Contents. Survey & Design...2. Blockout...3. Duplication Refractory Model Waxing Spruing & Burnout...11

Transcription

1 Technique Manu

2 Contents Survey & Design...2 Blockout...3 Duplication Refractory Model Waxing Spruing & Burnout...11 Torch & Induction Casting...12 Finish & Polishing Four Seasons Water-Mix Investment Welding...17 Trouble Shooting Procedures & Precautions...21 Bibliography...22 Illustrated Dent Terms...23 Conversion Charts...24 PREPARED BY: Niranium Company Division of CMP Industries LLC P.O. Box 350 Albany, NY WRITTEN BY: Elmer Rose, CDT Manny Alvarez 1997 All Rights Reserved 1

3 SURVEY AND DESIGN The proper survey and design of the master model is essenti to the overl success of a removable parti denture. The fin design is normly completed by the dentist. However, there are times the laboratory technician is required to complete the design process. Should this be the case, the technician must closely consult with the dentist concerning the treatment plan. The technician therefore must have a thorough knowledge of: 1) the function of the appliance; 2) its esthetic vue; and 3) the structure of the or anatomy. The proper design together with many of its associated theories become very complex, therefore the design process will not be a consideration in this manu. Surveying the teeth is the process of studying the relative parlelism or lack of parlelism in relationship to the path of insertion of the framework. (Path of insertion the direction of placement of the framework as it moves from the initi point of contact with the rigid or structure to its termin rest in the mouth.) Surveying is so used in determining and outlining the guide plane surfaces used in the direct placement of the appliance. In accomplishing the surveying one basicly identifies the desirable Niranium Fixed-Arm Surveyor #8000 and Broken-Arm Surveyor #8001 Each unit comes complete with a locking, tilt-top table with model clamps, and 6 accessory tools stored under the arm shaft cap. undercuts (undercuts necessary for retention) and undesirable undercuts (those undercuts which if involved with the cast framework would prevent its insertion). Surveying requires the use of a surveyor with a fixed or adjustable arm. It is essenti to use a stable survey table that is adjustable and can be locked into a fixed position. Anyzing rods, which may be straight or Surveyor with Model Locked & Tilted tapered ong with undercut gauges of various sizes including.010,.020 and.030, lead anyzing rods, a wax trimmer and blockout trimmer will be employed in the survey process. The first step in the surveying procedure is to select a path of insertion for the framework by tilting the model on the surveyor table and using the necessary undercut gauges (.010,.020 or.030) to determine the desired depth of undercuts and the proper placement of the undercuts. (Undercut areas are those areas below the height of the contour line.) The proper depth of undercuts for the clasp tip is essenti. Properly designed and placed, the undercut provides for the necessary function of the clasp and overl retention of the framework. The.010 gauge is normly used in the construction of chrome-cobt frameworks. Chrome-cobt is a very rigid loy and lacks the flexibility needed to engage in deeper undercuts, such as.020 and.030. Once the proper tilt has been determined the survey table is locked in position. Next step is to outline the height of contour using the surveyor, anyzing rods and lead. Using a waxed or other type of non lead pencil, transfer the design from the study model to the master model. Normly, a lead pencil should not be used in the transfer of design as this type of pencil may leave a deposit that may be incorporated in the refractory model and later carried into the fin casting. The carbon or lead may or may not be eliminated during burnout. 2

4 BLOCKOUT Once the path of insertion has been determined and the design has been transferred, proceed with the blockout. There are four types of blockouts used in the construction of removable parti denture frameworks: 1) Parlel using a straight rod, 0 taper to eliminate the wax. This blockout extends from the survey line to the gingiv areas. This type of blockout provides for the maximum contact of the framework and the least opportunity for food traps; 2) Tapered using a tapered rod of 2 or 6. This blockout gives you a looser fit and is desirable for those types of cases Surveyor Tapered Rod at 2-6 Surveyor Straight Rod, Parlel with 0 Taper where guide planes may cause some difficulty in seating or where teeth are too fragile; 3) Arbitrary gross undercut areas not important to the fit or design of the framework; and 4) Relief blockout of areas under the saddles, rugae, tori, clasp arms and major connectors. The parlel and tapered blockout areas are done using a medium to hard wax. Gross undercut or arbitrary blockout can be accomplished using a softer wax such as boxing wax or clay. The relief blockout requires a wax of uniform thickness such as 22 or 24 gauge pressure sensitive wax (a tacky surface relief wax). The edge of this wax should be trimmed at a 90 angle to the tissue surface of the cast and 1 mm to 1.5 mm from the blockout wax on the abutment teeth. For dist extension cases requiring tissue stops, cutout a 2 mm to 3 mm square from the relief wax over the crest of the ridge at the most dist point for placement of the mesh. The relief of lingu bars may or may not be prescribed by the dentist. Lingu bars may require 30 gauge relief, a thin layer of wax flowed onto the area, or no relief, as prescribed. Tori and other sensitive areas may be relieved using a thin wash of wax flowed over the area in question. Now that the blockout procedure has been completed, examine the master model and make sure the design of the framework is in compliance with the dentist prescription and the clasps are designed having the proper retention and reciprocation. The maxillary model may require pat beading. This should be accomplished before the remov of the master model from the survey table. The bead line is made using a sml sharp instrument and by scooping a smooth scribe line into the model, the beading in the model should be no deeper than 0.5 mm into the soft tissue areas and terminate approximately 4mm from the gingiv sulcus. The instrument used to scribe the bead line should be rounded and give the shape of a U rather than a V on the cast surface. Establish tripod marks or triangulation points on the master model before remov from the survey table. These marks will assist in relocation of the path of insertion should it be necessary to replace the model on this or another survey table at some future time. Tripod Marks on Master Model Bead Line on Maxillary Model The master model is now ready for duplication. 3

5 DUPLICATION Cut the hydrocolloid into sml pieces and feed them into the Redi-Melt Duplicator, following the manufacturer s instructions concerning cook down of the materi. The hydrocolloid should be lowed to cook down until l lumps are eliminated. Normly the cooking temperature of the hydrocolloid is between 190 F (88 C) and 195 F (91 C). Once the hydrocolloid is fluid, low it to cool to a temperature between 130 F (54 C) and 135 F (57 C) for pouring. Generly, the lower the melting or cook down temperature and the lower the holding temperature of the hydrocolloid, the longer the life of the hydrocolloid. and storage process prolongs the life of the hydrocolloid. The master model will require soaking in warm water 100 F (38 C) to 110 F (43 C) for minutes after the survey and design has been completed. Soak-time may vary depending on Master Models Soaking in Warm Water Set for minutes at 100 F (38 C) to 110 F (43 C). Redi-Matic Digit Colloid Conditioner #405811(Left) 2 Glon (7.57 Liter) Capacity, Semi-Automatic Operation Redi-Melt, Jr. Digit Colloid Conditioner #406711(Right) 3 Glon (11.36 Liter) Capacity, Fully-Automatic Operation When remelting the hydrocolloid after it has been used and stored in an air tight container, the liquid in the bottom of the storage container must be reincorporated into the hydrocolloid when it is remelted. It is vit that this solution be added to the hydrocolloid when it is remelted as it contains important sts and miners essenti to the proper chemic bance of the hydrocolloid, thus enhancing the life of the hydrocolloid. If there is no liquid solution in the bottom of the storage container, add about 8 ounces of distilled water per glon of hydrocolloid, this will aide in maintaining the proper consistency. Replacing water lost during the cooking the size and density of the model. It is important that the model be completely saturated so as not to produce air bubbles in the hydrocolloid impression. A bell or other type of vacuum may be used to accelerate the saturation process. Running water should never be used to saturate the master model as running water will erode the model thus tering the fit of the framework. The temperature of the water is important as it will have a direct effect on the temperature of the master model when poured. The temperature of the model needs to be close in proximity to the hydrocolloid when it is poured. If the master model is too cold, when the hydrocolloid comes in contact with it, there will be an immediate chilling or freezing of the hydrocolloid, causing irregularities in the refractory model. Likewise, if the master model is too warm, the hydrocolloid will be absorbed into the pours of the stone and cause the colloid to adhere to the model once it jells. When the soaking of the master model is completed, remove the model from the water and gently shake or blow off the excess water and prepare to pour the hydrocolloid over the master model. Select the type of flask to be used, the raised base or the flat base flask. In most instances the raised base flask will be used. The raised base flask will low for a thicker base on the refractory 4

6 Flat Base Flask #6022 Raised Base Flask #6025 too rapidly as it travels between the spout and the flask. This can cause irregularities in the duplicate impression. Conversely, if the pouring is done too rapidly, bubbles and other imperfections may occur in the duplicated model. model as well as providing for a thick base and more pronounced sprue hole. The depth of the sprue is of primary consideration at this point because the fines (scum) or doughy investment which forms a thin layer atop the refractory model will need to be eliminated, leaving a refractory model with a base at least 1/2" (13 mm) thickness at its thinnest point. Stabilize the master model on the flask base by using a pliable clay or very soft wax. In the case of very thin master models, it is important to build up the model base with clay. There must be at least 1/2" (13 mm) clearance between the highest point of the master model and the top of the duplicating flask. Pour the hydrocolloid into the duplicating flask by positioning the flask with the fill hole under the spout of the duplicator, open the dispensing vve and low a steady stream of hydrocolloid to flow into the flask. The stream should be about the size of a pencil. If the pouring process is too slow or the stream is too thin, the hydrocolloid may chill Pouring Hydrocolloid Into Flask From Redi-Melt, Jr. Note pencil-size stream of colloid entering flask. Fill the duplicating flask and low hydrocolloid to exit the vent hole of the flask, this insures the complete filling, prevents suck-back imperfections as well as eliminates trapped air bubbles. Allow the flask to bench set, uncovered, for approximately 5-10 minutes. The flask may then be placed in a water bath to complete the chilling process. A refrigerated recirculating water unit may be used in the cooling process. The temperature of the water should be approximately 55 F (13 C) to 70 F (21 C). Colder water may cause too rapid chilling, freezing or distortion of the hydrocolloid. Allow the flask to remain in the water for 30 minutes. For best results, the base of the flask should be the only portion submerged in the water. When cooling, the hydrocolloid will be drawn down and around the master model. If the flask is submerged in the water bath, the hydrocolloid is lowed to uniformly cool in the direction of the wls of the flask, lowing for the possibility of distortion of the hydrocolloid impression and ultimately the refractory model. Master Models Positioned on Flask Bases Models shown after duplicating with Instoid Concentrated Hydrocolloid # Duplicating Flasks Cooling in Water 5

7 Remove the flask from the water, trim any excess duplicating hydrocolloid from the top of the flask. Open the bottom of the duplicating flask, remove clay or wax used to extend the base during the duplicating Model Removed From Colloid process. Cut away After Proper Trimming any hydrocolloid around the base of the model. Remove the hydrocolloid from the duplicating flask with the stone model intact. Use a gentle tapping and rolling motion to remove the master model from the hydrocolloid. High pressure air should not be used for the remov process as it may cause rips or tears in the hydrocolloid. After the master model has been removed, an air hose using gentle pressure may be used to eliminate excess water from the hydrocolloid impression. 6

8 REFRACTORY MODEL The average size of the refractory model is approximately 300 grams of investment. (Refer to the investment of choice listed in this manu for exact powder and liquid measurements.) Using a sprue former, make an indentation in the hydrocolloid and withdraw the former. This procedure will provide for the placement of the sprue former in the duplicating materi. Use the large end of a #7 wax spatula and scoop out the circular area made by the sprue former. The depth of this cavity should be approximately 5-7 mm. Replace the sprue former and secure it in place. Usuly the former is held in place by securing it with a rubber band employing light pressure, spread over the base of the sprue former and wrapped around the flask. The Remov of Indentation for Placement of Sprue Former Making Indentation with Sprue Former plastic sprue may so be held secure by filling the hollow end of the former with investment, this is the preferred method. Using a laboratory mixing bowl and a heavy duty spatula, mix the investment. Incorporate the powder into the liquid thoroughly. Care should be exercised not to mix more investment than can be poured in 3 to 5 minutes, or about 2-3 models at a time. Position the flask on vibrator by tilting it slightly on its side. Scoop investment onto the posterior area of the hydrocolloid mold letting the investment seek its natur level in the anterior section. Fill the flask to the top using mild vibration. Allow the flask/investment to vibrate for addition 1 minute for most oxy-phosphate and Scooping Investment into Posterior of Mold minutes for most ethyl-silicate investment. Remove the duplicating flask from the vibrator and low to bench set an addition 25 minutes. As a rule, the tot setting time, both vibration and bench set, for most ethyl-silicate refractory models is 55 minutes. Ethyl-silicate refractory models will have an accumulation of excess liquid on the model base which will form into a gel as it sets. (This liquid/ Investment Bench Setting After gel is referred to as Vibration to Remove Bubbles Scum, Fines or Dough.) After sever minutes of vibration, the accumulated liquid atop the mold should be poured off before it sets. Return the flask to the vibrator and continue the vibration until the investment fully sets. Remove the sprue former from the refractory model by twisting and pulling it outward, once the model has set. Remove the hydrocolloid and refractory from the flask intact. Care must be exercised due to the fact that ethyl-silicate models are at their weakest in this Careful Peeling of Colloid green stage. The Away from Investment Model 7

9 refractory model is removed form the hydrocolloid using a sharp knife and creating 4 or 5 slices in the sides of the hydrocolloid and peeling the hydrocolloid away from the model, much like peeling a banana (see bottom of page 7). The model is now ready for trimming. Trim the refractory model on a dry model trimmer. The model should be trimmed so as to provide a base at least 1/2" (13 mm) thick at its thinnest point. In addition, the base should have angled undercuts (with the refractory model resting on its base the angles should be between 70 and 80 on l sides of the refractory model) to provide mechanic locking of the model during the investing process. Trimming Refractory on a Wheel-Type Dry Model Trimmer Clean out the sml end of the sprue hole with a smooth tapered instrument. Round off l sharp edges on the refractory model. Use a gentle stream of air to eliminate l loose particles of investment and debris from the refractory model. If there are fractured areas around the sprue hole, they will need to be smoothed to prevent carrying of loose particles of investment into the cavity during casting. Use a sml, flexible paint brush and coat the jagged sprue hole area with Niranium Precoat Paint-On. Allow the paint-on to air dry before placing the refractory in the drying oven. Dipping Refractory Model into Rosin Dip Submerge model for 3-5 seconds at 250 F (121 C). Place the model in the Model Drying Oven at 450 F (232 C) for at least 1 hour. Remove the refractory model from the oven and immediately submerge it into rosin dip for approximately 8-10 seconds or as recommended by rosin dip manufacturer s instructions.. The rosin dip should be at a temperature of 250 F (121 C). Remove the refractory model from the rosin dip and place the model on its heels or posterior section to low for cooling and drainage prior to waxing. Models Properly Placed on Shelves in Model Drying Oven # Heat at 450 F (232 C) for at least 1 hour. 8

10 WAXING Prior to beginning the waxing process, the design for the framework must be transferred from the master model to the refractory model. The transfer of the design is accomplished by using a waxed pencil. Never use a graphite pencil as the deposits left by this type of pencil may not be completely eliminated during burnout. Should these graphite deposits remain they may cause pitting and other imperfections in the fin casting. While transferring the design, examine the refractory model for sharpness of reproduction, making sure the bead lines, ledges, rugae and other landmarks are accurate. It is recommended that the transfer of the design be accomplished in Transferring Framework Design from Master Model to Refractory Model Note: Never use a graphite pencil, only a wax-type pencil as this will eliminate deposits that may cause pitting or other imperfections in the finished casting. the following sequence: major connectors, retentive mesh, tube teeth, facings, clasps & rests and other minor connectors. Note: One of the most common concerns of casting frameworks is, How much met should be used to cast this case? The formula for cculating the loy needed to Niranium Parti Denture cast the framework is as follows Ingot Alloys and must be employed prior to waxing the refractory model: 1) Weigh the refractory model after drying and dipping in rosin and before waxing begins. 2) Weigh the refractory model after waxing and spruing has been completed. 3) Subtract the weight of the un-waxed refractory model from the waxed refractory model; multiply the tot by the density of the loy, and add 6 Dwt for the sprue button. This will give the volume of loy needed to cast a specific framework. Should you find the volume of your buttons to be too large, reduce the number used in the equation for the sprue button. An example of the formula is outlined below: Weight Refractory Weight Waxed Refractory 14.4 Gm (9.3 Dwt) 20.0 Gm (12.9 Dwt) Weight Waxed Refractory 20.0 Gm (12.9 Dwt) Subtract ( ) Weight Un-waxed Refractory 14.4 Gm (9.3 Dwt) TOTAL Multiply (x) Met Density TOTAL Add (+) Sprue Former Volume TOTAL ALLOY VOLUME REQUIRED FOR CASTING 5.6 Gm (3.6 Dwt) 8.0 Gm/cc 44.8 Gm (28.8Dwt) 9.3 Gm (6.0 Dwt) 54.1 Gm (34.8 Dwt) This formula works well with any graduate sce, however is recommended for use with grams or dwt measurements. (The volume use in the equation is 6 Dwt for the button, however other numbers may be substituted depending on the size of the sprue button desired.) The tot volume of loy needed or some other identifying mark or number should be placed in the sprue hole after the fin weighing, so the individu casting the framework may identify the case as Alloy Identifying Mark in Sprue Hole after Weighing 9

11 well as the amount of loy needed to cast the framework (see bottom page 9). This identifying mark may be further transferred to the outer part of the casting ring for identification purposes. It is recommended that rouge be used to make these identifying marks on the refractory models and casting ring. Niranium Offers a Complete Line of Quity Plastic Patterns, Stipple Sheets & Waxes The fabrication of a framework or wax-up may be accomplished using a variety of strip waxes, sheet waxes, plastic patterns and free-hand waxing. Free-handing is not widely used due to the availability of plastic and preformed patterns. Generly, patterns are laid down and the only free-hand waxing done is the connecting of the various patterns and the placement of the rests. Flow inlay wax in areas such as the bead line, around gingiv sulcus, the rugae and tori areas. Note: It is important to keep this wash of wax thin, as it will have a profound effect on the fin thickness of the cast framework. This is so the time to add any intern spruing or strengthening bars. When filling the bead line, bring the inlay wax flush with the surface of the cast. Also flow inlay wax around the edges of the relief pads and into the tissue stops. Next paint the major and minor connector areas with tacky liquid. One should be careful not to use too much tacky liquid or low it to puddle. It so should not be applied too thickly under the clasp and mesh areas as this excess will cause flash in the fin casting. Once the tacky liquid has had sufficient time to dry, begin the placement of the plastic and waxed patterns. One should have a definite order in which the wax-up takes place. It is suggested that major connectors be placed first, retention grids, rests, minor connectors, and finly the extern finish lines. Once l the connections have been made, use a gentle flame from an cohol torch to smooth l the connections. Note: An ternate method of placing the extern finish line may be employed when stipple sheets are used. The extern finish line is laid in place and the stipple sheet is laid over the finish line and cut with a warm blade. This produces a clean smooth butt joint for the acrylic and lows for maximum use of the stipple sheet as well as reducing finishing time. FINISH LINES ARE VERY IMPORTANT AND THEIR PROPER CONSTRUCTION CAN NOT BE OVERSTATED! Super-imposing an extern finish line directly over an intern finish line will create a weak junction between the retentive mesh and the major connector. This is most evident with freeend saddles in both maxillary and mandibular. The extern finish line should be off set 1 mm to 1.5 mm from the intern finish line. This type of step in the framework eliminates the weak point and lessens the possibility of framework failure or breaking of the saddle areas. Niranium Wax-Ups are fabricated by skilled dent artisans from the finest lab materis available. Use Nobilium waxes with confidence. 10

12 SPRUING The average case requires the use of 8 gauge round wax sprues. The shape and direction of the sprues are dictated by: Design of the framework Bulkiness of the framework Flow of the molten loy Sprues should be curved in the direction in which the met is to flow. The curving of the sprues helps to eliminate the shrinkage between the framework and the reservoir. The sprues are then attached to the bulkier areas of the wax-up. The sprue should be tapered at the point of connection; this connecting point should be about hf the diameter of the sprue. The reduced diameter of the sprue forces the molten loy into the cavity under pressure (the venturi effect). The sprues are seed to the wax-up using a hot spatula and inlay or sticky wax. made for those cases having pontics and extra heavy areas. Cases of this type may require the addition of auxiliary sprues and reservoirs. BURNOUT The times and temperatures listed in this section are very gener. Consult the specific areas of this manu concerning your investment of choice. Oxy-Phosphate The cases are invested using met rings, cardboard rings or plastic rings. Remove the casting rings and place the mold in a room temperature furnace. Heat furnace to 400 F-500 F (204 C-260 C) and hold for 1 hour. Then increase temperatures to 1600 F-1800 F (871 C -982 C) and hold for 1 hour before casting. IMPORTANT: Care must be taken to make sure that the connection points do not produce any sharp angles. Typic Spruing Technique of Upper & Lower Cases Note the use of 3 & 4 sprues with 8 gauge wire (sprue) wax. All connections, as well as sprues, should produce curves for best flow of molten loy. Angles should never be used in the spruing process. Sprues come together at the base of the cast or at the sprue former, forming a smooth, flowing connection. Most cases can be successfully cast using three or four 8 gauge sprues. Exceptions may be 11

13 TORCH CASTING The torch remains a widely accepted method of casting Niranium Alloy. This type of casting requires the use of Oxygen and Acetylene, Oxygen and Propane, or Oxygen and Natur Gas. INDUCTION CASTING Follow casting machine manufacturer s recommendations for proper loy melting procedures. The type of torch used is a matter of preference, however, it is recommend a Harris type torch with a multi-orifice tip be utilized. A regulator that will low the adjustment of the pressure to about 8-10 lbs. is required when using Oxygen and Acetylene. The gauge for oxygen should be set at 10 lbs. and the acetylene set at 8 lbs. If using Oxygen and Propane, the oxygen pressure should be set at 20 lbs. and the propane is set at 10 lbs. If using Natur Gas and Oxygen, the oxygen pressure should be set at 30 lbs. and the natur gas vve open at full pressure. The torch flame may be adjusted to the proper dimension by increasing or decreasing the flow of oxygen or acetylene. The length of the white acetylene feather of the multi-orifice tip should extend approximately 1/8" (3 mm) from the torch tip, while the second inner cone is approximately 1-1/2" (38 mm) from the tip of the torch. The remainder of the flame is a brush flame or the outer cone. With a wind up casting machine, the arm should be wound approximately 4 turns (the amount of turns will be determined by the age or strength of the spring). Remove the crucible from the oven or preheating environment and place it in the cradle. Be sure the crucible is free of debris, carbon or other foreign materis that may have entered it form the oven or previous castings. Heat loy in crucible until it collapses, then apply flux. Remove mold from furnace and place it in the casting machine. Release the arm and remove the torch simultaneously. Allow arm to spin free to a complete stop. The entire melting process should not take longer than 1 minute. 12

14 FINISHING AND POLISHING After the cases have been cast, they should be lowed to bench cool 45 minutes prior to deflasking. A hot case should never be quenched, as this may cause warpage. It is not recommended the cases be placed in direct line of a fan or placed outside in the rain or snow to expedite cooling. The outer investment may be removed by tapping with a hammer, to loosen the larger pieces. Grasp the sprue button Removing Investment by Tapping with pliers and with Hammer & Holding with Pliers tap sharply on the sprue reservoir with a hammer. Repeat the tapping until the bulk of the investment has been eliminated. The case is now ready to be sandblasted. Sandblast thoroughly to remove remaining investment as well as traces of oxides, leaving a smooth, matte surface. Care should be taken during the sandblasting not to use Sandblasting Case with a Shell/Sandblaster air pressure higher than 100 psi. Remove the sprues from the casting using a high-speed lathe with a separating disk. Cut the sprues as close to the framework as possible. The same disk may be used to remove any flash, fins or other sharp corners and cleaning out narrow areas. From this point, the choice of stones become a matter of technician preference. Abrasive stones should be well bound, Removing Sprues with High-Speed Lathe and clog-free and Separating Disk have the ability to hold together while used in a high-speed lathe. Use mounted points and stones for shaping the casting. Each new abrasive should be finer than the previous. The primary objective of using various abrasives is to remove the cuts and scratches of the previous abrasive. Care should be exercised when using abrasive stones on the rugae and tissue areas. Stoning of these areas is not recommended. The casting is now ready to be sandblasted once again. Remove the framework form the sandblaster, wash off excess sand and let thoroughly dry. The electro-polishing process is designed to eliminate the need for mechanic polishing of the tissue side of the framework. Care must be taken to protect clasps, rests and other thin areas of the framework. These areas may be protected with a coat of wax or nail polish to prevent excess remov of met. The electrolytic solution used in the single stage electro-polishing should cover at least 2/3 of the copper ring and be heated to 120 F-140 F (49 C-60 C). The polishing unit should have the ability to produce 6-8 amperes. The average case will require 6-8 minutes in the acid solution. Remove the casting from the acid solution, rinse thoroughly and dry. The framework, at this point, may be fitted to the master model. Once the framework is properly seated, rubber 13

15 polishing may begin. The rubber wheels and points should remove l the remaining minute scratches. The fin stages of the polishing process involves the use of polishing compounds and bristle brushes, felt points and felt or rag wheels, first using the coarser of the abrasives and graduating to the finer compounds. Fin Finishing with Rubber & Felt Wheels and Points The framework may be cleaned using a soft bristle brush and mild soap solution, ultrasonic or steam cleaner. The framework is now ready for delivery. 14

16 WATER-MIX INVESTMENT NIRANIUM FOUR SEASONS Refractory Models The master model should be duplicated and lowed to set as described in the Duplication section of this manu. Once the colloid has reached its set, remove the hydrocolloid flask from the chill bath. Remove the hydrocolloid and master model from the duplicating flask, keeping the two intact. Gently remove the master model from the hydrocolloid. Return the hydrocolloid cavity to the duplicating flask. Remove any excess water from the inner surface of the impression with a gentle blast of air pressure. Add 22 cc of water to 198 grams of Four Seasons Investment and spatulate vigorously until thoroughly mixed. Place sprue hole former in desired position in the hydrocolloid. Secure the sprue former in place with a rubber band loosely wrapped around the flask. Position the flask on vibrator, holding it firmly with one hand and tilting it slightly on its side. Fill the flask to the top using mild vibration. Allow the investment to vibrate for an addition 10 minutes. Remove the duplicating flask from the vibrator and low to bench set for another 45 minutes. The tot setting time for refractory model is 55 minutes. CAUTION: During the summer or when the temperature goes above 80 F (27 C), keep water temperature at about 70 F (21 C), otherwise the investment will set too rapidly. It is advisable the pour no more than two mold at a time. The refractory model is removed with a sharp knife by creating 4 to 6 slices, from top to bottom, and peel the hydrocolloid away from the model, like peeling a banana. The model is now ready for trimming. Trim the refractory model on a dry model trimmer. The model should be trimmed in a manner so as to provide a base at least 1/2" (13 mm) thick, at its thinnest point. In addition, the base should have angled undercuts on the base between 70 and 80 to provide for mechanic locking of the model during the investing process. Clean out the sml end of the sprue hole with a smooth tapered instrument such as a pencil, round off l sharp edges of the refractory model. Use a gentle stream of air to eliminate l loose particles of investment and debris from the refractory model. If there are fractured areas around the sprue hole, they will need to be smoothed to prevent carrying of loose particles of investment into the cavity during casting. Use a sml flexible paint brush and paint the jagged sprue hole area with Green Liquid Paint-On. Allow paint-on to air dry at least 5-7 minutes before placing the refractory model in the drying oven. Place the model in a hot 450 F (232 C) for 1 hour. Note: Should the oven not be able to reach this temperature, the refractory model should be lowed to remain in the oven an addition 1/2 hour to insure complete dehydration. The temperature difference between the refractory model and the dip should be approximately 200 F (93 C). Remove model from drying oven and completely submerge model in rosin dip approximately 3-5 seconds. The rosin dip should be at a temperature of 250 F (121 C). Note: Longer time periods in the rosin may cause the refractory to soak up too much of the rosin or cause pooling and ultimately producing fins, rough castings or other imperfections in the fin cast product. Remove the refractory model from the rosin dip and place the model on its heels or posterior section to low for cooling and drainage. Investing Once the wax-up has been completed and the case sprued, lute the model to the flask base with hot wax. Place casting ring around the 15

17 waxed model either using a liner and split met, plastic or cardboard ring. (If a plastic ring is used, it should be removed when the investment reaches its initi set.) Ensure a minimum of 1/4" (6 mm) distance exist between the liner and the wax-up. Se the ring to the base. Pour debubblelizer into the ring to cover model and wax-up. Utilize a soft bristle paint brush to gently wash the surface of the wax-up to eliminate debris, air entrapment as well as eliminating the surface tension of the wax-up and low the investment to flow smoothly. Pour off the excess or remaining debubblelizer and gently air dry the wax-up using light air pressure. For average cases, mix cc of water with 594 grams of Four Seasons investment. Hand spatulate for 30 seconds and mechanicly for an addition 30 seconds and pour into the ring. Vibrate for 10 minutes for best results. Allow case to bench set for 1 hour. Remove the base and place in furnace with met ring intact. (If using plastic split ring, remove ring after investment has reached its initi set.) Burnout Place the mold in a room temperature furnace. Heat furnace to 500 F (260 C) and hold for 1 hour. Increase the furnace temperature to 1850 F (1010 C) and hold for 30 minutes before casting. Bench cool the casting 45 minutes to 1 hour before devesting. Note: More rapid run-up of the mold in the burnout furnace will cause fins and cracking of the mold. 16

18 WELDING Chrome-cobt frameworks may be repaired or added onto by welding. The loy may be soldered, however, welding produces the best results. The area to be welded should be prepared by either sand blasting or roughing the areas with an abrasive stone, especily if the framework has been high-shined. If sandblasting is utilized, make sure l the grit from the sand is removed with air pressure, ultrasonic or under running water, prior to investing. Any grit remaining may cause pits and other imperfections in the fin weld joint. Frameworks being repaired or having parts added must have the parts to be welded, luted into position and further secured by partily investing the framework and its parts in a gypsum product or an oxy-phosphate investment. The torch tip should be sml. Light the torch and adjust the neutr flame with about 1/2" (13 mm) of blue cone extending from the tip of the torch. Heat the end of the welding rod to a dull orange and dip the rod into the powdered flux. Heat both parts of the area being welded and bring to an even cherry red color. Keep flame in contact with the framework/weld area, bring the welding rod between the parts to be welded and proceed to melt. Keep the torch about 1/2" (13 mm) from the area being welded. The framework may be finished and polished using the wheels, stones, rubber abrasives and polishes of choice. Framework Luted Together and Ready for Welding Note: For best results, if wax is used to lute the parts together, the wax should be eliminated with steam or boiling water, ensuring no residue remains. Thicker areas to be welded should be ground to a V shape so that the top surface of the repair or weld area is wider than the bottom. Adjust gauges to 1 pound oxygen and 1 pound acetylene. 17

19 TROUBLE SHOOTING REFRACTORY MODELS Problem: Bubbles in the hydrocolloid impression. Cause: Master model is not lowed to soak properly to remove l air. Model should be lowed to soak at least 30 minutes in warm water prior to duplication. Cause: Hydrocolloid is too cold when poured. Adjust the pour temperature to 130 F (54 C). Problem: Refractory model too soft. Cause: Liquid is too cold. Investment is setting too slowly. Liquid should be 70 F (21 C) to low for the proper setting time of the investment keep in mind that humidity may so affect the setting time. Cause: Hydrocolloid materi may be too cold. The materi should not be lowed to chill in a refrigerator or ice bath. The temperature of the water bath should be F (13-21 C). Cause: Model removed from the hydro-colloid prematurely low 55 minutes setting time from pouring to recovering the refractory model. Problem: Too soft after dipping. Cause: Temperature of the drying oven or dip is too cold. The refractory model should be lowed to dehydrate 1 hour in a model drying oven at a temperature of 450 F (232 C). Rosin dip should be at a temperature of 250 F (121 C) and the refractory dipped for 5 seconds. Problem: Plastic patterns will not adhere to model. Cause: Tackyfier is too thin. Cause: Tackyfier is not lowed to dry sufficiently. Cause: Refractory model is too cold. MOLDS Problem: Investment cracking. Cause: Investment taking too long to set-up on vibrator. Investment should take minutes to reach its initi set. Humidity may effect the setting time. Cause: Liquid is too cold. Remove liquid from refrigerator at least 1 hour prior to usage. Ide temperature for liquid is 70 F (21 C). Cause: Liquid is not accurately measured and/or improperly mixed. Cause: Investment setting too rapidly. Liquid may not have cooled to room temperature. Improper ratios and/or mixing of liquids. Cause: Liquid is too warm. When removed from refrigerator, do not low to sit in an overly warm environment for extended periods of time. Ide temperature of liquid is 70 F (21 C). Cause: Lack of good vibration. Check the vibration of the cases when setting. If liquid at the top of the case begins to dance and peak, there is too much vibration. Vibrator should then be turned down until this condition disappears and bubbles begin to rise to the surface. Cause: Drying ring extenders. Dip extenders into wax to se l pours, preventing liquid from being absorbed into the extender and weakening the investment. This type of cracking, left unchecked, will low the cracking to continue into the main body of the invested ring. Cause: Investment is too thick when pouring the outer ring. Check the liquid to powder ratio recommended by the manufacturer (the mixture should be grainy the consistency of oatme). Note: If there is a thick crust atop the invested ring, the mix is too loose. The crust should be between 1/8 and 1/4 (3-6 mm) thick, 1/8 (3 mm) being better. If the crust is less than 1/8 (3 mm), the mixture is too thick. 18

20 Cause: Improper remov of the crust once the investment has set. If the complete layer of crust is not removed, the cracking formed in the crust may extend into the main body of the casting ring, causing intern cracking in the mold or fins in the casting. Cause: Case lowed to bench set too long before the crust is removed. Cause: Refractory models not properly dehydrated. Allow the refractory models to dehydrate 1 hour at 450 F (232 C) prior to rosin dipping. Problem: Therm cracking. Cause: Oven run up too fast on low fire. Burnout is important! Temperature should rise from room temperature to 700 F (371 C) in 1 hour. From 700 F (371 C) to reaching mature temperature should take approximately 1 to 1-1/4 hours and then be lowed to heat soak for an addition 30 minutes. The longer the heat soak, the greater the expansion. (Tighter fits = less time.) This soak time is especily cruci for pat castings as this so hardens the investment. Cause: Case left too long on the bench after investing or overnight. Cases should be placed in the furnace within 3 hours of investing and trimming. Should the period be longer before placing into a warm furnace, the cases must be refrigerated or placed in a humidified state (plastic bag and moist towel) until ready to be introduced into the furnace. Cases may be placed in the oven in the plastic bag ong with the moist towel. Cause: Furnace not warm when the cases are loaded. Make sure invested cases are placed into a warm furnace at about 200 F (93 C). If your oven does not possess this capability, the cases must be placed in a plastic bag with a moist towel if burnout cycle is not started within 3 hours of pouring investment. Cause: Outer investment layer is too thin at the outer wl. The pattern or model must be at least 1/4 (6 mm) from the outer wl of the investment. Cause: Sharp angles or corners on the refractory models. Cause: Stacking rings in the oven improperly. Make sure the rings are layered and staggered. Cause: Improper mixing of the liquids. Cause: Improper mixing ratio of liquid to investment. Cause: Not enough vibration to eliminate the proper amount of liquid from the investment as it sets. Moderate vibration is required. Vibration should continue until the investment reaches its initi set, 20 minutes. Cause: Low-fire burnout not long enough to thoroughly dry models and eliminate wax completely, causing pressure or steam buildup inside the ring. Low-fire burnout is F ( C), holding for 1 hour. Cause: Blower activated prematurely. Blower must not be turned on prior to molds being completely dry and plastic and wax is eliminated. This type of cracking is likely to be seen as fins. CASTINGS Problem: Pits in the castings. Cause: Sprue connections are too large. Check for tapered connections where the sprue connects to the wax-up. If sprue connections are good, consider using a reservoir. Cause: Sprues are too large. Use 8 gauge, round sprues with tapered connections. Cause: Case placed in the casting machine incorrectly. Make sure the case is placed in the casting machine with the main sprue(s) in the direction of rotation. Cause: Trash carried into the case with molten met. Make sure the sprue hole is free from debris before placing in the oven. Also, upon remov from the oven just prior to casting, 19

21 remove the case from the oven and gently tap tongs while the case is secure in tongs. Make sure the sprue hole is facing down when removing any loose investment from the sprue hole. Cause: Trash in the crucible. Check crucible for scraps of old or burnt loy. Also, examine the crucible for pitting, cracking or other defects. Cause: Imperfections in the sprue hole. Check to see if there are bubbles or rough surfaces in the sprue hole or the refractory model before dehydrating and rosin dipping. Smooth any rough surfaces of the sprue hole once removed from the hydrocolloid. After opening the hole with a round instrument, coat the roughened areas with Nobilium Green Paint-On, NobilCoat or Niranium Pre-Coat and let dry prior to dipping. Cause: Dirty rosin dip. The rosin pot should be cleaned periodicly. Debris and investment particles from the refractory models tend to settle in the rosin dip and may become stirred and adhere to the freshly dipped model. Cause: Thin areas of investment. Take care in the investing process as well as with the refractory models not to create thin slivers or sharp, thin angles in the investment. Problem: Bubbles on the surface of the castings. Cause: Green Paint-On, NobilCoat or Niranium Precoat applied too thickly. Cause: Paint-on investment not lowed to dry properly must set at least 15 minutes prior to pouring investment. Check manufacturer s recommendations. Cause: Paint-on investment lowed to dry too long. Prolonged bench-set of the paint-on will produce cracking and rough geographic castings. Cause: Premature remov of refractory model from hydrocolloid. Allow 55 minutes set-time from pouring to recovery of refractory model. Cause: Debubblelizer not lowed to properly dry. Problem: Short castings clasp and retention areas not completely cast. Cause: Case not completely burned out, carbon residue remaining in the mold. Cause: Insufficient turns on a spring driven casting machine. Cause: Too much time melting the loy. Outside of mold cooled too much prior to casting. Cause: Placed in the casting machine improperly. Check the direction of rotation in relation to sprues. Cause: Not enough loy. Cause: Alloy temperature too cold. Make sure the loy is properly melted. Check the melt procedure for the type of casting machine or torch used. Problem: Short castings clasp and retention cast complete but bars are shortcast/holes in the horseshoe pate. Cause: Alloy not molten enough. Cause: Not enough heat-soak. After furnace reaches mature temperature, heat-soak at that temperature for a minimum of 30 minutes prior to casting. Cause: Alloy too cold. If some loy remains in the crucible, met was not completely melted. Problem: Brittle clasps. Cause: Torch not adjusted properly too much acetylene. Cause: Alloy overheated. Cause: Met fatigue. Alloy cast or melted too many times without replenishing with 50% new loy. Problem: Sloppy hinges. Cause: Too much paint-on investment or not painted on properly. 20

22 Cause: Met too hot. Cause: Improper met oxidation during the burnout procedure. These cases should be among the first to be cast. Heat-soak no longer than 20 minutes. The norm heat-soak is 30 minutes, however, with hinges keep as much oxidation as possible, therefore the lower soak time. Problem: Porosity in casting. Cause: Buttons porous and spongy, usuly indicative of loy being overheated. Cause: Porosity at junction of casting and sprues. Sprues not large enough. Use larger diameter sprue or sprue with reservoir. Problem: Fins on sprues. Cause: Weak investment. Check the liquid mixing ratio as well as the liquid/powder ratio. Cause: Cases introduced into the oven too soon. Invested rings must be lowed to cure 1 hour prior to being placed in a warm oven. Problem: Intern fins on castings. Cause: Not enough vibration when investing. The invested ring must have sufficient vibration to low the proper amount of liquid to escape. I M P O R T A N T PROCEDURES & PRECAUTIONS FOR PROCESSING NIRANIUM PARTIAL DENTURES 1) Adequate loc exhaust ventilation should be provided for l operations such as grinding, polishing and finishing. Good industri hygiene practices will eliminate any possible hazard from dust created by investments, grinding wheels, sandblasters, loys, etc. 2) Adequate gener ventilation should be provided to l laboratory areas. 3) Dust remov from clothing and cleaning machinery should be accomplished by power suction methods, not by air hoses. 4) Every employee should be appraised of these recommendations. 5) Dent laboratories, like l other industries, must conform to OSHA regulations. Obtain a copy of l applicable standards as issued and conduct regular inspections to insure your laboratory is properly equipped and that l OSHA requirements are observed at l times. Problem: Fins around the clasps, mesh and borders of the castings. Cause: Too much tackyfier. Cause: Excessive wax used in seing down the patterns. Cause: Rosin dip not absorbed by the refractory model model too cold when dipped. Refractory model should be lowed to dehydrate 1 hour in a Model Drying Oven at a temperature of 450 F (232 C). The rosin dip should be at 250 F (121 C) and refractory model dipped for 5 seconds. 21

23 BIBLIOGRAPHY Air Force Pamphlet 162-6: Dent Laboratory Technology, Removable Prosthodontics, United States Air Force, Washington, DC., 1991, U.S. Government Printing Office. Grasso, Joseph E. & Miller, Ernest L.: Removable Parti Prosthodontics, Third Edition, St Louis, Missouri, 1991, Mosby Yearbook Inc., B.C. Decker. McGivney, Glen P. & Castleberry, Dwight J.: McCraken s Removable Parti Prosthodontics, Eighth Edition, St Louis, Missouri 1989, The C.V. Mosby Company Rudd, Kenneth D., Morrow, Robert M. & Rhoads, John E. : Dent Laboratory Procedures, Removable Parti Dentures, Volume Three, Second Edition St Louis, Missouri, 1986, The C.V. Mosby Company. United States Navy Training Manu NAVEDTRA 10679: Dent Laboratory Technology, United States Navy, Washington, DC., 1979, U.S. Government Printing Office. Stratton, Russell J./Wiebelt, Frank J.: An Atlas of Removable Parti Dentures Design, Quintessence Publishing Co., Inc. Chicago, IL., 1988, Quintessence Publishing Co., Inc. 22

24 ILLUSTRATED DENTAL TERMS BARS Lingu Apron Horseshoe Rugae Patat Circular SADDLES CLASPS BOXINGS BACKINGS Open Type (Full Finishing Line) Equi-Poise Double Porcelain Tooth / Plastic Dummy PONTICS Porcelain Facing Open Type (No Finishing Line) Akers Roach w/facing Solid Met Pin Facing Solid (w/extension) Arm Only Plastic Veneer Trupontic Solid (w/o Extension) MISCELLANEOUS Reinforcing Mesh RETAINERS Rest & Upright Indirect ONLAY Met Occlus PRECISION ATTACHMENTS Plastic Veneer Strength Bars Milled Direct STRESS RELIEVING ATTACHMENTS Hinge Univers Movement Embrasure Hook Prefabricated Control Movement Rest 23