Using the Siladent system describe in detail and correct sequential order the laboratory procedures to produce a Co/Cr denture framework from receipt of a secondary model.

Using the Siladent system describe in detail and correct sequential order the laboratory procedures to produce a Co/Cr denture framework from receipt of a secondary model.

1. 1. The master model is surveyed, choose the path of insertion.

   • 2. Record three lines on the model using the tripod method, which allows for easy reposition of the model back on the surveyor once the model has been removed.
     • 3. Undesirable undercuts are waxed out using surveying wax. A chisel is used to remove excess wax, and an undercut gauge of 0.25mm is used to produce any desirable undercuts for clasps.
       • 4. A thin layer of wax is placed onto the foundation area of future partial denture saddles which will be replaced by acrylic resin in later course and in this way enable mechanical bond between the acrylic resin and metal construction.
         • 5. A small square is cut out on any free saddles to produce a stop, this helps to prevent any movement when packing acrylic later on.
           • 6. Wrap the model in the Siladent 'ring tape'. Cut to size with a pair of scissors. The ring tape should overlap by at least 20-30mm.
             • 7. Peel off the yellow tape and stick the ring tape around the base of the model.
               • 8. Do not stick the edges of the tape together with selotape, as this can cause warpage.
                 • 9. Spray the model with Siladent model separator "Neutrasil".
                   • 10. Attach a mould support plate to the support stand by screwing it onto the rod. Secure the rod in place with the nut on the upper bar of the stand. Take a moment to check the mould support fits within the ring tape. Each stand position has been numbered, make a note of the number.
                     • 11. Attach a mixing cannula to the Siladent duplicating machine. Insert the cannula into the locking mechanism by lining up the cannula with the locking plate and twisting until it locks in place.
                       • 12. Check there is an adequate amount of silicone in the machine before use. Turn the machine on and run silicone into the mould. Remember to remove the mixing cannula from the machine immediately after use. Leave the duplicating silicone to set for 20 minutes.
                         • 13. Once set, take off the tape and put to one side. Gently remove the silicone from the model, trim any rough edges of the silicone.
                           • 14. Then reuse the tape, sticking it around the base of the silicone.
                             • 15. Spray the silicone with a surfactant spray, also known as debubblizer, which helps to reduce surface tension in order to permit better adherence and eliminate voids and bubbles while pouring stone.
                               • 16. Two duplicate models will be made, the first produced using SP dental stone, which will be used for partial denture fabrication. The second, using refractory investment material, which is used to the modelling and making of metal partial denture framework.
                                 • 17. Sprinkle the SP plaster slowly into the water in the plaster bowl. The plaster should not be "dumped in". Add plaster until it's visible above the surface of the water.
                                   • 18. Leave the plaster to stand for one minute to allow crystal growth to take place.
                                     • 19. Mix the plaster thoroughly with a plaster spatula. Good technique is to press the plaster against the sides of the bowl with the spatula to create more centres of crystallisation.
                                       • 20. Continue to mix the plaster until the plaster reaches the required consistency
                                         • 21, Place plaster on a vibrator to remove air bubbles from the mixture, then pour slowly into the silicone mould from one side of the mould, letting it vibrate to the other side. Let set for 20 minutes.
                                           • 22. Once set, the duplicate model is removed from the silicone. Clean the silicone, then mount a plastic cone for a future sprue on the mandibular cast.
                                             • 23. Stick tape around the base of the silicone, and again spray silicone with a surfactant spray.
                                               • 24. Measure out, then mix together the refractory investment powder and liquid under ventilation. Once wet, add lid and mix under vacuum.
                                                 • 25. Again, add the investment material to the silicone on the vibrating machine, adding to one side slowly letting the material run to the other side.
                                                   • 26. After approximately 30 minutes the investment material cast is separated from the duplication material, then trimmed on the dry trimmer. If trimmed with water, the wax will not stick to the model in the next steps.
                                                     • 27. The elements of a future metal construction are arranged and modelled on the duplicate cast made from investment material by means of stock wax elements: base, saddles, retention and stability elements.
                                                       • 28. After precise modelling of a wax pattern, wax sprues around 3.5 to 4mm thick are placed on the thickest part of the framework, usually from the major connector or occlusal rests.
                                                         • 29. Small 0.5mm sprues can be added to allow air to escape when casting.
                                                           • 30. All sprues must merge together smoothly.
                                                             • 31. Mandibular models can be stuck to a base with a cone, sprues can can then go directly into the cone made hole in the mandibular model.
                                                               • 32. Maxillary models are placed on a flat base and a cone can be placed on top of sprues, ensuring the cone will be level with the orange casting ring.
                                                                 • 33. Add the orange ring to the base, and spray the model with surfactant spray.
                                                                   • 34. Mix 2 packs of gransit powder with 52ml of investment liquid under ventilation. Then mix under vacuum.
                                                                     • 35. Pour the investment material to one side of the model on the vibrating machine, from a high level to prevent bubbles.
                                                                       • 36. After hardening of the material (after 40 minutes), the cone, ring and base can be removed then the flask is placed into a furnace and heated, so that the wax can flow out leaving a hole in which the molten alloy is poured after glowing the flask.
                                                                         • Reused cobalt chrome alloy can be weighed and trimmed to get the required weight of alloy. It is then sandblasted prior to casting to remove the oxidised layer.
                                                                           • 38. The weighed alloy is mixed with new ingots, they are pre-melted before flasks have been removed from the furnace, then once flask is put in casting machine, they are melted more then cast.
                                                                             • 39. Flasks are then placed into the hot box and left till cooled.
                                                                               • 40. After cooling the flask, the investment material is broken and the metal partial denture framework is taken out.
                                                                                 • 41. The remaining investment material and oxides are removed in the sandblasting device and sprues are eliminated using the high speed grinders.
                                                                                   • 42. After finishing it is necessary to check whether the fit of the casting to the original stone cast is tight.
                                                                                     • 43. Sandblasting is performed again after rough finishing of the cast, as well as fine finishing and polishing of the casting.
                                                                                       • 44. The first polishing phase consists of electrolytic polishing in an electrolytic polishing device.
                                                                                         • 45. The final phase consists of mechanical polishing by various polishing aids that enable polishing of metal partial denture frameworks to a high gloss. Such as rubbers and brushes for polishing with pastes and polish blocks.