Die and diematerials


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Die and diematerials

  1. 1. DIE AND DIE MATERIALS GYPSUM PRODUCTS : Gypsum (CaSo4 2 H2O) is a mineral mined in various parts of the world however it is also produced as a byproduct of some chemical processing operations. Chemically the gypsum produced for ductal applications in nearly pure calcium sulfate dehydrate. Production of Calcium Sulfate Hemihydrate : Plaster and stone are produced by cabining calcium sulfate dehydrate or gypsum. The gypsum in ground and subjected to temperatures of 1100 to 1200 C to drive off the water of crystallization and this is the amount of water needed to convert calcium sulfate dehydrate to calcium sulfate hemihydrate. CaSo4 2H2O CaSo4 ½ H2O CaSo4 CaSo4 Depending on the method of calcination, different forms of hemihydrate can be obtained. They are α, β and α-modified hemihydrates. α - hemihydrate is called artificial stone, die stone (or) improved stone, ti consists of smaller, regularly shaped crystalline particles in the form of rods / prisms. (fig. 10-2 pg. 258 phillyes). Irregularly shaped orthorhombic crystals particles with capillary pores. (Fig: 10.1 pg. 256 philly) α - modified hemihydrate is made by boiling the gypsum in a 30% aqueous solution of calcium chloride and magnesium chloride. This process yields the smoothest, most dense powder particles. 1300 C – 2000 C 1100 C – 1300 C 1300 C – 2000 C 2000 C – 10000 C Hexagonal anhydrite Orthorhombic anhydrite
  2. 2. Types of Gypsum products : The various types of gypsum products identified by ADA are : 1) Plaster, impression 2) Plaster model 3) Dental stone 4) Dental stone high strength 5) Dental stone high strength and high expansion. Properties of Gypsum products :
  3. 3. Type W/p ratio Setting tim es (mi nt) Setting expansion after 2 hr. Compressive strength after 1 hr. Mini Maxi Mpa Psi 1) Plaster impress ion 0.40-0.75 4 ± 1 0.00 0.15 4.0 580 2) Plaster model 0.45-0.50 12 ± 4 0.00 0.30 9.0 1300 3) Dental stone 0.28-0.30 12 ± 4 0.00 0.20 20.7 3000 4) Dental stone high strengt h 0.22-0.24 12 ± 4 0.00 0.10 34.5 5000 5) Dental stone high strengt h high expansi on 0.18-0.22 12 ± 4 0.10 0.30 48.3 7000 In type III the compressive strength is 20.7 Mpa but it does not exceed 34.5 Mpa. This is used for the construction of the casts in the fabrication of full dentures that fit soft tissues. Stone dies are reproductions of prepared teeth, on or within which prostheses are constructed. Because of the severe wear conditions that occur at the margins during carving of the wax patterns and because of higher
  4. 4. stresses induced in stone dies try-in and adjustments, greater strength and hardness are required of the die materials. Dental stone, high strength (Type IV) : The principal requisites for a die material stone are : • Strength • Hardness • Abrasion resistance • Minimum setting expansion. ↓ So α-hemihydrate of densite type is used. • It consists of cuboidal – shaped particles. ↓ The reduced surface area due to the shape of the particles produce above properties without under thickening of the mix. • It gives hard surface as the surface dries more rapidly. • It is resistant to abrasion. o They are necessary because cavity is filled with wax that in carved flush with the margins of the die. o As sharp instruments are used for caring stone must be resistant to abrasion. • The surface hardness of – Type IV – 92 Rock well hardness Where as Type III – 982 Rock well hardness. Even though the surface of Type IV in hard care should be observed when the pattern is being carved. Dental stone, high strength, high expansion (Type IV) :
  5. 5. • This type V has compressive strength (48.3 Mpa) higher than that of Type IV (34.5 Mpa). ↓ • This is due to making it possible to lower w/p ratio than Type IV. • The setting expansion has increased from 0.10% (Type IV) to 0.30 (Type V). ↓ The rationale for the increase in setting expansion is that base metals have greater casting shrinkage than do the traditional noble metal alloys. ↓ Thus higher expansion is required in the stone used for the die to aid in the compensating for the alloy solidification shrinkage. • Indicated in the cast crowns (when inadequate expansion have been achieved during the fabrication). • It is not indicated in the production of dies for inlays, since the higher expansion may lead to unacceptably tight fits. Propositioning : • The strength of the stone is inversely proportional to the water powder ratio. Strength α ↓ So amount of water should be as low as possible. ↓ It should not be so low that the mix will not flow into every detail of the impression. 1 W/P
  6. 6. • The water volume should be measured by using accurate graduated cylinder. • The powder should be proportioned by weighing balance. ↓ • Powder should not be measured according to volume became powder varies from product to product and does not pack uniformly. W/p raio Type IV : 0.22 – 0.24 Type V : 0.18 – 0.22 MIXING : 1) Hand mixing : • It is accomplished in a flexible rubber or plastic bowl by using a stiff bladed spatula. • The walls of the bowl should be smooth and resistant to abrasion. • Incorporation of air during mixing is avoided. ↓ Air bubbles are unslightly, weaken the material and produce surface in accuracies. • The water should be placed in the mixing bowl and the powder should be shifted into the water. ↓ When powder sinks into the water without an agglomeration of the particles, les air is carried down. • The mixing is completed when all the mixture is smooth and homogeneous in nature.
  7. 7. • The further mixing is likely to breakup the crystals of the gypsum formed and thus weaken the final product. • The time for hand mixing is approximately 1 to 2 month. • Addition of more powder to a mix that is judged to be too thin provides essentially 2 mixes of stone. ↓ It will set at different times ↓ Results in weakened product. • Addition of water to a too thick mixture causes ↓ Disarrangement of crystalline growth and a lack of intercrystalline cohesion. Mechanical Mixing : • The use of mechanical spatulator to mix gypsum products offers considerable advantage. • Rapidly moving blades of device tend to breakup any air bubbles into fine voids. ↓ And strength of plaster is increased. • Mechanical mixing time under vacuum approximately 20 seconds. Setting Reactions gypsum products : (CaSO4)2 H2O +3H2O → 2Ca So4.2H20 + Unreacted (CaSo4)2.1/2 H20 +Heat. • The calcium sulphate heucihydrate powder reacts with the water and produce the gypsum.
  8. 8. 1) When the hemihydrate is mixed with water, a suspension is formed that is fluid and workable. 2) The hemihydrate dissolves until if forms a saturated solution. 3) This saturated hemihydrate solution, super saturated in dehydrate, precipitates out dehydrate. 4) As dehydrate precipitates, the solution is no longer saturated with the hemihydrate, so it continues to dissolve. Dissolution of hemihydrate and precipitation of dihydrate proceeds as either new crystals form or further growth accurse on the crystals already present. The reaction is continuous and continues until no further dihydrate precipitates out solution. - The amhydrite is not formed in agueous media. It is a exothermic reaction, heat is evolved and it is equivalent to heat used in calcinations. SETTING TIME Type IV – 12 ± 4 minutes Type V – 12 ± 4 minutes. Control of Setting time : 1) Impurities : • If the gypsum particles remain in the powder. i.e. if calcination is incomplete Or if manufacturer adds gypsum Setting time is shortened because of the increase in the potential nuclei of crystallization. • If orthorhombic anhydrite is present → Induction period increases
  9. 9. • If hexagonal anhydrite is present → Induction period decreases. 2) Fineness :  The Finer the particle size of the hemihydrate Rate of hemihydrate dissolution increases . Rapid rate of crystallization occurs. Mix hardens faster. 3) Water powder Ratio :  If more water is used for mixing; ↓ Fewer nuclei are per unit volume; ↓ So the setting time is prolonged. 4) Mixing : • The longer and more rapidly the plaster is mixed, ↓ Gypsum crystals formed immediately when the stone is brought in contact with water ↓ As the mixing begins, the formation of crystals increases. ↓ During mixing the crystals are broken up and are distributed throughout the mixture, resulting in the formation of more nuclei of crystallization. ↓ Thus the setting time is decreased.
  10. 10. Retarders and Accelerators :  If the chemical added decreases the setting time, it is known as accelerator.  If the chemical added increases the setting time, it is known as retarder. Retaraders :  Retarders act by forming a layer on the hemihydrate to reduce the solubility.  Ex : Glue, gelatin, some gums, borax, potassium citrate, concentrated sodium chloride. (20%). (If less concentration act as accelerator). Accelerators  Accelerator that are used mostly are – Gypsum, potassium sulfate, sodium chloride is less concentrations. Setting Expansions :  Expansion of the mass can be detected during the change from hemihydrate to the dihydrate.  Crystals grow from nuclei and intermesh. And obstruct the growth of adjacent crystals. This process is repeated by thousands of crystals during growth And outward stress or thrust develops That produces an expansion of entire mass
  11. 11. Crystal impingement and movement result in production of micro pores. On drying, the excess water is lost And void space is increased.  Linear Expansion : - Low – 0.06% - High - 0.5%. Control of Setting Expansion : Sometimes a setting expansion is advantageous for a dental procedure, sometimes it is disadvantageous, because it may be a source of error. So setting expansion must be controlled to obtain the desired accuracy in the dental applications. - Low w/p ratio and longer mixing time increases the setting expansion. - Setting Expansion can be reduced by adding either potassium sulfate, sodium chloride and Borax. HYGROSCOPIC EXPANSION The most well accepted reason for the increased expansion when the hemihydrate reacts under water is the additional crystal growth permitted by allowing crystals to grow freely rather than being constrained by the surface tension when the crystals form in air. Fig 10-8; pg 270 Phillips In this theory - 1) In stage I the initial mix is represented by the three round particles of hemihydrate surrounded by the water. 2) In stage II reaction starts, and crystals of dihydrate begins to form.
  12. 12.  In normal setting the water around the particles is reduced and particles are drawn closely by the surface tension of the water.  In the hygroscopic expansion, as setting takes place under water the particles remains the same. 3) In stage III, in normal setting water reduced, particles are drawn closely, but contraction is opposed by the outward thrust of growing crystals.  In the hygroscopic expansion – crystals are not inhibited, the water is again replenished from the outside. 4) In stage IV and V-  In normal setting the crystals are habited and become intermeshed and entangled much sooner than hydroscopic setting.  In hygroscopic setting the crystals are grown freely before intermeshing and this inter meshing finally prevent the further expansion. So the expansion under water is more than that in the normal setting.  The reduction in w/p ratio results the hygroscopic expansion  In creased spatulation results in the hygroscopic expansion.  The hygroscopic expansion during setting of the dental stone is generally small in the magnitude. Eg ; Normal expansion of dental stone may be 0.15% and hygroscopic expansion of dental stone may be 0.30%. This difference may be sufficient to cause the misfit of the denture or similar device made on the cost/die. STRENGDTH OF DIE MATERIALS The strength of gypsum products is generally expressed in terms of compressive strength, although tensile strength should also be considered in order to secure satisfactory guide to the total strength characteristics.
  13. 13.  The strength of the plastu/stone increases rapidly as the material hardens after initial setting time.  The free water content of the set product definitely affects its strength. Table 10.5 pg 273 Phillips.  The water traces at last leave fine crystals of gypsum to precipitate. These fine crystals anchor the large crystals. Then if water is added or if excess of water is present. These small crystals are the first to dissolve Thus the reinforcing anchors are lost.  And also line of the w/p ratio is high, the greater is the porosity, the fewer crystals are available per unit volume for a given weight of hemihydrate; and the dry strength is less in the set material. COMPRESSIVE STRENGTH Mpa PSI W/p ratio IV 34.5 5000 0.22-0.24 V 48.3 7000 0.18-0.22 Electro plated Dies/Electro formed Dies : Besides resin, electro plating can be used to over come the poor abrasion resistance of gypsom. The metal dies that are produced from electroplated impression material have high strength, hardness and abrasion resistance.
  14. 14.  Detail reproduction of a line 4 µm or less in width is readily attainable when a non aqueous elastomeric impression material is used.  Variable degrees of distortion commonly occur, and the technique must be performed slowly, other wise distortion in the metal will subsequently stress the impression. CERAMIC DIE MATERIALS  Ceramic materials are supplied as a powder and liquid They are mixed to a putty like consistency. This material is placed over the impression And removal from impression after 1 hour. Then it is fired at 6000C for 8 minutes to produce a hard strong die. Common brands :  Ceramite H and V  Cosmotech Vest.  Ducera-Lay  Doric HT2  DVP Investment.  V.H.T. Investment  Vitadurvest. Properties :  Extremely abrasion-resistant.  Some shrinkage on firing. Applications :
  15. 15.  The prdoduction of dies for porcelain inlays, onlays and veneers. METAL SPRAYING  Many alloys and metals can be melted and dispersed in the fine droplets with an oxy acetylene or other flame. - These fine particles of molten metal or alloy can be sprayed on to many dry materials with out burning. - A Bismuth-tiss alloy which melts at 1380 C can be sprayed directly on to an impression to form a metal shell. - Then this is filled with the dental stone  This method is applicable to the - Elastomers. - Impression compound.  If the spraying is done slowly with care softessing of the compound does not occur. Advantages :  Accuracy is good. Disadvantages :  The alloy is rather soft care is needed to prevent abrasion of the die.  Special equipment is needed.
  16. 16.  Face mask must be worm to prevent inhalation of the fine spray of the metal. AMALGAM  Amalgam may be packed into rigid impression materials such as impression compound.  The dimensional accuracy achieved depends upon the efficacy of condensation and the dimensional changes of these materials. Disadvantages :  The this sections of impression compound occur in the impression and these may be damaged on condensing the amalgam.  There is a delay of 10-12 hours for the die to be hard enough to be used.  Location of dowel into the amalgam is not easy. So it is done later.  Mercury hygiene should be practiced.  Contamination of gold alloys by mercury can take place. Procedure :  An impression is made in a copper band with modeling compound.  A this piece of boxing wax 28 to 30 guage is wrapped around the impression and extended about 3/8 inch beyond and along gingival margins of the band and impression. The boxed impression is embedded in the mix of plaster in a small rubber ring with the opens end showing the cavity facing up.
  17. 17. After plastic has hardened then plastic mass of amalgam is condensed into impression. After setting the rubber ring and plaster is removed and the die is immersed in warm water to remove the impression compound and wax. Impressions of upper and lower arches is takers. Then amalgam die is placed in the impression of prepared tooth and cast is poured. Precaution : Amalgam dies and all metal dies are good conductors of heat and so softened wax applied to them cools rapidly. This rapid cooling of wax may produce internal stresses, which can cause distortion of wax pattern. So warming the metal die to mouth temperature or slightly below should be done. Polymeric Materials : 1) Auto – polymerizing Acrylic :  The self-cure acrylic is used as die material and it is fabricated in the same way like the fabrication of the self cure dentures. Disadvantages :  The monomer reacts with all except silicone impression materials.  The heat of reaction distorts thermoplastic materials.  Volumetric contractions takes place.
  18. 18. All these disadvantages makes the material unsuitable as a die material. 2) Filled Polymeric Materials : Ex ;  Epoxy Resins.  Polyesters  Epimines  Poly urethane resins. They are available as liquid and powder and postes; one of which is either liquid monomer or unsaturated polymer like epime, epoxy, poly ester or poly urethane resins and the other component may contain powdered polymer particles and a suitable initiator or activator for polymerizing or cross linking the fluid phase to produce a solid. Either of them may contain an inert metallic or ceramic filler. Common brands :  Diemet  Goldex  Impredur.  Polyroqq. Manipulation :  The constituents are mixed according to manufacturer’s recommendations into homogenous paste. Mixing time is 1 minute. The paste is then vibrated into the impression. Some elabtomers require coating with a separating medium; often finely powdered metal.
  19. 19. Applications : The production of dies from those impression materials with which they are compatible, generally elabtomers coated with separating medium. Advantages :  Rapid set (1hour)  More abrasion resistant.  Not as brittle as die stones.  Better reproductions of the details. Disadvantages :  Shrinkage (0.02-0.6%) on polymerization may be a source of inaccuracy-fillers reduce this shrinkage.  Water retards polymerization of resing-so epoxy resins can not be used with water containing agar and alginate impression materials. Advances of epoxy materials :  Recently fast setting epoxy materials have been supplied in automixing systems similar to those for automixing addition silicones.  The epoxy resin is in on cartridge and the catalyst is in the other.  Forcing the two pasts through the static mixing tip thoroughly mixes the epoxy material which can be directly injected into a rubber impressions. REFRACTORY MATERIALS There are advantages, of the die, together with its pattern, can be used directly for casting. This eliminates possible errors in the shape of the pattern on removing it from the die. The gypsum bonded material is available for gold castings. The use of phosphate bonded investment materials has also been suggested for high fusing alloys.
  20. 20.  A commercial gypsum-bonded material is available for gold castings. The use of phosphate bonded investment materials has also been suggested for high fussing alloys.  A commercial gypsum-bonded material called divestment is mixed with a colloidal silica liquid. The die is made from this mix and the wax pattern is constructed on it. Then the entire assembly (die and pattern) is invested in the divestment to eliminate the possibility of distortion of the pattern upon removal from the die or during the setting of investment. Precautions :  special seperator is used with polysurfides.  With out seperator the colloidal silica softens the elastomers and the die sticks firmly to impression.  It may lead to the destruction of the master die. Properties :  Compressive strength – 45-50 N/mm2 .  Setting time – 15 min  Setting expansion – 1%  Thermal expansion – 0.3%  Hygroscopic expansion – 0.3%. DIE SYSTEMS : In the fabrications of the wax pattern, it is used to establish inter proximal contacts, buccal and lingual contours and occlusion with the opposing teeth. The die is a model of the Individual prepared tooth on which
  21. 21. the margins of the wax pattern are finished. There are two basic working cast and die systems- 1. Working cast with a separate die. 2. Working cast with a removable die. 1. Working cast with a separate die : The working cast and the sectional cast for the die can be obtained from separate impressions or by pouring an impression twice.  The first cast is used for preparation of the die this procedure (double pour) can be used only with elastomeric impressions, since hydrocolloid is form and distorted too much to be used for an accurate 2nd pour. Procedure : 1. Impression pouring is done with the type IV /type die materials. 2. Build up the stone to height of approximately 1 inch (2.5 cm) over the preparation to allow bulk for an adequate handle on the die. Fig 18.3 pg : 310 shillinburs 3. Carefully separate the poured cast from the impression 4. A material such as Super-Sep (kerr) may be painted on the surface of the prepared tooth to guard against surface erosion. (Liquid/Latex).
  22. 22. 5. Trim the cast from which the die is made on a model trimmer to remove all excess stone around the prepared tooth. Fig 18.4 pg 311-shillin 6. The handle of the die should be slightly larger in diameter than the preparation and octagonal in cross section. Fig 18.5 pg 311-shillin 7. Sides should be parallel or slightly tapered towards the base.  Handle should not be angled. (Fig 18.6-311 shill) 8. The handle should be approximately 1 inch long. Fig 18.7-312-shillin 9. Use a pear shaped bur to trim the die apical to the finish line of the preparation. Fig 18.8-312 shillin 10. Finally trim the die with No.25 blade Fig 18.9-312 shill 11. Smoothers below the finish line with discoid end of tanner carver. Fig 18.10-312 Shillin. 12. Die contours should be maintained similar to those of natural tooth. Fig 18.12 313 shillin 13. should not have any sharp under cuts or ditching as instrument used for finishing the margins of the wax pattern will rest
  23. 23. against this portion of the die and this will result in thick gingival area as the restorations that is not good for gingival health. Fig 18.13 313. 14. The finish line should be highlighted with a sharp colo bite red pencil that facilitate carving of the wax pattern. Fig 18.14 313 shillin 15. Relief should be applied to the preparation area of the die to provide space for cement. Usually used relief’s – Enamels – Lacquers. Desired thick ness – 20-40 µm. Should be painted 0.5 mm above the finish line. Fig 18.15-314 shillin 16. A die hardening agent is applied to finish line area of a die to prevent abrasion by waxing instruments. Cyno acrylate – 1-25 µm (or) Acrylic lacquers – 4-10 µm 17. Then the wax pattern prep. Done. Advantages :  Ease of falorication.  Keeps relationships between abutments fixed and immovable.  Because the gingival tissue and other land marks are intact, it is easier to obtain physiologically harmonious restoration contours when fabricating the wax pattern.
  24. 24. Disadvantages :  Use of working cast with a separate die is that the wax pattern must be transferred from one to the other an din this process they destroy some of the internal adaptation of the wax pattern. 2. WORKING CAST WITH A REMOVABLE DIE : Requirements : 1) The dies must return to their exact original positions. 2) The dies must remain stable, even when inverted. 3) The cast containing the dies must be easy to mount on an articulator. Several methods can be employed to allow the repositioning of a die in its working cast. Most of these devices can either be oriented in the impression before it is poured i.e., pre-pour technique (or) attached to the under side of a cast that has already been poured.  Removable Die Systems – 1) Straight dowel pin. 2) Curved dowel pin. 3) Pindex System. 4) Die-lok tray.
  25. 25. 1. STRAIGHT DOWEL PIN :  Impression is taken.  Orientation of the dowel pin can be done by the anesthetic needles, paper clips and bobby pins.  Dowel pin is placed in between the arms of the bobby pin. Then this bobby pin is positioned bucco-lingually across the impression, so that the dowel pin will be centered directly over the preparation. - Push the straight pins into arms of the bobby pin and into the impression material on both buccal and lingual surfaces. Stabilize the dowel pins and straight pins with bobby pins with the sticky wax. Fig 18.8 pg-316 shillins  Then pour the die stone into the impressions of the teeth. The pins should be straight and not touch the impression. Fig 18.19 pg 316  After impression had set remove bobby and straight pins place a utility wax at the tip of dowel pin as an aid in locating dowels after the base has been poured. - Lubricate the stone around each dowel with a thin coat of petrolatum or seperating medium to permit easy seperation of the dies from the working cast later. Fig 18.20 pg 316 shillin  Place a wet paper towel into the open lingual space to enable complete base for the cast to be poured.
  26. 26. Fig 18.21 pg316 shillin  Use a sharp knife to uncover the utility wax Fig 18.22 pg 317  When the stone is hard and dry use a saw frame with a thin blade to cut mesial and distally through the layer of die stone. The cut should taper towards gingivally. Fig 18.23-317  Gently tap the dowel with instrument tip to loosen the die. Fig 18.24-317 shi  Take the die from the cast and tries away excess stone gingivally to the finish live. Fig 18.25-318 shi  Reseat the dies to make certain that they will seat completely and will be stable. Fig 18.26-318  Place wax around the tips of dowels and there mounted on to the articulator using mounting stone.  Then wax is removed from the ends of the dowel pins. 2. CURVED DOWEL PIN. Curved dowels can be incorporated into a working cast by fixing the dowels to the impression before it is poured or by cementing the dowels into the holes drilled in a previously poured cast. i) Installing the pins before pouring :
  27. 27.  To install pins before pouring the impression, use finger pressure to insert a curved dowel tip into the large opening in the positioning bar.  Bar is oriented taciolingually so that dowel extends 1-2 mm into impression of prepared tooth.  Place straight pins facio lingually to stabilize bar. Fig 18.28 pg : 319.  After die has hardened straight and positiong bar are removed. Depressions are made about 2 mm deep by acrylic bur on either side of dowels that will assist in orienting the unprepared tooth. Fig 18.29 319  This coat of petrolatum is applied to the stone and dowels. Fig 18.30 - 320  Boxing wax is placed around the impression, with the tips of the dowels sticking through. Fig 18.31 - 320  Then the cast is sectioned. Fig 18.32 - 320  Segment is removed by pressing on the exposed tip of curved dowel with knife handle or other instrument. Fig 18.33 – 320 shillin ii) Placing the pins after the Impression pouring :  Pour the impression with a die stone to form a horse-shoe shaped working cast. Trim the bottom of the cast flat on model trimmer so that not more than 10 mm from the necks of the teeth.
  28. 28. Fig 18.34 pg :320  Drill 5 mm deep hole with hand piece or drill press (pindex) in the bottom of the cast directly under the center of each prepared tooth, pontic area and segment containing unprepared teeth. Fig 18.35 pg : 320  If the removable segment is larger than width of two teeth, the stone on each side of the dowel hole should be keyed to a depth of 2 mm with large acrylic bur. Fig 18.36 pg : 321  A drop of cyno acrylate cement is placed into each of the drilled holes. Fig 18.37 Pg : 321  The head of a curved dowel is seated into the cement lined hole and tipes are faced facially. Fig 18.38 pg : 321  A curved dowel is cemented into each removable part and thus the boxing is done. Base is poured and dies are separated as explained previously. Fig 18.39 pg : 321 3. PINDEX SYSTEM In the pindex system a reverse drill press is used to create a master cast with dies that can be removed or replaced repeatedly.  Impression is poured without positioning dowel pins. Fig 18.41 pg : 322
  29. 29.  After impression is set, wet it and trim with model trimmer. Fig 18.42 pg : 322  The cast should be 15 mm thick, exclusive of the teeth. Fig 18.43 pg : 323  Periphery and tongue area should be trussed. Fig 18.44, 18.45 – Pg : 323  Location of pin holes is marked with the pencil. Fig 18.46 pg : 324  Switch on the pindex macline. A red pilot light will indicate that it is running. Fig 18.40 pg : 322  Place the prepared cast on the work table and align the pencil mark with the light beam director. Fig 18.47 pg : 324  Raise the handle bar with slow pressure ford 3-5 seconds. And when proper depth has reached the red pilot light will go off indicating hole is finished. Fig 18.48 pg : 324  Debris is removed from the pin holes with a brash. Fig 18.49 pg : 324  Use a hand reamer to remove debris from the pin holes. Fig 18.50 pg : 324  Cyno acrylate cement is placed on the pins prior to cementing the tips. Fig 18.51 pg : 325  Shorter pins are placed first, there longer pins.
  30. 30. Fig 18.52 pg : 325  White slews are placed on long pins and gray sleeves on the short pins. Fig 18.53 pg : 325  Utility wax is place on the ends of the long pins to facilitate removal of dies wax is filled over the gray slever to prevent the filling of the stone into sleves. Fig 18.56 pg : 325  A palatal/tongue filler is made by boxing wax. Fig 18.59 pg : 326  Boxing wax is applied around the cast. Fig 18.60 pg : 326  Thus the base is poured Fig 18.61 pg : 326  Wax is removed and sectioning of the die and die preparation and mouting are same as the previous procedures. 4. Di-LOK TRAY  A snap-apart plastic tray with internal orienting grooves and notches also can be used to reassemble the working cast and die.  Before using the tray for a given case, examine the mounting of the diagnostic casts on the articulator to determine weather there is space for the bulky tray.  Pour the entire full arch impression with die stone and it should be poured in a U-shape with no stone in the center. Fig 18.72 pg : 330  The lingual side and base are trimmed. With arbor band.
  31. 31. Fig 18.73 pg : 330  Horizantal grooves are cut in the base to give it retention. Fig 18.74 pg : 330  Stone is poured into the tray and cast is placed into the tray teeth should be 4 mm above the tray. Fig 18.75 pg : 331  To complete the dies, the cast must be removed from the tray. Fig 18.76 pg : 332  A saw cut is made on each side of the prepared tooth. Fig 18.78 pg : 332  The prepared tooth is broken free from the cast by finger pressure. Fig 18.79 pg : 332  Trim the die as previously Fig 18.80 pg : 333  Slide the buccal facing on to the base of the tray from front place the back down over the lugs on the buccal facing, locking the tray together. Fig 18.81 pg : 332  The wax pattern and mounting as explained previously. Fig 18.82 pg : 333 ************
  32. 32. 5)