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lab procedures in removable partial denture
- 1. 1 LAB PROCEDURES INRPD Presented by: Dr. Jyoti Sharan
- 2. 2 CONTENTS Preparation of mastercast Duplication of master cast Wax pattern & Spruing Investing & burn-out Casting of framework Finishing & Polishing Fitting the framework to the master cast Sectioning and resoldering the framework Review of literature Conclusion References and cross references
- 3. 3 INTRODUCTION A properly prepared andarticulated master cast Work authorization order Diagnostic cast with a specific design For the successful construction of the removable partial denture, the dentist must provide dental laboratory personnel with
- 4. 4 PREPARATION OF MASTERCAST Design transfer from diagnostic cast. Beading of maxillary major connector. Spraying. Block out. Relief.
- 5. 5 DESIGN TRANSFER FROMDIAGNOSTIC CAST It is the conveying the outline of the proposed prosthesis from the diagnostic cast to master cast or refractory cast. Relief, blockouts and beading should be seen easily. Drawing on refractory cast – use waxed pencils over graphite. Maxillary outline can be drawn through the beads. Outline of lingual plating (ant / posterior)- placing superior margin is crucial to draw the superior margin of the plate occlusal to survey lines, which is blocked out wax ended on the master cast Rudd and Morrow. Labortary procedures in removable partial denture fabrication.
- 6. 6 BEADING OF THEMAXILLARY MAJOR CONNECTOR Scraping the outline of the major connector into the master cast. A depth of half the diameter of a no.2 round bur. Positive contact against palatal tissues. Reduce the packing of food particles underneath major connector. 3to 4mm away from marginal gingiva. Rudd and Morrow. Labortary procedures in removable partial denture fabrication.
- 7. 7 SPRAYING Treating the mastercast with a surface sealer using a brush or an aerosol spray to seal the cast and protect the drawn design during the other steps of cast preparation and during duplication. Sealer application should be done in front of a suction vent because inhaling aerosol is potentially dangerous. Rudd and Morrow. Labortary procedures in removable partial denture fabrication.
- 8. 8 BLOCK OUT Elimination ofundesirable undercuts on the master cast with wax is commonly referred to as blocking out. Both hard and soft tissue areas will require block out. Types of block out: Parallel block out Shaped block out Arbitrary block out
- 9. 9 PARALLEL BLOCK OUT McCracken’sRemovable partial prosthodontics.11th edition
- 10. 10 SHAPED BLOCK OUT McCracken’sRemovable partial prosthodontics.11th edition
- 11. 11 ARBITRARY BLOCK OUT McCracken’sRemovable partial prosthodontics.11th edition
- 12. 12 RELIEF McCracken’s Removable partialprosthodontics.11th edition
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- 14. 14 WHAT PROBLEMS WECAN FACE DURING THESE PROCEDURES? Rudd and Morrow. Labortary procedures in removable partial denture fabrication.
- 15. 15 TISSUE STOP A smallsquare of 2mm of relief wax is removed at the distal end of the saddle. It provides stability of the framework during acrylic resin processing. McCracken’s Removable partial prosthodontics.11th edition
- 16. 16 DUPLICATION OF THEMASTER CAST Duplication with alginate
- 17. 17 Mc Cracken’s clinicalremovable partial denture.12th ed.
- 18. 18 REFRACTORY CAST MAKING Beambalance Add powder to liquid Vacuum mechanical mix Investment placed in increments
- 19. 19 Completely fill themold Properly filled mold Improperly filled mold A knife blade is placed on inside lip of spout
- 20. 20 Knife is turnedin complete circle Agar in neck is removed
- 21. 21 Push duplicating material Cutthe colloid from corners Peel the colloid carefully Place the cast into casting ring
- 22. 22 Draw the outlinefor trimming Use gentle blast of air to remove debris Cast is ready for treating with model spray or bees wax
- 23. 23 Cast is driedwith gentle blast of air and Sprayed with two coats of spray Cast is ground to shape and rinsed lightly in water Dried in drying oven for 1 to 2 hrs Coated with spray when it is hot
- 24. 24 Bees wax heatedin a pot at 138-149C
- 25. 25 WHAT PROBLEMS WECAN FACE DURING THESE PROCEDURES? Rudd and Morrow. Labortary procedures in removable partial denture fabrication
- 26. 26 WAXING FOR FRAMEWORK Beforethe waxing begins, design must once again transferred. Master cast is evaluated and measurements made with a Boley gauge to transfer exactly the outline of framework to refractory cast. Pre-made wax patterns are used for waxing the framework.
- 27. 27 WAXING TECHNIQUE Plastic patternsare glued to the cast with a mixture of acetone and plastic pattern scraps mixed to a watery consistency (tacky liquid). Tacky liquid is painted on the design outline with a fine brush and allowed to dry for a few seconds. Then patterns from the cards are removed with a quick snap to prevent distortion and placed on the refractory cast. Patterns are carefully adapted to the cast with the help of a soft rubber pencil eraser shaped into a wedge. Exercise extreme care not to stretch the pattern.
- 28. 28 Once the patternsare in place on the refractory cast, they must be joined together with wax. The areas where the retentive mesh work joins the major connector must be reinforced. For final contouring ,carvers with miniature rounded blades are most apt to be used. A tiny controlled torch made from a hypodermic needle and a piece of rubber hose attached to Bunsen burner provides a flame that is used to smooth even the finest details. Rudd and Morrow. Labortary procedures in removable partial denture fabrication
- 29. 29 SPRUING Spruing is attachingwax or plastic form to the wax pattern, to provide an entrance to the mold space and to serve as a reservoir of metal during casting procedure. Rules: The sprues should be large enough. The sprues should lead into the molten cavity as directly as possible. Sprues should be attached to the wax pattern at its bulkier sections. Rudd and Morrow. Labortary procedures in removable partial denture fabrication
- 30. 30 DIAMETER OF SPRUE Usuallylarge-diameter sprue is recommended. The diameter of sprue should be equal to the thickest portion the wax pattern. There are various gauges of sprue former gauge 6, 8, 10, 12, 14, 16, 18 (0.4cm - 0.1cm) Usually for molar and metal ceramic restoration 10-gauge (2.5mm) Premolars and partial coverage restoration 12-gauge (2.0mm) Rudd and Morrow. Labortary procedures in removable partial denture fabrication
- 31. 31 SHAPE The sprueformer should be straight to reduce chances of creating turbulence in molten metal entering the mold High turbulence of alloy cause porosity. Rudd and Morrow. Labortary procedures in removable partial denture fabrication
- 32. 32 TYPES OF SPRUING Thereare two basic types of sprues: multiple & single. A single sprue is preferred for complete denture metal bases. The majority of partial denture castings require multiple spruing. Rudd and Morrow. Labortary procedures in removable partial denture fabrication
- 33. 33 MULTIPLE SPRUES SINGLESPRUES • when metal has to get to thicker section after passing through thin section. • Mandibular cast is usually sprued through a hole in the centre of cast. • Keep all sprues short. • 7 mm diameter hole is placed and a wax of 7 mm diameter is passed through hole extending 10 mm to pattern side.
- 34. 34 MULTIPLE SPRUES SINGLESPRUES • Avoid abrupt junctions and reinforce every junction with additional wax to avoid any V shape section of investment that might break off. • Main & auxiliary sprue are attached 7 mm below central sprue ( overjet principle) • Metal sprue cones are also used.
- 35. 35 TYPES OF MULTIPLESPRUES Once the wax pattern for framework is over, the pattern is sprued either by Overhead spruing Base spruing Rudd and Morrow. Labortary procedures in removable partial denture fabrication
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- 38. 38 Sprue former formaxillary framework when sprued from above 8mm
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- 41. 41 INVESTING THE REFRACTORYCAST Two part mold: Refractory cast is soaked in a slurry water. Investment material is measured and mixed. A paint on layer about 3-4mm is painted on waxed refractory cast and ensure that no voids are present. As the layer reaches its initial set, the second part of investing procedure begins.
- 42. 42 BURN OUT Purposes: It drivesoff moisture in the mold. It vaporizes & eliminates the wax pattern & sprues by heating them to evaporation leaving a cavity in the mold. It expands the mold to compensate for contraction of the metal on cooling.
- 43. 43 STEPS OF BURNOUT Adjust time & temperature of the furnace. Put the ring & activate the furnace. When the temperature is 400 degree, the ring is inverted to put the sprue side downwards. Leave the ring in that position till the end of cycle. When the cycle is complete all the wax of the pattern have been eliminated.
- 44. 44 BURN OUT FURNACES Canbe either electric or gas and must be vented to allow the noxious fumes. Vary greatly in capacity. Industrial gas type furnaces can hold casting molds and small electric furnaces with a capacity of only 1 or two molds. Modern furnaces are controlled electronically to permit time/temperature relationship to be set exactly to the alloy manufacturer’s specifications.
- 45. 45 CASTING Molten metal isforced into the pre-heated mold by the use of force. Centrifugal force or air pressure is used. If little force is used, the mold is not completely filled before the metal begins to freeze. If excess force is used,turbulence may result in the entrapment of gases in the casting. Metal is melted with a gas-oxygen blow torch or by an electric muffle surrounding the metal. Induction casting is the method of choice.
- 46. CENTRIFUGAL CASTING MACHINE Utilizesthe centrifugal force, which is a radical force radiating outward from the centre of rotation of a body, for the casting. The casting machine spring is first wound from two to five turns. The metal is melted by a torch flame in a glazed ceramic crucible attached to the "broken arm" of the casting machine. Ceramic crucible for flame melting Micro flame melting torch
- 47. ELECTRICAL RESISTANCE-HEATED CASTINGMACHINE In this device, current is passed through a resistance heating conductor, and automatic melting of the alloy in a graphite crucible. Advantage, The crucible in the furnace is located flush against the casting ring. Therefore the alloy button remains molten slightly longer, again ensuring that solidification progresses completely from the tip of the casting to the button surface.
- 48. Vacuum- or Pressure-AssistedCasting Machine For this method, the molten alloy is heated to the casting temperature, drawn into the evacuated mold by gravity or vacuum, and subjected to additional pressure to force the alloy into the mold. For titanium and its alloys, vacuum arc heated argon pressure casting machines are required.
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- 51. 51 EVALUATION OF PHYSICALPROPERTIES AND CASTING ACCURACY OF CHROME COBALT ALLOYS WITH DIFFERENT CASTING SYSTEMS AND INVESTMENTS TZE SIEW ET AL. JOURNAL OF PHYSICAL SCIENCE 2012;23(2):91-102. Castibility and loss of mass from Co- Cr castings after polishing had been evaluated. Casting systems of centrifugal and vacuum type and two types of phosphate bonded investments were used. Cast plates were weighed before and after polishing to measure mass loss. Surface layer of cast specimens and porosity of investments was observed. Investments with more porous structure and centrifugal type casting system had shown significantly improved castability.
- 52. 52 RECOVERY OF THECASTING The mold is removed from the machine and allowed to cool according to manufacturer’s directions. At the appropriate time the mold is broken by tapping it with a wooden mallet to break off the outer layer of investment. This layer is then removed by sand blasting.
- 53. 53 FINISHING THE FRAMEWORK Separatingdisk to cut sprues
- 54. 54 Inverted cone stoneused with sharp edge in undercut Flat surface against finish line Separating disc to finish the finish lines Remove nodules from latticework Wire brush to shine nail heads
- 55. Red mounted fine-graingrinding stones Separating discs – for separating sprues Perforated discs – for grinding after separating sprues Rubber polishing wheeAls (WiroFlex) Rubber polishers
- 56. 56 Rubber wheels,rubber points,knifeedge wheels Magnification and bright light for defects Nodules removed with fine burs Point is formed on rubber abrasive cylinder
- 57. 57 Felt cylinder usedwith Tripoli on surfaces that contact teeth Hollowed rubber point to polish under rests Liquid soap and ammonia to remove tripoli Scrub with stiff brush
- 58. 58 Another felt coneused with jewelers rouge Rubber wheel on major connector Knife edge wheels for finish lines Felt point with Tripoli to finish groove
- 59. 59 Felt wheel topolish tissue side and tongue side of major connector Rag wheel with Tripoli to polish rest of framework From shoulder to tip of clasp use felt wheel and tripoli
- 60. 60 Final polish byrag wheel
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- 63. 63 ELECTROPOLISHING Ti-Lectro Polisher (CMPIndustries).
- 64. 64 PROBLEM AREAS Problems CausesSolutions Polished surface is dull with fine scratches 1. Sequence of finishing steps not followed. 2. Steps not carried to completion before proceeding to next step 1. Follow steps as outlined. 2. Complete one step before starting the next Major and minor connector overthinned or flexible 1. Incorrect wax up – thin casting 2. Framework overthinned with abrasive stones Use correct wax guage and do not use alcohol torch for flaming Care when finishing connectors to avoid thinning
- 65. 65 Problems Causes Solutions Claspis nicked or notched 1. Clasp was miscast 2. Clasp was nicked with stone bur during finishing Use correct thickness of wax Care while finishing framework Framework distorted Framework caught in lathe during finishing Take care as to avoid trapping of framework during finishing
- 66. 66 FITTING THE FRAMEWORK Thetechnician begins to fit the framework by carefully seating the casting on the master cast and attempts to identify the first spots that bind. The seating and spot grinding continues until the rests completely contact the cast. As the retentive clasp tip engages an undercut area, they will most likely be the first area that binds. Technician must carefully relieve the cast in the area of the clasp tip undercuts to allow the clasps to pass the height of contour.
- 67. 67 Some technicians bendthe retentive clasp arms away from the cast and then attempt to recontour the clasp back into contact. This attempt requires good deal of skill and seldom results in a truly passive clasp.
- 68. 68 RUBBER WHEELING ANDFINAL POLISH Once the casting seats completely on the master cast without rocking technician can proceed with rubber wheeling and polishing. Each alloy manufacturer sells a specific variety of polishing compound that best suits alloy. Ultrasonic cleaning is commonly used to remove all traces of polishing materials.
- 69. 69 SECTIONING AND RESOLDERINGTHE FRAMEWORK Framework must be fitted to oral cavity before denture bases and prosthetic teeth are added. If the framework cannot be seated, the clinician must: 1)decide to have new framework made or 2)attempt to correct fit of the existing framework by sectioning and soldering.
- 70. 70 Sectioned segments mustbe satisfactorily related in the mouth and then transferred with either a plaster index or a resin matrix to the laboratory. Technician carefully pours a soldering cast against the properly related segments. Foil is placed over the area of the proposed solder joint and the soldering operation is done.
- 71. 71 TWIN FLEX CLASP Thetwin-flex clasp is a unique application of wrought wire. This clasp can provide a flexible clasp that is less noticeable to the patient. Ticonium 19-gauge wrought wire is adapted into a measured undercut area on the proximal surface of an abutment on the master cast. A small amount of wax is added around the clasp, ultimately creating a channel in the tissue surface of the major connector following standard duplication and refractory cast procedures.
- 72. 72 USE OF CAD/CAMTECHNOLOGY TO FABRICATE A REMOVABLE PARTIAL DENTURE FRAMEWORK (J PROSTHET DENT 2006;96:96-9.)
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- 74. 74 McCracken’s Removable partialprosthodontics.11th edition Stewart’s clinical removable prosthodontics.3rd edition Dental laboratory procedures-Removable partial dentures.Morrow,Rhudd.Vol-3. Laser welding of a cobalt-chromium removable partial denture alloy. (J Prosthet Dent 1998;79:285-90.) Laboratory Fabrication Procedures of a Metal Partial Denture Framework. Acta Stomat Croat 2003; 95-98. An altered cast procedure to improve tissue support for removable partial denture.Contemporary clinical dentistry apr-jun 2010,vol-1;issue-2
Editor's Notes
- #3 Any thing less will compromise quality. It is necessary to point out that metals being considerably more resistant to fractures than acrylic resins enable fabrication of reduced forms of partial denture bases, which contributes to a better and faster adjustment of the patient to new conditions in the oral cavity.
- #6 Beading toward the gingival margins shud b shallow..in order to prevent impingment..
- #7 Content of model spray? Purpose?
- #9 Tooth supported rpd Surface of blockout held perpendicular to surveying base resulting o degree blockout(blockout parallel to path of insertion)
- #10 Ledge: areas associated with retentive clasps Blockout wax is shaped with hand instruments to provide slight ledge just apical to the clasp terminus. This guides the placement of the wax or plastic pattern and ensure that the clasp tip is accurately positioned in the desired undercut
- #11 Used in less critical areas to prevent the encroachment of metal on the soft tissues and to facilitate the withdrawal of the blocked out cast from the duplicating material. Soft wax, clay and mortite are commonly used. Duplicating materials such as reversible hydrocolloid can rebound from relatively 3mm undercuts,but tends to distort when largerundercut
- #18 Composition of investment liquid?
- #23 Cast is dried in hot oven 82 to 93 deg C. Dipped into bees wax at 138 to 149 deg Cfor 15 sec.
- #24 Why it the refractory cast is coated with bee wax? To ensure a smooth ,dense surface and to eliminate the need for soaking the cast prior to investment process.(ac stewart)
- #35 Top spruing: A cone-shaped plastic sprue is attached to the central sprue from which auxiliary sprues run to each corner of the wax pattern. INVERTED SPRUINGIn which the base of the refractory cast should have a hole in its center. A cone-shaped plastic sprue is placed into the hole. Auxiliary sprues are attached between the main sprue and the thick sections of the wax pattern.
- #36 Cut a 7 mm hole through the base of the cast. The hole should be in the center of the wax up. Hole should taper….slightly larger on the bottom side of the cast. Wax rod through the hole until it extends about 10mm on the pattern side of cast and sealed in position. Main and Auxillary sprues are attached at a level 0f 7 mm below the tip of central sprue.this method takes advantage of overjet principle. Initial thrust of molten metal is directed against the tip of the central sprue and resulting turbulence and impurities are confined to this area rather than being directed at the casting
- #37 8 or 10 gauge round wax sprue leads.auxillary lead with 14 gauge.Single sprue leads with auxillary lead or three sprues. All attached to central sprue at the same height. For maxillary 10gauge half round wax when sprue is through the cast. When sprue from above use round wax-10 gauge fastened together over centre of the wax up.
- #38 Adjust height of sprue leads so that base of cast will be approximately 8 mm from one end of the investing ring when wax crucible is in flush with the other end
- #39 Small,medium, large and small bevelled sprue cones. Small sprue attached to mandibular master cast.
- #40 Sprue leads are attached directly to metal sprue cone using overjet principle. In the overjet principle, the initial thrust of molten metal is directed against the tip of the central sprue and the resulting turbulence and impurities are confined to this area rather than being distributed to the casting.
- #44 Torch melting/centrifugal casting machine,electrical resistance heated casting machine, induction melting machine, direct- current arc melting, vaccum or pressure assisted casting machine. . The temperature inside the mold is held down during the early stages of the burnout by the vaporization of the water in the mold, regardless of the temperature setting of the furnace. Water temperature will not rise above its boiling point so the internal temperature of the mold will remain at 100 degree centigrade intil all of the water is vaporized. The water is usually driven off within an hour. The temperature inside the mold will then rise to the temperature of the furnace but it may require another hour before the temperature within the mold is completely equalized. During this period the furnace may be set at 538 degree C. after this 2 hr period the mold and the furnace should remain at a temp between 675 and 710 for another 1 ½ to 2 hr. this time is necessary to complete the removal of the carbon residue resulting from the vaporization and oxidation of the wax and plastic pattern and to complete the removal of the moisture from the interstices of the investment. The wax itself is eliminated early in the burnout usually befor the temperature has risen to 538.Prepare and balance the casting machine before casting ring is placed in the oven.
- #45 38-66 degree centigrade higher. wax pattern x density = alloy amounts. Formula Pattern Wax Weight(g) X Density of Alloy (g/cm³) = Weight of Alloy (g) needed for casting
- #46 Natural or artificial gas & air Natural or artificial gas & oxygen Air and acetylene Oxygen & acetylene Hydrogen oxygen generator
- #53 End point of bur should not be more than 2mm from end of chuck.
- #55 Seperating discs for cutting away sprues and grind with 7/8th inch stone remove sprue stumps and using same stone remove nodules of metal or flash that are present in accessible areas.
- #63 Electropolishing, a f o rm of electrolytic stripping, is usually the first step in polishing the framework. In this process, atoms of metal from rough projections on the framework go i n t o s o l u t i o n before those in smooth areas do. This results in a very consistent,satin-like surface. The polishing occursin a bath of 85% orthophosphoric acid, which isheated t o 4 9 ° C (120°F) t o 6 0 °C (140°F). The anodeis attached to the cast and the cast is immersed in thesolution (Fig 10-51). Each square inch of metal surfacearea requires 2 amperes of current for 6 minutes.The average setting is 6 amperes f o r 6 minutes
- #72 This article reports on the first patient-fitted chromium cobalt removable partial denture framework produced by computer-assisted design, computer-assisted manufacture and rapid prototype technologies. Once the dental cast was scanned, virtual surveying and design of the framework on a 3-dimensional computer model was accomplished. A rapid prototype machine was used for direct fabrication of the alloy framework. Traditional finishing techniques were applied, the framework was assessed by a clinician in a conventional manner, fitted to the patient, and judged to be satisfactory by both the patient and clinician
- #73 Although it is impossible for a clinician to do all laboratory steps in casting in regular practice, it is important for him to know the basics of casting and finishing the framework in order to guide the technician to fabricate a good framework