Dentin bonding agents/ rotary endodontic courses by indian dental academy


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Dentin bonding agents/ rotary endodontic courses by indian dental academy

  1. 1. Dentin bonding agents As we more through time, we are continuously faced with the opportunity to change. This is true for our restorative materials, as it is for anything else. In order to know whether or not we should change, we must have an understanding of where we are currently. If the change mill not provide improvement is it wise to pursue? How we determine improvement depends on our paradigm, our view of the objectives of restorative dentistry. Traditionally, dentists have believed that slowing down the restorative cycle as much as possible is the ideal persuit. We have in the time that challenges that paradigm. The earlier performance standard is centered on the concept of longevity. The longer the restoration lasts, the fever the number of times a tooth will require restoration in a lifetime. Therefore, pursuing a material that will withstand the rigors of oral environment has long held our attention. The materials commonly used for restorative purpose are amalgam, gold foil and cast restorations.The main disadvantage of any of these restorations is ‘colour’. Increasing environmental conserns and public awareness for tooth colored materials have heralded patients to demand more esthetic, biocompatible materials such as composites, glass inomer cements and porcelain.
  2. 2. Of all the innovative esthetic materials available today, the direct placement of resin composite has assumed the current thrust in restorative dentistry .One of the principle advantages in the use of these resin composites is the bondalility to the enamel and dentin; which has been possible due to mostly improved bonding systems. Dentin bonding agents have created a new in the field of dentistry, owing to its property of adherence to the tooth structure by both micromechanical and chemical means. This momentous change in dentistry is attributed to great scientists like Michal Buonocore, Rafel Bomen, Nubo Nakabayashi, Fusyama. Recent improvement in adhesive systems have generated a revolution in dentistry, placing adhesive restorations on the front stage.Clinicians have been confornted with this continuous and rapid turnover is adhesive materials. There has been an ongoing process in developing more refined and diversified restorative materials along with the production of steadily improving bonding agents creating confusion as to which and is better. This library dissertation discuses dentin bonding agents, with complete coverage of the bonding systems, hoping that this would help dental professionals in understanding bonding systems better.
  3. 3. HISTORY DBA have developed over several decades. The various historical events, which took place have led to our present day DBA. 1938 -Development of epoxy molecule by Castan 1951 -Development of glyerophosphoric acid dimetharylate molecule by Dr.Oscar Hagger. This molecule permitted seen adhesion to dentin. 1952 -Usage of glyrerophosphoric acid dimethacrylate by Kramer and Mclean (earliest description of hybrid layer) 1955 -Buonocore introduces etching of teeth any phosphoric acid; was he found that an acrylic resin binds well with etched enamel. 1956 -Buonocore pioneers the work on adhesion to dentin. Initial DBA developed was based on the glycerophospheric acid dimethacrylate molecule and bonds to hydrochloric acid etched dentinal surfaces, but bond strength diminishes greatly on immersion in water. 1957 -Bowen starts work on bis-phenol glycidyl methacrylate (BIS-GMA) resin systems. 1962 -Bowen conducts first workshop on adhesive restorative dental materials. 1965 -Causton describes how primers work. 1982 -Bowen, Cobb, Rapson develop the multilayer adhesive system.
  4. 4. 1982 -Nakabayashi reports the presence of hybrid layer. 1987 -Fusayama described the concept of total etching and bonding. 1991 -J.Kanca successfully promoted total etching 1997 -Ferrari et al establish the bonding mechanism of one bottle adhesive system to condition dentin. 2000 -Evaluation of bonding ability of sixth generation bonding systems done by Ferrari et al. 2003 -seventh generation by Ferrari et al. 1991 -J. Kanca successfully promoted total etching. Enamel Enamel is the hardest of the mineralized tissues of the body. It covers the anatomical crown of the tooth. This tissue is very brittle in nature but protects the underlying structure ie. dentin and pulp. The inorganic component of enamel is principally appetite in its, hydroxyl, fluoro carbonate forms. Calcium and phosphate are the two major inorganic elements (Brudefold, steadmar and Smith 1960) minor narration occurs is composition is with aluminum, barium, magnesium, strontium, radium and vanadium among others can be found in the little.
  5. 5. Crystallites are embedded is as organic matrix with comprises less than 1% of the nature of enamel (Estoe, 1963) less than one half of the organic component contains protein high glycolic acid and sig anlt of proliferation and glucose contains protein. During minimization of the crown, a significant shift occurs in the value of organic material. The amenoblasts produce large amounts of organic matrix among early phases of enamel development, then as crown saturation proceeds, the number of organic matrix decreases while the number of inorganic material issues and miniralization gradient (Chable and Darling 1960) exists in mature enamel, thus, the outer portion of enamel is relatively more mineralized than the inner portions. H2O exists in enamel in a significantly larger amt (up to 4% by value). About 25% of H2O is loosely bound to the crystallites. A dynamic gradient anushing fluid exists b/w the pulp and oral environment (Bergman 1963) in with enamel participates through its porous, permeable structures, but enamel is selectively permeable (Darliag and Others 1961) allowing the passage of H2O and cons but including large molecules (Poole, Fachy and Berry, 1963). Histo-chemical studies have shown the complex nature of the surface integument. This fully reacted low energy surface confers significance in the bonding equations, as does the traumatically or operatively imposed tissue. An understanding of the micro-morphological properties have been significant is remaining interactions b/w enamel and bonding agents.
  6. 6. Dentin Dentin forms the largest portion of the tooth structure. It is removed by the enamel on the anatomical crowns and by root on the anatomical root internally it forms the walls of the pulp cavity. The dentin comprise of dentinal tubule that are small canals that extend across the entire width of dentin, from DEJ/DCT to the pulp. Each tubule contains cytoplasmic cell process (James Fiber) of an odontoblast. Each dentinal tubule is lined with a layer of peri-tubular dentin that is much more mineralized than the surrounding inter-tubular dentin. The number of tubules increases from DEJ (15000-20000/mn2 ) to the pulp (45- 65000/mn2 ). The dentinal tubules are filled with dentinal fluid which makes it a difficult surface to bond. The chemical composition of dentin comprises of 75% inorganic 20% organic and 5% H2O and other materials. It is less mineralized than enamel but more mineralized than cementum or bone. The minimal content of dentin increases with age. This mineral phase is composed primarily of hydroxyapetite crystallites. The organic phase is primarily collagen (Type I with traces of type IV of). They consist of carboxyl, amino, hydroxyl surface groups. The other non- collagerous constituents that can be found are dentin phospho-protein, sialoproteins of ostecalcins. Dentin permeability is highly variable.Variation in permeability may arise from tubular irregularities associated with mineral deposits, organic components of the
  7. 7. odontoblasts processes. An outward flow of dentinal fluid occurs because of a small but positive pulpal pressure (10-15 mm Hg). The permeability characteristics of dentin are of crucial importance in dentin bonding because most of the current bonding systems rely on resin penetration or infiltration into dentin(Transdentinal Permeation). Resin penetrates into tubules to form tags that can contribute to resin adhesion. More important factor is permeation of resin intointer-tubulardentin(Intra-dentinalPermeation). Dentinal permeability is reduced with age and also in caries affected dentin as the lumina becomes narrow or may get obliterated by deposition of intra-tubular crystals and deposition of irregular sclerotic/reparative dentin. ADHESION Adhesion is definition by to “American society for testting and materials as “A substrate capable of holding material together”. The word adhesion is derived from the Latin word adherer, which means “ad”-to and” hearer” to stuik. Adhesion refers to the attraction b/w the atoms and molecules at the contacting surface of different materials (De Brayer et al 1951, Wake 1982). In adhesive terminology ,adhesion or bonding is the attachment of one substrate to another. The surface of the substrate that is adhered to is termed as adherent. The adhesive /bonding agent may be defined as the material that when applied to the surface of the substrate can join them together, resist separation and transmit loads across the bond.
  8. 8. An important requirement for any of these interphase phenomenons to take place is that two materials being joined must be sufficiently close and in an intimate contact and besides this sufficient wetting of the adhesive only occurs if its surface tension is less than the surface energy of the adherent. If the adhesive had a high surface tension, then it would roll up into droplet and not wet the surface. Based on this theory of melting and surface free energies, adhesion to enamel is much easier to achieve than adhesion to dentin. This is because enamel is primarily made up of hydroxyapetite without has a high free surface energy whereas dentin has a low free surface energy because it is composed of two distinct materials hydroxyapetite and collagen. In the oral cavity, the tooth surface is normally covered by a pellicle. This salivary pellicle is organic in nature and has a low critical surface tension that impairs adequate wetting of the adhesive. Moreover, instrumentation of the tooth substrate during tooth preparation produces a smear layer which has a low surface free energy. Hence, the natural tooth surface should be thoroughly cleaned and pretreated prior to bonding procedures to increase the free surface energy. Types of Adhesion Van Noort in 1994 suggested that one or more of the following mechanisms can create an adhesive bond: 1. Mechanical Adhesion
  9. 9. Here, retention is by the interlocking of one phase into surface of another. This type of adhesion can be due to a. Geometrical effects These are caused by microscopic porosity or roughness of the surface ie.mechanical locking provided by undercuts, grooves etc. b. Rheological effects This is caused by flow of materials in both liquid and semisolid phase Mechanical adhesion also referred to as micro mechanical adhesion ,results from the presence of surface irregularities that give rise to microscopic undercuts. The liquid adhesive can penetrate these undercuts and once set is locked in them. A prerequisite for this form of adhesion is that the adhesive can readily adapt to the surface of the substrate. The adaptation is determined by the wettability of the adhesive on the substrate, the ideal situation being that of perfect wetting when the adhesive spreads spontaneously over the surface. The degree of penetration of the adhesive may also depend on the pressure used during application of the adhesive that helps to force the adhesive into surface irregularities. The adhesive disengages from the substrate by fracturing because it cannot be withdrawn from the undercut. This is not unlike the concept of retention used for placement of restorations except that it occurs at a microscopic level. However, one important difference is that good wettability is not a perquisite for micro-retention
  10. 10. whereas for micro-mechanical interlocking it is of paramount importance. Examples of micro-mechanical adhesion one: a. Resin to enamel bond b. Resin to ceramic bond for veeners and inlays c. Resin metal bond for resin bonded fixed partial denture II. Physical Adhesion  When two surfaces come in close proximity to one another secondary forces of attraction can be generated through dipole-dipole interactions. The polar reaction occurs as a result of attractive forces between the positive and negative charges on the molecules. The magnitude of the interaction energy is dependant on the mutual alignment of the dipoles.  This type of bonding is a rapid and reversible process because the molecules remain chemically intact on the surface. Therefore, this weak physical adsorption is also easily overcome by thermal energy and is not suitable is a permanent bond is desired. It follows that non-polar liquids will not readily bond to polar solids and vice-verse, because there is no interaction between the two substances at the molecular level even if there is good adaptation. A familiar example of this problem is the inability of hydrophobic silicone rubber impression materials to adapt to the hydrophilic moist surfaces of the soft tissue (This problem is overcome by the use of surfactant). III. Chemical Adhesion
  11. 11. If an adsorbed molecule dissociates on contact with a surface and constituents alone rearrange themselves in such a way that as for covalent, a strong adhesive bond can result. This form of adhesion is called as chemisorption. The features that distinguishe the chemical bond from the physical type of interaction described previously is that a chemical reaction takes place between the molecules and the surface molecules of the substrate. Adhesives must be strongly attracted chemically to the surface of application to form strong bond and require identical reactive groups on both surface. Covalent bonding occurs for an isocyanate adhesive which can bond to soft tissues via surface hydroxyl and amino groups. Another such bond is believed to occur b/w the hydroxyl groups of the glass polyalkonate and the calcium ions in the enamel and dentin. In some instances the formation of a chemical bond will not take place spontaneously. This is the case with the metal to metal bond where high temperatures ellicited by soldering, brazing or welding are needed to encourage the formation of a bond .Another example is the porcelain to metal bond with is formed when the ceramic oxide fuses with the oxides on to the metal surface when the restoration is faces high temperature. IV Adhesion through molecular entanglement
  12. 12. So far it has been assumed that there is a distinct surface b/w the adhesive and the substrate. In effect, the adhesive as adsorbed on the surface and can be considered surface active. If the substrate is permissive to adhesive is able to penetrate through the surface of the substrate and absorb into rather than adsorb oncto the substrate. If the absorbing molecule is a long chain molecule or better still forms polymers within the pretreated layer, the resultant enlargement b/w the adhesive and the substrate is capable of producing very high bond strength. This approach is being adopted for resin bonding system. The coupling agent utilizes the concept of hydrophilic and hydrophobic groups i.e. it consists of a bi-functional molecule one part of outers into a chemical union with the tooth surface whilst the other attaches to resin. The coupling agents have basically the formula. M-R-X M- Methacrylate group, which eventually becomes bound to the resin by copolymers. X- represents a reactive group with interacts with the tooth surface. The reactive groups are end groups. R- is the clearing and spacing group spacing group must be able to provide the necessary flexibility to the coupling agent to enhance the potential for bonding of the reactive group. If the molecule is excessively rigid, the
  13. 13. ability of the reactive group to find a satisfactory conformational arrangement is jeopardized Eg-etyl / oxypropyl. In N- Phenyl, glyine glycidyl mehacrylate a shelate bond is found between the N- phenyl glycine group is the calcium of the tooth, while the methacrylate group becomes incorporated into the resin during polymerization. Another coupling agent with works by chelating with adhesive is 4-META. Bond strength of these coupling agents can be increased by pre px with certain mordant sons such as ferric and aluminum cons in the form of aqueous solutions of their chlorides/oxalate salts. A strongly bond surface layer concentrated in cons capable of reacting with the chelating species is formed. Systems based on the complied used of mordant cons and coupling agents are non-becoming available. The exact mechanisms or role of these mordent cons is not known. But it is possible that the ionic solutions are supplying acting as weak acid without solublize and re-precipitate the dentin smear layer. In some cases the acid may etc the dentin, opening up the dentinal tubules and encouraging mechanical attachment. A procedure with can be classified as multiplayer system has been suggested. This system enacts the Rx of the mechanically prepared cavity with a ferric oxalate solution and an acetone solution of NPG-GMA or NTA-GMA. An acetone solution of PMDM (the reaction product of promellitic diaxhydride and 2- hydroxyl
  14. 14. ethylmethacrylate) is placed and surface is air brown. Finally, the composite restorative materials is inserted and polymerized. The chemistry of such Rx is based on the assumption that the Rx with ferric oxalate solution initiates several reaction with the smear layer, resulting is a process layer cross-linked with metal ions. The layer constitution insoluble icon phosphospate and calcium oxalate attached to a continuous structure. During Rx with NPG-GMA these monomer are bonded to icon (III) ions by coordinative bonds. A continuous film is formed by polymerization of the methacrylate groups NPG-GMA contains benzers wings rin’s in II electrons. During Rx with PMDM monomer, this monomer is bonded to NPG-DMA by II complex or change transfer complex formation. The disadvantage of this system is discolonathprine due to reaction products of ferric oxalate. In “tenure” ferric oxalate has been replaced with aluminum oxalate. Other coupling agents with primarily bond to the inorganic component of dentin contain reactive phosphate groups. The interfaced bond is stabilized through attractions b/w the negative changes of oxygen on the dentin surface. The bond strength to9 dentin produced by this type of adhesive is typically around 5MPA although it is not certain how double this bond is in moist environment.
  15. 15. This R-O-P bond is thought to becomes hydrolyzed leading to a gradual reduction in strength M-R-X, here X= O-P Coupling agents utilizing this concept of hydropholic and hydrophilic groups are the monomers based on phosphates or phosphonates. The hydrophilic PO4 group is thought to interact with the calcium cons of dentin. All the systems are basically adhesive molecules with a potential for calcium bonding. It can be decided into 3 groups 1) Phosphate based adhesive M-R1-POYZ 2) Adhesive based on amino acid M-R2-NZ-R3-COOH 3) Adhesive based on dicarboxylic acid M-R4-COOH COOH All these involve attraction between negative changes on the adhesive and positive changes on the tooth calcium ions. Chemistry of adhesive systems
  16. 16. Dentin bonding systems contain monomers that have hydrophilic and hydrophobic groups these provide a stable back with the dentin and the restoration. The chemistry of adhesive agents can be explained as.  Chemical adhesion.  Adhesion by coupling agents.  Adhesion by grafting reaction. CHEMICAL ADHESION There are two types of chemical adhesion Primary valence Foxes  Covalent bonds  Co-ordinative bonds  Ionic bonds. Secondary valence foxes  Intermolecular adhesion (Vander Waal’s foxes)  Hydrogen bonds. ADHESION BY COUPLING AGENTS Sampling agents utilizing the concept of hydrophobic and hydrophilic groups are the monomers based on phosphate or phosphoxate.
  17. 17. The hydrophilic PO4 group interacts with Ca+ ions in dentin. This type of adhesion us seen to occur with the non-electrolyte adhesion. Bonding can be accomplished to the organic part of the dentin hydroxyapetite, or to the organic part else of coupling agents for bonding leads to only minor improvement in the bond strength. One coupling agent was 3-methacryloyloxy propyl trimethoxysilane. Another coupling agent was a butylanylate acrylic and copolymer with free carboxylic acid groups. NPG- GMA is another coupling agent used. I. Clinical factors affecting Adhesion Salivary or blood contamination Difficulty in controlling saliva or blood while accomplishing restorative dental therapy is a significant challenge. These contaminants act in a negative manner for adhesion. Although dentin is a not substance, the constituents of saliva and blood create an environment that can destroy dentin bonding. It has been prove that if contamination soon after etching the bond will fail while if contamination occurs after enamel and dentin surface are etched and a bonding agent has been used over these surfaces, the bond will not be compressed. Rubber dam and other dry field acids should be used to prevent contamination. Moisture and Oil contamination from Handpiece
  18. 18. Water leakage fro ioroter hand piece or air H2O syringes is an unrecognized problem in most situation. The moisture of H2O with restorative or bonding resin is interferes with adhesion of bonding agent to the tooth stuitane. The oil contamination may be due to oil coming from air compresses without not maintained well, Contamination with oil provides compredictable with oil provides im- predictable clinical results and potential clinical features. Surface Roughness of tooth structure Increased surface area created by surface roughness results in cutting bonds with dentin mechanical retention may be increased by the microscopic roughness produced on dentin or enamel by rotary cutting instrument tungsten carbide thus when used create more irregular surface than diamond layers. Mechanical undents in tooth preparation The mechanical underints placed in the tooth structure hold the restorative material from bodily displacement from the preparation, microscopic movement caused by thermal/ polymerization influences. This type of retention is further argument with the cement generation of DBA. Dentinal canal characteristics Dentinal canals at the external surface of tooth roots or near the DET have small diameters. As dentinal canals are observed loser to the dentinal pulp, they become larger. Older dentin has small dentinal canals, while younger dentin has larger
  19. 19. dentinal canals. Superficial abounded dentin may have included canals. If the canals are small, attachment is less and vice versa. Presence of plaque, calculus, extrinsic stains/debris Any enamel/dentin surface that requires bonding must be scrupulously cleared before the bonding procedure begins. Plaque present on the tooth surface prevents etcher with 37% phosphoric acid. Penetration of plaque by the acids used in DBA is not possible and will result in a clinical adhesive failure. Tooth surface stains and dental calculus if not removed will not permit bonding. Presence of basis on liners on F The presence of varnish eliminates the potential to bond restorative material to the tooth surface. Liners may result in creating moderate bonds with dentin but the bond strength is significantly lower than that created by placing seen on acid etched enamel surfaces. Tooth dehydration Ever drying the tooth preparation before placing bonding agents should be considered to be a negative factor. Drying only till the obvious shine of moisture is a good clinical guide. Dentin Bonding Agents The DBA are di or multifunctional organic molecules that contain reactive group, which interact with dentin and the monomer of the restorative resin.
  20. 20. Co +A D A Components of DBA Conditioner Premier Adhesive Requirements of DBA Ideally, dentin-bonding system should have  Sufficient bond strength, optimum 11-20 Mpa  Be compatible with dental tissues  Provide in immediate permanent high strength bond to dentin  Minimize micro-leakage at the margins of the restoration  Prevent recurrent caries and marginal staining  Easy to use and less technique sensitive  Reasonable shelf life  Compatable with all resins  No reduction in bond strength when applied to moist surface  No potential for sensitization of patient on gerator Problems in Bonding to dentin
  21. 21. The developments of adhesives that adhere to dentin have still been and still remain a challenge to researchers.  Dentin consists of 50% of volume inorganic HAP, 30% organic material and 20% volume of fluid.  Dentinal HAP is randomly arranged in an organic matrix  The high fluid content of dentin places certain requirements on restorative dental material (resin are hydropholic).  The tubular nature of dentin provides a valuable area through which the dentinal fluid might flow to surface and adversely affect adhesion.  Sucrosed dentin if present is difficult to penetrate (results from aging or mild irritation and causes a change in the structure of primary dentin is the peri-tubular dentin becomes wider, gradually filling the tubular with calcified material. The areas are harder, denser, less sensitive)  Presence of inter-tubular and peri-tubular dentin, each tubular is suspended by a collar of gyper-mineralized dentin called peri-tubular dentin. The less mineralized dentin between the tubules is called inter-tubular dentin.  The presence of smear layer complicates dentin bonding. The smear layer is present on cut dentin surface and is of limited strength so it must be either removed or penetrated by the resin.  Permeability of dentin differs at different sites variation is permeability may arise due to tubular irregularities associated with mineral deposits. It also increases resin the pulp and pulp horns than the adjacent areas. CLASSIFICATION OF DBA
  22. 22. 1. Depending on chemical composition 2. According to generation 3. According to treatment of linear layer 4. According to chronology, chemistry and sear bond strength 5. According to mode of curing 6. According to their adhesion strategy towards enamel/dentin or on the basis of number of clinical application 7. According to type of solvent 1. According to their chemical composition (Craig)  Polymethanes  Polyacrylic  Organic phosphonates  Mellitic anhydride and methylmethanylate (M-META)  Hydroxyethyl methacrylate + Glutealdehyde (HEMA+GA)  Ferric oxalate + NGP-GMA (N-phenyl glycine and glycidyl methacrylate) +PMDM pyromethalic dianhydride and 2HEMA) 2. On the basis of treatment of smear layer The smear layer of limited strength, so it must be either removed or modified before application of bonding agent a. Removed Example: -  Tenure (nitric acid)
  23. 23.  Mirage bond  Clearfil liner bond systems b. Preserved Example: -  Scotch ond dualina  Prisma universal bond c. Modified Example: -  All bond  Scotch bond 2  XR bond IV on the basis of shear bond strength (Elik et al.) Included dentinal adhesives without produce shear bond strength of 5-7Mpa Example: -  Dentin adhesit  Scotch bond dual cure  Glynia Category 2 Included the experimental and commercial products derived from Bowers work with ferric and aluminium onalalates and have produced shear bond strength between 8-14 Mpa Example: -
  24. 24.  Tenure  Mirage bond Category 3 Included dentinal adhesives, without produced shear bond strength values of about 17-20Mpa Example: -  Super bond  Scotch bond 2  Scotch bond multipurpose  All bond (Decreased failure was cohesive in nature) V. According to their mode of curing - Clinical sure Example: -  Amalgabond plus - Light cure Example: -  One bond  Glunia comfort bond - Dual cure Example: -
  25. 25.  Clearfil linear bond 2V  Prime and bond NT dual cure Category III: Included (dentinal adhesives, which produced shear bond strength values of about. 17-20 MPa. Ex: Super bond Scotch bond 2 Scotch bond multipurpose All Bond The failure was mainly cohesive in nature According to their mode of curing 1. Chemical cure Ex: Amalgam bond plus 2. Light cure Ex: One Bond Gluma comfort Bond 3. Dual cure Ex: Clearfil liner Bond 2V Prime and Bond NT Dual cure On the basis of Generations: 1.1-Generation Dentin Bonding Agents Developed by Bowen - 1965. Agents used in this generation are:
  26. 26. a. Glycerophosphoric acid dimethacrylate, b. Cyanoacrvlates c. NPG - GMA d. Polyurethanes Buonocore four decades ago found that a resin containing GPA-MA could bond to Hcl etched dentin surfaces. However, the bond strength was by water. To overcome this problem Bowen synthesized NPG-GMA a surface-active comonomer that theoretically produced water resistant bonds. NPG-C, MA acted as an adhesion promoter b/n the toot-h structure and resin material by chelating with surface calcium. Disadvantages: Poor clinical results Hydrolysis of GPA-DMA in oral environment Difficulty - in bulk polymerization of cyanoacrylates Instability of NPG-GMA in solution Hydrophobic resin Low bond strength (2.1 - 2.8 Mpa) Ex: Cervident (S.S.White Co.) First commercially available dentin bonding agent. Cosmic bond (Amalgamated Dental) Palakav (Kulzer, USA) 2. II Generation Dentin Bonding Agents: In general, the second-generation dentin bonding agent was much improved compared with the first generation. These were developed during the early 1980's.
  27. 27. Most of the agents were primarily - (polylmerizable phosphates in BIS-GMA) resin 1. Halophosphorous esters of BIS-GMA. Hence they were called as phosphate- bonding systems. 2. Polyurethane based compounds were also used. The bonding mechanism involves a surface wetting Phenomenon as well as ionic interaction b/n phosphate groups and dentinal calcium. The 11-generation systems required a smear laver intact. This was to create a Ca+ rich layer where the phosphate can combine with Ca+. Disadvantages: 1. Low bond strength (1-3 Mpa) (studies by Relief and others 1986 and Solomon & Beech) 2. Hydrolysis of phosphate Ca+ bond. A major reason for the poor performance of these bonding agents is the fact. that these bond to the smear laver rather than to the dentin itself. Ex: Scotch bond dual cure ('OM Dental) Bond Lite, (Kerr) Dentin Bonding Agent (Johnson &. Johnson) Prima Universal Creation Dentin Bonding Agent Clearfil (Kuraray) 3. III generation Dentin Bonding Agents Developed in mid 1980s
  28. 28. The third generation dentin adhesives showed increased bond strength and improved clinical performance. These systems required either total or partial removal of the dentinal smear laver. In addition they required a surface-conditioning step. They used a solution or a series of solutions to increase the wettability of dentin (i.e. priming solution). Their mechanism of bonding to dentin was by penetration of smear layer i.e. they used micro mechanical means of adhesion rather than the unreliable chemical bonding of previous material. Disadvantages: Time consuming (More of number of steps) Technique sensitive Ex: Gluma (Bayer Dental) Conditioner: EDTA 17% Primer: 35% 1-iEMA (Adhesion Promoter) 5% Glutaraldehyde Resin: 55% BISGMA 45% TEGDMA Bonding was achieved by Glutaraldehyde bonds to amino groups in collagen Charge compounds Reacts with OH group of HEMA And causes mechanical interlocking in the opened ends of dentinal tubules
  29. 29. 2. Tenure: Oxalate was the first available dentin-bonding agent developed by Bowen. Conditioner: 2.5% nitric acid + ferric oxalate (stains the teeth). SYSTEM CONDITIONER ADHESION PROMOTER BA 1 Gluma 17% ED'FA 35% HEMA 5% GA 55% BISGMA TEGDMA 2 Scotchbond 55% HEMA 2.5% Maleic acid BIS-GMA HEMA 3 TENURE (10.2-18.2 Mpa) 1% Nitric acid 2% Phos. Acid 2.5% Aloxalate 5% NTG- GMA PMDM BIS-GMA TEG- DMA 4 4. Prisma Univ. Bond 2 30% HEMA 6% PENTA 50% UDMA 25%TEG- DMA 4.5% PENTA 0.5% GA 4. Fourth Generation Dentin Bonding agent: In these systems there was complete removal of smear layer. Consists of primer and adhesive. These bonding systems involved the "Total etch" technique that is simultaneous etching of enamel and dentin with phosphoric acid or other acids. An improvement in dentinal bond strength by etching was first demonstrated by Fusayama in 1979 and became common in Japan. This gained acceptance in US much later. This is because
  30. 30. etching of dentin has been traditionally discouraged because of pulpal inflammation but it is found that very little acid actually penetrates dentin. These systems were also known as Universal bonding systems as these bonds to dentin, enamel, amalgam, porcelain and composite. Mechanism of bonding The mechanism of bonding offers for mild and strong etch adhesives Mild Sea (PH- I2) In this type of adhesive, 2 types of bonding are seen i.e. Hybridization +inter- molecular bonding. Here, the H.L is of such micron size and resin formation is less pronounced. In the H.L, HAP is not removed completely because of the weak acid. So a second type of bonding occurs, is a HAP act as a receptor for additional molecular interaction with specific carbonyl or PO4 groups of the monomer. Eg- The primary sonic bonding, potential of unifil bond GC., 2 carbonyl groups of YMETA with HAP were conformed in XP5 &TEM this 2 fold bonding mechanism may be advantage in terms of restoration longevity. Strong SEA (PH ≤1)  This is regular to the total etch systems.
  31. 31.  Mechanism of bonding is by hybrid layer. Formation he nearly all HAP is removed from collagen and thus any chemical reaction between HAP and function of monomers are excluded. ADVANTAGES  Simplified bonding process (-no post condition panix simultaneous demineralized and resin infiltration).  No etch and rinse phase.  Nano-leakage is reduced.  Dentin is covered at all times.  Reduced postoperative sensitivity.  Possibility of single dose packaging.  Consistent staple composition  Controlled solvent evaporation  Hygienic application (chances of noss infertum are less)  Possibility of particle filled adhesive carts as shock absorber).  Adequate monomer collagen infiltration.  Effective dentin desensitizer  Time saving. DISADVANTAGES
  32. 32.  Insufficient long-term clinical research.  Adhesion potential to enamel needs to the clinically proved yet. GLASS IONOMER ADHESIVES A third adhesion strategy differs from former approaches (perused by resin- based systems), as it involves glass-ionomer based interaction with the tooth substrate with the development of resin modified glass ionomer adhesives have that can bond resin to the tissue. A two-fold mechanism of adhesion is predicted acid pre-Rx without creases the tooth surface and exposes and surface collagen fluids to a depth of 0.5 to 1µm depth. Here, micro-mechanical bond (due to resin inter-diffusion) and a chemical bond (due to ionic interaction of the carboxyl groups of polyalkenoic acid with ca of HAP that reward attached to the collagen fibrils) take places. The underlying mechanism of glass ionomer adhesives and is similar to that of mild etch adhesives. A network of hydroxyapetite- coated” collagen fibrils interpenetrated by povers is typically exposed to a depth no deeper than 1µm. Up to 0.5 µm thick layer, often referred to, as “get-phase” remains attached to the tooth surface despite the conditioner being rinsed off. The basic difference with the First (I) Generation Dentin Bonding Agents This was developed by Bowen in 1965. Agents used in this generation are a) Gylycerophosphoric acid airrethacrylate. b) Cyanoacrylates.
  33. 33. c) NPG-GMA. d) Polymethanes. Buonocore four decades ago found that a resin containing GPA-MA could bond to HCL etched dentin surface. However, the bond strength was affected by the matter content. To overcome this problem, Bowen synthesized NPG-GMA, a surface-active ionomer that theoretically produced water resistant bonds, NPG-GMA acted as an adhesion promoter between the tooth structure and resin material by relating with surface calcium. (N-phenyl glycine and glycidyl methacylate). Disadvantages  Poor clinical results  Hydrolysis of GPA-DMA in oral environment  Difficulty in bulk polymerization of cyaroarrylater  In stability of NGP-GMA in solution  Hydrophobic resin  Low bond strength (2.1-2.8 Mpa) Example: - 1. Cervident (S. S. White Co) (first commercially available DBA) 2. Cosmic bond (Amalgamated dental) 3. Palakar (Kulzer, USA) Second Generation Dentin Bonding Agents
  34. 34. In the late 1970’s, the second-generation systems were introduced. Majority of these had halo phosphorous stress of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA), hydroxyethyl methacrylate (HEMA). These were weak bonds seldom increasing 1-3 Mpa. But were an improvement over the first generation systems. However, in these systems the phosphate bond to calcium in dentin was not strong enough to resist the hydrolysis resulting from H2O immersion. This hydrolysis resulting either from saliva exposure/moisture from the dentin caused micro-leakage. In these systems dentin was not etched, hence much of the adhesion was due to bonding to the smear layer. The inethane / isocyanate groups from covalent bonds with hydroxyl groups in both organic and inorganic part of dentin. The adhesive mechanism of these second generations bonding agents involved enhanced surface wetting as well as ionic interaction between negatively charged PO4 group and positively charged Ca. It was speculated that the clinical failure was due to inadequate hydrolytes stability in the oral environment and become then primary bonding was to SL rather than the underlying dentin. The presence of an intermediate SL presented intimate resin contact without is a prerequisite for a chemical reaction. Disadvantages  Low bond strength (1-3 Mpa) (studies by relief and others 1986 and Solomon and beech)  Hydrolysis of and PO4, Ca+ bond Example: -
  35. 35.  Scotch bond dual cure  Bond lite  Prima universal  Clearfil Third Generation Bonding Agents There were developed in the mid 1980’s. In this generation, the acid etching of the dentin partially removed or modified the smear layer. The acid opens the dentin tubules partially and increases their bonding permeability. The acid must be rinsed completely before application of primer. The primer contains hydrophilic resin modifies like hydroxyethyl trimellitate anhydride and bio-phenyl dineth arylite. The primers contain a hydrophilic group that infiltrates the dentin and the hydrophilic group that adheres to the resin. The dentin primers usually used in this generation system were 6% PO4 penta-acrylate (PENTA) 30% HEMA and 64% ethanol. After the application of primer the unfilled resin adhesive is applied. The most of these systems, the PO4 primer modified the SL by softening it after penetration. The adhesive is then applied attaching the cured primer to the composite resin. However, bonding was not the successful decrease the resins did not resin penetration is superficial penetrates the SL and SL was may weak. Disadvantages:  Time consuming  Technique sensitive
  36. 36. Example: -  Scotch bond and dentin bonding systems  XR bonding system  Gluma bonding system  Tenure dentin bonding system  4-META  Phenyl I-P  Mirage bond  Super bond  Prima universal bond 2 and 3  Clearfil liner bond Fourth Generation Dentin Bonding Agents This generation appeared in the early 1990’s. The complete removal of the SL was achieved in this generation. Fusayama and colleagues tried to simplify bonding to enamel and dentin by the preparation of 40% phosphate acid for etching of enamel and dentin. Unfortunately, it was not understood that dentin and resulted in the collapse of exposed collagen fibers due to over drying and acid. The use of total etch was one of the main characteristics of this generation. This technique permits the etching of enamel and dentin simultaneously using phosphate acid for 15-20seconds. The surface must be left moist should not be over dried, however in order to avoid collagen collapse. The application of a hydrophilic primer can infiltrate the exposed collagen network forming the hybrid layer (Nakahayashi resin 1982). The formation of resin tags and
  37. 37. adhesive lateral branches complete the bonding mechanism between the adhesive material and etched dentin substrate. The mineralized tissue of the peri-tubular and inter-tubular dentin are dissolved by the acidic caution, the initial surface penetration exposes the collagen fibulas. In this area, for a depth of 2-4 micrometer (Nakahayashi 1982) hybridization taken place and resin tags can seal the tubule orifice purely. This is thought to be the primary boning mechanism of most of the current adhesive system. There are bonding systems that use etching of denting with phosphoric acid or other acids. The fourth generation is commonly known as multi-purpose bonding systems as, 1. They can be used in cavities for both enamel and dentin 2. Same of their components can also be used for bonding to substrates such as porcelain and alloys. In each case, the mechanism of bonding is micro- mechanical into etched / grit blessed surfaces. The components of this generation are a set of chemical agents that proceed in a sequence from an initially hydrophilic component through to gradually more hydrophilic components. The term bonding agent no longer covers this multi-step application, procedure and has been replaced by adhesive system. Fusiyama in 1979, but the concept of total etch gained would wide acceptance only recently. It was mainly discouraged before became total acid etching was thought to produce pulp inflammation. The bonding system of this generation is basically a 3- step process. This was also called as a mineral binding system. 1. Conditioning
  38. 38. 2. Primer 3. Adhesive Example: -  Opti bond  Probond  Scotch bond multipurpose  Clearfil liner bond  Amalgam bond plus Advantage  Mets better  Bonds to met surface Disadvantages  Unless the primer and adhesive are applied consequently, the overlying composite resin will not bond to the surface. In the fourth generation system, the clinician had an option of converting the DBA from a light curing to a dual curing one. This was carried out by a self-activating agent (sulfuric acid derovative) to the bonding agent (I: 1 ratio). Fifth Generation Dentin Bonding Agents To simplify the clinical procedure by reducing the bonding steps and thus the working time, a better system was needed. Also clinicians needed a better may to prevent collagen collapse of demineralized dentin. So, the 5th generation bonding systems were made.
  39. 39. It consists of different types of adhesive materials “One bottle system” (JIDA Mason and Karca 1997). One bottle system These systems complained the primer and adhesives into one solution to be applied after etching enamel and dentin simultaneously with 35 to 37% of phosphoric acid for 15 to 20 seconds. These bonding systems create a mechanical interlocking etched dentin by means of resin tags, adhesion lateral branches and hybrid layer formation and show high bond strength values both to etched enamel and dentin. Sixth Generation Dentin Bonding Agents The sixth generation bonding systems are characterized by the possibility to achieve a good to enamel and dentin using only one solution. The first evaluation bond to conditioned dentin while bond to enamel was less effective. This may be due to the fact that the sixth generation systems are composed of an acidic solution that cannot be kept in place, must be refused continuously and have a PH that s not enough to properly etch enamel. Recently, a H2O based bonding has been introduced with centries with the functions of a conditioner, the primer and the adhesive. The active solution is mixed from two components resulting in the formation of an acidic (self conditioning) Moreover, without superficially etches dentin and enamel. The dentin bond mediated by this bonding agent seems to be adequate. However, the etching pattern that produced by phosphoric acid etching
  40. 40. Example: - It has 3 compartments  Compartment 1: Containing methgcrylated phosphoric acid, enters, photo initiators, stabilize  Compartment 2: Contains water, complex fluoride and stabilizes  Compartment 3: Has a micro brush The blister is activated by squeezing comportment 1, they realizing its content into compartment 2. The mixing ratio is 4:4.1 and the freshly mixed solution is released on the micro brush into compartment 3. On applying this to dentin, the SL well be dissolved. Then the demineralized dentin is leading with group with prop monomers leading to the formation of a hybrid layer. Seventh generation Binding Agents His example is the latest addition in the saves of bonding systems. According to manufactures, it a fluoride releasing, self-etching type of bonding agent. It has a color changing capacity.  The etching, priming and bonding is one simple application with no rending or drying.  It is available in two bottles, which have to be mixed and filled in the cavity.  Manufactured by a company called J Monta (USA) and the product is ONE UP BOND F. This is the only bonding system, which provides visual confirmation of complete polymerization by color charge.
  41. 41. YELLOW PINK WHITE (Liquid A and B) (Liquid A & B mixed) (Completely cured) Manufactures are claiming that this bonding system blocks postoperative sensitivity. Another manufacturing company H KULZAR have brought a product “BOND” in the market this has a single bottle system having self etch priming and bonding along with desensitizing capacity. It has the advantage of single bottle system and no need of mixing of any liquids. SMEAR LAYER Introduction Knowledge of the nature, structure and composition of the prepared surfaces of the teeth is the key to the formulation and understanding of adhesive destructive systems.
  42. 42. Smear layer was first suggested by Skinner (1961). It was first decreased in detail and termed as “smear layer” by Boyde et al (1963) The SL encompasses of any debris remaining on enamel, dentin or insertation after instrumentation and conventional methods of cavity preparation. The S.L can be discussed under the following:  Composition.  Formation.  Size.  Attachment to dentin.  Potential advantages/disadvantages. Composition  Smear layer in composed of debris generated during cavity preparation. Eculian KD lists the following as its components.  Inorganic tooth particles.  Bacteria and tissues  Saliva.  Blood. Smear layer is rich in nitrogen sulphur, carhon. The organic component consists of coagulated proteins denatured by functional heat during cavity preparation. The presence of hydroxyapetite crystals in S.L is because of its breaking away front the organic matrix and then resetting in the smeared at matrix.
  43. 43. Formation Smearing occurs when hydroxyapetite within (the tissue) is either phuked out or broken or swept along the resets in the smeared out matrix. Studies have shown that temperature will rise up to 6000 C in dentin when it is cut without a coolant. This valve is significantly comer than the melting point of appetite (15000 C – 18000 C) and has led to collude that smear layer formation is a physiochemical phenomenon rather than a thermal transformation of appetite involving mechanical shearing and thermal dehydration of the protein. Plastic flow of hydroxyapetite is believed to occur at low temperatures that its melting point. Size The smear layer thickness is about 5-10 microns but according to some studies it may range from 1-5µ. The size of the smear layer is influenced by the type of bur used, it speed of rotation and presence on absence of coolants. The steel and tungsten carbide bur produce an undulating pattern there is a rapid deterioration of the cutting edges. The cutting efficiency of these burs increases the frictional heat resulting in the smear layer formation. This smear layer formed is irregular in shape and non- uniform in size and distribution, and remains on the prepared surface even after thought levage with mater. The diamond burs produce relatively deep and uniform groves.
  44. 44. Significant difference exists between diamond burs used etch and without a coolant (water spay). The smeared debris does not form a continuous layer but exists as localized islands with discontinuities exposing the underlying dentin. The mater spray does not prevent smearing but significantly reduced its amount and distribution. The smear layer consists of two separate layers Superficial layer (outer) loose debris Layer loosely attached to underlying dentin (Inner) plug formation Attachment to the underlying tissue The smear layer is not always firmly attached to or continuous over the substrate. It may lift free in come cases. Potential Advantages & Disadvantages of the smear layer The main advantages of the presence of smear layer on dentin.  Reduction of dentin permeability to toxins and oral fluids.  Reduction of diffusion (usually inwards) & connection (outwards by hydrostatic pressure or inwards example by cementing restorations) of fluids prevents wetness of but dentin surfaces all to Brannstorm et al (1974) and Johnson et al (1976).  Bacterial penetration of dentinal tubules is prevented (Vojinovic et al 1973, Michelich et al 1980 Orgart et al 1974). The main disadvantages are:
  45. 45.  It may harbour bacteria, either from the original various lesions or saliva without may multiply taking nourishment from the S.L or dentinal fluid.  The S.L is permeable to bacterial toxins.  The S.L may prevent the adhesion of composite resin systems, bonding agents, glass ionomer polycarboxylate cements all to Schullen (1988), Dahl (1978), Powis et al (1982), Asmussen et al (1988) and Erickson (1989). HYBRID LAYER Sending to acid etched tooth surface requires an air-dried surface to allow the photo-polymerizable hydraulic bonding agent to be drown by capillary attraction into the pits created by acid etching. As a result, two kinds of tag- like resin extensions are formed. Macro-tags are formed at the cores of enamel primes where the resin curves into a multitude of distinct hypts of dissolved hydroxyapetite crystals, The underlying mechanism of adhesion to dentin is alike for three or two step total etch adhesives the dentin smear layer produced during cavity preparation removed by the etch and rinse phase which results in a 3-5µm deep demineralization of the dentin surface. Collagen fluids are nearly completely uncovered front hydroxyapetite and form a macro-retentive network for micro-mechanical interlocking of monomers this interlouh was first discussed by Nakabayashi, Kojima & Masuhma in 1982 and is commonly referred to as Hybrid layer.
  46. 46. Concurrent etch hybridization, resin tags seal the implugged dentinal tubules and offer additional retention through hybridization of the tubule orifice mall. Three specific ultra morphologic features have been described as resulting from this hybridization process. Shag carpet appearance stands for the loose organization of collagen fibrils that are detected towards the adhesive resin and often unrevealed into their micro-fibrils. This feature typically appears when the dentin surface, after being acid-etched, has been actively scrubbed with an acidic primer solution. The physical insuling action combined with chemical action of the citric acid was found to enhance the removal of acidically dissolved inorganic dentin material and surface debris. This resulted in a deeply tufted collaged fibril surface topography similar to appearance of a shag carpet thickness, the combined mechanical chemical action of mubling the acid etched dentin with an acidic premier dissolves additional chemical while fluffing and separating the entangled collage at the surface. This active rubbing application is thought to promote infiltration of monomers into the loosened collaged scaffold by a kind of “massaging effect”. A second typical hybridization characteristic has been termed as tubule- wall hybridization and represents the extension of the hybrid layer into the tubule wall area. Resin tag formation in the opened tubules is circularly surrounded by a hybridized tubule orifice wall that is thought to be farmable in hermetically sealing the pulp-dentinal complex against micro leakage and the potential subsequent ingress of
  47. 47. microorganisms. This effect may be especially protective when the bond fails either at the bottom or top of the hybrid layer, without are considered the two weak links in the micro-mechanical attachment. Then, the resin tags usually break at the hybrid layer surface keeping he dentin tubules and thus the direct connectors to the pulp sealed. In particular the resin tag necks at the top 5-10µm of the tubule orifice are thought or contribute most to retention and sealing effectiveness. Thirdly, lateral tubule hybridization has been descried as the formation of tiny hybrid layer into the walls of lateral tubule branches. This micro-version of a hybrid layer typically surends a central core of resin, called a micro-resin tag. Reverse Hybrid layer The acid etched surface of dentin is further sulyected to Rx with Naocl. This results in dissolution of the collagen fibrils that are exposed. Further, the use of self- etching primers results in superficial etching of the surface. Here, the hybrid layer is surrounded by more of inorganic material unlike the normal hybrid layer where the collagen fibers are encapsulated by resin, and so this layer thus formed is termed as reverse hybrid layer. Inter-tubular bonding
  48. 48. The hybrid layer has been considered to provide micro-mechanical bonding to dentin but resin tag formation may also contribute to the bond strength. Penetration of the bonding agent into the tubular may provide much retention, as there will be so path of withdrawal until same tags fracture this mechanism plays an important role in areas where dentinal tubules are large in number (i.e. in areas of dentin nearer to pulp). The action of these mechanisms is by  The resin tags, which significantly increase the bonding width.  Hybrid layer, which creates an elastic layer between the restoration and dentinal tissue (elastic bonding). CONDITIONING OF DENTIN Conditioning of dentin can be defined as only attention don after the creation of dentin cutting debris, termed the smear layer the objective of this to create a surface capable of micro-mechanical and possible chemical bonding to a DBA. The principal effects of conditioning of dentin may be classified as a) Physical changes. b) Chemical changes. Physical changes are principally  Increase or decrease in the thickness and morphology or the S.L.  Changes in the shape of dentinal tubules.
  49. 49. Chemical changes are principally  Modifications of the fraction of organic matter.  Decalcification of the inorganic portion. Removal of S.L generally results in increased permeability of the dentin (Pashley, Michelich, Kehl 1981). The small particles comprising of S.L have a large surface to volume ratio. The particles dissolve more easily then the intact dentin. If the S.L and smear plugs with in the tubules are last, the exposed dentin becomes more permeable and sensitive. For chemical success the conditioned dentin must be scaled to prevent sensitivity and pathology (Brannstrons 1981). Conditioning of dentin same be done by 1) Chemical: a) Acids b) calcium chelators 2) Thermal: Lasers. 3) Mechanical: Abrasion. Acid conditioners  Manufactures generally use the terms conditions or etchant to describe agents that are mashed off the dentin. Mode of action of chemical conditioners
  50. 50.  It has been suggested that mineralized collagen matures have appetite crystallites managed not only around collagen fibrils but also within them. The depth of demineralization because of either hyper-miniralization or formation of more acid resistant forms of calcium phosphate (Pashlkey 1992) Effect of chemical conditioners Chemical conditioners remove the S.L and expose a microspores scaffold of collagen fibrils thus increasing the micro porosity of inter-tubular dentin. Because this collagen matrix is normally supported by the inorganic dentinal fraction, demineralization causes it to collapse. On inter-tubular dentin the exposed collagen fibrils are randomly oriented and are often covered by an amorphous phase with selectively few micro-porosities and variable thickness. Etcharts thickened with silica leave residual silica particles deposited on the surface, but the silica does not appear to plug the inter-tubular micro-porosities. Sometimes fibrous structures probably renarts of odonto-blastic processes are pulled out of the tubules and smeared over the surface. With aggressive acid etchants the acids may tend to pull the collagen fibers away from the intact dentin/unaffected dentin leaving a submission space termed as hiatus with increasing aggressiveness of the conditioning agent a circumferential groove may be formed at the tubule orifice separating a cuff of mineralized peri-tubular dentin from the demanding enter-tubular dentin. Alternatively, the mineralized peri-tubular dentin may be completely dissolved to form a funnel shape structure.
  51. 51. Historically, several acids have been researched as dentin conditioners. These include hydrochloric acid, pycrimer acid, and phosphoric, citric, nitric, acids. The hydrogen ions from these acids diffuse into the dentin while etching. The surface reactions are violent as carbonate is commented to carbon dioxide and as calcium and phosphates are liberated. These products may be liberated faster than they can diffuse from the site leading to formation of reaction product that may limit further penetration of protons. Further, the hypertonic solutions when osmotically draw the fluid from the dentin towards the surface could restrict the inward proton diffusion. The removal of smear layer and demineralization of the dentin matrix may facilitate bonding through a number of mechanisms they are:  Removal of loose smear layer debris and exposure of dentin matrix.  Exposure of collagen fibrils and their Epsilon- Amino groups that may catalyze HEMA polymerization.  Exposure of intact collagen that serves as a scaffold for the creation of resin collagen hybrid layer. PHOSPHORIC ACID It was the first dentin conditioner that was successfully used to remove the smear layer, etch the dentin and restore with adhesive composite resin by Fuzayama and Others (1979). This helps in removing the surface dentin, leaving a clean, well-defined
  52. 52. etching pattern where the tubules are enlarged into a funnel shape. Phosphoric acid is the acid of choice recently for the etching purpose. However, the controversy remains about the optimal concentration of H3 PO4. The most widely used concertinos in clinical practice of H3 PO4 Chow and Brown (1973) demonstrated that the application of H3 PO4 solutions greater than 50% (10-20µm) resulted in the formation of monocalcium phosphate monohydrate that is not readily soluble and mould not be completely washed away in the clinical situation. If H3 PO4 is applied on dentin when ≤ 50µ of dentin removal it resulted in pulpal damage as and liberated gas that passed through the pulp producing thropulus and hemorrhage (Kozam and Burnett). Nitric Acid  It is stronger than phosphorus acid.  Easily removes the smear layer.  Used in concentration of 2.5% causes funneling of the orifice of dentin to a depth of 5µm in 40 seconds. Citric Acid 10% citric acid is used for the purpose of removing the smear layer. It has been reported by Nakabayashi (1989) that such Rx tends to lower the porosity or permeability of the demineralized surface possibly by denaturing the collagen.
  53. 53. Nakabayashi developed 10% citric acids plus 3% ferric chloride combination. The divalent rather seems to stabilize the dentin matrix during its demineralization by citric acid. This combination was found to be particularly effective for methacrylate based adhesives containing 4-META. Ferric appears to be necessary same the sitric acid alone yield poor results with this system. The higher bond strengths of 4-META/ MMA- TBB products conditioned by 10% citric acid and 3% ferric chloride solution can also be achieved by substituting cupric chloride for the ferric ions example super bond C and B metabond and amalgam bond. Kuraray Introduced 10% citric acid and 20% calcium chloride in the latest generation of smearfil linear bond system. This dough concentration of calcium may stabilize collagen during surface etching. It also decreased the extent of the demineralization of hydroxyapetite by a common ion effect. Here, the depth of decalcification is about and microns compared to the phosphor acid etching with results in 16- micron depth of decalcification (Inokshe and others 1989). Pyrumic Acid Pyrumic acid and prysumic acid suffered with glycine have been reposed to satisfactory acid etch both enamel and dentin (Asanussen and Munksgaard, 1988) when using the Gluma Bonding system Glyrine was used to adjust the PH and perhaps to facilitate polymerization reactions.
  54. 54. Calcium chelators Chelators are used to remove the S.L without decalcification or significant physical changes to the underlying substrate as apposed to the strong acid etchants. EDTA Brannstrom’s concern that bacteria might be incorporated into S.L and infect the dentin surfaces of cavities led bur to develop a dentin conditioner containing 0.1% ethylene diamine tetracetic acid and 0.15% Benzalkomum chloride as a surface active disinfectant (1980). This agent was marked under the name “Zubulicid”. It is scrubbed on the surface of the S.L for a few seconds, then left passively for another 60 seconds folled by additional scrubbing such Rx removes the S.L and generally leaves the smear plug intact the dilute solution of EDTA removes some Ca that is thought to be important in the mechanism of bonding. This was probably responsible for the fall in bond strength. EDTA was developed for its use in the Gluma system by Murksgoard and Asmussen in 1984. it removes the S.L but does not form significant surface concavity nor is the funnel shape change associated with phosphoric acid avided. The smear plugs in the dentinal tubules are not for removed completely by 30 sers of application of the conditioner. A significant hybrid layer is formed by the application of the prior containing both gluteraldhyold and EMA to the EDTA conditioned substrate. Maleic Acid
  55. 55. It removes the smear layer but not the smear plugs. It is used in scotch bond 2 and Dexthessive as a conditioner. Although it is grate acidic, it does not appear to decalcify deeply. The chybrid layer formed in this is comparatively thin. Thermal Modifications Lasers Hard tissue lasers in dentistry are an emerging technology. A pulsed Nd-YAG laser will not disturb the pulp, even the approached is as close as 1µm. Heat is dissipated b/w the 10 to 30 sers pubes per second. Most of the research has been conducted on dry dentin, but the laser operates on dentin immersed in saliva/H2O. The mechanism 9of dentin removal is through microscopic implosions caused by the thermal trannents. The carboxyed, black root that results easily washed off with H2O based surface results in desensitized dentin, presumably by occlusion of the open and permeable dentinal tubules. Microorganisms and organic debris are eliminated from the lazed surfaces. The laser decreases the organic fraction of the dentin surface. The bond strength is increased by about 60% when this was done presumably by increasing the bondable inorganic fraction of the dentin surface. The laser may create micro-mechanical retention. Mechanical Modifications
  56. 56. It is a mechanical mean of modification of dentin aluminum oxide is used for the purpose of micro-abrasion. It removes healthy as well as diseased dentin and results in a smear layer. Its abrasion action depends on the particle size as well as the velouty. The 0.5-micron or larger particles create a smear on the dentin and increase the surface area (Blacke, 1991). The smear layer formed might be used to eliminate the bond strengths of smear layer mediated dentin bonding agents. Polyacrylic Acid These acids are being used more recently. A 10 second application of durelon liquid (40% polyacrylic acid) nanults in opening of d.t. There is no chance of potential harm to the dental pulp here, due to the large molecular size without prevents the and to more through the d.t. PRIMERS Major advances have been achieved by the introduction of primers that promote meting of the dentin with the bonding agent, and penetration of the bonding agent into the dentin. Primer monomers are bifuntional molecules i.e they contain 1) hydrophilic groups (eg- OH2-COOH) for better compatibility of the resin monomers with the moist dentin, and 2) hydrophilic emthanylate groups for the co-polymerization with the bonding resin primers are monomer dissolved in solvents such as 1) aretone, 2) alcohol 3) metal and are capable applied to the etched/ conditioned dentin substrate last are not rinsed off organic solvents aid in displacing mater, expanding or re-expanding the collagen
  57. 57. network and thus promoting the infiltration of the monomer into the sulucron or monometer sized spaces with in the collagen fiber network. The first dentin bonding mechanism that gave reliable, high bond strengths reported by Nakabayashi et al (1982) was based on the use of 4- META/ methyl methacrylate tri-n- borane (MMM- TBB) and 3% ferric chloride in 10% citric acid as a conditioner. Effective primers contain monomers with hydrophilic properties that have an affinity for the exposed collagen fibril and hydrophilic properties for co-polymerize with adhesive resins. The objective of this step is to transform the hydrophilic dentin surface into a hydrophilic state. Besides HEMA primers contain other monomers, such as NTG- GMA, PMDM, BPDM an PENTA present day primers also underde a chemical/photo polymerization initiator so that these monomers can be polymerized in sitic. There are 2 types of bonding systems Water Based Primers The first approach to create a hybrid layer in wet dentin is the use of water- soluble primers containing HEMA. Examples of this type of monomer are scotch bond 2, scotch bond multipurpose. After application of the water HEMA mixture, the surface all devised to evaporate the H2O. As the H2O concentration falls, the HEMA concentration rises, until theoretically there should be no H2O and 100% HEMA on the surface water has a much higher napour pressure than does HEMA. In fact, at
  58. 58. atmospheric pressure, HEMA can be regarded as almost volatile. This permits its retention as its solvent; water is evaporated during air-drying. Use of water Miscible primer solvents The second method of creating hybrid layers in this category of bonding is to sequentially acid etch, rinse, leave moist on dry prime and them bond the HEMA will be in 2 types 1) 35% HEMA in water 2) 13% polyalkenoic acid copolymer in 50% HEMA. The intringic metness of dentin varies from about 1% in superficial to about 22% in deep dentin Iay et al using all Bond 2, Besco, have described the consequences of applying acetone based premiers to over net dentin; the authors found that small globules were formed within dentinal tubules. These were formed when the first one or two layers of primer were applied i.e. in the tubules filled with dentinal fluid there was too much water available to dilute the acetone with result that the monomer came out of the solution. As more globules funed, they accumulated on the walls of the tubule, reducing the permeability of the tubules, permitting successive primer applications to dehydrate the tubules enough to form normal resin tags. If successive extrinsic H2O is left on to surface prior to the application of primer (All Bond 2) without tends to bridge the excess H2O droplets to four a tiny insuster. This prevents resin tag formation in those tubules beneath the H2O droplet, clinically if the
  59. 59. clinician sees a rough denture on the primed surface that might be caused by this phenomenon , these droplets can be destroyed with the tip of brush, without can be used to add more primer . The danger is that, this may occur somewhere in a complex cavity design that is not easily visualized. This may result in a unbounded region, without changing its dimensions under thermial / ouhcal stress and produce sufficient fluid shifts to cause dentinal sensitivity (Brannstrom, 1992). It may also permit the concentration of stress that may lead to bond failure in that portion of the restoration (Watahe, 1992). Thus over drying /over wetting of dentin can have undisuable effects (Tay et al). The goal of priming is to replace all of the H2O/aretone monomer mixtures in the inter-fibular spaces with the polymerizable monomers Manel et al demonstrated that 100% acetone; ethanol and HEMA all cause a time dependent stiffening of demineralized dentinal matrix. Once stiffened, the matrix cannot collapse thus allowing efficient hybrid layer formation. Application of primer to smear layer covered dentin followed by bonding agent Bonding to the smear layer covered dentin was not very successful before 1990 as the resins aid not penetrate through the S.L. This led most manufacturers to use acidic conditioners. However, the resulting soft collagen with surface can collapse an interface with the number of bonding steps (Watenbe, 1992) developed a new bonding system with out an aqueous solution of 20% phenyl –p in 30% HEMA .This self etching and self priming system provided important new information on S.L as bonding substrates. The ideal self-etching self-priming bonding system is one that can penetrate
  60. 60. 2.0µm of S.L and engage underlying dentin to a depth of 1µm. However, as S.L are made up of dentin they have a significant buffer capacity and tend to buffer the acidity of the acidic monomer used as self-etching agent. This property in addition to the tight packing of S.L particles limit the penetration of monomer is about 2µm. So Toida et al advised the removal of smear layer by a separating etching steps to produce more reliable and durable bonds. Steps for effective priming Microscope examination of attachments reduced y primer has shown deficiencies Like Incomplete surface coverage. Incomplete inter-fibullar saturation within the hybrid zone. Incomplete penetration to a full depth of demineralized dentin. A – One method of improving surface coverage and diffusion of the primer is by the application of multiple coats. A second coat of primer of multiple coats. A second coat pf primer is shown to increase the shear bond strength significantly. B—The surface of dentin should not be over dried or over wet. C—The etching time should not exceed the time recommended by the manufacturers. The primer reacts with the side chain grouping of the amino acids in the collagen structures especially –NH2, -OH2 and COOH Masuhara and coworkers developed analysis bonding agents containing the polymerization initiator tributyl boron, without is said to induce grafting of the monomers and polymers on to the collagen structure.
  61. 61. Latest developments The latest developments in the field of self-etching bonding agents are self – etching bonding agents are self-etching premier- adhesives for composers (example- Promp L-pop, F-2000) (it has been shown that prompt L-prop showed higher bond strength to enamel than to dentin) Several concepts of the bonding mechanism of adhesive resins to dentin have been proposed.  Bonding via tag formation in to dentinal tubules of etched dentin (Nardennall and BRANNSTRON, 1980).  Formation of precipitates on pretreated dentinal substrate to with an adhesive resin may be chemically or mechanically bonded (Bowen, Cohh and Rapsdin, 1982)  Chemical union to either inorganic or organic components of the substrate (Nakalrayashi, Hayta and Maxchara, 1977)  Diffusion and impregnation of monomers into the sub surfaces of pretreated dentinal substrates and their polymerization creating a hybrid layer of resin reinforced dentin.  There are two types of handing systems they are wet and dry bonding system.  Wet bonding where dentin fluid us not removed completely example acetone is based in bonding where dentin fluid is removed by using air H2 O BASED and drying method. Wet Bonding
  62. 62. Earlier, placement of restoration on wet surface may have caused confliction b/w the dentist his tracing. However, the picture has changed now. When the etched dentin is air dried the collagen restoration will collapse L & the micro channels opened by the removal of the appetite systems will be closed from a compact coagulate that is imponderable to resin. Resulting in a layer of imperfect bonding termed as “Hybridoid region” (Tay, Guvett, 1995). This results in micro leakage at monometer level (1/1000 ton of a micron called “Naroleakage”. This type of bonding results with the bonding systems containing hydrophilic resin such as HEMA, with tolerate moisture. Methods without are being followed for wet bondigae. This chamical techneque commonly refered o as wet-bonding has been introduced by Karea 1992) abd Grinnett 1992).  Keeping the substrate field dry and use adhesive systems that provide mater based pumers example opti-bond FL, scotch bond multipurpose). There rehydrate and re- expand the collagen fibers allowing the resin to infiltrate.  Keeping the acid etched dentin surface moist and use acetone based primers (All bo9nd 2) prime and Bond 2) without have H2O chasing capacity. This technique was introduced by Karca (1992) and Gwinett (1992). In acetone containing primers, when the acetone covers in contact with H2O; the bonding patient of acetone is raised and boiling patient of H2O is lowered
  63. 63. (AZEOTROPHISM) without caused evaporation of both the acetone and H2O and resin is left behind. Alternatively conditioned dentin may be are dried and remoistened with H2O an antibacterial collection such as chlohenidere (Garimett and Kanca)> Also an aqueous collection of HEMA (35%) Gaquapup BISCO) are affective for compensating the dryness induced on dentin surface by air drying. Over wetting phenomenon When amount of H2O is present on dentine surface, this may interfere with the bonding because when primer is applied the solvent evaporates leaving the resin, if water is not completely replaced by primer, polymerization is affected. In such conditions excessive water causes phase separations of hydrophilic and hydrophilic components resulting in blister and globule formation at the resin dentin surface. Advantages of wet bond It is a technique sensitive procedure. Firstly, acetone quickly evaporates from the primer bottle, so that bottle should be immediately closed and the dispensed solution is should be applied immediately on the etched surface.
  64. 64. The evaporation of solvent will increase the ratio of monomers to the acetone solvent that will in have an effect on the eventual permeability of moners in the exposed collagen network. To format this primers is be available in pre-dosed single patient use capsules is primer and bond NT Quix (Deulply). In contract to adhesive systems that provide acetone based primers and show a restricted minnow of opportunity” as far as premise amount of H2O that should remain post-condition a on the dentin surface for efficient bonding to be achieved, adhesive systems that provide H2O-based primers appear less technique sensitive and bond equally well to varying degree of surface dry and wetness. Bonding to dry dentin has the advantage of being the clinically accepted and utilized standard used by most clinician. Sovents used in adhesives ACETONE  Highly nolatile.  Excellent H2Ochaser.  Strong duping agents (risk of over-drying dentin).  Storage and dispense problems. Example- one step (BISCO) Prime and bond NT (Dentsply) Guma one bond Ethanol
  65. 65.  Gold penetration capacity.  Enables self-etching of acid monomers.  Slow evaporation difficult to remove.  Remaining H2O may hamper the resin penetratum air polymerization. Example -Amalgam bond plus (Parkell). -Prompt-L-Pop. -Etch bond multipurpose. Water  Good penetration capacity.  Enables self-etching of acid monomers.  Slow evaporation difficult to remove.  Remaining H2O may hamper the resin penetratum air polymerization. Example -Amalgam bond plus (Parkell). -Prompt-L-Pop. -Etch bond multipurpose. Solvents may also be used in combination i.e. Acetone –H2O Example- tenure-quick Acetone-Ethanot. Example-All Bond 2(BISCO) Example-Guma comfort bond etch bond 1.
  66. 66. Adhesives The resin component of a bonding system consists of a combination of resin such as BISGMA, TEGDMA, UGDMA or other methamylate resins. These penetrate the preimed dentin and co-polymerize with the preimer to form the hybried layer some of these systems may contain fibers without may be silica or glass or fillers of nano size. A filled adhesive has  Greater film thickness.  Greater utility to flex.  Helpers dispate stress of polymerization. Example- Prime and Bond NT 4%. -Optibond solo plus 15%. -Surfaces resin film that stabilizer the hybrid layer. -Improved bond strength or bond stability. This is the final step of bonding process; application of adhesive layer spreading of the adhesive resin over the surface to without it is bonded should be done preferably with a brush rather than are spray the adhesive is copiously placed and evenly spread with a brush tip that can be separately squeezed out b/w a paper tissue. The when placed in a sufficiently thick layer, the adhesive resin may, due to its relatively higher elasticity, acts as a stress relaxation buffer. This will absorb by elastic elongation, in part, the tensile stresses imposed by polymerization contraction of the resin composite subsequently placed over the adhesive resin.
  67. 67. The polymerization contraction stress generated during the placement of composite restoration was found to be absorbed and relived by the application of an increasing thickness of low-stiffness adhesive. Blowing the adhesive resin layer may reduce its thickness to much, decreasing its elasticity buffer potential to relieve polymerization contraction stress. Amalgam Bonding Although retention and resistance forms were the hallmark of traditional amalgam preparations, modern consentive philosophy and the desire to extend the use of amalgam to more extensive restorations have stimulated a search for improved methods for retaining amalgam restorations mechanical adjuncts, including timeaded prims/ retentive groves placed in dentin have served well for years employing M-R-X type coupling agent have achieved some clinical sources where, M = a methacrylate molecule without bonds to the composite resin. R = a linking molecule. X = a molecule without interacts with the dentine surface or smear layer. One system used y-methacryloxyethyl trimelliate anhydride (y-META). However, the mechanism for responsible foe the bonding amalgam to resin is predominantly mechanical is native. It is produced by condentensory the plastic amalgam mass into an inset adhesive resin layer, there producing an intimate mechanical interlocking as macro retentive areas are produced within the resin after the resin has polymerized.
  68. 68. The results of controlled clinical trials have been mixed, but namely amalgam- bonding agents have placed an adjunct to comentional retentive areas if properly employed. Adhesive- there are unfilled resin components without is having low minority so that they can penetrate in the tags created by acid etching. -Example- BIS GMA.