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Adhesion in restorative dentistry


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Restorative Dentistry
Fifth Year

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Adhesion in restorative dentistry

  1. 1. 29/03/33 BONDING IN OPERATIVE DENTISTRY ENAMEL AND DENTIN ADHESION 5th year UOD 2012 Reference: -Fundamentals of Operative Dentistry (Schwartz, 2nd. Ed.)Chapter 8 -Art and Science 5th Ed chapter5 1
  2. 2. 29/03/33 Topic outline: Indications and advantages of adhesive dentistry Adhesion mechanism Factors affecting adhesion Adhesion to enamel VS adhesion to dentin Wet Vs dry adhesion technique Challenges facing an ideal adhesive bond microleakage hypersensitivity Requirements for an ideal bonding agent Topic outline Classification of bonding system Clinical significance of bonding Adhesion strategies and technique Amalgam bonding and glass ionomer 2
  3. 3. 29/03/33 Definitions 1. Adhesion (or bonding) is defined in dentistry as The forces or energies between atoms or molecules at an interface that hold two surfaces together. 2. Adhesive strength = load bearing capacity 3. Durability = the time period of effect bond in clinical use 4. Adaptation: maximum degree of proximity between two adjacent surface 5. Adhesive(adherent): the material or film added to produce adhesion 6. Adherend: the substrate to which the material adhered e.g enamel ,dentin 7. Abhesive: a barrier against establishing adhesive joint 3
  4. 4. 29/03/33 Adhesive failure: The bond that fails at the interface between the two substrate Cohesive failure: The bond fails within one of the substrates, but not at the interface. Adhesive joint; resin material ,tooth substrate and hybrid layer in between Hybridization : is the phenomenon of replacement of the hydroxyapatite and the water in the surface dentin by resin. This resin, in combination with the collagen fibers, forms a hybrid layer. In other words, hybridization is the process of resin interlocking in the demineralized dentin surface . This concept was given by Nakabayashi in 1982 4
  5. 5. 29/03/33 The thickness of a hybrid layer is not a critical requirement for success. Dentin bond strength is probably proportional to the interlocking between resin and collagen, as well as to the “quality” of the hybrid layer, not to its thickness 5
  6. 6. 29/03/33 HISTORY 1955 – Dr. M. G. Buonocore noted that metal was treated with acid before painting to provide a better bond between the metal surface and the paint. He then applied this procedure for the bonding of composite resin to teeth. ADVANTAGES OF ADHESIVE DENTISTRY 1. Less tooth structure removed 2. Reduces microleakage at margins 3. Better distribution of stresses 4. Possible reinforcement of tooth structure 5. Easy to repair fillings with minimal tooth prep. 6. Tooth colored restorative material may be added to teeth without preparations (veneers, Maryland bridge) 6
  7. 7. 29/03/33 Debonded composite restoration Tooth strength after restoration – amalgam vs C.R. Strength of uncut tooth = 100% MOD amalgam prep = 50% MOD prep. + varnish + amalgam = 50% MOD prep. + composite resin = 88% 7
  8. 8. 29/03/33 Indications Expanding Indications for Adhesive Dentistry 1. Restoration of carious teeth 2. Abraded and eroded surfaces 3. Veneers (esthetics) 4. Re-contouring (diastema) 5. Preventive sealants 6. Bonding orthodontic brackets 7. To treat dentinal hypersensitivity Mechanism of adhesion Four theories of adhesion (MADE): 1. Mechanical 2. Chemical -Adsorption - Diffusion 3. Electrostatic 8
  9. 9. 29/03/33 Requirement of ideal adhesion: Chemical affinity between the adhesive and the substrate Complete wettability of the substrate by the adhesive -absolute substrate surface smoothness -absolute substrate surface cleanliness -complete substrate surface homogenecity -strongly hydrophilic adhesive of minimal surface tension Requirements for good adhesion/bonding materials must be in contact wetting of the tooth surface must occur with low surface tension and low viscosity of the adhesive material Enamel = high surface-free energy + Dentin = low surface-free energy – Tooth surface must be clean to provide high surfacefree energy 9
  10. 10. 29/03/33 Wetting Wetting is an expression of the attractive forces between molecules of adhesive and adherent. In other words, it is the process of obtaining molecular attraction . Wetting ability of an adhesive depends upon two factors: • Cleanliness of the adherend: Cleaner is the surface, greater is the adhesion. • Surface energy of the adherend: More the surface energy, greater is adhesion. Factors Affecting Adhesion to Tooth Structure I. Tooth-related factors II. Material-related factors III. Prepared cavity-related factors IV. Technique of restoration V. Oral environmental factors 10
  11. 11. 29/03/33 I. Tooth-related factors 1. physiological effects: - surface energy - capillary attraction - osmotic pressure 2. Compositional differences of tooth tissues 3. Presence of smear layer 4. contaminants II. Material- related factors 1.Biodegradation in oral cavity 2. Thermal coefficient of expansion 3. Dimensional stability 4. Modulus of elasticity and transfer of stress at the interface 11
  12. 12. 29/03/33 III. Prepared cavity-related factors: 1.Adhesive cavity designs should be prepared 2.The resistance and retention required should be estimated and built in the preparation 3.All carious lesion must be removed 4.Adequate finishing, debridement and toilet of the cavity required IV. Technique of restoration 1. avoid moisture contamination 2. use of liner and bases( must be restricted Rd less than0.5mm) 3. constituents of temporary restorations 4.C-factor(bonded to free unbonded surface) operative and post restorative care 12
  13. 13. 29/03/33 V. Oral environmental factors 1. Occlusal loads 2. Chemical degradation potentials 3. Oral microorganisms 4. Humidity 5. Chewing habits All these factors are all highly contributed that affect the durability of the restoration 13
  14. 14. 29/03/33 Bonding to tooth structure Compositional and Structural Aspects of Enamel and Dentin “Because the composition of enamel and dentin are different, adhesion to the two tooth tissues is also different” Problems (obstacles)with bonding to dentin 1. High organic and water content 2. Smear unit 3. heterogeneous of dentin structure 4. Vitality of the pulp (pulpal and dentinal fluid) 5. Difference in D.permeability 14
  15. 15. 29/03/33 6. Intrapulpal pressure 7. Decreased percentage of hydroxyapatite 8. Divergence of dentinal tubules from the pulp Dentin contains dentinal tubules which contain vital processes of the pulp, odontoblasts. This makes the dentin a sensitive structure. • Dentin is a dynamic tissue which shows changes due to aging, caries or operative procedures. • Fluid present in dentinal tubules constantly flows outwards which reduces the adhesion of the resin composite to dentin . 15
  16. 16. 29/03/33 Smear unit: Basically, when tooth surface is altered using hand or rotary instruments, cutting debris are smeared on enamel and dentin surface, this unit is called smear unit (smear layer& smear plug) 16
  17. 17. 29/03/33 Components of Smear Layer Smear layer consists of both organic and inorganic Components. The inorganic material in the smear layer is made up of tooth structure and some nonspecific inorganic contaminants. The organic components may consist of heated coagulated proteins (deteriorated collagen by cutting temperature), necrotic or odontoblastic processes, saliva, blood cells and microorganisms. Densely or loosely packed to various depths into dentinal tubules. Factors affecting dentin permeability D.T diameter D.T length D.T No. Amount of D.fluid Intra pulpal pressure 17
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  20. 20. 29/03/33 Principles of dentin hybridization It involves: 1. Selective demineralization(conditioner) 2. Alteration of surface wettability(priming) 3. Resin impregnation(DBA) Selective demineralization can be done by 1. chemical conditioner )Acid) 2. physical conditioner (laser) 3. mechanical conditioner (micro abrasion) 20
  21. 21. 29/03/33 1. Chemical conditioners Acids used to prepare tooth surfaces Citric acid Nitric Oxalic Acetic acid Maleic acid (10%) Polyacrylic acid (10%) Phosphoric acid (10 - 37%) Acidic monomer(phenyl P) Conditioning It is the process of cleaning the surface and activating the calcium ions, to make them more reactive. Etching It is the process of increasing the surface reactivity by demineralizing the superficial calcium layer and thus creating the enamel tags (5-50 micron) . These tags are responsible for micromechanical bonding between tooth and restorative resin. 21
  22. 22. 29/03/33 Objectives of surface etching -The acid-etching of a tooth surface allows for the micro-mechanical adhesion of resin to the tooth -Etching with acid removes a portion of the superficial mineral component of enamel and Dentin(10 micron) -Micro porosities (5-50 micron depth)left behind produce a roughened surface, or open dentinal tubules, into which resin will penetrate and mechanically grip the tooth providing retention for an overlying restoration Pattern of etching Type I etching pattern: preferential removal of enamel prism core Type II etching pattern: preferential removal of prism peripheries Type III etching pattern: not related to prism morphology 22
  23. 23. 29/03/33 Effective etching of dentin does not require long times to produce acceptable dentin bond strengths. Usually, 15 seconds is employed. If etching time is too long and the etched zone is too deep, the decalcified dentin may not be fully impregnated. The etched but not impregnated space may reside as a mechanically weak zone and promote nanoleakage. Factors affecting successful acid etching Acid concentration Time of etching Cleaning of the surface Contamination 23
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  26. 26. 29/03/33 II.Priming: Primers are bonding-promoters e.g HEMA&TEGDMA They are essentially composed of active bi-functional hydrophilic/hydrophobic group of monomer molecules [ in water, organic solvents such as ethanol or acetone or a combination them]. Bifunctional gp The hydrophilic part increases substrate surface wettability and permeability enhance resin diffusion into de-mineralized dentin. The hydrophobic part penetrates inside the created pores where it polymerizes forming retentive tags inside, and co-polymerizes with the applied bonding agent 26
  27. 27. 29/03/33 They are used to facilitate complete resin infiltration of de-mineralized dentin with establishment of strong and gap-free resin-collagen hybrid The primer may be transported and agitated onto the substrate surface using a smooth brush. It is evenly spread, thinned out, and gently air-dried Primers contain solvents to displace the water and carry the monomers into the microporosities in the collagen network. During application of the primer, most of the solvent evaporates quickly. Thus several layers usually must be applied to ensure a complete impregnation. The rule of thumb is that one should apply as many layers as necessary to produce a persisting glistening appearance on dentin. 27
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  29. 29. 29/03/33 After acid is rinsed, drying of dentin must be done cautiously. Even a short air blast from an air-water spray can inadvertently dehydrate the outer surface and cause the remaining collagen scaffold to collapse onto itself. Once this happens, the collagen mesh readily excludes the penetration of primer and bonding will fail. However, excess moisture tends to dilute the primer and interfere with resin interpenetration. The ideal dentin moisture level varies according to the solvent present in the adhesive. 29
  30. 30. 29/03/33 Self-etch systems have the great advantages of eliminating the risk of incomplete primer/adhesive penetration into the collagen scaffold and also eliminating the subjectivity when determining the amount of moisture on the dentin surface ideal for primer diffusion. With these systems, the smear layer is dissolved and incorporated into the hybrid layer. 30
  31. 31. 29/03/33 Ethanol or acetone based bonding system Acetone or ethanol diffuses into the moist D while water diffuses into acetone or ethanol (water chasing effect). They occupy the spaces previously filled with water, and then evaporate rapidly leaving sufficient room to the coming infiltrated resin Acetone and ethanol generate less surface tension forces in collagen fibrils with ultimate increase in bond strength 31
  32. 32. 29/03/33 Moist vs Dry Dentin Collagen is one of the important factors in determining the dentin bonding. By etching of dentin, removal of smear layer and minerals from dentin structure occurs, exposing the collagen fibers . Areas from where minerals are removed are filled with water. This water acts as a plasticizer for collagen, keeping it in an expanded soft state. Thus, spaces for resin infiltration are also preserved. But these collagen fibers collapse when dry and if the organic matrix is denatured. This obstructs the resin from reaching the dentin surface and forming a hybrid layer. Reasons for better bonding in moist dentin 1. The acetone trails water and improves penetration of the monomers into the dentin for better micromechanical bonding. 2. Water keeps collagen fibrils from collapsing, thus helping in better penetration and bonding between resin and dentin. 32
  33. 33. 29/03/33 Disadvantage of self etch technique: 33
  34. 34. 29/03/33 Strong self-etch adhesives produce a similar pattern on enamel as that obtained with phosphoric acid. Mild self-etch systems present lower bond strength to enamel compared to etch-and-rinse systems, probably because of a shallower etching pattern. Enamel bonding system Enamel bonding depends on resin tags becoming interlocked with the surface irregularities created by etching. 34
  35. 35. 29/03/33 Macrotags: form between enamel rod peripheries. Microtags: smaller tags form across the end of each rod. Macrotags and microtags are the basis for micro-mechanical bonding. Microtags are much more numerous and contribute to most of the micromechanical retention. 35
  36. 36. 29/03/33 Requirements for an ideal D.B.A Should be hydrophilic in order to bond to wet D Should contain hydrophobic part to co-polymerize with the applied resin Should have low viscosity for better diffusion Should posses minimum film thickness for better wettability Should be biocompatible Should posses high bond strength to both E.D Should have good shelf life Should minimize micro to nanoleakage 36
  37. 37. 29/03/33 The Development of DBA Enamel etch (1955) Dentine etch (1960) Treatment of smear layer (1980) Wet Bonding technique(1990) First generation Second generation Third generation Fourth generation: Total etch technique Fifth generation: Sixth generation: All in one,2000 Seventh generation 37
  38. 38. 29/03/33 1960s and 1970s First and Second Generation Did not recommend dentin etching. Relied on adhesion to smear layer. Since dentin was not etched , the adhesion actually was due to bonding to the smear layer weak bond strength (2-3 Mpa( 1980s Third Generation Acid etching of dentin. Separate primer. Increased bond strength. Margin staining caused clinical failure over time 38
  39. 39. 29/03/33 Early 1990s Fourth Generation)Total etch technique) Acid etching of dentin. Separate primer. Increased bond strength. Fourth generation (total etch technique; etch &rinse tech ;three step technique) Concept complete removal of the smear layer Etching of both enamel &dentin Primer Bonding agent (three step) Concept of “wet bonding” also introduced in late 1990. Technique sensitive. These system incorporated monomers with high diffusivity and compatibility to wet dentin 39
  40. 40. 29/03/33 Moist dentin improve the performance Not to wet not to dry (the key factor) Strong and stable bond reach up to 27MPa 40
  41. 41. 29/03/33 Mid 1990s Fifth Generation (two steps ) Etch and rinse(total etch) (etch separately and then primer &bonding in one bottle) Combined primer and adhesive in one bottle. Maintained high bond strengths . Unit-dose packaging introduced less technique sensitive Post operative hypersensitivity Late 1990s, Early 2000s Sixth Generation (self etch approach) “Self-etching” primers. Reduced incidience of post-treatment sensitivity. Bond strengths lower than fourth- and fifthgenerations. More simple Post operative hypersensitivity 41
  42. 42. 29/03/33 Late 2002 Seventh Generation “All-in-One”. Combines etching, priming and bonding. Single solution. Good bond strength(18 to 25 Mpa)and margin sealing. They achieve the same objective as the 6th generation except that they simplified the multiple sixth generation materials into a single component, single bottle system, thus avoiding any mistake in mixing. Seventh generation bonding agents also have disinfecting and desensitizing properties. Another classification (clinical application) Three steps (etching,priming,and resin impregnation) Two steps( etching –priming)and resin impregnation/or etching then priming and resin impregnation together One step, all together (etchant, primer and resin) all in one step 42
  43. 43. 29/03/33 Recent classification of bonding systems (Van Meerbeek2003) 1.Etch and Rinse approach Three - step ;conditioner, primer, adhesive Two step; conditioner, (primer adhesive) 2.Self –Etch approach Two-step (conditioner primer),adhesive One step(conditioner&primer&adhesive) 3.Glass-Ionomer Approach Adhesive system based on etch and rinse (three step) technique are more clinically reliable and durable than the self etching adhesives 43
  44. 44. 29/03/33 Recent adhesive systems Bio-active adhesive system include anti-microbial monomer MDPB e.g clearfil HEMA free adhesive system e.g G-bond POSS nano-filled adhesive system e.g nano-bond 44
  45. 45. 29/03/33 Bonded Amalgam Adhesive systems, filled adhesives, and resin cements can be used in association with amalgam in the so-called bonded amalgam restoration. The purpose of this technique is to reduce the need for macromechanical retention, which would save tooth structure, and reinforce the remaining structure by creating a bonded interface between the restorative material and the cavity walls. The bonding between the adhesive and the amalgam is achieved by the establishment of an interpenetration zone. Although laboratorial studies show better results for bonded amalgams compared to conventional, nonbonded amalgam in terms of bond strength, microleakage, and retention, these findings are not supported by clinical data, which show no difference between bonded restorations and those retained by mechanical undercuts. 45
  46. 46. 29/03/33 Bonded Amalgam Restoration 91 Technique: Etch the enamel & dentin walls of the preparation with ~35% phosphoric acid gel for 15-20seconds. Wash & dry the preparation. Apply primer to the conditioned dentin. Then evenly apply dentin bonding agent. Before the bonding agent is dried, condense freshly triturated high copper amalgam into the uncured bonding agent, forcing the two materials to intermingle. They harden together in an interlocking matrix which provides tremendous adhesion of amalgam to dentin Carve, finish & polish the final restoration as usual Bonded Amalgam Restoration 92 Bonding to tooth structure: Bonded amalgam restoration has advantages of: Conservative tooth preparation. Better marginal seal along with improved retention & resistance. Decrease the micro-leakage so the postoperative sensitivity & recurrent caries. Strengthening of restored tooth. Bonded amalgam restoration has disadvantages of: It is time consuming. It is technique sensitive. It is expensive. 46
  47. 47. 29/03/33 Glass Ionomer: Glass ionomers are water-based, self-adhesive restorative materials in which the filler is a reactive glass called fluoroaluminosilicate glass and the matrix is polymer or copolymer of carboxylic acids. The setting reaction of these materials involves an acidbase reaction. There are two main types of glass ionomers: • Conventional glass ionomer • Resin-modified glass ionomer 47
  48. 48. 29/03/33 Adhesion Glass ionomer materials have good clinical adhesion to tooth structure. Unlike the resin-based composite materials, etching of the enamel or dentin surface by phosphoric acid is not needed. Hence these materials are sometimes referred to as being self-adhesive. Preconditioning of the tooth surface is recommended. Adhesion One of the following procedures is used for the pretreatment: • The cavity surface is conditioned using 10% to 20% polyacrylic acid(identified by manufacturers as (primer or self -conditioner) for 10 seconds, washed well and dried. • For some resin-modified glass ionomer restoratives a dilute polycarboxylic acid based solution is applied on the cavity surface and set through light. This ensures good contact of the viscous mix of the glass ionomer with the tooth while not impeding ion exchange reactions. 48
  49. 49. 29/03/33 The mechanism of adhesion to the tooth structure is mostly chemical in nature and proceeds through an exchange of ions arising from both the tooth Laboratory measurements of bond strengths of conventional and resin-modified glass ionomers to tooth structure have generally yielded lower values than with the combination of resin adhesives and composites. The failure is usually cohesive in the glass ionomer;and restoration. Resin-modified glass ionomers have been recognized as one of the best treatments for minimizing postoperative sensitivity in restored teeth. There are two reasons for this. First, because prior etching is not needed during placement, the collagen fibrils are not demineralized and collapse of the denuded layers cannot occur. Second, the dual setting mechanism and gradual build-up of modulus allow the material to absorb a considerable amount of shrinkage stresses, thus minimizing the effect of contraction forces at the tooth-restoration interfaces 49
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