Decalcification Concept Causes durable nano layering of 10-MDP Ca Salts in Hybrid and adhesive layer Improve clinical longevity of adhesive restorations 95

96. UNIVERSAL ADHESIVES/ MULTIMODE ADHESIVES - 2011 Can be used in E&R / SE /Selective etching modes Bonds to Enamel/Dentine/Glass rich Ceramics (through Silane) or Glass poor Zirconia (Via 10-MDP) and metal alloys Multitude of clinical situations-Direct, indirect restorations, resin coating, core built ups, Zirconia primer, tooth desensitizer Modifications of 1- Step SE adhesives Long term bonding - still unproven 96

97. SHORTCOMINGS 1. Low film thickness, less than 10 microns Oxygen inhibition-suboptimal polymerization Insufficient stabilization of adhesive layer-water sorption Reduce adhesive layers stress absorption capacity 2.Many UAs contain HEMA Highly Hydrophilic-Promotes water uptake from underlying dentine Adhesive interface undergoes hydrolysis 3.Compromised bonding bec of incorporated silane Silane unstable in acidic environment-Hence UAs should have pH more than 2. This decreases etching potential of UAs 97

98. 4.10-MDP spacer connecting methacrylate and phosphate groups at both monomer ends sensitive to hydrolytic degeneration 5.MDP concentration and quality affects bonding effectiveness Different brands of UAs- Different performance 98

99. FUTURE…. Bioactive adhesive materials Anti bacterial, anti enzymatic and remineralization effects- Bioactivity with mechanical stability is the challenge Antibacterial monomer 12-methacryloxyloxydodecyl pyridinium bromide (MDPB) Added to Clearfil SE Protect(Kuraray) Not clinically proven Chlorhexidine and Nano silver containing adhesives- Uncontrolled shot-lived burst release. 99

100. Cetylpyridinium Chloride(CPC) Added to bonding resin Antibacterial effect confined to area directly in contact CPC incorporated in poly 2 hydroxy ethyl methacrylate/trimethylolpropane trimethacrylate hydrogels Short release but can be recharged High water sorption CPC loaded into inorganic compounds for controlled release of CPC CPC incorporated in montmorillonite(Mont) Clay-CPC_ Mont Rechargeable Antibacterial No reduction in bonding 100

101. Self adhesive restoratives Eg. Vertise Flow (Kerr) - No etching No bonding Retention rate very low After 24 months-only 62.9% Self adhesive (bulk fill)restorative Surefil One (Dentsply Sirona) Withdrawn Activa Bioactive Restorative ( Pulpdent ) Chemically bonds to teeth Unacceptable very high failure rate Now Company advices etching and bonding 101

102. ALTERNATIVES TO PHOSPHORIC ACID(PA) Double layer application of Universal adhesives To increase enamel bonding Active application of UA in SE mode To increase enamel bonding Active application in E & R mode X Significantly lower enamel bond strength- (Imai A etal-2017) Alternative etchants with milder acidity than PA To prevent degradation of Dentin Phosphoric acid ester monomer - PPM Poly alkenoic acid Proprietary etchants-ME ( Yamakin )-EC- Shofu , ZON ( Ivoclar ) 102

103. CONCLUSIONS Adhesive Dentistry is fast evolving…. 103

104. References Van Meerbeek B, Yoshihara K, Van Landuyt K, Yoshida Y, Peumans M. From Buonocore's Pioneering Acid-Etch Technique to Self-Adhering Restoratives. A Status Perspective of Rapidly Advancing Dental Adhesive Technology. J Adhes Dent. 2020;22(1):7-34. doi : 10.3290/j.jad.a43994. PMID: 32030373. Jorge Perdigão ; Current perspectives on dental adhesion: (1) Dentin adhesion – not there yet; Japanese Dental Science Review 56 (2020) 190–207 Jorge Perdigao etal ;Adhesive dentistry: Current concepts and clinical considerations : J Esthet Restor Dent. 2020;1–18. Eliseu A. Münchow and Marco C. Bottino ; Recent Advances in Adhesive Bonding - The Role of Biomolecules, Nanocompounds , and Bonding Strategies in Enhancing Resin Bonding to Dental Substrates; Curr Oral Health Rep. 2017 September ; 4(3): 215–227. doi:10.1007/s40496-017-0146-y Takaaki Sato et al ;Update on Enamel Bonding Strategies; Front. Dent. Med. 2:666379. doi: 10.3389/fdmed.2021.666379 Duarte et al ; Adhesive Resin Cements for Bonding Esthetic Restorations: A Review; , Biomaterials update QDT 2011 104

105. Thank You 105