Restorative Composite Materials 2023-24 PDF

Prof. Dr. Bilinç Bulucu / Restorative Department Composite resins were developed by Dr. Rafeal Bowen in 1960. Dental composites are composed of following materials  Organic matrix or organic phase  Inorganic matrix (Filler or dispersed phase)  Coupling agent (an organosilane)  Activator-initiato...

Prof. Dr. Bilinç Bulucu / Restorative Department Composite resins were developed by Dr. Rafeal Bowen in 1960. Dental composites are composed of following materials  Organic matrix or organic phase  Inorganic matrix (Filler or dispersed phase)  Coupling agent (an organosilane)  Activator-initiator system  Inhibitors  Coloring agents Organic resins When the organic matrix phase is not polymerized sufficiently, waste monomer remains. So undesirable situations can occur: - Allergic reaction - Cytotoxicity - Volumetric shrinkage Resins are: Bis-GMA (Bowen’s resin), Dipentaerythritol pentaacrylate monophosphate, Urethane dimethacrylate (UDMA), Urethane tetramethacrylate, Hexamethylene diisocyanate Fillers Inorganic Phase: These are inorganic filler particles of various shapes and sizes spread in the matrix. In composite resin, the addition of filler  Reduces the coefficient of thermal expansion  Reduces polymerizaton shrinkage  Increases abrasion resistance  Decreases water sorption  Increases tensile and compressive strengths  Increases fracture toughness  Increases flexure modulus  Provides radiopacity  Improves handling properties  Increases translucency Fillers are; - Fused or crystalline quartz, Silicon dioxide, Borosilicate/Lithium aluminosilicate glass, Ceramics, Ytt erbium trifluoride, Radiopaque silicates,  Organically modified ceramics (ORMOCERS) 1 Silane coupling phase: Provides the bonding between the organic polymer matrix and the inorganic phase tightly. Functions of coupling agents - Bonding of filler and resin matrix - Transfer forces from flexible resin matrix to stiffer filler particles - Prevent penetration of water along filler resin interface, thus provide hydrolytic stability Examples: Organic silane. Coloring Agents Coloring agents are used in very small percentage to produce different shades of composites. Mostly metal oxides such as titanium oxide and aluminum oxides are added to improve the opacity of composite resins. Ultraviolet Absorbers They are added to prevent discoloration, in other words they act like a “sunscreen” to composites. Commonly used UV absorber is benzophenone. Initiator Agents These agents activate the polymerization of composites. Most common photoinitiator used is camphoroquinone. Currently most recent composites are polymerized by exposure to visible light in the range of 410 to 500 nm. Initiator varies with type of composites whether it is light cured or chemically cured. Inhibitors These agents inhibit the free radical generated by spontaneous polymerization of the monomers. For example, Butylated hydroxyl toluene (0.01%). PROPERTIES OF COMPOSITE RESTORATIVE MATERIALS Coefficient of Thermal Expansion Coefficient of thermal expansion of composites is approximately three times higher than normal tooth structure. This results in more contraction and expansion than enamel and dentin when there are temperature changes, and this can result in loosening of the restoration. This can be reduced by adding more filler content. Microfill composites show more coefficient of thermal expansion because of presence of more polymer content. Water Absorption Composites have tendency to absorb water which can lead to the swelling of resin matrix, filler debonding and thus restoration failure. Composites with higher filler content exhibit lower water absorption and therefore better properties, than composites with lower filler content. 2 Factors Affecting Water Absorption of Composites • More is the filler content, less is the water sorption • Lesser degree of polymerization causes more sorption • Type and amount of monomer and dilutent also affect water sorption. For example, UDMA based composites show less sorption and solubility. Wear Resistance Composites are prone to wear under masticatory forces or use of tooth brushing and abrasive food. Wear resistance is a property of filler particles depending on their size and quantity. The site of restorations in dental arch and occlusal contact relationship, size, shape and content of filler particles affect the wear resistance of the composites. Factors affecting degradation/wear of composites  Lesser is the polymerization, more is the degradation  Microfilled composites show less of degradation  Hydrolytic degradation of strontium or barium glass fillers can result in pressure built up at resin filler junction. This may cause cracks and fracture of composite restoration  Sudden temperature change can result in disruption in silane coating and thus bond failure between matrix and filler Surface Texture The size and composition of filler particles determine the smoothness of the surface of a restoration. Microfill composites offer the smoothest restorative surface. This property is more significant if the restoration is in close approximation to gingival tissues. Radiopacity Resins are inherently radiolucent. Presence of radiopaque fillers like barium glass, strontium and zirconium makes the composite restoration radiopaque. Modulus of Elasticity Modulus of elasticity of a material determines its rigidity or stiff ness. Microfill composites have greater flexibility than hybrid composite since they have lower modulus of elasticity. Solubility Composite materials do not show any clinically significant solubility in oral fluids. Water solubility of composites ranges between 0.5 and 1.1 mg/cm2. Creep Creep is progressive permanent deformation of material under occlusal loading. More is the content of resin matrix, more is the creep. For example, microfilled composites show more creep since they contain more of resin matrix. 3 Polymerization Shrinkage Composite materials shrink while curing which can result in formation of a gap between resin based composite and the preparation wall. It accounts for 1.67 to 5.68 percent of the total volume. Polymerization shrinkage  In light cured composites, about 60 percent polymerization occurs within 60 seconds, further 10 percent in next 48 hours; remaining resin does not polymerize. Since the material nearest to the light sets first. Shrinkage in light cured composites occurs in the direction of light.  For chemical cured composites shrinkage occurs slowly and uniformly towards the center of restoration. Polymerization shrinkage can result in:  Postoperative sensitivity  Seconder caries  Failure of interfacial bonding (Internal gap)  Fracture of restoration and tooth  Marginal staining Polymerization shrinkage can be reduced by:  Decreasing monomer level  Increasing monomer molecular weight  Improving composite placement technique: Placing successive layers of wedge-shaped composite (1–1.5 mm) decreases polymerization shrinkage  Polymerization rate: “Soft -start” polymerization reduces polymerization shrinkage. 4 Configuration or C-factor The cavity configuration or C-factor was introduced by Professer Carol Davidson and his colleagues in 1980s. The configuration factor (C-factor) is the ratio of bonded surface of the restoration to the unbonded surfaces. The higher the value of ‘C’-factor, the greater is the polymerization shrinkage. Therefore, three-dimensional tooth preparations (Class I) have the highest (most unfavorable) C-factor and thus are at more risk to the effects of polymerization shrinkage. C-factor plays a significant role when tooth preparation extends up to the root surface causing a ‘V’ shaped gap formation between the composite and root surface due to polymerization shrinkage. Microleakage and Nanoleakage  Microleakage: is passage of fluid and bacteria in microgaps between restoration and tooth. It can result in damage to the pulp. Microleakage can occur due to: Polymerization shrinkage of composites  Poor adhesion and wetting  Thermal stresses  Mechanical loading Microleakage can result in bacterial leakage which can further cause discoloration, recurrent caries and pulpal infection.  Nanoleakage: It is passage of fluid/dissolved species in nanosized gaps. These nanosized porosities occur within hybrid layer. These can occur because of:  Inadequate polymerization of primer before application of bonding agent  Incomplete resin infiltration.  Polymerization shrinkage of maturing primer resin.  Nanoleakage can result in sensitivity during occlusal and thermal stresses. 5 Esthetics of Composites Composites have shown good esthetics because of their property of translucency. Composites are available in different opacities and shades so they can be used in different places according to esthetic requirements. But due to oxidation, moisture and exposure to ultraviolet light, etc. some chemical changes can occur in the resin matrix which results in discoloration of composite with time. But improvements in composites like increase in filler content, decrease in tertiary amines and improvement in light curing techniques have shown more stability in composite shade. Biocompatibility Since composites are made from petrochemical products, studies have shown that the major components are cytotoxic if used in pure state. Further biological liability of composite depends upon release of these components from the polymerized composite, which further depend upon type of composite and method used to polymerize it. These products have shown to cause contact allergy in those who regularly handle uncured composite. These have shown to cause: • Inflammation • Toxicity • Mutagenicity • Leaching of TEGDMA, HEMA, etc. • Deposition of plaque on restoration • Allergic response • Genotoxicity • Mutagenicity • Carcinogenicity. Biocompatibility of composites  Unpolymerized monomers are responsible for toxic effects of composites  HEMA is known to cause allergy. Working and Setting Times Light Cure Composites In case of light cure composites, application of light source to the composite material starts the polymerization. Usually, 70 percent of polymerization takes place during the first 10 minutes, though the polymerization reaction continues for period of 24 hours. Self-cure Composites Self-cure composites comes in two pastes. One paste contains the catalyst while other paste contains the amine accelerator. They are dispensed in equal amounts and then thoroughly mixed for 20 to 30 seconds. For mixing, plastic or wooden spatulas are preferred. Use of metal spatula is avoided because inorganic filler particles are abrasive, they can abrade small amount of metal and thus discolor the composite. The working time 6 for self-cure composite resins is 1 to 1 ½ minutes. Once the mix starts hardening, it should not be disturbed for 4 to 5 minutes (setting time). POLYMERIZATION OF COMPOSITES/DEGREE OF CONVERSION • Degree of conversion measures the percentage of carbon-carbon double bonds that have been converted into single bond to form a polymeric resin. • Complete polymerization of the composite is determined by degree of conversion of monomers into polymers. • Strength of resin is directly linked to the degree of conversion. Degree of conversion of the composite is dependent on following factors: Curing Time Curing time depends on different factors like shade of the composite, intensity of the light used, temperature, depth of the preparation, thickness of the resin, curing through tooth structure, composite filling. Shade of Composite It has been seen that darker composite shades polymerize slower when compared to lighter shades. Distance and Angle between Light Source and Resin The recommended distance between light source and resin is 1 mm. Intensity of light decreases as the distance is increased. If the cavity is deep, then use highpower density lamp (about 600 mW/cm2) so that deeper layer is also cured. Polymerization can also be achieved in tooth preparation with deep proximal box by curing from proximal surface. The angle of source should be at 90° to the resin. If angle diverges from 90°, intensity of light decreases. Temperature Composite curing would be less if it is taken out immediately from refrigerator. Composite should be at least kept at room temperature 1 hour before use. Resin Thickness Resin thickness is also one of the main factors for its curing. It should be ideally 0.5 to 1.0 mm for optimum polymerization of resin. Inhibition of Air Oxygen in the air also affects the polymerization of the resin. 7 Intensity of Curing Light Intensity of curing light usually decreases as the lamp ages. Decrease in intensity of light affect the properties of composites significantly. For optimal results, wavelength of light should range between 400 and 500 nm. To make it sure that 400 mW/ cm reaches the first increment of the restoration, a power density of 600 mW/cm is needed. INDICATIONS OF COMPOSITE RESTORATIONS • For restoration of mild to moderate class I and class II tooth preparations of all teeth. • Restoration of class III, IV and V preparations of all teeth especially when esthetics is important. • Restoration of class VI preparations of teeth where high occlusal stress is not present. • Esthetic improvement procedures: – Laminates – Partial veneers – Full veneers – Treatment of tooth discolorations – Diastema closures • To restore erosion or abrasion defects in cervical areas of all the surfaces of premolars, canines and incisors where esthetics is the main concern. • For restoration of hypoplastic or other defects on the facial or lingual areas of teeth. • As core build up for grossly damaged teeth and endodontically treated teeth. • For cementation of indirect restorations like inlays, onlays and crowns. • As a pit and fissure sealants • For periodontal splinting of weakened teeth or mobile teeth • For repair of fractured ceramic crowns • For bonding orthodontic appliances. CONTRAINDICATIONS OF COMPOSITE RESTORATIONS • Wide posterior restorations. • When isolation of operating field is difficult. • Where very high occlusal forces are present. • Class V lesions where esthetics is not the prime concern. • When clinician does not possess the necessary technical skill for the restoration. • When lesion extends extends subgingivally 8 • Patients with high caries susceptibility. • Patients with poor oral hygiene. Advantages of composites ♥ Since composite restoration requires minimal tooth preparation, maximum conservation of tooth structure is possible. ♥ Esthetically acceptable. ♥ Less complex tooth preparation is required. ♥ Composite resin can be used in combination with other materials, such as glass ionomer, to provide the benefits of both materials. ♥ Composites have low thermal conductivity, thus no insulation base is required to protect underlying pulp. ♥ Restorations are bonded with enamel and dentin, hence show good retention. ♥ Restoration with composite resins can be finished immediately after curing. ♥ It can be repaired rather than replaced. ♥ Composite restoration show low microleakage than unfilled resins. ♥ It can be used almost universally. ♥ They have extended working time, this makes their manipulation easier. ♥ Restoration can be completed in one dental visit. ♥ Composite restorations can bond directly to the tooth, making the tooth stronger than it would be with an amalgam filling. ♥ Indirect composite fillings and inlays are heat-cured, increasing their strength. ♥ No galvanism because composite resins do not contain any metals. ♥ Composite resins have adequate radiopacity to enable their detection in radiographs. Disadvantages of composites  Because of polymerization shrinkage, gap formation on margins may occur, usually on root surfaces. This can result in secondary caries and staining.  More difficult, time consuming.  Expensive than amalgam.  More technique sensitive.  Low wear resistance.  Postoperative sensitivity due to polymerization shrinkage.  In large preparation, composites may not last as long as amalgam fillings. References: 1- Textbook of Operative Dentistry. Nisha Garg, Amit Garg 2 nd Ed. 9 Prof. Dr. Bilinç Bulucu/ Restorative Department Composite Resins: The meaning of composite; combining at least two different materials in each other, as an insoluble form is called composite materials. Dental composite resins were developed by Dr. Rafeal Bowen in 1960. CLINICAL PROCEDURES OF COMPOSITE RESINS For achieving optimal results, thorough examination, diagnosis and treatment plan should be finalized before initiating composite restoration. Following steps are undertaken for composite restoration: Steps of clinical procedure for composite restoration  Local anesthesia  Preparation of operating site  Composite selection  Shade selection  Isolation  Tooth preparation  Bonding  Composite placement  Polymerization of composite resins  Final contouring, finishing and polishing of composite restoration Local Anesthesia As and when required, local anesthesia is given in many cases since it makes the procedure pleasant, time saving and reduces the salivation. Preparation of the Operating Site Operating site is cleaned using slurry of pumice in order to remove plaque, calculus and superficial stains prior to the procedure. Composite Selection Composite selection is dependent on: • Position of the tooth preparation: For restoration requiring high mechanical performance, like class IV preparations, large class I, II and class VI, choice of composite is that with the highest inorganic load. For restorations of anterior teeth, esthetics is the main concern. So, composites with submicronic fillers or nanoparticles are preferred in these cases. Composites which are highly polishable are preferred for cervical lesions both in the posterior and in the anterior areas to avoid plaque accumulation on them. • Esthetic requirements: In special cases where esthetics is the main concern like treatment of defective shape, discolored teeth, diastema, malpositioned teeth and for caries in anterior teeth, opacity and the translucency of the composites are to be kept in mind for attaining optimal results. 1 Shade Selection For posterior composite restorations, shade selection is not as critical as for anterior restorations. Sometimes more than one shade is needed to attain optimal esthetics. The number of shades to be used depends on the: • Complexity of the restoration • Polychromatic characteristics of the tooth to be restored • Relationship with adjacent teeth. In cases where the dentin is to be replaced, composites having dentin shade and opacity are preferred while when enamel is to be replaced, composite that has enamel shade and translucency is preferred. Initial Shade Selection The following guidelines are followed for shade matching: • Teeth and shade guide should be wet to simulate the oral environment. • Shade matching should be carried in natural daylight. • The dentin shade is usually selected from the cervical third of the tooth, whereas the enamel shade is selected from its incisal third. • To confirm the final shade, a small increment of selected composite is placed adjacent to the area to be restored and then light cured for matching. Isolation To achieve the optimal results of composite restoration, moisture and salivary contamination must be prevented, in other words isolation is must. Contamination of etched enamel or dentin by saliva results in a decreased bond strength and contamination of the composite material during insertion results in degradation of its physical properties. Isolation is best done by using rubber dam, though it can be done using cotton rolls, saliva ejector and retraction cord. Tooth Preparation Following features are to be kept in mind while doing tooth preparation for direct composite restorations. • Tooth preparation is limited to extent of the defect that is extension for prevention, including proximal contact clearance, is not necessary unless it is required to facilitate proximal matrix placement. • To facilitate bonding, tooth surface is made rough using diamond abrasives. • Pulpal and axial walls need not to be flat. • Enamel bevel is given in some cases to increase the surface area for etching and bonding. • Cavosurface present on root surfaces has butt joint. Designs of Tooth Preparation for Composites The following three types of designs or their combination are most commonly prepared for composites  Conventional  Beveled conventional  Modified (conservative). 2 1. Conventional: Conventional design is similar to the tooth preparation for amalgam restoration, except that there is less outline extension and in tooth preparation, walls are made rough. Indications for conventional tooth preparation • Preparations located on root surface. • Moderate to large class I or class II restorations. Features • Prepared enamel margins should be 90 degree or greater • Butt joint cavosurface margin is made on root surfaces. • The prepared tooth surface is roughened to increase the bonding. 2. Beveled conventional tooth preparation: This design is almost similar to conventional design but some beveled enamel margins are incorporated . A: Beveled cavosurface B. Butt joint no bevel Indications • When restoration is being used to replace an existing restoration exhibiting a conventional design. • To restore a large preparation and especially indicated for classes III, IV, V and VI restorations. 3. Modified (conservative tooth preparation): It is more conservative in nature since retention is achieved by micromechanical bonding to the tooth. 3 Indications: For initial or small carious lesions. Features • Preparation has scooped out appearance. • It does not have specified wall configuration or pulpal and axial wall depth. • Extent and depth of the preparation depends upon the extent and the depth of carious lesion. • In combination preparations, that is part of the preparation is on crown and part is on root, the root surface is prepared as conventional preparation and enamel surface portion is prepared as beveled conventional preparation where enamel margin is beveled. Bonding Adhesion of composites to tooth structure can be attained with any of following methods: • Total-etch involving 3-step adhesives that is etching, priming and bonding. • Total-etch involving 2-step adhesives that is etching and bonding. • Self-etch primers involving 2-step adhesives that is priming and bonding. • Self-etch adhesives involving single step of bonding. Composite Placement Instruments Used for Composite Insertion Following instruments are used for the placement of composites in the prepared tooth. Hand instruments: Hand instruments used for placing composites are usually made up of coating with Teflon so as to avoid sticking of composite to the instrument. These instruments are simple and easy to use but the problem of air trapping during insertion of composite can occur. Composite gun: Composite gun is made up of plastic. It is commonly used with composite filled ampules. For use composite ampules are fitted in the gun and the pressure is applied so that composite comes out from the ampule. Syringe: Composite syringe usually carries the low viscosity composite which can easily flow through needle. This technique has advantage of providing an easy way for placement of composite with decreased chances of air trapping. 4 Irrespective of the location of the restoration, composites should be placed and polymerized in increments. This ensures complete polymerization of the whole composite mass and aids in the anatomical build-up of the restoration. Each increment should not be more than 2 mm in thickness, thickness of more than 2 mm is difficult to cure and result in more polymerization shrinkage stress. Incremental Layering Technique • Advocated for use in medium to large posterior composite restorations to avoid the limitation of depth of cure • This technique is based on polymerization of resin based composite layers of less than 2 mm thickness • It helps to attain good marginal quality • It prevent deformation of the preparation wall • It ensures complete polymerization of the resin-based composite • Incremental layering of dentin and enamel composite creates layers with high diffusion which allow optimal light transmission within the restoration, thus increasing esthetics. Horizontal Technique • In this, occlusogingival layering is done. • It is usually indicated for small restorations. • This technique increases the C-factor. U-shaped Layering Technique • First increment in the form of U-Shape is placed at the base, both gingival and occlusal. • Over that place horizontal and oblique increments to pack the preparation. • Then, curing is carried out from all the sides. 5 Vertical Layering Technique • Place small increments in vertical pattern starting from one wall, i.e. buccal or lingual and carried to another wall • Start polymerization from behind the wall, i.e. if buccal increment is placed on the lingual wall, it is cured from outside of the lingual wall • Reduces gap at gingival wall which is formed due to polymerization shrinkage, hence postoperative sensitivity and secondary caries. Oblique Technique • In this technique, wedge-shaped composite increments are placed to prevent deformation of preparation walls. • It reduces the C-factor. • In this technique, polymerization is started first through the preparation walls and then from the occlusal surface • This technique directs the vectors of polymerization toward the adhesive surface, this is indirect polymerization technique. Three-site Technique • In this technique, polymerization vectors are directed towards the gingival margin • This technique uses clear matrix and reflective wedges. 6 Successive Cusp Build-up Technique • The first composite increment is applied to a single dentin surface without contacting the opposing preparation walls • After this restoration, built up is done by placing wedge shaped composite increments • This technique minimizes the C-factor in three dimensional tooth preparations. Bulk Technique • It is done to reduce stress at the cavosurface margins • It is usually recommended with packable or bulk fill composites. Polymerization of Composite Resins According to polymerization method, the composite resins can be divided into two main categories: 1. Self-curing composites 2. Light-activated composites. Self-curing Composite Resin The earliest self-curing composite resins were mixed as a powder and liquid. Soon after, the composite resins were made available in paste/paste mixed system in form of a catalyst and a base material. One part of this consists of an organic tertiary amine accelerator and the other part consists of benzoyl peroxide initiator. Catalyst and base materials are mixed in a ratio of about 1:1. On mixing, their polymerization process is chemically activated. These chemicals showed poor color stability. Light-activated Composite Resins In the late 1960s and early 1970s, ultraviolet (UV) light cured composite resins were introduced. These composite resins tried to overcome some of the problems of self-cured composites but the problem with UV light polymerization was the limited depth of cure. In late 1970s, visible light curing of composites replaced the UV light curing. Light activation in visible light curing ranges between 460 and 470 nm wavelength. On activation, photoinitiator (camphoroquinone) combines with amine accelerator and releases free radicles which start the polymerization. Since this reaction eliminated the need for tertiary amines, visible light cured composite resins showed improvement in the color stability of composite resins. Curing Lamps Several techniques have been used for curing of light cure composite resins. The various types of light used in curing of composite are: • Tungsten-quartz halogen (TQH) curing unit 7 • Plasma arc curing (PAC) unit • Light emitting diode (LED) unit • Argon laser curing unit. Tungsten-quartz Halogen Curing Unit Tungsten-quartz halogen (QHL) curing unit is conventional and most commonly used curing light for composite resins. It is incandescent lamp which uses visible light in the wavelength in the range of 410 to 500 nm. Halogen bulbs have limited effective lifetime of around 100 hours. At the start of curing cycle, this light emits a low power density (400-900 mW/cm2). It means, there is lesser polymerization at the start of cycle and maximum polymerization at the end of cycle. Disadvantages of this technique are: • Limited bulb life, i.e. 100 hours. • Intensity of bulb decreases with time. • Time consuming. Plasma Arc Curing (PAC) Unit In late 1990’s, this system has been introduced as a means of rapid light curing. Mechanism: In this, high frequency electrical field is generated using high voltage. This field ionizes the xenon gas into a mixture of ions, electrons and molecules, thereby releasing energy in the form of plasma. Light guide helps in filtering the light to spectrum of visible light (450-500 nm) for peak absorption of camphoroquinone. PAC produces high intensity light more than 1800 mW/cm2 curing cycle in PAC is 6 to 9 seconds. Disadvantages of this technique are: • Expensive • Large size. Light Emitting Diode Unit Light emitting diode (LED) unit usually have long life and emits powerful blue light. This light falls in narrow wavelength range of 400 to 500. This corresponds to range of camphoroquinone photoinitiator found in most of composite resins. Advantages • Low power consumption • It can be used with batteries also • It does not require filter • Long life, i.e. 10,000 hours (approximately) • Minimal changes in light output over time. Disadvantage • Only suitable for camphoroquinone based composites (because it has limited wavelength spectrum). Argon Laser Curing Unit Argon laser light has a wavelength of 470 nm which is monochromatic in nature. It produces intensity of 200 to 300 mW. Advantages • Polymerization is uniform, not affected by distance 8 • Greater depth of curing achieved with this light • Degree of polymerization is higher with dark shades as compared to conventional halogen lights. Disadvantages • May affect adjacent restorations • Chances of damage to pulp can occur due to rise in temperature. Attention: - Distance between light tip and composite must be very close. A little distance will cause poor polimerization. - Do not look directly to the light, eyes will be affected. Use a protective barrier while working. - Light output must be checked at regular intervals with Radiometre (Curing light meter). Below there are different modes of light cure lamps: Final Contouring, Finishing and Polishing of Composite Restorations For composite restorations, the amount of contouring required after final curing can be minimized by careful placement technique. Always take care to remove the excess composite which is almost always present. The decreased need of contouring of the cured composite ensures that margins and surface of the composite restoration remain sealed and free of microcracks that can be formed while contouring. The main objectives of contouring, finishing and polishing of final restoration are to: • Attain optimal contour • Remove excess composite material • Polish the surface and margins of the composite restoration. For removal of excess composite burs and diamonds are used. For areas which have poor accessibility, composite strips can be used. Strip must be placed from the non - abrasive middle space and then place down to 1/3 cervical region and then start to abrasive. Do not give harm to the contact point. 9 Final finishing of a composite restoration is done with finishing diamond points (yellow lined burs). Polishing is done using polishing composite rubbers, abrasive discs or pumice impregnated points. Aluminyum discs are used for esthetic anterior restorations like incisal fractures, laminate, diesthema closures. FAILURES IN COMPOSITE RESTORATIONS Composite restorations may show failure because of  Incomplete removal of carious lesion  Incomplete etching or incomplete removal of residual acid from tooth surface  Excess or deficient application of bonding agent  Lack of moisture control  Contamination of composite with finger/saliva  Following bulk placement technique during polymerization of composite  Improper polymerization method  Incomplete finishing and polishing of composites  Inadequate occlusion of restored tooth. Following failures are commonly seen in composite restorations with time;  Discoloration, especially at the margins.  Fracture of margins  Secondary caries  Postoperative sensitivity  Gross fracture of restoration  Loss of contact after a period of time  Accumulation of plaque around the restorations. Marginal Defects in Composite Restorations Marginal defects in composites can occur in following forms: • Surface fracture of excess material • Voids in restoration because of air entrapment during placement • Composite wear resulting in progressive exposure of axially directed wall • Gap formation. Certain guidelines should be followed which can minimize the chances of composite failure: • The tooth preparation should be kept as small as possible since composite in bulk lead to failure • Avoid sharp internal line angles in tooth preparation, which increases stress concentration • In deep preparations calcium hydroxide is placed as liner and above it glass ionomer cement as base material. • Strict isolation regime is to be followed. • Avoid inadequate curing, since it lead to hydrolytic breakdown of composites • Use small increments, holding each increment with Teflon coated instruments. • Fill proximal box separately and create proper contact areas • Composite, especially at the beveled areas, should be finished and polished properly. References: 1- Textbook of Operative Dentistry. 2 nd Ed. 10 11 Prof. Dr. Bilinç Bulucu Composite Application Effect of Enamel Etching: • Cleanses debris from enamel surface (organic matrix of enamel tissue will dissolve and disappear) • Produces a complex three-dimensional microtopography at the enamel surface • Increases the enamel surface area, available for bonding. (The surface energy of the etched enamel surface will increase) • Produces micropores into which there is mechanical interlocking of the resin • Exposes more reactive surface layer, so this will provide better wetting of the enamel by resin and monomer. Steps for Etching Enamel & Dentin • Perform oral prophylaxis procedure using non-fluoridated and oil less prophylaxis pastes. • Clean and wash the teeth with water. Isolate to prevent any contamination from saliva or gingival crevicular fluid. • Apply acid etchant in the form of gel for 20 to 30 seconds for enamel, 15 seconds for dentin tissue. Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth. • Wash the etchant continuously for 10 to 15 seconds with water • Note the appearance of a properly etched surface. It should give a frosty white appearance on drying • If any sort of contamination occurs, repeat the procedure. Difference in appearance of etched and unetched enamel rods Factors affecting effects of acid etching on enamel • Type of acid used in either gel or liquid form (Gel form is advised, it can be controlled) • Concentration of acid used and time of etching (% 37 phosphoric acid) • Type of acid used • Chemical nature of enamel • Whether enamel is fluoridated or demineralized 1 • Type of dentition, i.e. primary or permanent. Among the factors that affect bonding of enamel are its fluoride content, arrangement of crystals and impurities, e.g. presence of magnesium and carbonates in the hydroxyapatite crystals. Acid Etching Steps -Caries is removed and cavity design is prepared. Do not forget to set the clock before applying materials. - Apply acid agent on enamel structure, wait 20-30 second. After 15 second, spread acid on dentin tissue, wait 15 second. 2 * Etching time: For Enamel tissue 20-30 second, For Dentin tissue maximum 15 second. Wash with water (Rinse) nearly 10-15 second. Then gently dry Dry with air 10-15 seconds. Air distance must be 10-12 cm above from tooth surface. After etching, rinsing and drying enamel must be observed frosty (opaque). If the dentist will not see opaque view, then apply extra acid for 10 second more, wash, dry, until the opaque view is seen. The dried surface must remain dry. If the etched surface is contaminated with saliva blood, it must be reetched for another 15 seconds. Adhesive Application 3 Current adhesive strategies Due to adhesives application method there are terms as; Total etch: Apply acid etch on both enamel (20-30second) and dentin structure (15 second). Self etch: No acid etching procedure (%37 phosphoric acid) nor on enamel or dentin . It can be; - Two Step; primer (10 sec) spread, dry & Bonding agent. - One step; Apply adhesive agent on both enamel and dentin. Selektif etch: Only enamel is etched (20-30 second), rinse, dry. Then adhesive agent is applied both on enamel& dentin. * Adhesive agent may have a special application order. Dentist must learn, read the application procedure instructions for each adhesive agent. General application of adhesive agent; - Cavity must be isolated perfectly. Avoid any contamination ( saliva, blood). - Apply bonding agent for 20 seconds actively on all teeth tissue. - Wait 5 seconds to let the solvent evaporate and DRY slightly. - Drying procedure must not be so hard or very slight. The procedure must thin the bonding agent but do not thin too much. There must not remain bonding agent in the cavity (göllenme olmayacak), spread the excessive agent. - Than with light curing unit polymerizate adhesive for 20 second. Tip of the light must be very near to the studying area. After bonding procedure, the surface must have a shiny appearance. Placing Composite Resin - After adhesive application, composite resin will be placed incrementally. There are different placement techniques. None of them are superior. Placing the increment without leaving any void in the material is important for success. - The increment of composite must not exceed 2 mm. Each layer must be polymerized for 20 seconds. If the color is very dark or light apply an extra polymerizing time ( like; 20+ 4 20, 20 +10). In two sided Black cavities the first layer must be placed in the gingival area, and because there will be a distance between the tip of the light cure unit and composite layer, apply an extra curing time (20 +20 seconds). In two sided cavities after removal of matrix and band apply from the buccal and palatinal side extra light ( 10 seconds) for proper polymerization. - There are special tips for curing proximal region. - Composite is placed incrementally into the cavity, and always condanse each layer properly. - When the cavity is filled with composite after placing the last layer on surface give the anotomic morfhology. Never place a lot of composite material, cure and trimm it with burs. This will cause a defect between tooth outline and material. Always remove the excessive material. - After the last cure and restoration is over, finishing & polishing procedures are applied. 5 Thin particule diamond burs (yellow line) are used for finishing. While grinding care should be taken to preserve enamel surface. Procedures must be done only on composite resin. Height control is done with articulation paper. Dark dye areas are eliminated. Then composite is polished with rubber tips under water cooling. Aluminyum disc are used usually at labial anterior restorations (laminate, diesthema closure). * After all of the procedures are finished apply an extra light on occlusal surface and from mesial – distal sides at Black 2 cavities. This procedure is named post cure. (Post cure; after trimming, polishing the composite surface can lose the polymerized top 6 surface, with adding extra light makes the soft composite surface harder). References: 1- Textbook of Operative Dentistry. Nisha Garg, Amit Garg 2 nd Ed. Prof. Dr. Bilinç Bulucu / Restorative Department Bonding to Enamel and Dentin Adhesive systems are performed to enamel and dentin to obtain a good adhesion between resin composites and tooth structure. Indications for Use of Adhesives • To treat carious and fractured tooth structure • To restore erosion or abrasion defects in cervical areas • To correct unaesthetic contours, positions, dimensions, or shades of teeth • To treat dentinal hypersensitivity • For the repair of fractured porcelain, amalgam and resin restorations • For pit and fissure sealants • To bond composite restorations • To bond amalgam restorations • To lute crowns • To bond orthodontic brackets Advantages of Bonding Technique • Adhesion of composite resin restorations to enamel and dentin • Minimizes removal of sound tooth structure • Management of dentin hypersensitivity • Adhesion reduces microleakage at tooth restoration interface • As a part of resin cements for bonding cast restorations • Adhesion expands the range of esthetic possibilities • Bonding of porcelain restorations, e.g. porcelain inlays, onlays and veneers • Reinforces weakened tooth structure • Reduction in marginal staining • For repair of porcelain or composite • Bonding amalgam restorations to tooth • Repairs amalgam restorations • Bonds orthodontic appliances ENAMEL BONDING Enamel, the hardest tissue in the human body consists of 95 percent mineralized inorganic substance, hydroxyapatite arranged in a dense crystalline structure and a small amount of protein and water. To bond to enamel, it is very important to focus on the mineral component (hydroxyapatite) of enamel. Buonocore, in 1955, was the first to reveal the adhesion of acrylic resin to acid etched enamel. He used 85 percent phosphoric acid for etching, later Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel. Usually 37 percent phosphoric acid is used for 15 to 30 seconds. If the concentration is greater than 50 percent, then monocalcium phosphate monohydrate may get precipitated while at concentrations lower than 30 percent, dicalcium phosphate monohydrate is precipitated which interferes with adhesion. Several changes have taken place regarding the acid etching of enamel surfaces. These include: 1 • Development of phosphoric acid gels: Gels provide the clinician a greater control and precision in the placement of etching agents. Earlier most gel etchants used to contain silica as a thickening agent. But recently available gels employ polymeric thickening agents which have better wetting abilities and rinse-off more easily than silica containing gels. • Percentage and form of etchants used: %37 phosphoric acid and gel form is used. Avoid excessive demineralization of the dentin. Decrease in the acid application time: The standard treatment protocol for the etching of enamel has been application of % 37 percent phosphoric acid for 60 seconds. But studies show that enamel should not be etched for more than 15 to 30 seconds. If enamel is etched for more than the required time, deeper etch of the enamel surface occurs. Since a bonding agent has a high viscosity, the surface tension effect of the agent would not allow full penetration of the etched enamel. This will result in a ‘dead space’ beyond the bonded area. When enamel bends, or the weak resin based bond breaks off, the dead space becomes exposed to oral fluids which has lower surface tension and thus penetrates the dead space. This may result in secondary caries or discoloration of the margins. Many acids have been developed recently for conditioning like nitric acid, citric acid and oxalic acids. These acids cause mild etching/conditioning, so for total etching it is advisable to use phosphoric acid. Etching: It is the process of increasing the surface reactivity by demineralizing the superficial calcium layer and thus creating the enamel tags. These tags are responsible for micromechanical bonding between tooth and restorative resin. Steps for Enamel Bonding • Perform oral prophylaxis procedure using nonfluoridated and oil less prophylaxis pastes. • Clean and wash the teeth with water. Isolate to prevent any contamination from saliva or gingival crevicular fluid • Apply acid etchant in the form of gel for 15 to 30 seconds. Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth • Wash the etchant continuously for 10 to 15 seconds • Note the appearance of a properly etched surface. It should give a frosty white appearance on drying • If any sort of contamination occurs, repeat the procedure • Now apply bonding agent and low viscosity monomers over the etched enamel surface. Generally, bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent. The bonding agents due to their low viscosity, rapidly wet and penetrate the clean, dried, conditioned enamel into the microspaces forming resin tags. The resin tags which form between enamel prisms are known as Macrotags. 2 • The finer network of numerous small tags are formed across the end of each rod where individual hydroxyapatite crystals were dissolved and are known as microtags. These microtags are more important due to their larger number and greater surface area of contact. The formation of resin micro and macro tags within the enamel surface constitute the fundamental mechanism of enamel-resin adhesion. Etching of enamel effect: • Cleanses debris from enamel • Produces a complex three-dimensional microtopography at the enamel surface • Increases the enamel surface area available for bonding • Produces micropores into which there is mechanical interlocking of the resin • Exposes more reactive surface layer, thus increasing its wettability. Difference in appearance of etched and unetched enamel rods Factors affecting effects of acid etching on enamel • Type of acid used in either gel or liquid form • Concentration of acid used and time of etching • Type of acid used • Chemical nature of enamel • Whether enamel is fluoridated or demineralized • Type of dentition, i.e. primary or permanent. Read more Among the factors that affect bonding of enamel are its fluoride content, arrangement of crystals and impurities, e.g. presence of magnesium and carbonates in the hydroxyapatite crystals. DENTIN BONDING Bonding to dentin has been proven more difficult and less reliable and predictable than to enamel. This is basically because of difference in morphologic, histologic and compositional differences between the two: • In enamel, it is 95 percent inorganic hydroxyapatite by volume, in dentin it is 50 percent. Dentin contains more water than does enamel. • Hydroxyapatite crystals have a regular pattern in enamel whereas in dentin, hydroxyapatite crystals are randomly arranged in an organic matrix. 3 • The presence of the smear layer makes wetting of the dentin by the adhesive more difficult. • Dentin contains dentinal tubules which contain vital processes of the pulp, odontoblasts. This makes the dentin a sensitive structure. • Dentin is a dynamic tissue which shows changes due to aging, caries or operative procedures. • Fluid present in dentinal tubules constantly flows outwards which reduces the adhesion of the composite resin. Dentin bond strength is quite variable because it is dependent upon the following factors: • Different quality of dentin including the number, diameter and size of dentinal tubules in deep and superficial dentin. Dentin permeability is not uniform throughout the tooth, it is more permeable in coronal dentin than root dentin. There are differences within coronal dentin also. Since tubules are more numerous and wider near the pulp, there is more fluid and less intertubular dentin, this makes dentin bonding less effective in deeper dentin than superficial dentin. • Amount of collagen: As dentin ages, there is an increase in mineralization, the ratio of peritubular/intertubular dentin and a decrease in the number of dentinal tubules which overall affects the adhesion quality of dentin. Adhesive systems consist of; Dentin conditioner and Dentin primer. Conditioning of Dentin Conditioning; It is the process of cleaning the surface and activating the calcium ions, so as to make them more reactive. Dentin Conditioning is necessary to remove or modify the smear layer and to condition dentine and enamel before the application of adhesive materials ( ex: composite, glass ionomer, hybrid ionomers). Conditioner’s purpose is to * Demineralize dentin, * Open the collagen network, * Facilitate monomer infiltration For removal or modification of the smear layer, many acids or/and calcium chelators are used: • Acids: Commonly used acid for conditioning dentin is 37 percent phosphoric acid. It not only removes the smear layer but also exposes the microporous collagen network into which resin monomer penetrates. Usually, it forms exposed collagen fibrils which are covered with an amorphous layer, a combination of denatured collagen fibers and the collapsed residual collagen layer. This is collagen smear layer which is resistant to monomer penetration. It is always preferred to maintain conditioned dentin in a moist state to prevent the collapse of unsupported collagen fibers. Other acids used for dentin conditioning are nitric acid, maleic acid, citric acid, oxalic acid, and hydrochloric acid. • Calcium chelators: These are used to remove and/or modify the smear layer without demineralizing the surface dentin layer. A commonly used chelator is ethylenediaminetetraacetic acid (EDTA). 4 One end is hydrophilic which attaches with fluids from the dentitinal tubules. And the other end Is hydrophobic which attaches to the adhesives Priming of Dentin Primers are agents that contain monomers having a hydrophilic end with affinity for exposed collagen fibrils and a hydrophobic end with affinity for adhesive resin. Commonly used primers have HEMA and 4-META monomers, dissolved in organic solvents (such as water, acetone and ethanol). * Solvent: solvents include acetone, ethanol and water. The solvent affects the evaporation rate on the tray and in the mouth. Acetone evaporates quickly and requires the shortest drying time in the mouth. Ethanol evaporates more slowly and requires moderate drying time. Water evaporates very slowly and requires longest drying time. Bonding agents should be dispensed immediately before use to prevent premature evaporation of the solvent. Primers are used to increase the diffusion of resin into moist and demineralized dentin and thus optimal micromechanical bonding. For optimal penetration of primer into demineralized dentin, it should be applied in multiple coats. Also it is preferred to keep the dentin surface moist, otherwise collagen fibers get collapsed in dry condition resisting the entry for primer and adhesive resin. Note: Hydrophobic monomers interact with restorative materials and copolymerize, while hydrophilic monomers increase the wettability of dental hard tissues. The biggest difference between hydrophilic and hydrophobic adhesives is the chemistry of their monomers and solvents. Systems consist of hydrophobic monomers such as; - Bisphenol A-glycidyl methacrylate (BisGMA) - Urethane dimethacrylate (UDMA), - Viscosity regulators such as triethylene glycol dimethacrylate (TEGDMA) - Wetting agents such as hydroxyethyl methacrylate (HEMA). HEMA: HEMA; can be fully mixed in water and acts as a polymerizable wetting agent perfect for dental adhesives.  2 Hydroxyethyl methacrylate  Has both hydrophilic and hydrophobic ends  Helps in increasing the wettability of hydrophobic agents  Its low molecular weight infiltrates into the dentinal tubules  It retains water within adhesive formulations to decrease bonding  It can polymerize only by linear polymerization so show weak polymerization in high concentrations. Bis-GMA Bis-GMA is much more hydrophobic and when polymerized, absorbs only about 3% water by weight into its structure. The mixture of the two is like an intermediate and serves as a useful adhesive for dental hard tissues. META  4-methacryl-oxyethyl trimellitate anhydride  Contains both hydrophilic and hydropholic ends  Bonds to tooth due to excellant infilteration and chelation with Ca2+ ions as coupling agents  Available as powder (containing PMMA) and liquid (containing MMA, META, TBB)  Used as amalgam bonding agent and as a component in resin luting cement. 5 Moist vs Dry Dentin By etching dentin, the smear layer and minerals from it are removed, exposing the collagen fibers. Areas from where minerals are removed are filled with water. This water acts as a plasticizer for collagen, keeping it in an expanded soft state. Thus, spaces for resin infiltration are also preserved. But these collagen fibers collapse when dry and if the organic matrix is denatured. Collapsed collagen fibers, Blocks the Resin from Reaching Denton surface This obstructs the resin from reaching the dentin surface and forming a hybrid layer. Thus, the desired effect of acid etching, which is increased permeability, is lost. For this reason, presence of moist/wet dentin is needed to achieve successful dentin bonding. When primer is applied to wet/moist dentin, water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules. Sensitivity to dry or moist dentin varies according to the type of solvent used for the primer resin. Reasons for better bonding in moist dentin: • The acetone trails water and improves penetration off the monomers into the dentin for better micromechanical bonding. • Water keeps collagen fibrils from collapsing, thus helping in better penetration and bonding between resin and dentin. Wet Bonding In this, primers consisting of hydrophilic resin monomers dissolved in water miscible organic solvents like ethanol and acetone are used. Acetone-based primers are dependent on a moist dentin surface for hybridization because the acetone displaces water present in the interfibrillar spaces of the collagen network and carry hydrophilic resin along with it for hybridization. Dry Bonding In this, water-based primers are used. Water-based primers are not dependent on moist dentin because of their ability to self-wet a dried dentin surface and thus separating the collapsed collagen fibers. Because we have seen that moist dentin is friendly with all primer types, it is advisable to have moist dentin for resin-dentin bonding. To get moist dentin after etching, do not dry the dentin with compressed air after rinsing away etchant. Instead use high-volume evacuation to remove excess water and then blot the remaining water present on the dentin surface using gauze or cotton to leave dentin optimally moist. 6 If the dentin surface is made too dry  Collapse of the collagen fibers and demineralized dentin occurs  This results in low bond strength because of ineffective penetration of the adhesive into the dentin. Overdrying of dentin causes collapse of collagen fibers and thus ineffective penetration of adhesive If the dentin surface is too wet One cannot check for the “frosted” etch appearance of the enamel There is reduction in bond strength because:  Presence of water droplets dilute resin primer and out-compete it for sites in the collagen network which prevents hybridization The phase changes occur in the ethanol or acetone based resins. If dentin is overwet, presence of water dilutes the monomer and competes it for sites in collagen network. This lowers the bond strength FAILURE OF DENTIN BONDING for failure of dentin bonding Dentin can show poor bonding because of following reasons:  Variable structure of dentin  Contamination of dentin with sulcular fluid or saliva  Structural changes of dentin close to the pulp make it difficult to bond  Thickening of bonding agent because of evaporation of solvent.  This reduces the penetration of the bonding agent.  Contamination of tooth surface by lubricants used in handpieces  Any contact of tooth surface with blood, can result in decrease in bond strength. References: 1- Textbook of Operative Dentistry. Nisha Garg, Amit Garg 2 nd Ed. 7 Reminder notes from the second class (2022-2023) lecture notes: 1- Smear layer: As a result of the tissue removal procedures performed during cavity preparation by using milling tools, the dentine surface is covered by a smear layer consisting of blood, saliva, bacteria, hydroxyapatite crystals and denatured collagen. The smear layer, which protects the dentin and pulp tissue against irritation, is about 0.5-2 µm thick and is porous and amorphous in appearance. The different thickness of the smear layer also causes differences in the permeability of dentin tissue. Dentin tubule mouths are clogged with smear plugs, which reach a depth of 1 to 10 µm of tubules. These smear plugs are a continuation of the smear layer consisting of fragmented and denatured hydroxyapatite. There are various opinions about the removal or modification of this layer, which is effective in adhesion bonding. Some of the researchers have argued that the smear layer creates a barrier for rnicroorganisms to reach the pulp, and have reported that with removal of this layer, dentin permeability will increase 5-10 times. Another group of researchers have shown that the smear layer is a shelter for bacteria to settle and multiply. 2- Current classification (according to clinical application types)  Etch&rinse (ER) adhesives -Three-stage etch & rinse (ER) adhesives (Fourth generation) -Two-stage etch & rinse (ER) adhesives (Fifth generation)  Self-etch adesives - Two-component self-etch adhesives (Sixth generation) -One-component and one-stage self-etch adhesives (Seventh generation) (All-in-one) - Eighth generation -Universal (Multi-mode) 3- Hybrid Layer The hybrid layer was first identified by Nakabayashi in 1982 and expressed as a mixture of demineralized dentin compounds and polymerized adhesive resin at molecular-level. After demineralization of the dentin surface by acidification process, collagen fibrils are released. Low-viscosity monomers fill the nano-cavities formed by 8 demineralized hydroxyapatite crystals by penetrating into this region and surround the collagen. By polymerization process, adhesive resin is micromechanically bonded with dentin collagens. This resin-reinforced, acid-resistant layer is called “hybrid layer”. The main binding mechanism of adhesive restorative materials is based on the formation of the hybrid layer. Hybridization; is the process of formation of a hybrid layer. Diagrammatic representation of hybrid layer 4- Resin Tags: Adhesive resin extensions directed/flowing into open dentin tubules are called “resin tags”. The structure of these tags varies according to the; - Application technique of acid, -The thickness of the remaining dentin, -The surface moisture and structure of the dentin. When the peritubular dentin is removed from the tubule wall by the acidification process, the adhesive resin diffuses into the demineralized matrix. After polymerization, resin tags are attached to the tubul