Bonding agents/ continued dental education


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  • Bonding agents/ continued dental education

    1. 1. BONDING AGENTS Its application in prosthodontics INDIAN DENTAL ACADEMY Leader in continuing dental education
    2. 2. TABLE OF CONTENTSTABLE OF CONTENTS  Introduction  Historical Perspective  Terminologies  Acid etching  Requirements of Adhesion  Chemistry of Adhesive Agents  Factors affecting adhesion to mineralized tissue  Classification of Dentin Bonding System  Bonding Procedure  Material Selection  Surface treatments-Alloys, Ceramic  Conclusion &
    3. 3. Adhesion of restorative material to mineralized tooth structure has been a goal of dental researchers for many years. Accomplishing such a bond has many principle advantages like: INTRODUCTION 1. Retention of restoration, 2. Conservation of tooth structure, 3. Elimination of marginal microleakage, 4. Reinforcement of remaining tooth structure 5. Increasing the clinical life time of restorations.
    4. 4. Due to lack of adhesion between dental restorative resins and tooth structure, microleakage of salivary components and bacteria occur, which may lead to: Marginal staining. Breakdown at the margins of the restoration interface. Secondary caries. Post operative sensitivity. Pulp pathology.
    5. 5.
    7. 7. Interest in esthetic restorations is definitely not a modern concept. In 1856 prefabricated ceramic inlays were used as an esthetic filling to be sealedsealed with gold foilswith gold foils (Hoffman-Axthelm, 1973). Another example is the development of fired ceramic inlays in 1882 by Herbst in Germany, reported in the dental literature for the first time by Bruce in1891. The fabrication of fired ceramic inlays over platinumfired ceramic inlays over platinum foilfoil was developed a few years later by Land, in 1888.
    8. 8. It is interesting to note that ceramic inlays were introduced to the dental profession well before amalgam (1895). However, the absence of a satisfactory lutingabsence of a satisfactory luting material was a serious obstacle to the clinical success of these techniques (Nyman, 1905) until recently, when resinous adhesives and porcelain etching were combined to bond the restoration efficiently to the tooth (Simonsen and Calamia,1983)
    9. 9. The real development of direct esthetic materials began with Silicate cementsSilicate cements 1871. Unfilled resinsUnfilled resins in 1937, which have been advocated for esthetic fillings since 1945 Epoxy moleculeEpoxy molecule developed by the Swiss chemist Castan in 1938 Acid conditioningAcid conditioning of dental tissues by Hagger, another Swiss chemist, in 1951. First description of the so called "hybrid layer""hybrid layer" (McLean and Kramer; 1952)
    10. 10. Enamel EtchingEnamel Etching by Michael BuonocoreMichael Buonocore 1955 Composite ResinComposite Resin with Bowen's BIS-GMA formulationBowen's BIS-GMA formulation (Bowen, 1962).
    11. 11.
    13. 13. Acid-Etching-Acid-Etching- Process of roughening a solid surface by exposing it to an acid and thoroughly rinsing the residue to promote micromechanical bonding of an adhesive to the surface. Adhesion-Adhesion- A molecular or atomic attraction between two contacting surfaces promoted by the interfacial force of attraction between the molecules or atoms of two different species; adhesion may occur as physical adhesion, chemical adhesion, mechanical adhesion (structural interlocking) or a combination of all types. Adhesive-Adhesive- Substance that promotes adhesion of one substance or material to another. Adherend-Adherend- A material substrate that is bonded to another material by means of an adhesive.
    14. 14.
    15. 15. Adhesive Bonding-Adhesive Bonding- Process of joining two materials by means of an adhesive agent that solidifies during the bonding process. Dentin Bonding-Dentin Bonding- The process of bonding a resin to conditioned dentin. Dentin Bonding Agent-Dentin Bonding Agent- A thin layer of resin between conditioned dentin and the resin matrix of a composite. Dentin Conditioner-Dentin Conditioner- An acidic agent that dissolves the inorganic structure in dentin, resulting in a collagen mesh that allows infiltration of an adhesive resin. Hybrid Layer-Hybrid Layer- An intermediate layer of resin, collagen, and dentin produced by acid etching of dentin and resin infiltration into the conditioned dentin.
    16. 16. Microleakage-Microleakage- Flow of oral fluid and bacteria into the microscopic gap between a prepared tooth surface and a restorative material. Primer-Primer- A hydrophilic, low viscosity resin that promotes bonding to a substrate, such as dentin. Resin Tag-Resin Tag- Extension of resin that has penetrated into etched enamel or dentin. Smear Layer-Smear Layer- Poorly adherent layer of ground dentin produced by cutting a dentin surface.
    17. 17. An adhesive joint is the result of interactions of a layer of intermediate material (adhesive) with two surfaces (adherends) producing two adhesive interfaces. CLASSIFICATIONCLASSIFICATION The interactions which occur at the interface are classified generally in terms of types of atomic interactions which may be involved. Adhesion is classified as: 1. Physical. 2. Chemical. 3. Mechanical. Micro Macro
    18. 18. Physical bondingPhysical bonding involves Vander waals or other electrostatic interactions that are relatively weak. It may be the only type of bonding if surfaces are smooth and chemically dissimilar. Chemical bondingChemical bonding involves bonds between atoms formed across the interface from the adhesive to the adherend. Because the materials are often dissimilar, the extent to which this bonding is possible is limited and the overall contribution to bond strength is normally quite low. Mechanical bondingMechanical bonding is the result of an interface that involves undercuts and other irregularities that produce interlocking of the materials.
    19. 19. Almost every case of dental adhesion is based primarily on mechanical bonding. Chemical bonding may occur as well, but generally makes only a small contribution to the overall bond strength. Common method for producing surface roughness for better mechanical bonding is to grind or etch the surface. Grinding produces gross mechanical roughness but leaves a smear layer of hydroxyapatite crystals and denatured collagen that is approximately 1 to 3 microns thick.
    20. 20.
    21. 21. Acid etching or conditioning dissolves this layer and produces microscopic relief with undercuts on the surface to create an opportunity for mechanical bonding. If the interlocked adhesive and adherend with dimensions less than about 10 microns, then the situation is described as micro- mechanical bonding.
    22. 22.
    24. 24. Perhaps the most significant discovery in dentistry during the last three decades is that of Dr. Michael Buonocore in 1955Dr. Michael Buonocore in 1955. Working in New York, he discovered that the bonding strength between human enamel and acrylic resin could be tremendously enhanced by exposing the tooth to a mild acidic solution before applying resin to the enamel surface.
    25. 25. In his first experiments Dr. BuonocoreDr. Buonocore was actually following the lead of industry. By the mid- 1950s it was already commonplace to pre-treat surfaces, such as metals, with phosphoric acid before applying resins or paint. In fact, his original trial used 85% phosphoric acid, which had by then become the industrial standard. The dramatic results obtained through this technique were recognized instantly. Almost immediately following Buonocore's initial discovery of binding to human enamel, efforts intensified to improve the
    26. 26. It is fortunate that there is a difference between the resistance of the enamel prisms and the inter-prismatic enamel to acidic attack. Thus, as Dr. BuonocoreDr. Buonocore discovered, placing a weak acidic solution on the enamel surface causes a differential etch rate between these two areas; this results in an irregular and pitted surface.
    27. 27. In addition to the presence of the enamel prisms, it has been discovered that the enamel contains approximately 0.1 % to 0.2% space by volume. Although this means that enamel is only minutely porous, it is possible that these porosities also play a role in the bonding process. This results in augmentation of the bond strength achieved by the differential etch.
    28. 28. Enamel Etching PatternsEnamel Etching Patterns Four major etching patterns of enamel are reported in the literature. The first, Type IType I, is created when the center of the prisms erode more rapidly than the inter-prismatic enamel. The average width of the craters usually found in Type I etching pattern is about 5 µ. This fact is of particular significance when selecting the luting agent for the bonding and fusing techniques. Any filler particle of greater diameter would simply not penetrate the enamel surface.
    29. 29. Type I
    30. 30. A second topography, Type IIType II, is created when the inter-prismatic enamel erodes more rapidly than the prism cores. Although Types ITypes I and IIII patterns are complete reverses of each other, both are suitable for mechanical retention. Interestingly, both patterns are often found in adjacent areas of the same tooth surface, even in adjacent prisms
    31. 31. Type II Type I & Type II
    32. 32. In the Type III etching pattern no rod structures are evident. Type III pattern results when the enamel being etched is composed of a homogeneous mass instead of the more commonly found prismed structure. Deciduous teeth often exhibit just such a stratum in their outermost layer. Since the outer layer is homogeneous in structure, applying an acid etchant results only in a reduction of enamel bulk, not the differential etch necessary for bonding. The Type III pattern can be troublesome for bonding because it does not allow the resin to grip the enamel.
    33. 33. Type III
    34. 34. Unfortunately, recent reports show that areas of prism-less enamel are not confined exclusively to deciduous teeth as previously believed. In fact, when surfaces of premolar and molar teeth are divided into zones, the cervical two thirds of the crown often exhibit enamel completely devoid of rod patterns after etching. Fortunately, this prismless enamel usually comprises only the outer 13 to 20 µ of the enamel. Since applying an acid etchant not only roughens the outer surface, but actually dissolves it, it is possible to etch past this prismless layer using the etchant itself.
    35. 35. A 50 second application of 30% orthophosphoric acid results in a loss of approximately 10 µ in surface contour and approximately 20 µ in depth of histologic change. Once 20 µ of enamel have been removed from the surface, the underlying structure usually exhibits one of the other three etching patterns. Thus, the time needed to etch an area of enamel displaying prism-less outer structure is considerably greater than an area of normal enamel.
    36. 36. COMPONENTS OF BOND STRENGTHCOMPONENTS OF BOND STRENGTH Chemical, electronic, and van der Waals forces play a critical role in keeping the filling material in contact with the tooth over the first 48 hours. After 2 days of submersion, however, simple mechanical gripping is the only major component involved.
    37. 37. The currently accepted value for bond strength in both the tensile and shear directions is approximately 980 to 1400 psi. Fourteen hundred psi is an extremely high bond strength for this type of simple micro-mechanical retention. This degree of tenacity can be explained by the fact that once the enamel surface has been roughened by the etchant, the enamel "pores" also become enlarged.
    38. 38. Since these pores often interconnect (Bergman and Hardwick hypothesized that they are the pathways used for transport of ions and tissue fluid), their increase in size not only allows relatively large resin molecules to penetrate the sub-surface of the enamel, but also allows these resin tags to interconnect. This exceptional degree of enamel and resin interlocking partly explains the high bond strength afforded by the acid etch technique.
    39. 39. ENAMEL PREPARATIONENAMEL PREPARATION To create these exceptional bond strengths consistently the enamel must be prepared carefully before bonding. Enamel itself is a reliable substrate for bonding, but in its usual condition there are several mechanical barriers to the development of a strong bond with composite resin. Without meticulous attention to detail, the bond strength can become significantly diminished.
    40. 40. At the time of a tooth's eruption it is completely covered with Nasmyth's membraneNasmyth's membrane. This is the final stage of ameloblastic activity. If present, this organic integument can prevent adequate etching of the enamel surface, but it measures only 1 µ to 2 µ in thickness when the tooth first erupts, and some thickness is soon lost owing to abrasion. By adulthood it is usually quite worn down or even completely missing and, therefore, is not usually of concern for most direct bonded retainers.
    41. 41. Nasmyth's membraneNasmyth's membrane is not the only barrier to preparing enamel properly. Since proteins from saliva continually adsorb to the enamel surface, even in areas of high abrasion, the enamel retains a thin organic layer. This further post eruptive integument is called pelliclepellicle, and it is on this stratum that colonies of microorganisms known as plaqueplaque form.
    42. 42. Plaque products, along with the fluid and solid food constituents, become associated with and integrated into this layer. They form a pellicle- plaque complex containing fats and protein- carbohydrate complexes. This layer serves as a barrier to enamel etching by mild acids. For this reason untreated enamel can be a poor substrate for bonding.
    43. 43. Not only is the enamel in its natural state contaminated with a layer of material that makes it mechanically unsuitable for bonding, but its surface is normally chemically fully reacted and therefore of relatively low energy. Thus, the enamel is normally chemically unsuitable for bonding as well.
    44. 44. CLEANINGCLEANING Obviously, then, the first step in preparing enamel for bonding has to be to remove the surface layer of contaminants. For a time it was felt that the acid etchant itself might be sufficient for this purpose, but in 1973 Mura1973 Mura and his coworkers showed that maximum bond strength could be achieved only if an oral prophylaxis was performed before etching. Gwinnett demonstrated that etched enamel that had not been prepared with a prophylaxis was often contaminated by remnants of the pellicle as well as by microorganisms, even after acid treatment. Calculus even further impedes proper preparation and must be meticulously removed before etching.
    45. 45. It is standard procedure for the prophylaxis to be carried out with unflavoredunflavored and unfluoridatedunfluoridated pumice. The reason for using an unflavored abrasive is that most flavorings in dental paste come from essential oils, often containing glycerin. These substances can interfere with the work of the acid. Further observations suggest that the fluoride should be removed from the polishing agent because it reacts with the calcium hydroxyapatite of the enamel to form calcium fluorapatitecalcium fluorapatite, a substance much more resistant to acidic attack.
    46. 46. Recently a new device has been designed for the removal of plaque and stain during prophylaxis (Prophy Jet, Dentsply). It uses a stream of sodium bicarbonate and water under pressure aimed at the teeth much like a sandblaster. This has a potential advantage over other methods of cleaning because it is able to gain access to areas in which the contacts are quite close.
    47. 47. ETCHINGETCHING The teeth should be rinsed, dried, and properly isolated from the saliva. Acid is then applied to the enamel with a cotton pellet, mini-sponge, brush, or other similar means. If the acid is in liquid form, it must be agitated gently on the surface of the tooth for optimal results. This agitation is usually accomplished either by a dabbing or by a very light swabbing motion. It is critical to avoid burnishing the enamel during the application of the acid since the enamel rod ends exposed during the etching process are extremely fragile. Even a mild rubbing is sufficient to di-minish substantially the final bond strength.
    48. 48. The optimal application time for the acid is generally believed to be 60 to 90 seconds,7 but several factors can affect the ideal etching time. One is the presence of prismless enamel. Such an enamel morphology usually requires doubling the normal etch time in order to erode past the prismless layer. The presence of high levels of fluoride in the teeth can similarly increase the time necessary for an optimal etch because the free fluoride ions in the enamel environment allow the calcium hydroxyapatite to react with them, thus producing calcium fluorapatite.
    49. 49. Clinically, this is accomplished by relying on the appearance of the tooth after etching, rather than on the clock, to measure the effectiveness of the etching. When properly etched, the tooth should exhibit a dull, frosted, matte finishdull, frosted, matte finish. Under- etching results in a tooth that retains its glossgloss. Over-etching results in a surface chalkychalky in appearance due to the formation of an insoluble salt during the etching process.
    50. 50. Many different acids have been suggested for the etching process, and much investigation has gone into determining the ideal etching solution. The popular current choice is orthophosphoric acidorthophosphoric acid, which is commercially available in concentrations ranging from approximately from 30% to 65%.
    51. 51. SilverstoneSilverstone did an interesting study. He tested 20%, 30%, 40%, 50%, 60%, and 70% concentrations of orthophosphoric acid, 50% orthophosphoric acid plus boric acid buffered with 7% zinc oxide by weight, 5% and 50% citric acid, 10% polyacrylic acid, and 5% and 50% neutral and acid solution of EDT A for exposure times varying from 1 to 5 minutes. HisHis conclusion was that 30% orthophosphoric acid wasconclusion was that 30% orthophosphoric acid was the solution of choice.the solution of choice.
    52. 52. In addition to the wide range of concentrations of the acid solutions, acids are available in gel as well as liquid form. The clinical decision to use an acid gel or an acid solution is a matter of personal preference. The clinical advantage of a gel over a liquid is the increased control in placing the acid. This is of particular help when the clinician has to etch in an area that surrounds some exposed dentin.
    53. 53. The major objection to using etching gels is that they require increased wash time after the etching procedure is completed. Most brands of etching gels have added colorants to help the dentist visualize exactly where the etchant has been placed. Immediately after etching, the enamel should be completely cleaned of any etching material. The combination of 60 seconds of etching time and 10 seconds wash time seemed to create the most powerful bond strength.
    54. 54. SURFACE ENERGYSURFACE ENERGY The removal of inert enamel surface structure exposes a fresh reactive surface with an energy level greatly increased over its unetched counterpart. The resulting surface, which is much more wettable in this state, must be protected. Both the application of fluorides and contamination from saliva should be carefully avoided, since these would alter the surface energy of the enamel and greatly reduce the bond strength.
    55. 55. If saliva does contaminate the etched enamel, it is extremely important that the surface be re- etched for at least 10 seconds with the phosphoric acid. If the dentist fails to do this, he will compromise the bond strengths. The reason that etched enamel surfaces which have contacted saliva must be retreated is due to the high degree of chemical and electrical activity in those enamel surfaces treated by the etching procedure. Once etched, the exposed enamel is extremely reactive.
    56. 56. When saliva comes into contact with the reactive enamel, even for a second, it adsorbs chemicals to its surface and lowers the activity of the enamel. This dramatically alters its wetting characteristics, which, in turn, severely reduces the bond strength. Besides creation of a new topography, perhaps the most profound result of the acid etching is the greatly increased surface area of enamel available for interaction with the resin.
    57. 57. RISKSRISKS Almost immediately upon the discovery of the potential benefits of the acid etch system, questions of potential risks arose. These questions dealt primarily with risks to the pulpal tissue, gingiva, and unbonded enamel. It is now clearly accepted that there is no danger of pulpal irritation from the etchants when they are placed over sound enamel. When they are placed over dentinal or cemental tissue, however, there is danger of pulpal inflammation. This danger increases with the proximity of the acid to the pulp, the concentration of acid used, and the duration of its application. 
    58. 58. Gingival irritation resulted from exposure to upto 50% orthophosphoric acid when the clinician had allowed cotton rolls that were saturated with the acid to remain in the buccal fold for 5 minutes or longer. 
    59. 59. From a practical standpoint, much concern has been voiced about the possible consequences of etching enamel, only to leave it exposed and unbonded. After much investigation, there is no evidence at present indicating any permanent damage to the enamel tissue caused by the etching technique. Several studies indicate that the clinical appearance of enamel that has been etched, but not subsequently bonded, is restored from 48 to 72 hours from etching.
    61. 61. To develop good adhesion, it is necessary to form a microscopically intimate interface. To produce good bonding, there must be good wetting. The ability of an adhesive to wet the surface of the adherend is influenced by. a) Cleanliness of the surface :a) Cleanliness of the surface : Surfaces being joined must be clean. Surfaces are cleaned by application of solvents or acids to dissolve or dislodge contaminants. Clean surfaces are at high-energy state and rapidly absorb contaminants from the air such as moisture and dust.
    62. 62. b) Adsorbed moisture :b) Adsorbed moisture : The major factor that limits spreading of organic phases on clean inorganic surfaces is the presence of adsorbed moisture. An increasing amount of water adsorbed, the critical surface tension continues to decrease and approaches that of a bulk water surface. Therefore, liquid devoid of hydrophilic groups in contact with moisture surface do not spread but instead exhibit appreciable contact angles.
    63. 63. CONTACT ANGLE :CONTACT ANGLE : The extent to which the adhesive will wet the surface of the adherend is generally determined by measuring the “contact angle” between the adhesive and the adherend. Contact angle of Zero degree indicates that spontaneous spreading of the liquid takes place. Contact angle between 0 and 180° indicate poor or incomplete surface wetting by the liquid.
    64. 64.
    65. 65. CLINICAL FACTORS AFFECTING ADHESION 1. Salivary and Blood contamination1. Salivary and Blood contamination These contaminants can influence some dental adhesion concepts in a negativenegative manner. Although dentin is a ‘wet’ substance, the constituents of saliva and blood create an environment that can destroy dentin bonding. Use of a rubber dam or other dry-field aids is necessary to avoid salivary or blood contamination during placement of tooth adhesion materials. Over use of dry field aids may produce another potential problem related to adhesion /
    66. 66. 2. Moisture contamination from Hand pieces or2. Moisture contamination from Hand pieces or Air-water syringesAir-water syringes This is got a negative influencenegative influence. The source of leakage may be due to a) Lack of drying devices on air lines leading from the compressor, allowing wet air to be carried to the syringe or hand piece. b) Condensation of water in air lines. c) Leakage of water through gaskets.
    67. 67. 3. Oil contamination of hand pieces or Air water3. Oil contamination of hand pieces or Air water syringesyringe :- negative influencenegative influence. Oil comes from air compressor. Dentin bonding agent combined with oil contamination provides an unpredictable clinical result and potential clinical failure. Oil filters are placed on the airlines after the air compressor and before the air syringe or hand piece and should be changed frequently. Water and Oil contamination are the most significant negative factors present in tooth adhesion.
    68. 68. 4. Surface roughness of tooth structure4. Surface roughness of tooth structure Positive influencePositive influence. Tungsten carbide steel burs make scratches and irregularities in tooth surfaces, diamonds cut irregularities in tooth structure that are related directly to the size of the diamond particles. Increased surface area created by surface roughness helps in increasing the bond to dentin.
    69. 69. 5. Mechanical under cuts in Tooth preparations5. Mechanical under cuts in Tooth preparations Mechanical undercuts when present helps in holding restorative materials from bodily dislodgment from the preparation, they also resist some microscopic movement of the restorative material caused by thermal or polymerization shrinkage. Therefore restorations with traditional dentin-placed undercuts as well as chemically produced bonding, may produce better clinical resultsproduce better clinical results such as less leakage and less sensitivity.
    70. 70. 6. Fluoride content of teeth6. Fluoride content of teeth Fluoride presence in dentin appears to influence bonding with dentin adhesive agents negatively.negatively. Increased fluoride content of enamel resist acid etching, hence increasing the etching time to allow for acid to degenerate the enamel surface and produce move roughness. 7. Use of Fluoride after Restorations have been7. Use of Fluoride after Restorations have been placedplaced Stannous fluoride gel (pH at 3.6) cause degeneration of zinc-phosphate and glass-ionomer cements. Influence of fluoride on bond of adhesive agent needs additional research.
    71. 71. 8. Dentinal Canal Characteristics8. Dentinal Canal Characteristics Dentinal canals at the external surface of roots or near dentinoenamel junction have small diameters. Dentinal canals closer to the dental pulp become larger, older dentin has small dentinal canals. Dentinal bonding agents use some form of mechanical attachment into dentinal canals. In small canals attachment is less and in larger canals attachment is enhanced.
    72. 72.
    73. 73. 9. Presence of plaque, calculus, extrinsic stain or9. Presence of plaque, calculus, extrinsic stain or debrisdebris Negative influenceNegative influence. After etching, the plaque- covered surface remains shiny and prevents an etch with 37% phosphoric acid. Penetration of plaque by acids used in dentin bonding agents is not possible and clinical adhesive failure will result. Tooth stains and calculus are easier to see and are removed usually, if not the bonding agents will not work. Enamel or dentin tooth surfaces that are expected to bond to resin to other materials should be cleaned thoroughly before attempting bonding.
    74. 74. 10. Presence of bases or liners on prepared teeth10. Presence of bases or liners on prepared teeth (a) Varnish:(a) Varnish: Although reduced tooth sensitivity, they should not be used if bonding of subsequent materials to tooth surface is expected. (b) Glass-ionomer liners :(b) Glass-ionomer liners : Create a moderate bond to dentin but it is lower than the bond created by placing resin on acid-etched enamel. If resin is placed over glass-ionomer liner, the bond of the resin to the tooth can be no stronger than the bond of the glass ionomer to dentin or the bond of the resin to the glass ionomer. (c) Resin Liners:(c) Resin Liners: Resin liners have little or no bond to dentine and subsequent restorations placed over the resin liners have no effect on bond to
    75. 75. 11. Tooth dehydration11. Tooth dehydration Bond strength could be related to wetness of dentin (Prati, Pashley and Montanari 1991). Overdrying can lead to increased tooth sensitivity. Drying only until the obvious shine of moisture is gone is a good clinical guide.
    76. 76. 12. Constituents of Temporary Cements12. Constituents of Temporary Cements Eugenol containing temporary cements or sterate- containing noneugenol temporary cements may have different bonding characteristics to resin. Fresh liquid eugenol placed on dentin or enamel just before attempted bonding could be a negative factor in adhesion.
    78. 78. Adhesive agents must have the ability to wet and then to adhere to hard dental tissues. Dental bonding systems contain monomers that have hydrophilic and hydrophobic groups. Adhesion to tooth structure depends on several factors:Adhesion to tooth structure depends on several factors: 1) There must be intimate contact between the tooth structure and the restorative material. 2) Cavity walls must be clean. 3) Liquid part of the restorative material must wet both enamel and dentin. 4) The surface tension of the liquid must be less than the surface free energy of the enamel and dentin.
    79. 79. A freshly acid-etched enamel surface has a surface energy more than twice that of an un-etched enamel surface and easily wetted by the monomer. Good adhesion after polymerization and good adaptation can only be obtained if the polymerization shrinkage is low.
    80. 80. A gap may be formed at the filling and dentin interface due to: 1. Polymerization shrinkage of the filling material. 2. Adhesive strength to dentin being weaker than the polymerization stress. 3. Stresses developed from the differences in coefficient of thermal expansion of tooth and filling material. 4. Functional occlusal forces A dentin adhesive with an initial strong bond is needed to resist polymerization shrinkage.
    81. 81. Types of Chemical Adhesion :Types of Chemical Adhesion : Two main types 1) Primary valence forces. 2) Secondary valence forces. The strongest and most stable primary valenceprimary valence bondsbonds are the covalent and coordinative bonds, which are both electron pair bonds. Ionic bonds may also give strong adhesion. Secondary valence bondsSecondary valence bonds or intermolecular bonds are classified as Vander waals forces and hydrogen bonds.
    82. 82. Adhesion based on ionic polymers:Adhesion based on ionic polymers: Adhesion of the poly (alkenoic-acid) based materials to apatite can be achieved by ionic bonding with calcium ions acting as bridges. Two types of dental materials zinc carboxylate and glass ionomers are classified as poly alkenoates. Polyalkenoates are based on polyacrylic acid, maleic acid or itaconic acid. Ions diffusing from cement particles or from dentin apaitite allow cationic bridges to be formed between carboxylic groups of the poly (alkenoic acid) and collagen (acidic groups). The ability of glass ionomer to adhere to enamel and dentin, has led to use G.I. as a base of composite resin (McLean 1985)
    83. 83. Adhesion by coupling Agents:Adhesion by coupling Agents: 1) Silane – for Silanization of fillers 3 – methacryloyloxypropyl – tri methoxysilane 2) Another coupling agent was butylacrylate – acrylic acid copolymer with free carboxylic acid groups. 3) Coupling agents utilizing the concept of hydrophobic and hydrophilic groups are the monomers based on phosphates or phosphonates. Scoth Bond (2nd gen) Clearfil New Bond (2nd) Adaptic Dentin Bond Prisma universal Bond (2nd gen) Examples:
    84. 84. Adhesion by Hybrid Zone/Layer:Adhesion by Hybrid Zone/Layer: When the primer is applied to a properly treated dentin surface, they form ‘micro-tags’‘micro-tags’ into the dentin substrate, there by creating a zone ofzone of primer/resin infiltrated dentinprimer/resin infiltrated dentin at the interface. Eg: All Bond IIAll Bond II, ProBondProBond, SyntacSyntac, Scotch bondScotch bond multipurposemultipurpose, prime and Bondprime and Bond.
    86. 86. FACTORS RELATED TO THE ADHERENDFACTORS RELATED TO THE ADHEREND Physiochemical properties of Enamel and the effectPhysiochemical properties of Enamel and the effect of acid etching:of acid etching: # Inorganic content : 96-97 % by weight # Water : 4% # Organic Content : 1% Collagen Bonding to enamel is poor because organic pellicle covers the enamel surface. Etching raises the critical surface tension of enamel. The creation of such a high energy surface together with the increase in bonding area and surface roughness make the bonding of hydrophobic resins possible.
    87. 87. Physiochemical properties of dentin thatPhysiochemical properties of dentin that complicate dentin adhesioncomplicate dentin adhesion The ultrastructure and chemical composition of dentin does not permit micromechanical interlocking as occur with the enamel. Dentin consists 70% hydroxyapatite, 18%70% hydroxyapatite, 18% organic material (Collagen) and 12% material (Collagen) and 12% water. Etching of dentin leaves a sponge-like structure with little compression, tensile or shear strength (Standford 1985 ) .
    88. 88.
    89. 89. The high protein content is responsible for the low surface energy of dentin compared to enamel. Constituents are unevenly distributed in inter and peritubular dentin so the tissue is heterogeneous. The dentinal tubules lodge the odontoblast process as a direct connection to the vital pulp (Yamada and others 1983). Near the pulp, peritubular dentin represents 66% and intertubular dentin only 12% while 22% of the surface area is occupied by water.
    90. 90. DentinalDentinal smear layer and dentin permeabilitysmear layer and dentin permeability When the tooth structure is worked with rotary tools, cutting debris is smeared over the enamel and dentin surfaces. (Pashley 1984 and 1988). EDTAEDTA was found to be the most potent conditioner in removing the smear layer and opening up the orifices of the dentinal tubules. Other Conditioners include:- citric acid, poly acryliccitric acid, poly acrylic acid, Lactic acid, Phosphoric acid.acid, Lactic acid, Phosphoric acid. (In vitro study). The depth of the smear layer depends on the type of instruments and the condition of irrigation employed normally varying from 1 to 5 mm (Elick and others 1970 Pashley 1984).
    91. 91. Smear Layer
    92. 92. Transformed dentin structure due toTransformed dentin structure due to physiological and pathological proceduresphysiological and pathological procedures Transformed dentin structures like carious and eroded dentin, exhibit dentinal tubules that are very narrow and obliterated by deposition of sclerotic dentin and dentin permeability is reduced. Reduced permeability of aged sound dentin attributed to a progressive deposition of peritubular dentin and crystal formation in the tubules. In hypersensitive areas of wedge-shaped erosive cervical areas, 75% of the tubular orifices will be open, where as in insensitive areas of same dentin most of the dentinal tubules are obliterated.
    93. 93. FACTORS RELATED TO THE RESTORATIVEFACTORS RELATED TO THE RESTORATIVE RESINS.RESINS. a) Physical properties of Adhesivesa) Physical properties of Adhesives Primer and adhesive must wet the solid surface, have relatively low viscosity in order to penetrate the microporosites, and be able to displace air and moisture during the bonding operation. Primers contain hydrophilic monomers like HEMAHEMA as surface active agents to enhance the wettability of hydrophobic resins. In addition, solvents like ethanol or acetone assure adequate removal of air and liquid by evaporation.
    94. 94. b) Polymerization contraction of restorative resinsb) Polymerization contraction of restorative resins Dimensional rearrangement of monomers into polymer chains leads to volume shrinkage (Bream 1985, Feilzer 1989). Higher filler loading considerably reduces polymerization contraction. In clinical situations curing contraction is not allowed to develop freely but is restrained by the simultaneously developing bond of the restorative material to the cavity walls (Kemp- Scoholte 1989). This restriction of free contraction induces polymerization contraction stress, which counteracts the developing bond of the restorative resin to the cavity walls.
    95. 95. c) Contraction stress relaxation by Flowc) Contraction stress relaxation by Flow Throughout the entire polymerization process, plastic deformation or flow of the composite resin occurs and partially compensates for the shrinkage stress. (Davidson and De Gee 1984) Restriction of flow capacity by the configurationconfiguration of the restoration enhances the contraction stresscontraction stress (C-factor)(C-factor).. The higher the ratio of free surfacefree surface over bondedbonded resin surfaceresin surface, the more flow may compensate for contraction stress.
    96. 96.
    97. 97. d) Young’s modulus of Elasticityd) Young’s modulus of Elasticity Composites with higher filler content resulting a much higher stiffness or young’s modulus, reduce volumetric contraction but will cause higher contraction stress, which effects the composite dentin interface. Viscous adhesive resins like Scotchbond 2Scotchbond 2 and Visar sealVisar seal produce a thick bonding layer creating artificial “elastic cavity wall” with a low young’s modulus as a buffer between the shrinking restoration and the cavity walls. Clearfil linear bond systemClearfil linear bond system with this concept of an elastic buffer layer providing a low viscosity composite resin as a liner underneath the subsequently applied restorative resin.
    98. 98. e) Initial polymerization sitee) Initial polymerization site Initial setting for chemical cure composite occur at the center part of the bulk material. Initial setting for light cure composite occur towards the light source. For both instances tensile stresses operate across the composite-dentin interface, tearing the material away from the cavity walls.
    99. 99. Fusayama argues that initial setting of chemical – curing resins start at the bottom dentin part of the cavity, due to the locally higher temperature of body heat (1991). By incorporating champhoroquinone in the adhesive resin the polymerization is initiated at the very surface of the dentin, this pretreatment is highly effective in reducing the gap sizes in cavities in both enamel and dentin.
    100. 100. f) Relaxation of contraction stress byf) Relaxation of contraction stress by hygroscopic expansionhygroscopic expansion Polymerization shrinkage is tempered by fluid absorption, which may offset the residual elastic stress. Microfilled composites absorb more water than macrofills due to the greater resin volume. Hygroscopic expansion takes place during the days and weeks immediately following the placement of restoration.
    101. 101. CLASSIFICATION OFCLASSIFICATION OF DENTIN BONDINGDENTIN BONDING SYSTEMSSYSTEMS Dentin bonding agents are often grouped into generationsgenerations, based on their bonding procedures and the relative bond strength they could achieve.
    102. 102. First GenerationFirst Generation “bonding” materials were far more useful for enamel than dentin. These bonding agents were designed for ionic bonding to hydroxyapite or for covalent bonding (hydrogen bonding) to collagen. These materials tended to be hydrophobic. With bond strength of 2 Mpa – 6 Mpa2 Mpa – 6 Mpa, they had a tendency to debond within a short time. The bond strength, was limited by strength of the bond of the smear layer to the dentin.
    103. 103. Materials:Materials: A surface active comonomers, N- phenylglycine glycidyl methacrylate (Bowen, 1965) was developed that acted as a primer or adhesion promoter between enamel / dentin and resin materials by chelating with surface calcium. E.g. Cervident. DisadvantagesDisadvantages 1. Poor bond to dentin familiar amalgam type retentive cavities. 2. Used only for small class III and class V restorations where there was adequate enamel in which to bond. 3. Post operative sensitivity in attempted posterior occlusal restorations.
    104. 104. Second Generation Dentin Bonding SystemsSecond Generation Dentin Bonding Systems Performed better than the 1st generation products. The 2nd generation of dentin adhesives primarily used polymerizable phosphates added to BIS-GMA resins. Adhesives that used phosphate group to promote bonding to the calcium in mineralised tooth structure were referred as phosphate bonding systems. These materials had a weak bond to dentin (4 to 6 Mpa), hydrophobic. The bond strength was limited by relative attachment strength of the smear layer to dentin substrate.
    105. 105. Phosphate ester bonding agentsPhosphate ester bonding agents Based on halo phosphorous esters of BIS-GMA and HEMA commonly known as phhosphate bonding agents. They bond to dentin as a result of interaction between the bonding agent phosphate group and calcium in the tooth structure. Polymethane bonding agentsPolymethane bonding agents Based on polymethane polymers with isocyanate groups believed to bond chemically to amino, hydroxy and carboxy groups on dentinal collagen.
    106. 106. MaterialsMaterials a) Clearfil b) Scotch Bond c) Prisma Universal Bond d) Dentin Adhesit DisadvantagesDisadvantages 1. Weak bond to dentin 2. Mechanical retention form was still necessary since bond strength alone was inadequate. 3. Margins on dentin were problematic since the low dentinal bond strengths permitted extensive marginal microleakage. 4. Restoration failure occurred most commonly due to hydrolytic
    107. 107. Third Generation Bonding SystemsThird Generation Bonding Systems A Newer – generation adhesive system have been developed that use a conditioning step on dentin in conjuction with a bonding agent. Bowen (1982) developed a multistep adhesive system. Importantly third generation adhesives were the frist to bond to metal and ceramics. Components are :Components are : a) Dentin-conditioner b) Dentine primers / adhesive c) Bonding agent
    108. 108. Dentin Conditioners :-Dentin Conditioners :- Are agents that either modify or remove the smear layer and subsequently interact with superficial dentin and rinsed off after application. Brannstrom’s developed a conditioner containing 0.2% EDTAEDTA and 0.1% benzalkonium chloridebenzalkonium chloride as a surface active disinfectant – Eg. 1) 1.0% Nitric acidNitric acid + 2% Phosphoric acidPhosphoric acid + 2.5% Aluminium oxalateAluminium oxalate -eg Tenure. 2) 2.5% Nitric acidNitric acid –eg: Mirage bond. 3) 17% EDTAEDTA – eg Gluma
    109. 109. 4) 2.5% maleic acidmaleic acid & 55% HEMAHEMA) eg Scotchbond –2. 5) 10% maleic acidmaleic acid – eg Scotchbond MP 6) 35% HH33POPO44 – eg a) Scotch bond Dual Cure b) Prisma uni b-3 c) Optibond. 7) HEMAHEMA – eg. All bond 8) 10% HH33POPO44 – eg All bond 2. 9) 10% Citric acid 20% CaclCacl22 – eg Clearfil liner bond.
    110. 110. ChelatorsChelators Chelators are used to remove the smear layer without decalcification or significant physical changes to the underlying substrate. The best chelating conditioner is ethylene diamineethylene diamine tetraacetic acidtetraacetic acid (pH about 7.4) used in GLUMA system. The smear plug in dentinal tubules are not fully removed by 30 second application of the conditioner, this results in a significant hybrid layer formation. Maleic acid (Scotch bond 2) also results in removal of the smear layer but not the smear plug. Although it is quite acidic, it does not appear to decalcify deeply and the hybrid layer is comparatively
    111. 111. LasersLasers A pulsed Nd:YAG laser will not disturb the pulp, even when the approach is as close as 1mm (White & others 1990). The mechanism of dentin removal is microscopic explosions caused by the thermal transients. The lased surface result in desensitized dentin by occlusion of the open and permeable dentianal tubules. Microorganisms and organic debris are eliminated (white & cohen 1991).
    112. 112. White & others (1991) in their study with ScotchScotch bond 2bond 2 concluded that the bond strength increased about 60% after lasing, by increasing the bondable inorganic fraction of the dentin surface. Micromechanical retention may be created by the laser, which is analogous to the effect seen on laser-etched enamel.
    113. 113. MicroabrasionMicroabrasion Microabrasion with aluminium oxide removes healthy as well as diseased dentin and results in a smear layer. The abrasion action depends on the particle size as well as on the velocity. Particle size 0.5 microns or less in diameter do not affect the enamel except to cleanse it. The 0.5 micron or larger particles create a smear on the dentin and increased surface area (Blake 1991)
    114. 114. Dentin Primer / AdhesiveDentin Primer / Adhesive (Adhesion promoters)(Adhesion promoters) A primer is an agent which enhances the wettability of a bonding agent onto the dentinal surface. The primer usually contains an adhesion promoter in a solvent such as water, ethanolwater, ethanol or acetoneacetone. Primers are applied to the surface and dried, presumably leaving the adhesion promoter absorbed on the dentin with hydrophobic gourps exposed to create a favourable surface for the bonding agent ( hydrophilic compatible with dentin). The concept of a self-etching primer has been discussed by Hasegawa and others (1989).
    115. 115. Examples for Dentin primers are :Examples for Dentin primers are : 1. 35% HEMA + 5% Glutaraldehyde –eg. Gluma 2. 55% HEMA + 2.5% maleic acid (self etching primer) eg. Scotchbond 2 3. 5% NTG-GMA + PMDM eg. Tenure 4. Mirage Bond (self etching primers) – 4% NPG & 2.5% Nitric acid 5. 2% NTG-GMA + 16% BPDM – eg. All bond. 6. Prisma universal bond 3 – 30% HEMA; 6% PENTA (Primer)
    116. 116. Fourth Generation Dentin Bonding SystemFourth Generation Dentin Bonding System The fourth generation dentin bonding system are characterized by hybrid zone formationhybrid zone formation in the dentin. The concepts of total etchtotal etch and moist dentinalmoist dentinal bondingbonding (for acetone containing primers) are also hallmarks of the fourth generation materials.
    117. 117. Fifth Generation Bonding SystemFifth Generation Bonding System The current state of the art in bonding materials is the single component bonding systems. This system provide entire priming and bonding sequence in a single liquid and single bottle. Dentin adhesives are based on combinations of conventional hydrophobic resins such as BIS-GMA, together with hydrophilic resins and solvents. HEMA (Hydroxyethyl methacrylate) is often used as a hydrophilic monomer. Acetone, alcoholAcetone, alcohol or a combination of both can be used as hydrophilic solvents. Several systems include water in various quantities to make the compound as an aqueous
    118. 118. MaterialsMaterials 1) Prime & Bond 2) One Step Bond 3) Tenure Quick 4) Syntac single 5) Opti Bond
    119. 119. AdvantagesAdvantages 1) Dentin bond strength are well above 15mpa. 2) Post-operative sensitivity is extremely rare. 3) Some of the 5th generation systems have incorporated fluoride release and elastomeric components to improve marginal integrity. 4) Time saving, and simplicity of use.
    120. 120.
    122. 122.
    123. 123.
    124. 124. Cleaning of Cavity SurfacesCleaning of Cavity Surfaces If interim restorations were placed, the complete removal of temporary cement is the first step. This is preferably performed with hand instruments and pumice brushed over the cavity surfaces, or with an air-powder abrasive device, which proved to be the most effective final cleansing method. Actually, further adhesive procedures mandate that the tooth substrate be perfectly cleaned and decontaminated.
    125. 125. Restoration Try-InRestoration Try-In The influence of precision on the quality of adhesively luted restorations is a confusing issue in the related scientific literature. This problem should be analyzed according to the following different points:
    126. 126. 1. Thickness of the cementing space.1. Thickness of the cementing space. It is now recognized that in thin resin cement layers, the polymerization shrinkage is mainly directed uniaxially (Feilzer et al, 1989). The resulting "wall-to-wall contraction""wall-to-wall contraction" of the composite is therefore largely proportional to its thickness under usual clinical conditions. The marginal fit of semidirect and indirect restorations (composite or ceramic) should lie within 100 microns (Ariyaratnam et al, 1990; Dietschi et al, 1992).
    127. 127.
    128. 128. Internal gaps may be greater (up to 300 microns) because of the use of dye spacers and adjusting procedures. This means that well-fitting restorations will reduce the polymerization strains exerted on the adhesive interfaces and should therefore provide better adaptation and seal.
    129. 129. 2. Compensatory movements.2. Compensatory movements. On the other hand, giving the restoration and tooth the possibility to undergo micro movements during the luting composite contraction partially compensate for the polymerization stresses (Dietschi et al, 1992, 1995; Sorensen and Munksgaard, 1995). In that respect, it is probable that perfectly fitting units will lock inside the cavity during insertion and impede any compensatory movements, such as restoration descent and flexion of remaining walls.
    130. 130.
    131. 131. 3. Adhesion potential.3. Adhesion potential. As already mentioned, numerous studies have demonstrated the advantage of luted restorations regarding adaptation and seal. However, it seems that this benefit is under exploited in the case of direct bonding to dentin when the usual procedures of modern adhesives are applied. Actually, it was shown that adhesive failures often occur between the hybrid layer and luting composite (Dietschi et al, 1995)
    132. 132.
    133. 133. This problem is supposedly related to the compression of the frail collagen network exposed by dentin-etching during restoration insertion, while the hybrid layer structure is not stabilized by cured bonding resin. The same phenomenon and its detrimental consequences on dentin adhesion were described previously in relation to dentin dehydration (Pashley et al, 1994).
    134. 134. It therefore appears pertinent to apply an adhesive lining in each possible case, so that all of the advantages of modern adhesives can be exploited. One has to be aware that traditional lining materials, such as chemical and light-curing glass ionomers, are not appropriate for this because of their insufficient adhesion potential (Dietschi et al, 1995). The combined application of a modern DBA and a mechanically resistant base-lining material is mandatory. For that purpose, only compomerscompomers and filling composite resinsfilling composite resins should be considered.
    135. 135. 4. Wear of the luting cement.4. Wear of the luting cement. Luting composites undergo more wear than the restorative composites (Suzuki et al, 1995; O'Neal et al, 1993) and that occlusal wear is proportional to the interfacial gap (Noack et al, 1992; Leinfelder et al, 1993). Therefore, it seems important to reduce the cementing gap, at least occlusally.
    136. 136.
    137. 137. Practical and clinical considerationsPractical and clinical considerations In clinical conditions, the removal of luting composite excesses is probably the most critical step of the whole procedure. The difficult task is to avoid over-hangs or under-hangs resulting from cementation. Margins providing a satisfactory continuity between the restoration and the tooth will be obtained only in perfectly fitting restorations
    138. 138. Considering all factors, it appears that precise restorations are preferable because they will reduce polymerization stresses within the interfacial gap, limit wear of the cement, and facilitate the removal of cement excesses, providing even restoration margins In larger spaces, satisfactory adaptation and seal may also be obtained as compensatory phenomena take place (Dietschi et al, 1992), but this may result in faster margin degradation. Currently, dentin adhesion is perhaps a perfectible aspect of the technique and requires further research to define the best protocol.
    139. 139. When marginal inaccuracy is found, composite restorations allow corrections to be made. This may be performed very easily after cavity insulation and in situ polymerization of a small amount of restorative composite.
    140. 140. Tightening of proximal contacts may be performed in a similar manner if the surfaces to be corrected are properly roughened and covered with bonding resin, especially with lab-made or post-cured restorations. The ability to perform chair-side restoration corrections before and after luting is a definite advantage of composite resins over ceramics.
    142. 142. Apart from their physicochemical properties, the consistency and working time of the luting cements are two of their basic properties. Sufficient working time is critical to placing the restoration in its correct position and eliminating cement overflow before chemical curing. Unfortunately, working time is inversely related to the efficiency of chemical curing.
    143. 143. This means that the dual-curing materials that provide complete polymerization in dark conditions generally provide insufficient working time! Practically, the working time necessary can vary greatly according to the surface number, general design, and margin accessibility of the restorations. Although it is theoretically contraindicated, changing the paste-catalyst ratio to extend working time may occasionally be mandatory.
    144. 144. The flow and removal of cement from the cementing gap is problematic in proximal areas. In this respect, high viscosity materials permit the cement excesses to be cut rather than wiped off, which generally spreads the luting composite and contaminates larger surfaces.
    145. 145. Surface Treatments
    146. 146. The luting of semi-direct or indirect restorations implies a double bond: one between the luting composite and the tooth, the other between the luting composite and the ceramic or composite restoration.
    147. 147. Tooth SubstrateTooth Substrate A successful marginal adaptation and seal can be achieved when enamel completely surrounds the preparation limits. Where free marginal dentin surfaces exist, the application of a modern dentin bonding agent and resin base is advisable to improve the restoration seal and prevent postoperative sensitivity.
    148. 148. Bonding to CeramicsBonding to Ceramics The composite-ceramic bond generally relies on the standard procedures of ceramic etching with hydrofluoric-based acid and silanization (Simonsen and Calamia, 1983 and 1984) (Fig 10-12). This combination of micromechanical anchorage and chemical coupling proved to be more efficient in vitro than each single procedure (Stangel and Nathanson, 1987; Lacy et ai, 1988; FeU et ai, 1991). The heat curing of the silane can improve the composite-to- ceramic bond (Bailey and Bennet, 1988; Roulet et ai, 1994). Silanes that are activated chairside are preferred to preactivated products. It is noted that, there is a tendency for silanes to undergo hydrolytic degradation.
    149. 149.
    150. 150. Bonding to CompositeBonding to Composite Depending on the fabrication method, the restoration interface is likely to be contaminated by model silicone material, dental hard stone, or insulating media. Consequently, roughening of the internal surfaces is required not only to create microretentions, but also to provide a clean ground for a chemical bond of the luting composite with remaining free radicals, if they still exist. This can be achieved very simply by roughening with coarse diamond burs or sand-blasting (Boyer et ai, 1984; Latta and Barkmeier, 1994; Swift et ai, 1992)
    151. 151. Untreated Treated
    152. 152. The application of a thin adhesive resin layer over the inlay interface is still desirable for good surface wettability. Some clinical and in vitro data questioned the efficiency of these procedures (Tam and Mc Comb, 1991; Scott et al, 1992; Kreci et al, 1994) (Fig 10-14). However, the clinical and SEM follow-up of semi-direct composite inlays made with a modern restorative system did not substantiate these observations, even after several years of service (Gladys et, 1995; Spreafico et al, 1996).
    153. 153. Although the occurrence of partial debonding between luting and restorative composites presumably depends on the materials used, this problem is unlikely to have major clinical significance. Etching with hydrofluoric acidhydrofluoric acid and silanizationsilanization (Matsumura et ai, 1995) of the composite have been proposed to ameliorate this bond
    154. 154. Actually, the etched surface may subsequently be difficult to fully impregnate with resin, which could result in the weakening of this layer.
    155. 155. Clinical ApplicationClinical Application Although it has been advocated, the placement of a matrix prior to cementation is contraindicated because it guides luting material excesses subgingivally. The cement is preferably placed or injected inside the cavity to facilitate manipulation of the restoration. Insertion of the restoration has to follow immediately, as polymerization activa-tion will speed up at mouth temperature.
    156. 156. Clinically, the technique of two-phase insertion (partial insertion-removal of main cement excesses-complete insertion) is tricky and, of course, contraindicated when using a fast- curing dual cement. Overflows of luting composite are removed, before polymerization, with a probe and a brush damped in bonding resin, for accessible margins; floss is best used interproximally. A last consideration is that the restoration has to remain held down during the removal of cement excesses to avoid unpropitious displacement.
    157. 157. Since these conditions are rarely encountered in clinical reality, the use of dual-cure materials is once more validated for the luting of adhesive restorations (Uctasli et al, 1994). Because the efficiency of the chemical activation of dual-cure composites is insufficient, proper light activation remains essential to ensure the optimal curing rate of the material (Breeding et al 1991; Hase-gawa et al, 1991; Darr and Jacobsen,1995; Peutzfeldt, 1995).
    158. 158. Therefore, powerful light-curing is mandatory. It is also strongly recommended that each restoration surface be exposed to the curing light for at least one minute. In this respect, it must be stressed that the bulbs and light guides of the curing units have to be regularly checked with a curing radiometer to make sure they emit sufficient light energy.
    159. 159. Thank you For more details please visit