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Lab procedures for cast partial dentures. /certified fixed orthodontic courses by Indian dental academy


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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit ,or call

The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit ,or call

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  • 2. INDIAN DENTAL ACADEMY Leader in continuing dental education
  • 4. INTRODUCTION ► The removable partial denture framework should be constructed in such a manner requiring a high level of communication between clinician and technician if a quality denture is to be achieved. ► Knowledge of the laboratory phase of partial denture construction is essential for the clinician, who must assume total responsibility for the design and the quality control of all aspects of its construction.
  • 5. For the laboratory construction of the removable partial denture following steps should be kept in mind: ► Presence of a properly prepared and articulated master cast. ► A diagnostic cast with a neat and specific design carefully drawn on it. ► A work authorization order covering all aspects of the desired denture must be given to the technician if the partial denture is being fabricated in a dental laboratory. ► Anything less will compromise quality of the partial denture.
  • 6. ► Dental laboratory technology has increased rapidly during the past several decades that has resulted from the build up of military services during 1940 and 1950 such as ceramics , porcelain bonded to metal and precision attachments requiring more specialized training. ► Therefore , the dentist must provide the clinical and professional aspect of patient treatment planning and processing of the prosthesis.
  • 7. DUPLICATION OF THE CASTS. PURPOSE OF DUPLICATION     Preservation of original casts. To check the fit of the frame work. Processing of interim prosthesis with wax relief and block out on the original cast for successful duplication. Formation of investment cast for framework fabrication.
  • 8. Duplicating machine Slowly flowing of investment material into the flask
  • 9. FORMATION OF INVESTMENT CAST FOR FRAMEWORK FABRICATION. Retripoding Of The Cast: Determine a specific path of insertion and removal for the denture and prepares both hard and soft tissues to be in harmony with path of insertion and removal, it is critical that this exact relation must be maintained. ► Three widely separated marks are placed on the master cast with the dental surveyor vertical rod in a fixed position will allow rapid repositioning of the cast in the laboratory. These marks must be placed in areas that are not involved with design outlines. To simplify this repositioning for the technician if the processing is being done in laboratory the marks are placed on the lingual surfaces of the cast such that all three can be seen from the same view. ►
  • 10. Vertical rod in surveyor used to place the mark on the cast. Reference points on the cast
  • 11. ► Height of Contour: With the master cast positioned on the survey table by the three tripod marks, carbon marker substitutes for the analyzing rod in the surveyor arm which must be placed in the height of contour line on the involved teeth and soft tissue areas. The survey table is moved smoothly along the surveyor base to contact the lead. ► Design Transfer: Without removing the master cast from the survey table by changing the tilt, the design is transferred from the diagnostic cast. A dense cast of improved dental stone is unlikely to be damaged by the design transfer drawing. In situations where the master cast is weak with a chalky surface, care must be taken not to abrade the cast surface with the carbon marker.
  • 12. Height of contour line is placed on the cast with marking lead in surveyor. Transferring of the framework from diagnostic cast to the master cast.
  • 13. BLOCK OUT AND RELIEF. ► Elimination of undesirable undercuts on the master cast “ block out”. ► Before this the maxillary cast is beaded – outlining of the master cast with no 2 diamond bur, to get a positive contact against palatal tissues to reduce the packing of the food beneath the major connector as it stops 3-4 mm from the gingival margin, also spraying of the master cast with aerosol spray that deposits a seal on the cast prevents inhalation of aerosol plastic..
  • 14. Placement of bead with a round bur no. 2 for outlining of maxillary major connector. Spraying of model spray on the cast to prevent inhalation of aerosol plastic. Placing of fluid block out wax.
  • 15. Fluid block out is done with a thin sheet of soft base plate wax sheet with one stick of green inlay wax ,it must not be placed above the survey line or in the area of retentive clasp, shaping of the block out wax is done by contouring the wax in predetermined in the area of path of insertion, excess is removed by the blade of surveyor which lies perpendicular to the surveyor base. ► All tooth borne partial dentures should be blocked out parallel to the path of insertion and tooth – tissue- borne dentures should be given a tapered block out for freedom of movement during function . ► Wax contouring is done with the block out blade positioned properly beneath the height of contour to get smooth layer of wax to eliminate undesirable undercuts. ►
  • 16. ► Attempts to remove wax from above the contour line with the block out instrument has the risk of removing some of the cast surface. When the cast's surface is weak or chalky, this scraping action subtracts from the dimension of the cast and inevitably results in a casting that is too large to seat without reshaping. ► The duplication colloids can rebound from the distortion caused by removing the cast from the mold only if there are no large undercuts present (2 to 3 mm maximum). Larger undercuts will distort or even tear the fragile colloid.
  • 17. Block out wax must not be placed in the area of survey line or in the area of retentive clasp tip. Placement of excess block out wax in the undercut area.
  • 18. ► This block out is arbitrary and is not contoured with the block out instrument. Areas of gross soft tissue undercuts can be arbitrarily eliminated using soft wax, clay, mortite. ► Deep maxillary palatal clefts and irregularities in the area covered by the major connector are filled with wax to eliminate potential sharp areas on the tissue surface of the casting. One margin of the relief wax forms the internal finish line of the framework.
  • 19. Application of investment on the cast for complete adaptation of investment. Trimming of investment mold for preparing the sprue for burn out
  • 20. Arbitrary block out of non critical areas with clay. Covering of area to be covered by mandibular major connector with a thin layer of wax for smooth surface.
  • 21. Filling of Palatal cleft and other irregularities with wax to be covered by maxillary major connector.
  • 22. DUPLICATING MATERIALS AND FLASKS Materials are of two types : o Silicone o Colloidal – made fluid by heating and return to a gel state while cooling. Duplicating Flasks: A number of flask are available.  WILLS FLASK TYPE E , TYPE F both of them have a Formica ring of 4 inch of diameter inside and 2 inch height ,  BELL SHAPED FLASK ,  KERR FLASK ,  LIGHT WEIGHT BRASS FLASK.
  • 23. Wirosil duplicating flask with stabilizing insert and 3 replaceable palate formers Wirotop automatic mixing and metering unit
  • 24. TECHNIQUE OF DUPLICATION Cast is placed at the bottom of the flask after immersion into water and the material is broken into small pieces and heated to avoid lump formation, small continuous stream of material is flowed in the posterior area, after filling the flask material is added to completely fill the feeder ring, place the flask under running water 2.5 cm deeper till the material feeder ring completely gels after which the flask is completely immersed in water for 15 mins.
  • 25. Placement of master cast after relief and block out on the base of duplicating flask. Duplicating flask filled slowly with hydro colloid material.
  • 26. ► Removal of feeder ring and cutting of projecting material , exposure of base of the cast by inverting the flask , application of rubber suction cup at the base of the flask and removal of mold from the flask is done carefully. ► After which the stone or investment material is properly mixed and spatulated and vibrated around the tooth to avoid air trapping completely filling the flask and is covered by wet towel for prevention of dehydration of mold due to loss of water of crystallization .
  • 27. Wiropress pressure compaction unit Casts after hardening is taken out by blowing compressed air between mold and cast.
  • 28. Placement of duplicating cast in vacuumed jar for 2 mins , hardening of cast under pressure , detachment of cast by blowing compressed air between cast and mold, finally spray the surfactant to prevent the reaction between investment material to get accurate casting surface . Spraying of surfactant.
  • 29. Base of flask placed in running water. Teasing of cast from hydro colloid duplicating material
  • 30. REFRACTORY CAST Refractory (or investment) materials must be measured and mixed exactly according to the manufacturer's instructions to ensure that the expansion of the mold during burnout will match the shrinkage of the alloy. ► Gypsum-bonded investments, commonly called low-heat investments, are used for casting Type IV partial denture gold and Ticonium alloys. This refractory materials can be burned out at 704°C (1300 OF) without causing breakdown of the investment.
  • 31. Investments used for Vitallium, Nobillium, Jelenko's AEG, and other chrome-cobalt alloys are termed highheat and are burned out at temperatures in the area of 1037' C (1900' F). These high-heat investments are phosphate-bonded and usually require a special liquid to mix with the refractory material. ► The manufacturer's instructions give the time required for complete set of the refractory material When this stage is reached, the cast is carefully re moved from the mold and placed in a drying oven at 93' C (2000 F). When dry, the cast is trimmed to within 6 mm of the proposed design. The trimming is done on a dry cast trimmer to eliminate the possibility of a slurry mixture accumulating on the cast and changing its contours and dimensions. ►
  • 32. WAXING OF THE PARTIAL DENTURE FRAMEWORK. Preformed plastic wax patterns are available which are made from soft plastic material which tend to stretch on removal from their backing . Design Transfer: Before the actual waxing can begin, the design must once again be transferred. The master cast is evaluated and measurements made with a Boley gauge to transfer exactly the outline of the framework to the refractory cast .
  • 33. Preformed plastic wax patterns available commercially.
  • 34. Boley gauge used to determine the position of inferior border of major connector. Use of soft sharp pencil for transfer of design on the refractory cast. Ledge created bywww.indiandentalacademy.comused for positioning block out wax of retentive clasp arm.
  • 35. A common soft lead pencil, sharpened to a point, is used. Care must be taken to draw with a minimum of pressure so that no damage to the cast surface can occur. Waxing Technique: The plastic patterns are "glued" to the refractory cast with a mixture of acetone and plastic pattern scraps mixed to a watery consistency. The tacky liquid is painted on the design outline-with a fine brush and allowed to dry for just a few seconds. The pattern can then be adapted with confidence that it will adhere to the cast Should the pattern separate from the refractory cast.
  • 36. Use of surveyor and an electrically heated shaping blade to remove excess wax. Removal of excess wax for shaping excess wax.
  • 37. SPRUING THE FRAMEWORK TECHNIQUE ► The actual spruing construction depends almost entirely on the instructions provided by the manufacturer of the alloy system. Ticonium uses a single sprue approach through the refractory cast.Gold castings and a number of high-heat chrome-cobalt alloys sprue the casting from above with multiple sprues. ► Sprue Size: Gauges of the wax used for the sprue leads are critical, and the manufacturer's directions must be followed. There must be no constrictions in the sprue lead that would cause the molten metal to flow 'from a thick to a thin area and then back to a thick area. The turbulence set up by this type of sprue often results in internal mold deformation and castings that have inclusions.
  • 38. FUNCTIONS OF SPRUE ► ► ► ► ► Acts as a channel opening leading from the crucible to the cavity in which the framework is to be cast. Leads the molten metal from the crucible into the mold cavity- large enough to accommodate the entering stream and proper shape to lead metal into the mold cavity with least amount of turbulence . Acts as a reservoir of molten metal preventing porosity caused by shrinkage. Sprue channels must be long radii and easy turns and enters the mold cavity from a direction designed to prevent splashing of the molten metal so the sprue channels must not be at right angle turns which create turbulence creating gases entrapment leading to faulty castings. Attachment of sprue at a bulky point of the mold pattern , if two bulky points exists with in a thin section between each of the bulky spots must be sprued , points of attachment should be flared out preventing local constrictions.
  • 39. SPRU TYPES Multiple.: A majority of cast partial dentures requires multiple sprue using 8- 12 gauge round wax for main sprue, and 12 – 18 gauge round wax shapes for auxiliary sprue. However a single sprue is preferred for cast palates and cast metal bases for the mandibular arch . Use of a few sprues of large diameter rather than several smaller sprues. All sprues must be short and direct as possible. No abrupt changes in the direction of the sprue( no T shaped junctions). Reinforcement of all the junctions with additional wax to prevent constrictions in the channel to prevent v shaped sections of investment that might break during casting. Single: A single sprue must be attached to the wax pattern in such a way that the direction of flow of molten metal is parallel to the long axis of the single sprue. Auxiliary sprue: Is attached to the framework of long span bridges to ensure sufficient flow of molten metal , also is required in cases to support heavy metal pontics – in which the molten metal flows from thinner area to thicker areas .They are made form round wax forms one third to one forth of diameter of the major sprue.
  • 40. Mandibular sprued pattern with three 8 gauge sprue attached to the denture base minor connector and direct retainer joined at a centre sprue hole. Maxillary wax up with 8 gauge multiple sprues or a single main sprue located posteriorly
  • 41. Single sprue transversing through base of the cast to mandibular framework. Attachment of multiple sprue used to cast gold and high heat chromium cobalt alloy.
  • 42. Placement of secondary spure for easy flow of molten metal in thin areas of pattern.
  • 43. Wax pattern sprued to all the parts.
  • 44. INVESTING THE SPRUE PATTERNS It can be divided into: ► Investment cast on which the pattern is formed. ► The outer investment surrounding the cast and the pattern
  • 45. Injection process for flasking
  • 46. ► Investment cast on which the pattern is formed is confined within the metal ring which may or may not be removed after the outer investment is set so the inside layer is lined with a layer of cellulose , asbestos or ceramic fiber paper for thermal and setting expansion compensation in all directions. ► According to Peyton 1949 for the outer alloy having higher melting temperature , an investment containing quartz is held together by an ethyl silicate or sodium silicate binder. In cases of gold alloys the casting shrinkage is 1.74% and for cobalt chromium alloys it is 2.3%.
  • 47. BRUMFIELD GAVE PURPOSE OF INVESTING ► Strength necessary to hold the forces exerted by entering stream of molten metal till it hardens. ► Provides a smooth surface for the mold cavity so that final casting requires less finishing and polishing. ► Acts as an avenue of escape for most of the gases entrapped in the mold cavity. ► Provides necessary compensation for the dimensional changes of the alloy from the molten to solid , cold state.
  • 48. BRUMFIELD FACTORS INFLUENCING THE DENTAL CASTING PROCEDURE ► ► ► ► ► ► ► ► ► ► Care and accuracy with which the cast is reproduced. Designing of the framework Care and cleanliness in waxing up the cast. Expansion of the wax caused by temperature change Size , length, configuration, points of attachments and manner of attachment of the sprues. Choice of investment. Location of pattern in the mold. Mixing water: amount, temperature, and impurities. Spatulation of the investment during the mixing. Restrain offered to the expansion of the investment due to investment ring.
  • 49. ► Setting time. ► Burn – out temperature and time ► Method of casting. ► Gases: adhered, entrapment and absorbed. ► Forces used in throwing the metal into the mold ► Shrinkage on cooling ► Removal from the investment a after casting ► Scrubbing ,pickling ► Polishing and finishing ► Heat handling.
  • 50. BURNOUT PROCEDURE ► It serves three purposes : (i) Absorbs moisture from the within the mold. (ii) It vaporizes the gases and eliminates the pattern creating a vacuum cavity in the mold. (iii) Expands the mold to compensate for contraction of the metal on cooling.
  • 51. ► Investment must be moist at the start of the burnout cycle. ► It should not be burned out on the same day but must be soaked in water for a few minutes before to be placed in the furnace. ► Mold must be placed in the oven with the sprue hole down and the orientation mark forward .
  • 52. FURNACES ► Burnout furnaces can be either electric or gas and must be vented to allow the noxious fumes that result from the burnout to escape the work area. They vary greatly in capacity, from industrial-type gas furnaces capable of holding 25 dental casting molds to small electric furnaces with a capacity of only 1 or 2 molds. ► Induction casting is based on the electric currents in a metal core caused by induction from a magnetic field. A heating coil of copper tubing is shaped to fit closely around the casting crucible and is attached to an alternating current source. The alternating current in the coil sets up eddy currents of electrons in the crucible and the alloy in it. Excellent casting can be achieved by combination of gas and oxygen for alloys that melt close to 1093 degree centigrate . Oxyacetylene mixture is available for casting requiring higher heat ► Modern induction casting machines are normally set to cast once the desired temperature has been achieved. Some alloys require a heat soak period of up to 3 seconds during which the alloy is kept at the casting temperature by a rapid on and off of the alternating current. These machines can be set to allow the operator to determine the exact moment to cast.
  • 53. Electric Burn out furnace. Small Burn out Furnace.
  • 54. An Electric eye for An induction Casting Machine. measuring of temperature inside the casting machine.
  • 55. A clean crucible loaded with alloy. A manual release handle in centrifugal casting machine.
  • 56. REMOVAL OF CASTING FROM THE INVESTMENT ► After the casting is complete the mold is allowed to cool and at the approximate time the mold is broken by tapping it with a wooden mallet to break off the outer layer of investment. First layer of investment if removed by sand blasting.
  • 57. Investment pattern removed from burn out oven and investment placed in the induction casting machine.
  • 58. Divesting of the framework Divesting of framework with aluminum oxide.
  • 59. FINISHING AND POLISHING OF THE CAST PARTIAL DENTURE It can be divided into: ► rough finishing and polishing. ► fitting of the frame work. ► rubber wheeling and final polishing. ► sectioning and resoldering of the frame work. ► occlusal adjustment.
  • 60. Rough finishing and polishing: Areas of major connector must be shaped and rubber wheeled to a satin surface , surfaces contacting the tooth only positive blebs are removed, Areas of rest and rest seats , retentive clasp tips, guiding plane of minor connectors must be minimally polished , cast clasp arm should not be polished too much as it will distort . ► Fitting the framework: viewing of first spots the bind the framework to seat properly on to the cast, use of special powered sprays and liquids that act as disclosing media to seat the frame work properly on to the cast, seating and spot grinding until the rest completely seat on to the cast as the retentive clasp may engage into the undercut area so that the area of clap tip allows the clasp to pass under the height of contour. ► Rubber wheeling and final polishing: It is done after the casting completely seats the master cast without rocking or distortion, use of rag and felt wheels are used at high speeds lathe to give a smooth and shining surface to the framework, ultrasonic cleaning is finally done to remove the traces of polishing materials ►
  • 61. Use of coarse abrasive disk to detach the sprue from the casting at a high speed lathe. Shaping of critical areas such as retentive clasp tips using a fine stone.
  • 62. Removal of undercut area of clasp tip for proper fit of the frame work to seat on the mater cast. Carborundom rubber wheel used to smoothen the scratches and irregularities caused by finishing procedures.
  • 63. Gross finishing with abrasive stones or sintered diamonds. Polishing framework finished with a rubber polishing prior to final “ high – shine polishing.
  • 64. Use of disclosing agents to improve the fit of framework on the cast . Areas of interference indicated by displacement of disclosing medium.
  • 65. ► ► Sectioning and resoldering of the framework: It is done only when the final framework appears to rock or does not fit to the master cast or in the patients mouth so sectioning is done to seat the sections and solder the parts together, minor connectors and some of the major connectors are sectioned and soldered with precious metal solder or non precious brazing alloys which is done by electro soldering device. Occlusal adjustment: occlusal and incisal rests must be waxed heavily enough to allow them to cast completely , minimum clearance of less than 1.5 mm is kept for rest and embrasure clasps
  • 66. WROUGHT WIRE RETENTIVE CLASP ARMS ► ► Retentive clasp arms can be constructed of wrought wire as well as cast alloy. Many clinicians prefer the wire clasp, believing that they will have a greater degree of control in adapting and adjusting the clasp. Since wrought wire is normally round, it will flex equally in all directions. This uniform flexibility is thought to be "kind" to the abutment tooth. Wires available for removable partial dentures normally run from 17 to 20 gauge and can be made of either precious metal alloys (gold, palladium, platinum, silver) or non precious alloys (stainless steel, nickel chromium, nickelchromium-cobalt). Eighteen- and nineteen-gauge nickelchrome-cobalt wires are currently the most popular. The high cost of precious metals has reduced the use of these wires. While non precious wires are not as resilient as precious wires they have proven to be clinically dependable.
  • 67. Electro soldering machine. Reassembling of sectioned parts of the frame work . Placement of electro soldering tips for joining of the parts of the sectioned framework.
  • 68. Smoothening of soldered joint . Heavily waxed occlusal rest for proper casting of the rest .
  • 69. Use of wrought wire Contouring of clasps used in temporary wrought wire. prosthesis.
  • 70. Checking the position of clasp by positioning it on the cast Addition of wrought wire clasp by embedding it into the acrylic resin
  • 71. ► ► Wrought wire clasps are almost universally used as repair additions for fractured or distorted cast clasps and on a variety of temporary and transitional prostheses as well. It is essential that the clinician develop and maintain skill in the manipulation of the wrought wire clasp. Wrought wire can be attached to the framework in 4 ways: embedding of the wire piece into the acrylic denture part, induced in the wax up of the framework and the metal casts to the wire, soldering of the wrought wire on to the frame meshwork well away from the area were it flexes,
  • 72. Addition of wrought wire clasp to the framework by soldering to all parts of framework. Shaping of wrought wire to the tooth after soldering.
  • 73. Master cast with relief , block out, completed pattern on master cast with major connector , plastic clasp form resting on investment ledges , wrought wire and with open mesh with lingual bar Finished casting placed on the master cast
  • 74. SUMMARY AND CONCLUSION ► ► Although it is certainly impractical and perhaps impossible for the clinician to be actively involved with the construction phases of the removable partial denture framework, so the dentist must keep himself update to the newer techniques developed for the processing of the prosthesis in turn to achieve a harmonious and effective prosthesis keeping patients needs in mind . The dentist who has the confidence to interject personally into the construction phase of the framework and establish and maintain a rational dialogue with the laboratory gains not only a better mechanical product but also the respect of the auxiliary worker.
  • 75. REFERENCES. ► ► ► ► ► ► ► Applegate O. C. :Alloys for removable partial dentures; Factors considered choosing an alloy; Dent Clin North Am; 4: 583-590;1960. Asgar K. A.: New alloy for partial dentures. J Prosthet Dent 23:36-43; 1970. Blatterefein L. et al.: Minimum acceptable procedures for satisfactory removable partial denture service. J Prosthet Dent. 27:84-87;1972. Brown E.T. : The dentist , the laboratory technician and the prescription law. J. P.D: 15:1132-1138;1965. Calomeni AA: Problem areas encountered by dental laboratories. J Prosthet Dent. 19:523-529; 1968. Clinical removable partial prosthodontics: Kenneth L. Stewart D.D.S , Kenneth D. Rudd and William A. Kuebker- second edition Dutton DA.: Standard abbreviations (definitions) for use in dental laboratory work authorizations. J.P.D. 27;94-95: 1972.
  • 76. ► Elbert C.A, and Reyge G.: The effect of heat treatment on micro hardness of cobalt chromium alloy. J.P.D. 15;873-879:1965. ► Fletcher C. F .: Combating the illegal practice of dentistry. J.P.D. 35:92-96;1976. ► Grunewold A.H et al.: Role of dental technician in a prosthetic service. Dent Clin North Am. 4;359-370: 1960. ► Henderson D and Frazier Q.: Communicating with dental laboratory technicians: Dent Clin North Am.14:603-615;1970. ► Mc Craken’s removable partial prosthodontics- Glen P. Mc Givney, Alen B. Carr: tenth addition. ► Mc Craken’s removable partial prosthodontics- Glen P. Mc Givney, Alen B. Carr, David T. Brown.:Eleventh addition. Morris H. F. et al:The influence of heat treatment on several types of base metal removable partial denture. J.P.D. 41:388395;1979.
  • 77. Olin P.S. et al: Current prosthodontics practice- a dental laboratory service. J.P.D. 61:742-745;1989. ► Payene S.H: The school , practitioner and the denturist J.P.D. 12;812-816: 1962. ► Rudd K.D , Morrow RM and Rhoads J E: Dental laboratory procedures: vol 3;removable partial dentures: 2 nd edition. ► Smith G.P: The responsibility of the dentist toward dental -laboratory procedures in fixed and removable partial denture prosthesis. J Prosthet Dent. 13:295-30 1; 1963. ► Taylor D.F . Et al: Physical properties of dental chromium cobalt alloys: Jam Dent Assoc. 56:343-351; 1958. ► Weintraub G..S: Dental student as a technician: to what degree ? J.P.D. 39;459-465;1978. ►
  • 78. Leader in continuing dental education