Factors affecting the accuracy of indire

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Published on October 11, 2009

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Factors affecting the accuracy of indirect restorations : Factors affecting the accuracy of indirect restorations Presented by Dr Gaurang Matariya MDS Part - I DEPARTMENT OF CONSERVATIVE DENTISTRY,ENDODONTICS AND AESTHETIC DENTISTRY Content : Introduction. Tooth factors. Impression recording. Wax pattern. Investing. Casting. Pre-cementation adjustment,finishing and polishing. Cementation. Final finishing and polishing. 11 October 2009 2 Content Introduction : Indirect restoration is divided into : 11 October 2009 3 Introduction Slide 4: The cast metal restoration is versatile and is especially applicable to class II preparation. To be satisfactory, the restoration procedure requires meticulous care both in preparation and in proper manipulation of dental materials, and the dentist and the laboratory technician must be devoted to perfection. The high degree of satisfaction and service derived from a properly made cast metal restoration is a reward for the painstaking application required. 11 October 2009 4 Slide 5: Tooth-colored indirect systems include laboratory- processed composites or ceramics such as porcelain fired on refractory dies or hot pressed glasses. In addition, at least one chairside computer-aided design/computer-assisted manufacturing( CAD/CAM) system is currently available and is used to fabricate ceramic restorations. 11 October 2009 5 Slide 6: Restorations made using indirect techniques require a high level of operator skill. A devotion to excellence is necessary during preparation, impression, try-in ,cementation and finishing the restoration. Diligence is required during all stages of the process to obtain a high-quality restoration. 11 October 2009 6 Tooth factors : Non-metallic restorations: Before beginning any procedure, the clinician should have decided what type of restoration is indicated. Compromised restoration should be completely removed. 11 October 2009 7 Tooth factors Slide 8: Preparations for indirect tooth colored restorations basically are meant to provide adequate thickness for the restorative material and at the same time a passive insertion pattern with rounded internal angles and well defined margins. All margins should have a 90 degree butt-joint cavosurface angle to ensure marginal strength of the restoration. 11 October 2009 8 Slide 9: All line and point angles, internal and external, should be rounded to avoid stress concentrations in the restoration and tooth,thereby reducing the potential for fractures. 11 October 2009 9 Slide 10: The carbide bur or diamond used for tooth preparation should be a tapering instrument that creates occlusally divergent facial and lingual walls. The junction of the sides and tip of the instrument should be rounded. 11 October 2009 10 Slide 11: Divergence can be increased from cast metal restoration because tooth colored restoration will be adhesively bonded and because very little pressure can be applied during try-in and cementation. There should be no undercuts that would prevent the insertion or removal of the restoration. Small undercuts can be blocked out using a GIC liner. 11 October 2009 11 Slide 12: The facial ,lingual and gingival margins of the proximal boxes should be extended to clear the adjacent tooth by at least 0.5 mm. These clearances will provide adequate access to the margins for impression material and for finishing and polishing instruments. The gingival margin should be extended as minimally as possible because margins in enamel are greatly preferred for bonding and because deep gingival margins are difficult to impress and to isolate properly during cementation. 11 October 2009 12 Slide 13: During, preparation stains on the external walls ,such as those often left by corrosion products of old amalgam restorations should be removed. Such stains could appear as black or gray lines at the margin after cementation. 11 October 2009 13 Slide 14: Metallic restoration: Evaluate the occlusal relationships in maximum intercuspation where the teeth are brought into full interdigitation and the occlusal contacts that occur during mandibular movements. 11 October 2009 14 Slide 15: No. 271 and the No. 169L burs are recommended for inlay cavity preparation. The marginal bevels are placed with a slender, fine-grit, flame shaped diamond instrument, such as the No. 8862. 11 October 2009 15 Slide 16: General rule is to maintain the long axis of the bur parallel to the long axis of the tooth crown at all times. 2 to 5 degree taper. 11 October 2009 16 Slide 17: The facial and lingual extension in the mesial pit region should provide the desired dovetail retention form, which resists distal displacement of the inlay. 11 October 2009 17 Slide 18: Remove remaining caries if present and build up with light cure GIC. 11 October 2009 18 Slide 19: The slender flam shaped, fine grit diamond instrument is used to bevel the occlusal and gingival margins. This should result in 30 to 40 degree marginal metal on the inlay. Width of the occlusal bevels – one fourth the depth of the respective wall. 11 October 2009 19 Slide 20: While cutting the gingival bevel, reduce the rotational speed to increase the sense of touch, otherwise overbeveling may result. The instrument should be tilted slightly mesially to produce a gingival bevel with the correct steepness to result in 30 degree marginal metal. The gingival bevel should be 0.5 to 1 mm wide. 11 October 2009 20 Impression recording : The impression material used for the final impression should have the following properties. It must become elastic after placement in the mouth. It must have adequate strength. It must have adequate dimensional accuracy, stability and reproduction of detail. Must be free of toxic or irritating components. 11 October 2009 21 Impression recording Impression materials : Reversible agar hydrocolloid. Irreversible alginate hydrocolloid. Polysulfide rubber base. Condensation polymerization silicone rubber base. Additional polymerization silicone rubber base. Polyether rubber base. 11 October 2009 22 Impression materials Irreversible alginate hydrocolloid : If the impression is porous, this could result from whipping air into the mix during spatulation. After the powder has been wetted by the water, the alginate should be mixed so as to squeeze the material between the spatula blade and the side of the rubber bowl. 11 October 2009 23 Irreversible alginate hydrocolloid Slide 24: Distortion may occurs if the tray moves during gelation or if the impression is removed prematurely. Amount and duration of compression should be considered, since the weight of the tray can compress or distort the alginate. If the impression is not poured immediately, distortion could occur. 11 October 2009 24 Polysulfide rubber base : Too much load cause distortion. Because recovery after deformation is dependent on the amount and duration of loading. Improper removal from the mouth. Rapid removal. 11 October 2009 25 Polysulfide rubber base Slide 26: Premature removal from the mouth may lead to loss of detail. Removal prior to sufficient polymerization or before the material is sufficiently elastic will result in inaccurate registration of detail. This may also result from incomplete mixing or movement of the tray prior to the time of removal could also cause loss of detail. 11 October 2009 26 Slide 27: Surface bubbles or voids may caused by the incorporation of air into the mix. The impression material should always be mixed carefully with only the flat surface of the blade. If the material is partially polymerized prior to insertion in the mouth, voids may occur in the impression. 11 October 2009 27 Condensation silicone rubber base : Distortion may cause if incorrect separation from impressed structures. Failure to remove the impression in a rapid, jerking motion. If there is inadequate support of the impression after removal from the mouth. Excessive delay in poring cast (30 min or more). 11 October 2009 28 Condensation silicone rubber base Additional silicone rubber base : Loss of detail could occur if unmodified addition silicones are used. These hydrophobic materials cannot displace any moisture or hemorrhage that is not removed prior to placement of the impression material. 11 October 2009 29 Additional silicone rubber base Slide 30: The stone surface may appear porous if hydrogen gas is evolved. If this is the case, it is recommended that the pouring of dies be delayed for at least 1 hour. Distortion occur if the polysiloxane adhesive does not provide adequate retention. Mechanical retention may be required in combination with the adhesive. 11 October 2009 30 Polyether rubber base : The impression may distort due to moisture absorption and plasticizer extraction. These phenomena may result in dimensional change when impressions are stored in high-humidity environments or are exposed to water. Delay in impression placement may cause distortion. 11 October 2009 31 Polyether rubber base Slide 32: The choice of impression material is usually made by comparisons of cost, ease of use, working time, shelf life and pleasantness of odor, taste and color. The most common impression materials used for the indirect casting technique are the polyvinyl siloxanes. 11 October 2009 32 Tissue retraction : When margins are subgingival, it is necessary to use retraction cord to temporarily displace the free gingiva away from the tooth and to control the flow of any gingival hemorrhage and sulcular fluids. The objective of gingival retraction is to widen the gingival sulcus to provide access for the impression material to reach the subgingival margins in adequate bulk to resist tearing during impression withdrawal. 11 October 2009 33 Tissue retraction Impression technique : Most dental manufacturers offer their polyvinyl siloxane impression materials in automix dispensing systems. The advantages are speed, consistent and complete mixing of accelerator and base paste. 11 October 2009 34 Impression technique Slide 35: The incorporation of very few air voids during mixing and delivery to the teeth. This technique requires two viscosities of impression material, a light bodied to inject around the preparation and heavy bodied to fill the tray. 11 October 2009 35 Slide 36: 11 October 2009 36 Slide 37: All preparation surfaces should be clean, dry, and exposed to view. To avoid trapping air, keep the tip directly on the gingival and pulpal walls. Light bodied also injected on the occlusal surface of unprepared adjacent teeth to eliminate trapping of air on the occlusal grooves. 11 October 2009 37 Wax patterns : Types of wax The ADA specification No. 4 for dental inlay casting wax covers two types of inlay wax. Type I – Medium wax ( for direct technique) Type II- Soft wax ( for indirect technique) 11 October 2009 38 Wax patterns Slide 39: FLOW The maximum flow permitted for type- I waxes at 370 C is 1%. The low flow at this temperature permits carving and removal of the pattern from the prepared cavity at oral temperature without distortion. Both type I and type II waxes must have minimal flow of 70% and a maximum flow of 90% at 45 0 C. 11 October 2009 39 Slide 40: At approximately this temperature, the wax is inserted into the prepared cavity. If the wax does not have sufficient plasticity, it will not flow into all of the areas in the preparation and reproduce the required detail. 11 October 2009 40 Slide 41: Inlay wax has high coefficient of thermal expansion. Wax may expand as much as 0.7% with an increase in temperature 20 0 C or it may contract as much as 0.35% when it is cooled from 37 0 to 25 0 C. This is one of the disadvantages of waxes when they are used in direct technique. 11 October 2009 41 Wax distortion : Wax distortion is probably the most serious problem that can occur during forming and removal of the pattern from the mouth or die. This distortion results from thermal changes and the relaxation of stresses that are caused by contraction on cooling, occluded air, molding, carving, removal and the time and the temperature of storage. 11 October 2009 42 Wax distortion Slide 43: There are four ways of minimizing pattern distortion. First of all , wax for the direct technique should be heated uniformly at 500 C for 15 minutes before heat. The pattern should be invested quickly. The rigid walls of the set investment constrain the pattern and reduce distortion due to recovery and residual stress. 11 October 2009 43 Slide 44: The pattern should be stored at a low temperature if not invested right away. Elastic recovery is slower at low temperatures therefore, if immediate investing is impractical, storage in a refrigerator is preferred. If a pattern is refrigerated,however, it should be allowed to warm to room temperature before investing. 11 October 2009 44 Slide 45: Finally, it is essential that no wax residues are left in the mold after burnout in the lost wax process. Residues will result in poor casting because of inclusions or incomplete margins. 11 October 2009 45 Slide 46: Preparation of wax pattern Lubricate the die and incrementally add liquid wax from wax spatula by the “flow and press” method to form the proximal, facial and lingual surface aspects of the pattern. Add thin layer on the occlusal surface. Wax shrinks as it cools and hardens and therefore tends to pull away from the die. 11 October 2009 46 Slide 47: This effect can be minimized and pattern adaptation thus improved, by applying finger pressure for at least several seconds on each increment of wax soon after surface solidification and before any subsequent wax additions. In this incremental technique, the wax is flowed on the previously applied wax must be hot enough,or else voids will be formed. 11 October 2009 47 Slide 48: Lack of a proximal contact is usually undesirable because it opens the possibility of proximal drifting of teeth, shifting occlusion, food impaction and damage to the supporting tissues. There must be a continuous adaption of wax to the margins, with no voids, folds or faults. If adaptation is questionable, remelt the marginal wax to a distance into pattern of approximately 2 mm. 11 October 2009 48 Slide 49: Apply finger pressure immediately after surface solidification and before subsequent cooling of the wax, maintaining this pressure for at least 4 seconds. This finger pressure helps develop close adaptation to the die by offsetting the cooling shrinkage of the wax. Wax that is along the margins is now carved back to the cavosurface outline with a warmed No.7 wax spatula with light pressure so that the margins will not be damaged. 11 October 2009 49 Investing : The wax pattern should be cleaned of any debris, grease or oils. A commercial wax pattern cleaner is used. Any excess liquid is shaken off and the pattern is left to air-dry while the investment is being prepared. The thin film of cleanser reduces the surface tension of the wax and permits better wetting of investment . 11 October 2009 50 Investing Slide 51: Now the distilled water is added to a clean,dry mixing bowl and the powder is gradually added to the liquid with care to minimize air entrapment. Mixing is performed gently until all the powder has been wet. Mechanical mixing under vacuum removes air bubbles created during mixing and evacuates any potentially harmful gases produced by the chemical reaction of the high-heat investment. 11 October 2009 51 Slide 52: For investing by hand, the entire pattern is painted with a thin layer of investment. With vacuum investing, the same equipment used to mix the investment is employed to invest the pattern under vacuum. The amount of porosity in the investment by vacuum is reduced. Excessive vibration should be avoided which may cause solids in the investment to settle and may lead to free water accumulation adjacent to the pattern,resulting in surface roughness. 11 October 2009 52 PART - II : Casting. Pre-cementation adjustment,finishing and polishing. Cementation. Final finishing and polishing. 11 October 2009 53 PART - II Casting : Causes of defective castings Defects in casting can be classified under four headings: Distortion. Surface roughness and irregularities. Porosity. Incomplete or missing detail. 11 October 2009 54 Casting Slide 55: Distortion Distortion of the casting is probably related to a distortion of the wax pattern. It can be minimized by proper manipulation of the wax and handling of the pattern. Some distortion of the wax pattern occurs as the investment hardens around it. Less the setting expansion of the investment, the less the distortion. 11 October 2009 55 Surface roughness,Irregularities, and Discoloration : Air bubbles Best method to avoid air bubbles is to use the vacuum investing technique. If a manual method is used, the use of a mechanical mixer with vibration both before and after mixing should be practiced. 11 October 2009 56 Surface roughness,Irregularities, and Discoloration Slide 57: Rapid heating rates: This factors may result in fins or spines on the casting. The mold should be heated gradually, at least 60 min should elapse during the heating of the investment-filled ring from room temperature to 7000 C. The greater the bulk of the investment, the more slowly it should be heated. 11 October 2009 57 Liquid/Powder Ratio : The amount of water and investment should be measured accurately. The higher the L/P ratio, the rougher the casting. If too little water is used, the investment may be unmanageably thick and cannot be properly applied to the pattern. 11 October 2009 58 Liquid/Powder Ratio Slide 59: Prolonged heating When the high-heating casting technique is used, a prolonged heating of the mold at the casting temperature is likely to cause a disintigration of the gypsum-bonded investment and the walls of the mold are roughened as a result. 11 October 2009 59 Casting pressure : Too high a pressure during casting can produce a rough surface on the casting. A gauge pressure of 0.10 to 0.14 MPa in an air pressure casting machine or three to four turns of the spring in an average type of centrifugal casting machine is sufficient for small castings. 11 October 2009 60 Casting pressure Composition of the investment : The ratio of the binder to the quartz influences the surface texture of the casting. In addition, a coarse silica causes a surface roughness. If the investment meets ADA specification No.2, the composition is probably not a factor in the surface roughness. 11 October 2009 61 Composition of the investment Foreign bodies : Any casting that shows sharp, well defined deficiencies indicates the presence of some foreign particles in the mold, such as pieces of investment and bits of carbon from a flux. Surface discoloration and roughness can result from sulfur contamination,either from investment breakdown at elevated temperatures or from a high sulfur content of the torch flam. 11 October 2009 62 Foreign bodies Porosity : Porosity may occur both within the interior region of a casting and on the external surface. Internal porosity does not only weaken the casting but if it also extends to the surface,it may be a cause for discoloration. If severe it can cause plaque accumulation at the tooth-restoration interface and secondary caries may result. 11 October 2009 63 Porosity Slide 64: Porosities in castings may be classified as I. Solidification defects A. Localized shrinkage porosity. B. Microporosity. II . Trapped gases A. Pinhole porosity. B. Gas inclusions. C. Subsurface porosity. III. Residual air 11 October 2009 64 Localized shrinkage porosity : Localized shrinkage is generally caused by premature termination of the flow of molten metal during solidification. The linear contraction of noble metal alloys in changing from a liquid to a solid is at least 1.25%. Therefore continual feeding of molten metal through the sprue must occur to make up for the shrinkage of metal volume during solidification 11 October 2009 65 Localized shrinkage porosity Prevention : Use of large reservoir in the sprue close to the pattern. Use of sprue thickness more than the thickest portion of the pattern. Attaching one or more 18 gauge sprues. 11 October 2009 66 Prevention Microporosity : It also occurs from solidification shrinkage but is generally present in fine-grain alloy castings when the solidification is too rapid for the microvoids to segregate to the liquid pool. This type of defect is not detectable unless the casting is sectioned, and generally it is not a serious defect. Temperature of casting should be high. 11 October 2009 67 Microporosity Pinhole and Gas inclusion porosities : They are related to the entrapment of gas during solidification. Both are characterized by a spherical contour, but they are decidedly different in size. Gas inclusion porosities are usually much larger than pinhole porosity. It can be minimized by pre-melting the gold alloy on a graphite crucible or a graphite block, if alloy has been used before, and by correctly adjusting and positioning the torch flame during melting. 11 October 2009 68 Pinhole and Gas inclusion porosities Pre-cementation adjustment,finishing and polishing : The main objectives of this phase of cast restoration fabrication are to determine that casting recovered from the investment has reproduced all bulk and surface details that were present in the wax pattern, to detect any discrepancy in the casting and determine whether or not it is correctable, to modify, as necessary, the casting to insure that it fits and covers all details of the preparation internallly and marginally. 11 October 2009 69 Pre-cementation adjustment,finishing and polishing Slide 70: Gross excesses: The tooth surface and circumferential tie constituents of the casting are examined visually and compared to the tooth and cavity preparation surface. Any noticeable excesses detected should be ground away, being careful not to injure, crack or perforate the circumferential tie constituents of the casting. 11 October 2009 70 Slide 71: Fine excesses: The casting is now tried on the die to evaluate its fit. It should be examined using magnifying lens. Pressure indicating pastes or water soluble dyes are available to aid in locating descrepancies. Fine excesses are usually in the form of veins, small nodules etc, which should be removed with extreme care. 11 October 2009 71 Rocking : If the casting rocks from side to side while on the die, it should be carefully watched while it is rocked in a slow motion and the fulcrum of this rocking should be determined. At this fulcrum,internal or marginal excesses or bent margins may be found, it should be trimmed very cautiously. 11 October 2009 72 Rocking Gross marginal deficiencies : This presence necessitates that the casting be done over, insofar as they will interfere with the strength, retention and caries prevention capabilities of the restoration. 11 October 2009 73 Gross marginal deficiencies Fine marginal deficiencies : If the deficiencies are internal in the form of blebs, pores, unreproduced details etc. and they do not involve critical retention areas, they may be allowed to remain, if few in number and isolated. Burnishing will not be done at this stage, circumferential tie casting constituents are to be burnished only once, for fear of brittle fracture of these very non-bulky cross sections. 11 October 2009 74 Fine marginal deficiencies Surface pores or deficiencies : If isolated and small in dimension, can be corrected by adding solder for alloys or porcelain for cast ceramics. If they are gross and multiple, the casting should be done over. 11 October 2009 75 Surface pores or deficiencies Contacts : The casting should now properly fit the die. Now on the working cast contact with the adjacent teeth is checked. If an excess is present, the die with the cast will not seat or the cast will loosen from the die. Excesses should be removed carefully in small increments. 11 October 2009 76 Contacts Contour : Any gross excess should be ground away. If surface porosity discoloration or gross excesses cannot be corrected by grinding and finishing without compromising the casting contour, the casting should be done over. 11 October 2009 77 Contour Occluding surfaces : With the casting in place in the working model, the articulator is moved in all possible movements, being sure the casting is immobile. To ensure this casting should be cemented with water soluble adhesive. Any prematurities should be removed. 11 October 2009 78 Occluding surfaces Finishing and polishing : Gross finishing: This should remove roughness imparted on the casting from the investment mold walls, eliminate surface discoloration not removed by pickling and eliminate fine excesses and obliterate minute defects. It is done using abrasive stones and discs, ranging from sand and silicone carbide to alumina, until no surface discrepancies are detected. 11 October 2009 79 Finishing and polishing Slide 80: Final lustre: This creates a reflective,non-adhesive surface. It is done using rouge on a felt cone or wheel. The alloy surface should be extremely shiny by the end of this stage. The entire oral surface of cast alloys should be finished and polished with the exception of the circumferential tie constituents. 11 October 2009 80 CEMENTATION : Metallic restoration: The selection of cement for permanent cementation is very important to the success of final restoration. To obtain optimal performance from the cement, carefully follow the manufacturer’s instructions for dispensing, mixing and application. 11 October 2009 81 CEMENTATION Slide 82: Before cementing the casting, isolate the tooth from saliva with the aid of cotton rolls. With the air syringe, dry the preparation walls, but do not desiccate them. With the cement mix applied generously to the preparation side of the casting, start the casting to place with the fingers or with operative pliers. 11 October 2009 82 Slide 83: Next, place the ball burnisher in the pit areas, exerting firm pressure to seat the casting. Then place a Burlew disc over the casting, remove the saliva ejector,and request the patient to close and exert biting force. When the disc is removed,much of the occlusal area should be clean of the cement mix and therefore easier to inspect and verify complete seating of casting. 11 October 2009 83 Slide 84: After the cement has hardened, excess is cleaned off with an explorer and air-water spray. Dental floss should be passed through the contact, carried into the interproximal gingival embrasures and sulci, and pulled facially and lingually to help in the removal of cement in this region. Tying a small knot in the floss will help dislodge small bits of interproximal cement. 11 October 2009 84 Slide 85: When cementing has been properly accomplished, a cement line should not be a visible at the margins. 11 October 2009 85 Non-metallic restoration: : For most laboratory-processed composite inlays/onlays, the resin matrix has been polymerized to such an extent that few bonding sites are available for the composite cement to chemically bond to the internal surfaces of the restoration. To improve the bond of the cement to the processed composite restoration, some systems require the use of a solvent to soften the internal surfaces of the restoration before cementation. 11 October 2009 86 Non-metallic restoration: Slide 87: Other systems recommend sandblasting the inside of the composite restoration with aluminum-oxide abrasive particles to increase surface roughness and surface area for bonding. For ceramic inlays and onlays, hydrofluoric acid is usually used to etch the internal surfaces of the restoration. 11 October 2009 87 Slide 88: Such acid-etching increases surface relief and therefore not only increases the surface area,but also results in micromechanical bonding of the composite cement to the ceramic restoration. Chairside ceramic etching is done with a 2- minute application of 10% hydrofluoric acid on the internal surfaces of the inlay/onlay. 11 October 2009 88 Slide 89: After etching, the ceramic is treated with a silane coupling agent to facilitate chemical bonding of the composite cement. Clear plastic matrix strips may be applied in each affected proximal area and wedged. A dual-cure composite cement is mixed and inserted into the preparation with a paddle-shaped instrument or a syringe. 11 October 2009 89 Slide 90: The internal surfaces of the restoration also are coated with the composite cement and the inlay is immediately inserted into the prepared tooth,using light pressure. A ball burnisher applied with a slight vibrating motion is usually sufficient to seat the restoration. Excess composite cement is removed with thin-bladed composite instruments,brushes,or an explorer. 11 October 2009 90 Slide 91: The operator must be careful not to remove composite from the marginal interface between the tooth and the inlay. The cement is now light cured from occlusal, facial,and lingual directions for a minimum exposure of 60 seconds from each direction. 11 October 2009 91 Final finishing and polishing : Non-metallic restoration: All marginal areas are checked with an explorer tine. Because wedges and matrix were used interproximally, these areas-which are difficult to finish- should feel quite smooth, with little if any composite flash extending beyond the margins in a gingival direction. 11 October 2009 92 Final finishing and polishing Slide 93: For ceramic restorations, medium or fine grit diamond instruments are used initially to remove any excess composite cement back to the margin. Care must be taken to preserve glazed surface of ceramic restorations as much as possible. 11 October 2009 93 Slide 94: Slender flame shapes are used interproximally. Larger oval or cylindric shapes are used on the occlusal surface. After using fine grit diamond instruments,30-fluted carbide finishing burs are used to obtain a smoother finish. 11 October 2009 94 Slide 95: Further smoothing is accomplished with a series of rubber abrasive points and cups used at slow speed with air-water spray. Final polishing may be achieved by applying a diamond polishing paste with a bristle brush or another suitable instrument. 11 October 2009 95 Slide 96: For indirect composite restorations, finishing may be started with 12-fluted carbide finishing burs instead of diamonds. Interproximally,a No12 surgical blade can be used to remove excess composite cement when access permits. Care must be taken to avoid damaging the gingiva or the root surfaces. 11 October 2009 96 Slide 97: Metallic restoration: Slow-speed handpieces should be used in finishing and polishing for metallic restoration. Contour with carbide burs, green stones(silicone carbide),or heatless stones. Finish with pink stones (aluminum oxide), or medium-grade abrasive impregnated rubber wheels and points (brown and green). 11 October 2009 97 Slide 98: Apply fine abrasive-impregnated rubber wheels, cups, and, if necessary apply tripoli or rouge with rag or leather wheels. 11 October 2009 98 References : Phillips’ science of dental materials- Anusavice 11th Edition. Art and science of operative dentistry-sturdevant’s 4th Edition. Dental materials and their selection - william J.O’Brien 3rd Edition. Operative dentistry- Marzouk. 11 October 2009 99 References Slide 100: 11 October 2009 100 THANK YOU

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