FINISHING AND CEMENTATION
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Contents Introduction Procedures Abrasives Zones of the casting Cementation Ideal requirements Types Conclusion References www.indiandentalacademy.com
The unpolished surface is relatively rough, and a series of finishing procedures are needed to produce a highly polished surface to limit the accumulation and retention of plaque and facilitate maintenance the health the supporting periodontal tissues.
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Cast metal restorations needs a series of finishing procedures before try in and cementation.
1. 2. 3. 4. 5.
Preliminary procedures Try in and adjustment Pre cementation polishing Cementation and Post cementation polishing.
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ABRASIVES AND POLISHING MATERIALS
Abrasion : It is the smoothening of rough surface before preparing it for polishing. The smoothening is carried out by cutting action.
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COMMON ABRASIVES USED
1. Diamond: chips are bound to a metal
shape by ceramic bond or electroplating.hardest of all abrasives used on enamel or porcelain.
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2. Silicon carbide: basic material for carborundom. It is sintered or pressed with a binder into grinding wheels or discs.
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3. Emery: it is a mixture of aluminium oxide and iron oxide.Hard and black natural mineral can be used on gold and porcelain.
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4. Garnet: several minerals having similar properties.used for grinding plastics and metal alloys. 5. Sand paper: form of quartz,rounded or angular in shape.they are typically bonded to Paper discs for grinding metals and plastics.
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6. Aluminium oxide:common abrasive used in dentistry in the form discs and strips. It is also impregnated into rubber wheels and points. Used to adjust enamel or finish metal alloys and ceramic materials
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Zone-1 Internal margins: Objective: To minimize any dissolution of the luting agent, a 1mm wide band of metal must be obtained that is closely adapted to the tooth surface.
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Here we should inspect the internal portion for small nodules or bubbles and should be removed with a hand piece using round bur,but care should be taken to avoid damage to the margin and annoying remakes.
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Zone-2 Internal surface: Objective: is that no contact should exist between the disc and the internal surface of the casting. It should be examined for the nodules.
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Nodules should be removed with a round bur and carefully seated on the die. Force should not be applied as any nodule present may scratch the die and this will result in a restoration with poor margins and poor prognosis.
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In the areas of the nodule, deliberate removing of slightly greater amount of alloy is recommended and should be removed in one single step.
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Marking agents Several agents are commercially available to facilitate identifications seating interference between the casting and die. 1.Water soluble dies eg;ligna mark. 2.Solvent based dies eg;accufilm 3.Powdered sprays eg;occludent 4.A suspension of rouge in chloroform. www.indiandentalacademy.com
Zone-3 The sprue: Objective; Is to establish proper coronal morphology and function. A corborundum separating disk is used to cut the sprue Cutting should be done circumferentially Excess in the area of the sprue attachment is removed with the disk, and the area is refined with stones and sandpaper disks www.indiandentalacademy.com
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Zone-4 Proximal contacts Objective: is to adjusted so that they will be in correct when evaluated in the mouth. Proximal contacts on the stone cast can be achieved by careful scraping of the adjacent teeth with a blade.
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Articulating strips between adjacent castings or between the castings and the adjacent tooth is helpful, as it allows the areas where binding contact occurs to be adjusted through grinding.
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Connectors The connectors require special attention when fixed partial denture is finished Periodontal health is compromised if they are not properly contoured and finished. Parabolic configuration
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Rotary instruments such as rubber wheels, which allows access to the cervical margin are used so that they do not jeopardize the margins
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Zone-5 Occlusal surface Objective is to re-establish Occlusal contacts in static and dynamic relationship to the opposing arch. Occlusal contacts are checked with Mylar articulating strips. Occlusal prematurities are a result of excessive heavy contact on the wax pattern as the wax is subject to elastic recovery. www.indiandentalacademy.com
The adjustments are done with flame shaped finishing burs.The entire ridge or cusp should be redeveloped rather than grinding only the point of interference. After refinement of the Occlusal contacts ,they should be altered with extensive polishing. www.indiandentalacademy.com
Zone-6 Axial walls Objective: The axial walls should be smoothly contoured and polished so that the patient can carry out plaque control. Surface defects are removed by grinding with abrasive particles Polishing should be carried out by using the abrasives in a sequence. The finer abrasive should be used last because the coarser grits will remove material efficiently www.indiandentalacademy.com
Zone-7- External margins Objective: for the restorations longevity. Cavo-surface margins should be finished directly on the tooth. Those parts that cannot be finished on the tooth should be finished on the disc The edges of the margin should not be distorted www.indiandentalacademy.com
A fine grit stone is used to remove casting roughness, followed by soft rubber wheel and finally by rouge or a brush, during all these procedures, the casting should be supported by the finger.
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Once the laboratory procedures are completed the restoration should be evaluated in the patient’s mouth before final finishing and cementation •It should be evaluated for the following: 1.Proximal contacts 2.Margin integrity 3.Stability 4.Internal fit 5.External contour 6.Occlusion 7.Surface finish www.indiandentalacademy.com
Proximal contacts Proximal contacts should be like those of natural teeth Use of floss is a convenient method to compare the contacts If the floss does not pass, the contact is too tight Ideal contact should allow for positional stability of the abutments and adjacent teeth as well as easy maintenance of the supporting structures
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EXCESSIVE TIGHTNESS.
1. Metal restorations Adjustments are made with rubber wheel. The satin finish produced helps to identify where binding occurs because a shiny spot will appear where adjustment is necessary.
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2.porcelain restorations If high proximal contact in unglazed porcelain is easily adjusted with cylindrical mounted stone. Area identified by red pencil. If adjustment of glazed porcelain is needed, it can be polished with diamond impregnated silicone points or diamond polishing paste www.indiandentalacademy.com
Deficiency Usually corrected by soldering. Armamentarium: Soldering tweezers Gold solder Paste flux Bunsen burner Antiflux and polishing armamentarium www.indiandentalacademy.com
1. 2. 3. 4.
Roughening the area with disk Adding antiflux- granite Roughened surface is painted with flux Then the casting is held on the bunsen flame at the height of the reduction portion of the flame
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5. As the solder heats up it starts to fuse and rapidly spread. It should be tipped to help the solder flow in the desired direction. 6. Proximal contact is then readjusted.
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Porcelain restorations Deficient porcelain contact requires additional fixing, it is at bisque stage. If restoration has been completely finished, add on or convection porcelain can be used
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Margin integrity The completed restoration should go into its place without binding and the best adaptation should be at its margins. A sharp explorer moved from restoration to tooth and from tooth to restoration can be evaluated for marginal adaptation. www.indiandentalacademy.com
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Stability The restoration should be checked for stability. It should not rock or rotate, any degree of instability is likely to cause failure during function.
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Occlusion The occlusion contact with the opposing teeth is carefully checked.any undesirable eccentric contacts as well as centric interferences must be identified. Use of two different colored ribbon tapes or articulating paper is used for excursive movements and centric contacts. Ant interferes are then corrected with diamond or white stone www.indiandentalacademy.com
Ceramic restorations Ceramic restorations need certain additional steps during evaluation to satisfy esthetic, biologic and mechanical requirements. Contour, surface characteristics and color match.
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Contour The contours of the gingival third is verified Excessive bulk may be associated with periodontal disease When adjustment is necessary porcelain and metal should not be grounded together.
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If at all grinding both is absolutely necessary, the direction of grinding is parallel to the metalceramic junction. The incisal edge should be checked for proper position and shape This is the key for good esthetics and function. www.indiandentalacademy.com
The negative space should be evaluated (incisal embrasures) The absence of embrasures draws attention to the prosthesis When viewed from the incisal inter proximal embrasures should be as narrow and deep as possible www.indiandentalacademy.com
Cementation Cement: Binding agent used as a substance to make objects to adhere to each other, or something serving to firmly unite. GPT-8 Luting agent: Material that on hardening will fill a space or bind adjacent objects. GPT-8
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Cementation- The process of attaching parts by means of cement or attaching a restoration to natural teeth by means of cement.GPT-7. Luting materials play a central role in indirect dentistry by aiding the retention of restorations and in the prevention of leakage at their margins.
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The ideal luting material should be: Bio- compatible with the tissues Adhere to tooth surface and restoration either chemically, mechanically or both. Prevent leakage by producing a good marginal seal Have sufficient mechanical properties to resist forces transmitted to the lute through the restoration that is it should have high tensile and compressive strength, high fracture toughness and fatigue strength and a modulus of elasticity which is appropriate for stress absorption www.indiandentalacademy.com
Be cariostatic Be insoluble in the dilute organic acids Resist water sorption Be available in sufficient range of shades Achieve optimal physical properties as quickly as possible Allow easy removal of excess and clean- up
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It should have sufficiently low film thickness, so that the restoration may seat fully. Should have radio-opacity similar to or greater than dentine Additionally the luting cement should be technique insensitive
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They can be classified according to the material from which they are formed and more generally, as active and passive.
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Active luting materials They are bonded both to tooth and restoration make the restoration and tooth synergistic and there by play a role in the retention of the restoration,as well as sealing its margins and filling the space between restoration and tooth.
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Passive luting materials They merely fill the gap between the indirect restoration and tooth, with no chemical adhesion at the restorative or lute and or tooth or lute interface.
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PASSIVE LUTING MATERIALS Zinc phosphate cement: Oldest of the currently available luting materials Powder- liquid material has zinc oxide as the main constituent of the powder and liquid is an aqueous solution of phosphoric acid. Zinc oxide powder react with phosphoric acid to form an insoluble phosphate
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Setting time can be lengthened by mixing on a chilled glass slab and working time can be prolonged by adding small increments of powder to the liquid PH of freshly mixed cement is between 1.6 – 3.6. Clean – up is relatively simple, as the setting cement reaches a rubbery stage and can be peeled off the restoration. Compressive and tensile strengths are adequate but the solubility of the set material is high in solutions of lower ph. Another major disadvantage is the lack of adhesion to the tooth surface. www.indiandentalacademy.com
Zinc-polycarboxylate Fore runner to glass ionomer cements Introduced by SMITH in 1968, showed true adhesive attachment by molecular bonding to tooth structure. Based on the reaction of zinc oxide and polyacrylic acid to form zinc polyacrylate
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Clean –up is difficult as it will stick to the mucosa and should be removed as soon as possible after placement. They are as strong as zinc phosphate with higher tensile strength, however, they are more soluble than zinc phosphate and may absorb water.
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Glass ionomer cements The first glass ionomer cements were developed in 1978 These cements contain anion- leach able fluoroalumino-silicate glass which reacts with a water soluble polymeric acid The outer layer of glass particles are decomposed leading to release of Ca+,Al+ and F- ions.thus the set cement is therefore a core of unreacted glass particles sheathed by a siliceous hydro gel bounded together by the reaction products. www.indiandentalacademy.com
These materials also release fluoride. The value of this fluoride release in cariostatic is questionable. These cements adhere to enamel and dentin and contribute to the retention of the restoration. 2030% higher retention than zinc phosphate or zinc polycarboxylate cement. However these cements have been reported to cause inflammatory response in pulpal tissue under deep restorations They have superior compressive strength but their tensile strength is low and fracture toughness is also low www.indiandentalacademy.com
Resin modified glass ionomer cements These materials were developed to overcome some of the short comings of traditional glass ionomer cements In addition to components of glass ionomer they contain a monomer such as 2 hydroxy-ethyl methacrylate (HEMA) or BIS-GMA.
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Advantages over Conventional Glass Ionomers are: Improved bio-compatibility Better fluoride release Improved adhesion to tooth and Improved physical properties, specially tensile strength Clean- up is easy as it goes through a rubbery phase.eg: Fujiplus,Fuji-cem and rely-X
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Active luting agents Resin based luting materials These cements bond to the tooth by the cure of dentin – bonding agent. These materials may also be bonded to a ceramic surface which has been rendered micro-mechanically retentive by treating with acids such as hydrofloric acid, while bonding to metal surfaces may be achieved by oxidising ortin plating gold surfaces www.indiandentalacademy.com
Bonding is usually achieved with organophosphates, HEMA or 4-META(4-methacryl ethyl trimellitic anhydride)
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Their physical properties include= Excellent compressive and tensile strength and fracture toughness Low solubility in oral fluids Low potential for microleackage when bonded to a tooth by an intermediary bonding systems. High bio-compatibility when used with dentin bonding systems
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CHOICE OF LUTING AGENT Zinc – phosphate
1. Cast restorations 2. Normal conservatively prepared tooth
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Zinc polycarboxylate cement
1. Recommended on retentive preparations with minimal pulp irritation. Eg: children with large pulp chambers.
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Glass ionomer cement Popular for luting cast restorations
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Resin modified glass ionomer luting agents Most popular because low solubility and low micro leakage and reduced post cementation sensitivity.
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Adhesive resin Material of choice with all ceramic restorations.
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Cementation with zinc phosphate The field must be dry Isolated with cotton rolls Protection of pulp by application of varnish|\dentin bonding agent Mixing done by adding increments Mixing done on a wide area www.indiandentalacademy.com
When the consistency is right,load the cement on to the restoration. Tell the patient to put force to the Occlusal surface by closing on a plastic wafer. Once the cement has set remove the excess with explorer.
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Cementation with polycarboxylate Isolate the quadrant Blot dry the tooth Dispense proper powder-liquid ratio Spatulation should be complete in 30 secs Cement is coated on the inside of the casting and seated on the tooth.
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Cementation with glass ionomer Clean and dry the tooth The preparation can be dried with pumice to increase retention. Powder liquid ratio is 3.4:1 Mixing should be fast,applied on to the restoration and seat the crown. Excess cement removed after it has become brittle
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Resin cements For metal restorations Air abrade the the inside of the crown,rinse it and dry it. Dentin activator is appliued for 10 secs Base catalyst ratio is 4:1,to this 2 scoops of powder is added and stirred gently for 5 secs to produce a creamy mixture Apply the cement onto the restoration and placed over the tooth.10 mins is the setting time. www.indiandentalacademy.com
Ceramic restorations Crown is is silaned by applying the silane agent onto the internal surface of the crown. The prepared tooth is cleaned with pumice washed and dried. Etch the enamel,rinse for 30 secs Apply primer to dentin and polymerize for 30 secs Dispense equal amount of base and catalyst mix for 20 secs,apply thin layer onto the internal surface of the crown and seat the crown Light cure at marginal areas from facial,lingual and Occlusal directions. www.indiandentalacademy.com
Conclusion When a restoration is tried in the mouth the proximal contacts,margin integrity,and occlusion must be verified. With metal ceramic restorations the contour in the cervical third is critical for the maintenance of health of supporting structures. Proper shaping of gingival and incisal embrasures will improve the esthetics. www.indiandentalacademy.com
No matter what type of cement is used for cementation,proper moisture control is essential . Cement should be protected from moisture during initial set,and removal of excess from the gingival sulcus is critical for continued periodontal health. Active luting, in which the material bonds the restoration to the tooth is the most desirable feature, which make the resinbonded the material of choice but they are technique sensitive. www.indiandentalacademy.com
References Contemporary Fixed ProsthodonticsRosenstiel Fundamentals Of Fixed ProsthodonticsShilling burg Trends In Indirect Dentistry-Dental Update 2005.
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