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Working cast and dies /certified fixed orthodontic courses by Indian dental academy


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Working cast and dies /certified fixed orthodontic courses by Indian dental academy

  2. 2. CONTENTS  Introduction  Definitions  Review of literature  Requirements of working cast  Requirements of die preparation  Requirements of die materials  Materials used for die preparation  Cast & die systems a) - Working cast with removable die Straight dowel pin Curved dowel pin Di – lok tray Pindex system Accutrak
  3. 3. Solid cast with individual die DVA model system Zeiser model system - Preparation of the die for wax patterns. - Drawbacks of ditching. - Gum mask. - Die spacers - Die lubricants - Conclusion - References
  4. 4. INTRODUCTION  Direct fabrication of patterns for extraoral restorations in mouth:- - Inconvenient - Difficult - Time consuming - Virtually impossible  Practically all wax patterns are made in laboratory with indirect technique. This technique requires an accurate reproduction of prepared tooth, soft tissue & the adjacent & opposite teeth.  A cast & a die system captures the necessary information so that it can be transferred to
  5. 5. DEFINITIONS  WORKING CAST- is the replica of the prepared teeth, ridge areas & other parts of dental arch. (Rosensteil)  DIE- is a positive reproduction of the prepared tooth, & consists of a suitable hard substance of sufficient accuracy(i.e. of improved stone, metal or resin).
  6. 6. REVIEW OF LITERATURE  Nomura G.T., Reisbick M.H. & Preston J.D. (1980) – conducted an investigation of epoxy resin dies. They evaluated 3 commercially available epoxy resin die systems & used an improved stone die material as a control for comparison with the epoxy resin dies. They concluded – 1. Complete crown epoxy resin dies are undersized. 2. MOD onlay epoxy resin dies are accurate. 3. Detail duplication of epoxy resin dies is comparable to that of die stone. 4. Hardness values of epoxy resin are generally less than those of die stone. (KHN – 17.76 – 29.80)
  7. 7.  Myers M., Hembree J.H.(1982) – conducted a study on the relative accuracy of four removable die systems. 4 die systems were studied i.e. the brass dowel pin, the Plastipin, the J-pin, & Logix Model System & they determined the vertical shift & the horizontal shift of the dies. They concluded that Plastipin exhibited least amount of horizontal shift & the brass dowel pin exhibited greatest shift in both directions.
  8. 8.  Covo L.M., Ziebert G.J., Balthazar Y., Christensen L.V. (1988) – conducted a study on the accuracy & comparative stability of three removable die systems. They evaluated the accuracy of Accu-Trac system, Pindex system, & conventional brass dowel pin positioning technique & evaluated the stability in 3 directions( Mesio-distal, buccal-lingual & vertical). They concluded- - In horizontal direction – no significant differences were found between the mean displacements. - In vertical direction – slight displacement did occur in upward direction with pindex system & conventional dowel pin system while a significant displacement in a downward direction was found with the Accu-Trac system.
  9. 9.  Richardson D.W., Sanchez R.A., Baker P.S., Haug S.P. (1991) – conducted a study to evaluate the positional accuracy of four die tray systems. The die trays were:- Accu-trac Precision die system, Model-tray system, Sterdo Split model tray & Tricodent One cast die tray system. Positional change of the dies was measured by using an Olympus binocular scanning tunneling microscope. They concluded – - No significant changes were found between Accu-trac, Sterdo & Tricodent systems. - In Model tray system, measurement was significantly lingual with respect to the reference point.
  10. 10.  Gerrow J.D., Price R.B. (1998) – conducted a study on the comparison of the surface detail reproduction of flexible die material systems. The purpose of the study was to compare the surface detail reproduction of 7 potential flexible die materials when used in combination with 7 elastomeric impression materials. They concluded that- - Certain combinations of impression materials & flexible die materials were incompatible & should not be used to fabricate flexible dies. - Use of a separator is necessary to make polyvinyl siloxane impressions compatible with polyvinyl siloxane dies, but when a separator was used, the surface detail reproduction was not as good as other die system or die material combinations.
  11. 11.  A study was conducted in our department under the able guidance of Dr. N.P. Patil sir, in 2004, on evaluation of the effect of die spacing on the retention of complete coverage cast crowns. They concluded that cast crowns fabricated with 4 layers of die spacer relief will provide maximum retention & at least 2 layer of die relief is essential to avoid crown to tooth contact/frictional fit.
  12. 12. Requirements of a Working Cast:- 1. Must reproduce both prepared & unprepared tooth surfaces. 2. Unprepared teeth adjacent to preparation must be free of voids. 3. The anterior teeth involved in anterior guidance and occlusal surfaces of all teeth should allow precise articulation with the opposing teeth. 4. The relevant soft tissue should be covered including the edentulous spaces and contours of residual ridges, that will be involved in fixed partial denture.
  13. 13. Requirements for Die Preparation:- 1. All surfaces must be accurately duplicated & no bubbles or voids can be accepted. 2. All the details of prepared tooth should be reproduced. 3. The unprepared tooth surface immediately cervical to finish line should be accurately produced in order to allow the technician to prepare accurate finish line in wax pattern. 4. Adequate access to margins is necessary.
  14. 14. Basic Requirements of Die Materials:- 1. Should have accuracy and dimensional stability. 2. Should have a smooth, hard surface which should not easily abrade. 3. Should be compatible with impression material. 4. Should have high strength. 5. Should have good color contrast. 6. Economical. 7. Should be able to manipulate easily and fast. 8. Have ability to reproduce fine details & sharp margins.
  15. 15. Materials used for Die Fabrication:- 1. Gypsum products - Type IV - Type V - Divestments   2. Amalgam used for making dies.   3.  Cements - Silico phosphate cements   4.  Polymers and filled polymers - Self curing acrylics - Epoxy resins
  16. 16.                5.  Electro deposition of metals               - Copper plated - Silver plated       6. Metal sprayed dies.        7. Flexible die materials        8. Refractory materials for die preparation.
  17. 17. Gypsum Products:-  Are available in five forms (ADA Type I-V) Type I- Impression plaster. Type II- Model plaster. Type III- Dental stone. Type IV- Dental stone with high strength. Type V- Dental stone with high strength and high expansion.  Depending on method of calcination, different forms of hemihydrate can be obtained.
  18. 18. Die Stone, High Strength (Type IV):- - The principle requisites for die material stone are strength, hardness, abrasion resistance & minimum setting expansion. - α- hemihydrate of the “Densite” type. - Cuboidal shaped particles & reduced surface area produce such properties without undue thickening of mix. - W/P ratio – 0.22 – 0.24 - Setting time - 12±4min. - 2hr Setting Expansion – Maxi. 0.10% - 1hr compressive strength – 5000psi. - Because surface dries more rapidly so, the surface hardness increases more rapidly than does the compressive strength. - Average dry hardness of Type IV is approx. 92 Rockwell hardness & of Type I is 82 Rockwell hardness.
  19. 19.
  20. 20. Die Stone, High Strength, High Expansion (Type V):- - Higher compressive strength than Type IV. (attained by making lower w/p ratio). - Setting Expansion – Maxi. Of 0.10% - 0.30%. - W/P ratio – 0.18 – 0.22 - Setting time - 12±4min. - 1hr compressive strength – 7000psi. - Use is contraindicated in dies for inlays.
  21. 21. - As gypsum products are less abrasion resistant, so to compensate surface abrasion, so called gypsum hardeners are used such as: Colloidal silica: It increases resistance to surface abrasion but there is little increase in setting expansion, which is minor. Low viscosity resins i.e. cynoacrylate, which is used to impregnate the die surface, care is taken while applying it so as to produce uniform thickness. - In order to improve the properties of dental stone: 1. Additives use in industrial applications (e.g. concrete manufacturers) are added in gypsum products e.g. liquid dispersing agent or microcrystalline additives. 2. Gum arabic. 3. Calcium hydroxide mixture. 4. Resin strengthened gypsum products such as Resin Rock with high strength and low expansion (particularly for implant casts)
  22. 22. Die Stone – Investment Combination:- Have comparable composition. Commercial Gypsum Bonded Materials:- 1. The divestment is mixed with colloidal silica liquid. 2. Die is made & wax pattern is constructed on it. 3. This entire unit is invested in mixture of divestment & water, thereby eliminating the possibility of distortion of pattern on removal from the die. 4. When heated to 677ºC, - Setting expansion – 0.9% - Thermal expansion – 0.6%.
  23. 23. 5. Not recommended for high fusing alloys. 6. Highly accurate technique for conventional gold alloys especially intracoronal preparations. Phosphate bonded die investment materials formulated for use in making ceramic prosthesis can be used when casting high fusing alloys.
  24. 24. Amalgam:-(used for making dies) 1. They are made by packing amalgam into impression made of impression compound. 2. Dies made of amalgam exhibit superior strength, resistance to abrasion & reproduce fine details & sharp margins. 3. It require wrapping in wax or tape & embedding in a rigid matrix such as plaster to resist the pressure necessary to condense amalgam. Disadvantages:- 1. This technique is time consuming but it also requires some degree of skill to condense the amalgam into impression properly. 2. Alloy takes atleast 12hrs to harden before it is possible to recover the die. 3. Improper manipulation of amalgam can lead to clinically significant dimensional changes.
  25. 25. Silicophosphate Cement:-  Is similar to the filling & cementing material.  The powder is a mixture of silicate powder & zinc oxide & liquid contains phosphoric acid. Advantages:-   - Strength & surface hardness superior to those of die stone. Disadvantages:- 1. Material contracts during setting & may be dimensionally inaccurate. 2. Loss of water on standing since viscosity is relatively high. 3. Presence of surface voids can occur.
  26. 26. Polymers or filled polymers:-  Self curing acrylic, epoxy resins.  The curing contraction is excessive 0.6% in self curing acrylic resins. Advantages(epoxy resins):- 1. Superior abrasion resistance. 2. Less brittle. Disadvantage:- 1. Shrinkage on polymerization. 2. Less dimensional stability. 3. Expensive. More viscous than stone, so more prone to trap air in preparation.
  27. 27. Supplied as:- - A paste to which a liquid activator(amine) is added. - Amine is toxic (should not come in contact with skin). - Recently, fast setting epoxy materials have been supplied in automixing system. - The fast setting epoxy hardens rapidly, so dies can be waxed 30min. of injecting.
  28. 28. Properties:- 1. Working time – 15min. 2. Setting time – 1-12hrs. 3. KHN – 17.76 – 29.80 4. Compressive strength after 7 days – 16,000psi. 5. Abrasion resistance superior to stone dies. 6. Cannot be used with water containing agar & alginate material, since it retards the polymerization of resin. 7. Polymerization shrinkage – 0.1-0.2%.
  29. 29. Electro deposition of metals:-  Can produce detailed reproduction upto 30µm.  Have moderately high strength, adequate hardness & excellent abrasion resistance. Basic system consists of:- - An electrolyte solution - A source of direct current. - An anode – pure copper pure silver regenerates solution during the migration of copper from cathode & to the surface of impression.
  30. 30. Procedure:- For silver plating polysulfides & silicone impressions are used. 1. Cleaning & drying the impression. - Metallize the area to be plated with a fine silver powder by burnishing it with a sable brush. - Various metallizing agents are:- - Bronzing powder - Aqueous suspension of silver powder. - Powdered graphite. 2. Insert cathode wire in the border of impression in the metallized area but not too close to the preparations.
  31. 31. 3. Fill preparations & the teeth with electrolytic solution by using an eye dropper to prevent air bubbles & resulting voids. 4. Completely submerge the impression in plating solution. The silver anode immersed in the solution should be atleast equal in size to the area of the surface to be plated.
  32. 32. 5. Proceed plating initially at approx. 5mA per tooth for 1hr. & check for even deposition of metal & make certain there are no voids. Resubmerge the impression in plating solution & plate it for approx. 12hrs. at 10mA per tooth. 6. Wash & dry impression & use dental stone.
  33. 33. Problems:- 1. Silver cyanide solution is extremely dangerous, because if it contacts acid, it produces fumes of extremely toxic hydrocyanic acid. 2. These dies are not significantly more or less accurate than stone dies. 3. The possibility of continued polymerization & distortion of impression during electroplating may lead to a clinically significant dimensional change in the impression. 4. Friable metal deposit current if setting too high. 5. Silicone difficult to electroplate, because of low surface energy. 6. Polyether cannot be plated accurately, since it imbibes water. 7. Polysulfide can be silver plated but difficult to copper plate.
  34. 34. Metal Sprayed Dies:- Bismuth alloy with fusing point of 136ºF is melted by placing at constant temperature held at 145ºF. Die is poured & solidify at 30 pounds of pressure. Advantage:- A metal coated die can be obtained rapidly from elastomeric impression materials. Disadvantage:- Alloy is soft, care is needed to prevent abrasion of the die.
  35. 35. Flexible Die Materials:- - Similar to heavy bodied silicone or polyether impression material. Use:- - To make provisional restoration. - Indirect composite resin inlays Advantage:- - More rapid setting – 10min. - Ease of removal of provisional restoration. Care should be taken to select compatible impression material & die material.
  36. 36. Refractory Dies:- - These are made for preparation of full ceramic restorations. Advantages – Excellent marginal adaptation Technique of preparation – - After the working cast and dies are prepared with a convenient technique, a low viscosity polyvinyl siloxane duplicating material is used to reproduce dies (low viscosity allows registration of minute details)
  37. 37. - Adapt a strip of putty around the prepared teeth on working cast and dies to limit the flow of mold material. It should extend several teeth beyond the dies and beyond edge of tray on both buccal and lingual sides of tray. - To avoid air entrapment, fill the putty reservoir by pouring the mix. - The duplication material should be at least 3.00mm thick and it should extend 3 mm beyond incisal edges of teeth to provide adequate support refractory material. - The duplicating material is allowed to set for about 30 minutes.
  38. 38. - When duplicating material is set, remove silicon putty reservoir and disassemble the plastic tray. - By applying pressure on base of tray, master cast is loosened with duplicating material intact. - The master dies removed from cast and duplicating material.
  39. 39. - The refractory material is poured and vibrated in the area of missing dies. - Allow the refractory dies set for about 1-2 hours.
  40. 40. Care to be taken while pouring refractory die material- - The refractory material should be mixed according to manufacturer’s directions - Recommended powder liquid ratio must be followed since it may causes uncontrolled expansion or, shrinkage during setting and possibly a weakened die. Technical considerations of refractory die material - - Liquid powder ratio – 6ml / 30gms(depending upon the brand used) - Working time – 3mins - Setting time – 1 hour - Wax burnout furnace – upto 700°C for degassing to eliminate sulfur and ammonia gasses and then ceramic furnace – upto 1080°C in vacuum.
  41. 41. - Cooled down at room temperature - Application of die sealant i.e. application of 2 thin wash of half glaze, half dentin porcelain to prevent porous die material to absorb water from porcelain & fire.
  42. 42. Cast & Die Systems:- 1) Working cast with removable die i. Straight dowel pin ii. Curved dowel pin iii. Di-lok tray iv. Pindex system v. Accutrak system 2) Solid cast with individual die 3) DVA model system 4) Zeiser model system
  43. 43. Working cast with removable dies:- These have become very popular. It should satisfy following requirements – 1) It must refit accurately in its original position. 2) It must be stable, even when the cast is inverted 3) The cast carrying removable dies must be easily mounted on an articulator.
  44. 44. Advantages:- 1. It is the simplest means of fabricating a working cast. 2. It also keeps the relationship of abutments fixed & immovable. This is a sure method of accurately orienting the preparation models to each other, which is considered important step in minimizing casting adjustments. 3. Because gingival tissue & other landmarks are intact, it is easier to obtain physiologically harmonious restoration contours when fabricating the wax pattern. Disadvantages:- 1. Procedures are quite difficult. 2. Encounter of poorly seating dies & dowels. 3. Difficulty in sawing the die out of cast. 4. Interproximal margins can easily be damaged.
  45. 45. Dowel pins:- Types of antirotational dowel pins – A. Flat sided single dowel pin B. Single curved dowel pin C. Double dowel pins with single head D. Two separate parallel dowels (Pindex system) E. Keyed plastic outer tray
  46. 46. Bi-V-Pin with sleeve Bi-Pin long/short with sleeve Brass Dowel Pins
  47. 47. Straight dowel pin:- - The flat sided brass straight dowel pin is most commonly used in preparing die. - Serrano J.G et al (1998) found that, it is most accurate in terms of resting horizontal movement and rotation with least occlusogingival reseating discrepancy i.e. vertical deviation.
  48. 48. - A no. of items found in dental laboratory are commonly used for orienting the dowels, such as anesthetic needles, paper clips, bobby pins. - Place the dowel pin between the arms of bobby pin with the round side of dowel pin in one of the corrugations and flat surface of dowel against flat arm of pin. - Position the bobby pin buccolingually across the impression so that dowel pin will be centered directly over preparation.
  49. 49. - Placing head of a dowel too deep in impression may weaken the die. Positioning the dowel at incorrect angle may make die removal impossible. - Stabilize the dowel pin with bobby pin and the bobby pin with straight pins with sticky wax.
  50. 50. - Pour die stone in impression, filling impressions of teeth covering the dowel pin. - For small preparations thin instrument may prove helpful to place stone in most critical area. Bubbles will be trapped if too much stone is added abruptly. Stone is teased into preparation along axial walls by tilting impression & guiding material. - Care should be taken while pouring, if stone too runny, dowels will not remain in place.
  51. 51. - When stone is set, the straight pin and bobby pin is removed from impression. Head of dowels must be covered with stone at first pour.
  52. 52. - Small ball of utility wax is placed on tip of each dowel. - Lubricate the stone around each dowel with thin coat of petroleum jelly of facilitate removal of die from working cast. Excess lubricant is removed. - A filler is placed in the lingual space and base is poured. - When it is set base is trimmed to remove excess. - Utility wax is removed with sharp knife.
  53. 53. - When the stone is hard and dry, a saw frame is used with blade to cut this layer of die stone. - Cuts should be on mesial and distal side of each die. They should be parallel to each other or, little fit tapered towards each other towards the pin.
  54. 54. - Evenly tap on end of dowel pin with an instrument handle to loosen die. - Take the die away and excess stone gingival to finish live is trimmed with no. 25 blade as acrylic bar. - Finish line is marked with pencil. - Same procedure is reperated with each die. - Make certain that the dowel hoses are free of any debris - Then dies are reseated into the cast - Cast is ready for mounting - Utility wax is placed at the tips of dowels to avoid contamination with moving stone. - When the stone is set, the wax is removed insuring that no debris is remaining.
  55. 55. Curved dowel pin:- - Can be fixed by pre-pour or, post-pour technique.       Pre-pour technique – - To install pin before pouring the impression, use finger pressure to insert tip of dowel into large opening of position bar. - Hold the bar faciolingually, so that head of the dowel is 1-2mm into the proposed area of impression. - The tail of dowel extends facially; however if the tooth is linguoversion, turn it towards lingual side for easy removal.
  56. 56. - Insert a straight pin into one of 3 holes into the facial aspect of bar and into the facial flange of impression and another pin into lingual flange through lingual holes of bar. - The dowel should not touch the impression and its head should be parallel to long axis of prepared tooth or teeth. - This procedure is repeated for all abutments and pontic areas. - One pin is placed near the center of each segment of unprepared teeth, this wall help in removal of segment for better access of gingival wax pattern. - Impression is poured with die stone until it covers heads of dowel. This will fill the impression about 4 mm above gingival finish line. - The straight pins and positioning bar are removed as soon as stone is set.
  57. 57. - To orient the large segments of unprepared teeth, 2mm deep holes are made with acrylic bur on either side of the each dowel pins. - Petroleum jelly is applied on stone and also an exposed part of dowel so that can easily separate from base. Impression is boxed with modeling wax with tips point outside wax.
  58. 58. - Base is poured with stone. - After stone is set, vertical saw cuts are made on both sides of dies without damaging prepared finish lines. - Cuts must extend through die stone to underlying base, then separate each segment from the working cast by pressing or tapping on the protruding tail of curved dowel with a knife handle.
  59. 59. Post-pour technique - - Pour the impression with die stone to form a horse-shoe shaped working cast. - Trim the bottom of cast flat to level 10mm from the necks of teeth. - This is done because thin cast are easy to saw and short dowels are more stable than larger ones.
  60. 60. - Drill a 0.5mm hole directly below the center of each prepared tooth, pontic area, and segment containing unprepared teeth. - This can be made with 2mm diameter drill in hand piece or drill press. - If the width of removable segment is greater than that of two teeth keyholes are made on each side of dowel holes with 2mm depth with large acrylic bur for orientation.
  61. 61. - Clean the dowel holes, insert the curved dowel pin properly and then adjusted for proper fit. - Cement the dowels into holes one at time with placing a drop of cynoacrylate cement into each hole. - Seat the heads completely with tail pointing facially. - Then same procedure of pouring base and preparing dies is repeated.
  62. 62. Pindex system :-(Colten, Whaledent, Makwak, MJ) The Pindex system consist of :- 1. A special drill press 2. Brass dowels and plastic sleeves 3. A stone cast trimmed to horse shoe shape - The impression is poured with die-stone adding approximately 20mm of stone beyond the edge of tray. This should allow enough stone to trim without having to add more die stone.
  63. 63. - Allow the cast to set for 60-min and then remove it. - Thoroughly wet cast prior to trimming to prevent accumulation of sledge of prepared teeth. - The bottom of cast is then trimmed flat and its thickness from base to prepared finish line should be minimum 15mm. - Remove any excess stone in palate / tongue area with arbor band on lathe. The faciolingual width should be approximately 10mm.
  64. 64. - Use a pencil to mark the desired location of the pins on occlusal surfaces of teeth or preparations. - There should be 2 pins for each die, two for each pontic area and two for segment containing unprepared teeth. - Place the cast on worktable of drill press with red pilot light on. - Align the first pencil mark with illuminated dot from light beam.
  65. 65. - Using both hands, exert firm downwards pressure on the cast with thumbs. - Raise the handle bar with slow, even pressure and the drill assembly moves upwards cutting the pinholes. - When proper depth is achieved, red light goes off. - Same procedure is repeated with each mark. - For better results, cast is made slightly damp to prevent dust formation. - Compressed air and brush is used to remove debris from holes.
  66. 66. - Pinholes are refined with hand reamer. - Prior to cementation, complete seating of pins is insured. - Pins are cemented with cynoacrylate cement and cast should be thoroughly dry.
  67. 67. - Short pins are cemented on lingual / palatal side first, then longer ones on facial side, this facilitates easy removal. - When cement is dried, place the plastic sleeves over pins with flat sides of their bases facing each other.
  68. 68. - Apply a thin coat of petroleum jelly on bottom of cast as separating agent. Wipe off excess as it could cause sitting errors when dies are repositioned. - Place small amount of molten wax at the end of short sleeves to prevent the sleeve from filling with stone when base is poured. - Run a strip of utility wax on long pins to facilitate removal of die later. - Place a small ball of wax on ends of isolated pins.
  69. 69. Two methods can be used to pour base 1) With boxing the cast 2) In a specially designed mold - Allow the cast to dry before sectioning, the pinned cast is removed from base which permits sectioning from downside. (This is helpful in cases where there is limited interdental space and therefore possibility of damage to finish lines.) - Utility wax is removed from tips; saw cuts are marked on facial and lingual aspects.
  70. 70. - With the handle of an instrument all exposed pins are tapped lightly to remove cast in one piece. - Pencil marks are extended on underside of cast. - The saw cuts should end approx. 1 to 2mm short of finish line with final separation accomplished by squeezing two part gently. This assures clean separation. -
  71. 71. - To remove a single die, a large amalgam condenser or, handle of an instrument is used to push the end of exposed pin until the die is loosened from base. - To allow easy removal of dies, the saw cuts should be parallel or taper slightly towards the pin. - After the dies are sectioned, trim them in conventional manner, mark the finish line, apply die hardener and die spacer. - Then mount the working cast on articulator. - Place a small amount of utility wax on the end of die pins. This will prevent the mounting stone from blocking access of pins. Once the mounting stone has set, remove wax on pins and cast is ready for wax pattern.
  72. 72.         Di-lok tray system :– - In this system, a snap apart plastic tray with internal orienting grooves and notches is used to reassemble working cast and dies. - Dilts, Podshadly, Sawyes and Netman (1971) found that this system has least vertical error. Care to be taken – 1. Should be kept clean for greatest accuracy. 2. When the casts must be mounted near upper member of articulator or, near hinge axis, examination of mounting casts on articulator should be done to determine whether there is space for bulky tray.
  73. 73. Technique – - Pour the entire full arch impression with die stones without putting stone in the open lingual / palatal area and as little as possible on vestibular folds and building it up to a ht of 2.5cm. - When stone is set, separate it from impression. - Cast is trimmed in horseshoe configuration to fit in Di-lok tray and the buccal border is tapered towards base with arbor band.
  74. 74. - Horizontal grooves are cut on outer and inner aspect of bottom of cast for retention. - Soak the base of cast with water for 5 min. - Pour the base in tray, until ¾ of its is filled - Seat the cast on base; in such a way that gingival finish line is approximately 4mm above the level of base. - Wipe out the excess stone. - Allow the base to set.
  75. 75. - To prepare dies, cast must be removed from tray. - Dissemble the tray by lifting the back-up and then slide the buccal segment forward. - Cast can be easily be loosened by tapping at the front of base of tray with handle of knife and then cast is separated from tray.
  76. 76. - With saw frame and blade cut between the prepared tooth and adjacent tooth in interdental papilla area and extend downward with light taper inwards. - The occlusal saw cut should extend ¾ through stone base. - Use finger pressure to break the die and attached teeth from cast. - In the similar manner dies is separated from the segment. Repeat the procedure
  77. 77. - Remove excess stone gingival to finish line with a pear shaped acrylic bur. - Finish trimming and blending the concave area adjacent to finish line with no. 25 blade. Mask the finish line. - Clean the tray with compressed air and brush to remove flash. - When tray is completely cleaned, reassemble the dies and segments into the tray.
  78. 78. - Slide the buccal facing on the base from front place the back down and lock it with buccal facing. - The Di-lok tray is placed onto face bow or, in occlusion with previously mounted diagnostic cast. - It is ready for wax pattern.
  79. 79. Accutrak System:- - Can be used for fabrication of veneers (similar procedure). - It is a modification of plastic tray with internal orientation grooves and notches.
  80. 80. Solid cast with individual die:- - Also reffered to as Multiple-pour technique. Advantages:- 1. Primary advantage is its simplicity. 2. Slightly more accurate. 3. Working cast requires only minimum trimming. 4. Since gingival tissues around the prepared teeth are left intact, used as guide when contouring the restoration. 5. No need of special equipment.
  81. 81. Disadvantages:- 1. It may be difficult to transfer complex or fragile wax patterns from cast & die & porcelain stages difficult. 2. Seating the pattern on the master cast may be problematic because of 2nd pour of many impression materials is slightly larger than the first. 3. Technique can be used only with elastomeric impression material.
  82. 82. Procedure:- 1. Impression is judged to be satisfactory is poured in type IV or V stones in the area of preparation only. When set it is separated. 2. Second pour is then made of entire arch.
  83. 83. 3. First pour, which is more accurate is trimmed into a die with a handle of sufficient length. 4. Complete arch cast (2nd pour) is mounted on an articulator. 5. Wax pattern is started on the initial pour (the die) & is then transferred to the articulated cast for refinement of axial contours & occlusal anatomy. When completed this pattern is returned to the die so the margins can be readapted immediately before investing.
  84. 84. DVA Model System:- Trimmed impression on alignment fixture. Marking dowel pin locations on clear plate Drilling holes for dowel pins as marked Inserting dowels in the baseplate
  85. 85. Impression is poured, stone placed around dowel pins & alignment fixture replaced over poured impression Set cast is removed from baseplate
  86. 86. Cast is trimmed Cast is sectioned Trimmed working casts using the DVA Model System
  87. 87. Zeiser Model System:- Advantages:- Allows advantage of allowing for the expansion of stone which is relieved by sawcuts. Disadvantages:- Use a precision drill & special baseplates that are aligned & drilled to provide die removal.
  88. 88. Zeiser Model System Impression is leveled, blocked out with silicone putty,& positioned over baseplate Pin locations are determined & the pinholes drilled in the base.
  89. 89. Pins are inserted into the base. Impression is poured Base is inverted into the stone
  90. 90. Cast is separated from the impression when set & then separated from the base. Precision saw aids sectioning Sectioned cast
  91. 91. Preparation of die for wax pattern:- - After the die is separated from working cast, die hardner such as (cynoacrylate or acrylic resin lacquer) may be painted on the surface of prepared teeth to prevent abrasion erosion or, etching when casts are trimmed or by waxing instruments. - The thickness for cynoacrylate ranges from 1 to 25 mm and for acrylic lacquers 4 to 10mm. - The die is held by base while cutting it down to handle. - Handle should be slightly larger than preparation & octagonal in cross section, with sides slightly tapered towards base or, parallel. It should be parallel to long axis of tooth. It should be approx 2.5cm long. (If it is short, it is difficult to hold wax pattern on it and does not allow adequate access for margin finishing).
  92. 92. - A pear shaped acrylic bur is used to trim die apical to finish line. Final trimming done with 25 no. blade. - Area apical to finished line is smoothened with discoid end of carver. - The center of the die apical to finish line should approximate that of root to facilitate good axial contours in finished restoration. If the finish line on preparation is not adequate sharply under cutting or, ditching the die below finish line is advised and if it is adequate it is not advised.
  93. 93. Drawbacks of ditching:- - Because the instrument used for finishing the margins of wax pattern will rest on this area, its angulation can be exaggerated by the undercut. This will result in thick gingival area on restoration and axial contour that is not conductive to good gingival health.
  94. 94. GUM MASK A silicone index made on the master cast before sectioning. After die preparation, polysulfide or polyether impression material is applied to the inside of the index. Index filled with impression material is again seated on the master cast with the prepared dies. Master cast with artificial reproduction of the marginal gingiva around the prepared
  95. 95. Creating gum mask before model making Model of the prepared impression with gum mask
  96. 96. Die spacers / die relief agents – Objectives – - To provide space for cement while cementing final restoration in mouth. - It allows accurate adaptation of casting on die. Materials used – Enamels and lacquers Thickness – No. of coats are applied to produce a relief 20-40mm. The tooth preparation of die is painted within 0.5mm of finish line for proper adaptation of casting at the finishing line.
  97. 97. Die lubricators – - Die-lubricators such as die lub can be used to coat the die directly over die spacer. - It helps in easy removal of wax pattern without adherence to die.
  98. 98. CONCLUSION
  99. 99. REFERENCES 1. Anusavice K.J.-“Phillips’ Science of Dental materials” 11th edition , 2003 2. Catalog – Renfert. 3. Covo L.M., Ziebert G.J., Balthazar Y., Christensen L.V. – “Accuracy & comparative stability of three removable die systems”. JPD1988;59:314-318. 4. Craig’s R.G., Powers J.M. – “Restorative Dental Materials” 11th edition, 2002 5. “Evaluation of the effect of die spacing on the retention of complete coverage cast crowns,” 2004. 6. Gerrow J.D., Price R.B. – “Comparison of the surface detail reproduction of flexible die material systems” JPD1998;80:485-489.
  100. 100. 7. Johnston J.F,Phillips R.W.- “Modern practice in fixed prosthodontics.4th edi.Philadelphia,Saunders co. 8. Myers M., Hembree J.H. – “Relative accuracy of four removable die systems.” JPD1982;48:163-165. 9. Nomura G.T., Reisbick M.H. & Preston J.D. – “An investigation of epoxy resin dies” JPD1980;44:45-50. 10. Richardson D.W., Sanchez R.A., Baker P.S., Haug S.P. – “Positional accuracy of four die tray systems” JPD1991;66:39-45 11. Rosenstiel S.F., Land M.F. – “ Contemporary fixed prosthodontics” 3rd edi. 2001. 12. Rudd K.D., Morrow R.M. – “Dental laboratory procedures” FPD 2nd edi, 1986. 13. Shillingburg H.T. – “Fundamentals of fixed Prosthodontics.” 3r edi.quintessence 14. Toreskog S.,Phillips R.W., Schnell R.J. – “Properties of die materials – A comparative study” JPD1966;16:119-131.