lec 1 Bonding to Dental Substrates or Adhesion.pptx

Substrates

1. Adhesion & Bonding to Dental Substrates Dr. Memuna Kausar Satti Senior Lecturer Dental Materials Rawal Institute of Health Sciences

2. Introduction Every dental restoration requires retention by some system of connection or attachment. Dentures are held in place by combination of tissue irregularities, saliva and adhesives. Crowns are held in place by luting cements that joins with minor irregularities along the crown and dentin surface. Partial dentures are held in place by clasps.

3. Dental amalgam is retained by under cut regions in the cavity preparation There is always a desire for a dental adhesive that could provide a bonded or sealed interface Scientific beginnings of dental adhesion originated in the 1950s with studies of bonding to Enamel or Dentin Now-a-days bonding agents are used routinely in various procedures in restorative and preventive dentistry Introduction

4. Definitions Adhesion When two unlike substances join together on being brought into contact, because of forces of attraction between them. Cohesion When two like substances join together on being brought together into contact, because of forces of attraction between them.

5. Adhesive & Adherend The substance that binds the two materials is defined as the adhesive and the substance to which the adhesive is applied is called an adherend. Adhesive Joint When the adhesive is joined to the adherend an adhesive joint is formed. Interface The point at which the substrate meets the adhesive is described as the interface. Definitions

6. Bonding Bonding is used to refer to adhesion attachment and can be defined as: “When a liquid flows into pores or crevices in the surface of the material, a strong bond can be formed due to mechanical interlocking which occurs when the fluid material sets.” This phenomenon is known as bonding or mechanical adhesion. Definitions

7. Criteria for Adhesion The factors that govern the ability of the adhesive to make intimate contact with the substrate are The wettability of the substrate by the adhesive. The viscosity of the adhesive. The morphology or surface roughness of the adhesive.

8. Wettability: The two materials (adhesive & substrate) must have intimate contact such that no air voids are formed. Good wetting is the ability to cover the substrate completely , so that the maximum benefit is obtained from whichever adhesive mechanism is activated. The interaction between the adhesive and the substrate is governed by Driving force (Surface energy) that tends to spread the adhesive over the substrate. Resistance to spreading that depends on the viscosity of the adhesive. Surface irregularities Presence of contaminants Criteria for Adhesion

9. Other factors affecting wetting Hydrophilic (WET) Hydrophobic (DRY) Criteria for Adhesion Surface energy is the increase in energy per unit area of surface and is measured by the internal angle of a droplet on a surface (dynes/cm). Smaller angles means better spreading. Enamel which primarily is hydroxyapatite has high energy. Contaminants containing any organic material could lower surface energy .

10. Wetting of the adhesive : In current systems primers contain 1) Hydrophilic monomer to improve wetting of the hydrophobic resin. 2) Solvent like acetone or ethanol to replace water and air. Criteria for Adhesion

11. The adhesive should have a suitable viscosity to enable it to flow readily over the surface of the adherend . The setting of the adhesive should occur without excessive dimensional changes – that is little expansion or no contraction. Criteria for Adhesion

12. The thickness of the adhesive layer is important; too great a thickness can lead to poor bond strength. The strength of the set adhesive must be taken into consideration. The adhesive must be converted from a liquid to a solid form, to achieve mechanical strength and reasonably high rigidity. Surfaces should be clean of any debris for good adhesive bonding, otherwise air can be entrapped between the adhesive and the adherent leading to failure of adhesion. Criteria for Adhesion

13. Factors Affecting Adhesion in Dentistry Wettability and intimate contact (tooth and adhesive) Surface energy of tooth surface – it must be higher than the adhesive liquid component) Contamination of tooth surface by saliva and air Polymerisation contraction of a materials on setting Different coefficient of thermal expansion between adhesive material and tooth Interpenetration (formation of hybrid zone) Micromechanical interlocking and Chemical bonding Jones SEB. Story of adhesion….. Int J Adhesion and Adhesive 15:1995:109-113

14. Factors Affecting Adhesion (1) Clean adherend (2) Good wetting (3) Intimate adaptation (4) Bonding (5) Good curing physical bonding chemical bonding mechanical bonding + –

15. Modes of Adhesion Three major modes of adhesion can be identified: Bonding through micromechanical attachment; e.g. bonding of resins to enamel using the Acid Etch Technique Bonding through chemical adhesion to either Enamel or Dentin; e.g. use of coupling agents or cements containing poly acid Bonding through a complex mechanism involving wetting, penetration and the formation of a layer of bound material at the interface between the restorative and the substrate ; e.g. Dentine Adhesives

16. ENAMEL BONDING SYSTEM

17. ENAMEL MICROSTRUCTURE Inorganic phase is made of hydroxyapatite crystals. Which are packed to gather in the form of the prism . hydroxyapatite crystals are in hexagonal shape, so there are unfilled spaces between them  filled by water and organic components Enamel Organic 1 % wt Inorganic 95% wt Water 4 % wt Composition of enamel Prismatic structure of enamel

18. Acid-etch systems for bonding to Enamel Surface of enamel is smooth and has little potential for bonding by micro mechanical attachment. Bonding can also be achieved through chemical adhesion. On treatment with certain acids, the structure of enamel can be modified considerably and can allow micromechanical attachment. Primarily, the bonding is through micro mechanical retention, seen in resin bonding to enamel using acid etch technique

19. Acid Etch Technique

20. Acid etch technique Definition A technique in which resin composites are bonded to the enamel of the tooth providing micro mechanical retention or micro mechanical inter lock . Steps Four (04) steps are involved: Etch (37.5% phosphoric acid for 15 sec.) Wash Dry Apply

21. Acid etch technique Steps Four (04) steps are involved: Etch Wash Dry Apply

22. 1. Etchants A wide range of acids have been investigated as Etchants Maleic Acid Citric Acid Tartaric Acid EDTA Poly acrylic acid The recommended conc. of phosphoric acid is 25 – 50%. Most reliable etchants' are phosphoric acid solutions and gels (37%, 35%, 10%). Acid Etchants are also called as conditioners. Originally etching solutions were free flowing liquids which were difficult to control. Gel etchants were developed by adding ‘micro fillers’, ‘cellulose thickening agents (polymer beads or colloidal silica.

23. Acid etch technique 1. Etch Gel etchants are dispensed from a syringe onto the tooth surface to be etched. Etching time should be between 10-60 seconds with 37% solution of phosphoric acid. The standard time for etching is 15 seconds. 2. Wash Following etching the enamel surface should be washed with copious amount of water to remove debris. Washing time is usually 60 seconds.

24. Etched enamel prisms The individual features evident in the above figure corresponds to the ends of enamel prisms, each being about 5 µm in dm. The surface is now suitable for micro mechanical attachment since it contains a myriad of small undercuts into which resins can gain ingress, set and form a mechanical lock . The acid etched enamel has a high surface energy and an increased surface area because of dissolution of the inorganic part of the tooth due to acid.

25. Acid etch technique 3. Dry Surface of the etched enamel should be thoroughly dried ( Chalky white appearance : change in refractive index of the etched enamel & increase in porosities) using oil free compressed air. Should be maintained in an un contaminated state before application of the resin (if contaminated-remove the contaminant and re-etch for 10 sec.). It is a critical step if the enamel is coated with a hydrophobic resin ( BisGMA ). When a Dentine Bonding Agent is being used to attach resin to dentine, bonding to enamel can also be achieved when the etched enamel is damp.

26. Acid Etching Effects of etching on Enamel : INCREASED PERMEABILITY Removes residual pellicle exposure to the inorganic crystallite component of enamel. Creates a porous layer with the depth of pores ranging from 5 – 10 µm. Increases the wettability and surface area of the enamel substrate. Raises the surface energy of enamel with creation of reactive polar sites.

27. Acid etch technique 4. Apply Resin is either directly applied to the enamel surface or An additional bonding agent is applied first and the composite is applied to the surface of the bonding agent. In case of direct application of composites to the enamel surface without the bonding agent the resin flows from the composites in to the enamel and sets, forming rigid ‘Resin Tags’, each being about 6 µm in dm. and 10-20 µm long which retain the filling.

28. 4. Apply Where as, incase of indirect application in which the bonding agent is used, the bonding agent contains resin similar to the composite but has no filler. It enhances the strength which is usually required for hybrid composites. Acid etch technique

29. Acid Etch Technique Mode Of Action:- It creates microspores by discrete etching of the enamel. It increases the surface area. Etched enamel has a high surface energy, allowing the resin to wet the tooth surface better and penetrate into the microspores, when polymerized it form micro- tages .

30. Bonding: The mechanism of bonding to enamel involves the penetration of resin into the relatively porous surface layer of the etched enamel to create a mechanical interlocking. Bonding occurs readily at the unfilled resin to composite interface. This is aided by the fact that surface layers of resins polymerized by a free radical polymerization remain soft and un polymerized due to the inhibiting effect of oxygen on the polymerization process. On applying a composite material to the surface of a “cured” unfilled resin, mixing of the two resin systems occurs at the interface followed by a degree of copolymerization and entangling which effectively bonds the filled and unfilled resin together. The resulting shear bond strength achieved between etched enamel and restorative resins is 16 – 20 Mpa . Acid etch technique

31. Three (03) distinct patterns to etch enamel are available: Acid-etch systems for bonding to Enamel Type 1 Preferential removal of enamel prism cores, prism peripheries remaining intact (most common). Type 2 Preferential removal of peripheries, cores remain intact Type 3 Areas resembling Type 1 and 2 with some less distinct areas, unrelated to enamel prism morphology.

32. Acid Etch Technique Type 1 Type 2 Type 3

33. Acid etch technique Advantages Provides excellent micro mechanical retention or mechanical inter locking for resin bonding to enamel Disadvantages Time consuming Rough surface caries prone

34. Acid etch technique Applications Composites For most of the composite fillings as a means of aiding retention and reducing microleakage . Class IV cavity Treatment of choice for class IV cavities replacing gold inlays Cavity prepared weakened teeth Strengthening or splinting teeth which have been weakened by cavity preparation Fissure Sealants In case of Fissure Sealants Brackets In bonding orthodontic brackets with RMGICs Bridges In bonding of composites with bridges especially Rochette bridges and Maryland bridges Labial veneers For attachment of acrylic or porcelain labial veneers, in order to improve appearance of stained or discolored teeth

35. DENTINE BONDING SYSTEM

36. Structure of Dentine

37. Indications for Use of dentine Bonding For bonding composite to tooth structures. Bonding composite to porcelain and various metals like amalgam, base metal and noble metal alloys. Desensitization of exposed dentin or root surfaces. Bonding of porcelain veneers.

38. DENTIN MICROSTRUCTURE Scanning electron micrograph of a normal dentin surface Dentin surface illustrating the different components of dentin

39. Bonding to Dentine Bonding can be achieved through chemical adhesion or micro mechanical retention Primarily bonding is by chemical adhesion as micro mechanical retention was found to be in effective and un acceptable because of the following reasons.

40. Bonding to Dentine Reason Current philosophy Concerns over the potentially damaging effects of acids on the vital dentin, which can cause irritation or irreversible damage to the pulp Currently it is accepted that most cases of pulpal irritation are because of ineffective seal and that dentine and pulp are able to withstand a greater chemical insult with acids. Etching dentin can open up dentinal tubules and encourage fluid flow which is a draw back as for an effective bond, dryness is a major concern Current thinking appreciates the damage by desiccation of dentine and tries to overcome the moisture problem by the use of primers and solvents. It is also recognized now that dentinal tubular fluid is negligible in anaesthetized teeth. The dentinal tubal openings occupy only about 5% of the cut dentinal surface in superficial dentine and rises to 20% in deep dentine. Therefore resin tags will be limited by the small proportion of the area being utilized. It is currently accepted that whereas tags in dentinal tubules can contribute to bonding, other mechanisms involving all the exposed dentine surface are at least equally as important. Current philosophy for chemical bonding to dentine

41. Dentin near the DEJ (outer) and near the pulp (inner) are compared to show relative differences in intertubular and peritubular dentin and in lumen spacing and volume

42. DENTIN MICROSTRUCTURE Scanning electron microscopic images of dentin. a At the enamel-dentin junction. b Close to the pulp, same tooth

43. DENTIN MICROSTRUCTURE Scanning electron microscopic images of dentin. Number and diameter of dentin tubules of the same tooth are much higher close to the pulp ( a ) than distant from the pulp ( b )

44. Chemical bonding Emphasis was placed on trying to achieve bonding to dentin through the formation of chemical links between ‘Restoratives’ and ‘Chemical Moieties’ in the dentin surface i.e. 50 % hydroxyapatite and 30 % Polypeptide ( e.g. collagen). Dentine offers the possibility of utilizing reactive groups, such as –NH which are present in dentine proteins, for achieving chemical union with the adhesive.

45. Chemical bonding Use of coupling agents: In order to bridge the gap between the restorative and the tooth surface a series of difunctional coupling agents were developed. The principle of coupling agent is that it consists of difunctional molecule, one part of which enters the tooth and the other is bonded to the resin.

46. Attempts at bonding restorative resins to dentine by direct chemical coupling led to limited clinical success in the absence of any form of dentine pre-treatment or conditioning. Chemical bonding

47. Steps in Dentine Bonding Dentine Conditioning. Priming. Bonding.

48. Schematic Drawing of Dentin Bonding

49. The smear layer It is a loosely bound layer of cutting debris including dentine chips, micro-organisms, salivary protein and collagen from the dentine. It is formed by the process of cavity preparation and extends over the whole prepared surface of the dentine and into the dentinal tubules (smear plug). It is 3–15 μm thick, prevents interaction of the adhesive with the bulk dentine and this prevents the formation of any effective or durable bond. Fractured human dentine showing smear layer (SL) and smear plug (SP) which look solid but have been shown to be permeable to both solutes and solvents. SL SP

50. The smear layer Schematic diagram showing the histology of the dentin surface with a smear layer attached

51. The smear layer Dentine conditioning and adhesion. (a) Freshly cut dentine surface. (b) Conditioned dentine. (c) With bonding agent applied.

52. Smear layer and bonding The smear layer can reduce dentin permeability. This is helpful for hydrophobic bonding materials, since the smear layer permits a drier bonding surface with increased micro porosities. Most newer dentin bonding systems remove or greatly alter the smear layer before bonding. Scanning electron micrograph of a dentin smear layer.

53. Hydrophilic Hydrophobic Hybrid layer Smear layer Bounding agent Composite Dentine Bonding

54. Dentine conditioning –the Smear layer The problems with dentine bonding were Bonding a hydrophobic resin to a hydrophilic substrate. Presence of the dentinal smear layer. It prevents the interaction of the adhesive with the bulk dentin which in turn prevents the formation of any effective or durable bond. Any bond that is formed is only to the smear layer which is not strong and durable.

55. Smear layer An adherent layer of debris and can be found on tooth surface after having been cut with rotary or hand instrument. It is loosely bound layer of cutting debris including dentine chips, micro-organisms, salivary protein and collagen from the dentine. Average thickness 3-15 µm. Smear layer irregular morphology depends on the technology used for cavity preparation (air abrasion, laser ablation, manual). It extends over the whole prepared surface of freshly cut dentine and into the dentinal tubules ( smear plug ). Has advantages and disadvantages. Reduces dentine permeability by 86%. Attached weakly to dentin but cannot be removed by rinsing. Can be removed by conditioners (mild acid).

56. Dentine Bonding There are 3 main steps in preparing a tooth surface prior to the use of a dentin adhesive : Conditioning (remove or modify the smear layer) Priming (change the chemical nature of the dentine surface) Bonding (Many manufacturers now try to combine at least two of the three stages)

57. Dentine bonding - Conditioning the Smear Layer Conditioners are the liquids used for dentin pre treatment prior to bonding. They are acids which dissolves the smear layer or at least solubilize the smear layer so that the underlying dentin is exposed to the bonding agent. So, in order to form an effective bond or seal this layer has to be removed , disturbed or modified in some way to gain access to the underlying bulk dentin.

58. Conditioning the Smear Layer Acid used for dentine conditioning can also be used for acid-etching enamel and now a single agent is available for both purposes. Dentin can tolerate this acidic conditioning and When rinsing is done after conditioning , smear layer is totally removed leaving smooth dentin surface with patent dentinal tubules. When there is no rinsing stage after conditioning , the smear layer becomes redeposited on the dentine surface .

59. Dentine Conditioning Function of conditioning:- Conditioners typically clean the tooth surface by removing the smear layer and provides substantial opening of dentinal tubules. Demineralizing the dentin, this step is similar to etching enamel, since both processes create surface microporosities. Provides modest etching of the inter-tubular dentin.

60. Dentine After Etching Effect Of Conditioning On Dentine Dentine Before Etching

61. Dentine After Etching Effect Of Conditioning On Dentine Dentine Before Etching

62. Effect Of Conditioning On Dentine

63. Dentine Bonding - Priming Priming stage follows the conditioning stage. It is a key stage as it is: Designed to change the chemical nature of the dentin surface and to over come the normal repulsion between the hydrophobic resin and the hydrophilic substrate. They are similar to the coupling agent. They are difunctional materials with a methacrylate group (having affinity for the resin) and another reactive group having affinity for the dentine. This other reactive group may be an amino group, a phosphate group or a 4-META

64. Priming agents are difunctional monomer that has a hydrophopic group - M , that bonds to the composite resin and a hydrophilic group - X , which bonds to the collagen or calcium in the tooth structure. They have a general formula ‘ M-R-X’ Where; M is methacrylate gp ., hydrophobic & is attached to the composite R is the hydrocarbon chain linking molecule X is commonly phosphate molecule, hydrophilic & is attached to the smear layer or dentin. Most commonly used primer is HEMA ( Hydroxy Ethyl Meth Acrylate). It is the hydroxyl group which makes HEMA an effective primary agent Dentine Bonding - Priming

65. R M X Methacrylate Reactive group Linking/ spacing part

66. Wetting of the adhesive : In current systems primers contain 1) Hydrophilic monomer to improve wetting of the hydrophobic resin. 2) Solvent like acetone or ethanol to replace water and air. After priming the nature of the dentin surface has changed. It is more hydrophilic and ready to accept resin based bonding agent Dentine Bonding - Priming

67. Effect of primers Wet the surface (reduce the contact angle) and improve contact between the resin and the hydrophilic tooth structure. Increase the permeability of the smear layer (if present) and allow the resin adhesive to permeate the smear layer. Provide mechanical interlocking of the bonding agent to its surface. Potentially provide some chemical bonding between the resin and the altered dentin.

68. Dentine Bonding The bonding agent used is fluid in nature. It is similar to the composite resin but contains no filler. It flows easily in to the primed dentin surface to complete the formation of an effective bond. Curing is done by light for single component materials. Manufacturers have simplified the needs to apply these conditioners, primers and bonding agents.

69. Dentine Bonding There are two ways of application : Primer is sometimes incorporated within the conditioner and following the combined conditioning /priming the smear layer is incorporated within the primer which now has direct contact with the bulk dentine surface. Alternatively, the primer may be incorporated with the bonding resin and the combined liquid applied to the conditioned and rinsed dentine .

70. Resin tag

71. Different self-etch adhesives with dentin. (Left) Unaffected dentin with SL. (Right) Interaction of three classes of self-etch adhesives with dentin and the smear layer. Because mild self-etch adhesives do not completely remove the smear layer, a relatively thin submicron hybrid layer is formed without resin tags. The intermediary strong self-etch adhesives remove the smear layer along with a shallow demineralization of dentin. Short resin tags (±10 μm ) are formed, and a limited lateral wall hybridization takes place. In the bottom third of the hybrid layer, not all hydroxyapatite crystals have been dissolved. The micromorphologic aspect of strong self-etch adhesives is very similar to that of etch-and-rinse adhesives and is characterized by a 3-to 5-μm-thick hybrid layer, dentinal tubule funneling, extensive resin tags, and tubule wall and lateral tubule wall hybridization

72. Hybrid layer It is now believed that efficient dentine conditioning not only involves removal of the smear layer and smear plug but also causes a significant decalcification of inter-tubular dentine to a depth of a few microns. The decalcification process leaves a three-dimensional collagenous network which can be infiltrated by primer and resin to form a resin infiltrated /reinforced layer or hybrid layer at the interface between the bulk dentine and the resin. illustrating the presence of the resin reinforced or hybrid layer.

73. Adhesion to dentin. Schematic showing that etching removes hydroxyapatite crystals within intertubular dentin and along peritubular dentin. Primer penetrates intertubular spaces and fluid-filled tubular spaces. Cured primer forms microtags within intertubular dentin and macrotags within tubules.

74. Hybrid layer: resin-dentin interpenetration layer This is the zone (10-20µm thick) where the adhesive resin of the dentin bonding agent micromechanically interlocks within the tubular dentin and surrounding collagen fibers Efficient dentine conditioning Removes smear layer & smear plug Removes hyroxy appetite with in the intertubular dentin i.e. causes significant decalcification of inter-tubular dentine to a depth of few microns Three-dimensional collagenous network is left behind Primer & Adhesive Infiltration by Total etch method / Self etch method Resin infiltrated / resin-forced layer or Hybrid layer at Interface between bulk dentine and resin Hybrid layer is formed in the following manner:

75. The ability of primers and resins or both combined to the demineralized dentine surface is the key to the formation of the hybrid layer . Hybrid layer (conditioned dentin, resin, collagen, dentinal smear layer) Components of Hybrid Layer It can be considered to have a composite structure of two continuous phases The resin phase and Fibrous collagenous phase When the resin is polymerized, Hybrid layer strongly binds the resin and dentine together.

76. Hybrid layer

77. Dentine Bonding Two different approaches have been developed Total etch Self etch

78. Conditioning the Smear Layer Acid used for dentine conditioning can also be used for acid-etching enamel and now a single agent is available for both purposes. Dentin can tolerate this acidic conditioning and Total etch When rinsing is done after conditioning , smear layer is totally removed leaving smooth dentin surface with patent dentinal tubules. Self etch When there is no rinsing stage after conditioning , the smear layer becomes redeposited on the dentine surface .

79. Current concepts in dentine bonding – the hybrid layer Total etch method This involves application of a strong acid (commonly 37% phosphoric acid) followed by rinsing with water in order to completely remove the smear layer and demineralize the surface of the bulk dentine. Following demineralization the collagenous network is supported only by moisture and any attempt to rigorously dry the dentine at this stage will lead to the collapse of collagen fibres and impair the formation of a hybrid layer.

80. Current concepts in dentine bonding – the hybrid layer … Total etch method … Due to the presence of hydrophilic group in the primer molecule and the presence of a solvent such as acetone, primer solutions can wet and penetrate moist dentine Acetone is able to ‘chase’ away the water in the porous dentine surface, allowing the spaces to be filled by primer and resin. Acetone solvent is lost by evaporation before curing.

81. Current concepts in dentine bonding – the hybrid layer … Self-etching primer method . In this method self-etching primers are used, which can solubilise the smear layer and at the same time perform the functions of a difunctional primer. The application of the self-etching primer is not followed by rinsing as this would remove the primer and interfere with bond formation. In some materials the manufacturers have combined the bonding resin with acidic primer to form single component systems.

82. Schematic of self-etch and total-etch adhesive systems. The differences between hybrid-layer (HL) thickness anddentinal tubule (T) penetration by adhesive are displayed.

83. Etch-and-rinse-adhesives

84. Self-etch adhesives

85. Total etch method Self etch method Complete removal of smear layer. Solubilize the smear layer. Etching &priming are always separate. Acidic primer solubilize the smear layer and work as a primer simultaneously. 30 – 40% phosphoric acid is used. Stronger the acid, more complete removal. Both weak and strong acids are used. Etching is followed by rinsing. No rinsing. Removal of smear plug with open dentinal tubules exposing water and affecting wetting. No removal of smear plug with no stage of open dentinal tubules and reduces pulpal sensitivity. Danger of drying which may lead to collapse of collagen fibers. No danger of over drying as no open dentinal tubules. Conventional and effective etching of enamel with phosphoric acid can be performed at the same time as conditioning of the dentine. Self etching systems may not be as effective at etching enamel as phosphoric acid. Risk of over etching No risk of over etching. Time consuming as multiple steps and need for rinsing. Time efficient as self etching and no rinsing is required. Most consistent long term results Less research with no long term data Expose high surface energy that improves wetting and spreading of adhesive. Leaves the surface with lower energy but the bonding agent can penetrate and incorporate into the bonding layer.

86. Wet and dry bonding Dentin bonding systems use three measures of dryness: Dry bonding , all moisture is removed from the surface and the dentin is dehydrated. Moist bonding , usually indicates that excess surface water is removed but the surface is fully hydrated. Wet bonding , usually means there is a thin layer of standing water in the preparation

87. Collagen Network and Drying Schematic illustration of open, collapsed, and reopened collagen fibers. Open (hydrated) fibers are necessary for bond strength.

88. By etching dentine, smear layer and minerals from it are removed, exposing the collagen fibrils. Areas from where minerals are removed are filled with water. This water acts as a plasticizer for collagen, keeping it in a expanded soft state. Thus space for resin infiltration is also preserved. However, these collagen fibers will collapse if dry and if the organic matrix is denatured. This obstructs the resin from reaching the dentine surface and the formation of a hybrid layer . The ethanol or acetone solvent displaces the moisture and takes the bonding agent in to the collagen. After it is cured, this layer is called the Hybrid layer. Wet versus Dry Bonding

89. Wet versus Dry Bonding

90. The desired effect of acid etching is increased permeability. For this reason, presence of wet / dry dentine is needed to achieve successful dentine bonding. When primer is applied to moist / dry dentine, water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules. Wet versus Dry Bonding

91. Wet versus Dry Bonding

92. Wet versus Dry Bonding

93. Wet versus Dry Bonding Wet bonding: Acetone and ethanol based primer Displace remaining water Carry monomer into collagen Gently air dried (leaving monomer behind). Cannot check for enamel “frosted” etch. Technique sensitive (not too wet or too dry). Solvents may evaporate which may reduce monomer penetration. Dry bonding: Water based primers (effective on wet / dry dentine causing self-rewetting effect and re-expand collapsed collagen). Permits check of “frosted” enamel

94. Generations of bonding agents

95. Stage Type Description Three-stage etch and rinse 1 Application of etchant and washed off to create demineralized dentine layer. Application of primer. Application of sealer. Two-stage etch and rinse 2 Application of etchant and washed off to create demineralized dentine layer. Application of primer and sealer in single solution. Two-stage self-etching 3 Application of self-etching primer. Sealer applied separately. Single-stage self-etching 4 Self-etching primer and sealer applied as a single solution. Classification of dentine bonding agents and their applications

96. Alloy bonding: Bonding of orthodontic brackets & resin-retained bridges Mechanical retention by building in retention either into the design of the metal structure or by creating a retentive surface through electrolytic etching or abrasion. Resin based luting agent is preferred because of its chemical union with the alloy in the absence of any natural retentive forces. Bonding to base metal alloys It is quite straightforward as the naturally formed oxide layer on the alloy surface is thought to be involved in the bonding process and the only preparation required is a moderate roughening. Bonding to precious alloys It can be more difficult, tin plating is recommended for some products in order to generate an oxide layer. For other alloy / adhesive systems heating of the alloy to 400ᴼC in air for 10 minutes generates a copper oxide layer on the metal; surface, whilst other products claim to bond adequately to a sand blasted alloy surface. Other applications for bonding

97. Other applications for bonding Alloy bonding: The most effective means of preparing metal surfaces for conventional composite resin lutes is to etch the metal surface producing a micro porous surface analogous to etched enamel (the Maryland technique ). Another approach depends on preparing the surface of the material with a specialized form of blasting sand in which silica coated corundum particles are blasted against the surface to be bonded. This silicated surface can then be treated with a silane coupling agent before bonding with a conventional composite resin. This technique can be used for all surfaces from composite resin through ceramics to metals.

98. Other applications for bonding Amalgam Bonding: Helps sealing the margins and prevent tooth staining, increases shear stress and stronger bond in vitro. No clinical results suggest better results than conventional amalgam. Autocure , or lightcure

99. Ceramic Bonding: Both mechanical and chemical bonds exist between adhesive and silica based ceramic. Usually etched with hydrofluoric acid to increase porosity and micromechanical bonding. Dual cure cement is recommended unless less than 2.5mm thickness of penetration. Other applications for bonding