Working Cast and Die PDF

‫بسم هللا الرحمن الرحيم‬ 1/1/2023 2 Lecture outline 1/1/2023  Definitions  Requirement of master cast  Requirement of the Die  Requirement of the Die Materials  Working cast and Die systems 3 1/1/2023 4 Definition Die is a positive replica of the individual prepared tooth o...

‫بسم هللا الرحمن الرحيم‬ 1/1/2023 2 Lecture outline 1/1/2023  Definitions  Requirement of master cast  Requirement of the Die  Requirement of the Die Materials  Working cast and Die systems 3 1/1/2023 4 Definition Die is a positive replica of the individual prepared tooth on which the inlays, crowns, bridges are made. These are individual tooth replicas prepared for; 1. Easier handling during wax pattern fabrication 2. Finishing of inaccessible areas of the cast DIE MATERIALS  It includes :  Gypsum      Type1-Impression Plaster Type2-Model Plaster Type3-Dental Stone Type4-Dental Stone(High strength) Type5 –Dental Stone(High strength and high expansion)  Resin  Epoxy Resin  Polyurathane  Electroplated Dies  Copper plated  Silver plated     Flexible Die Materials Amalgam die material Refractory die Metal sprayed die 1/1/2023 Rosensteil (2001) Contemporary Fixed Prosthodontics 3rd edition Mosby 6 1. Gypsum Dies • Advantages: 1.Dimensional accuracy. 2. Good surface detail reproduction with Type IV and Type V gypsum products. 3. Inexpensive. 4. Easy to use. • Disadvantages: Poor resistance to abrasion. 1/1/2023 7 2. RESINS Dies Epoxy Resin Used effectively with rubber based impression materials. available in the form of a paste to which an activator is added to initiate hardening. Care should be taken that the activator not come in contact with the skin as it is toxic. 1/1/2023 8 Resin dies 2. Advantages More resistant to abrasion Dimensionally stable  Disadvantage 1. The epoxy resin cannot be readily introduced into the  1. details of a large impression as dental stone and requires a centrifugal machine for the same. 2. It shrinks by about 0.1to 0.2% in about 24 hours. 3. It is expensive. 1/1/2023 9 3. ELECTROPLATED DIES  Electroplated dies are the ones that are produced when an impression material is electroplated.  When a die is made in this manner this process is known as electroforming The impression materials which can be electroplated are impression compound and elastomeric materials. The types of dies are- Copper plated dies - Silver plated dies The popularity of copper plated dies began in the early 1930’s    1/1/2023 10 ADVANTAGES No dimensional changes occur during electro deposition of a metal It reproduces the impression accurately The die is tough and has good strength •Disadvantages: o Time consuming and tech. sensitive. 1/1/2023 11 4. FLEXIBLE DIE MATERIALS  They are similar to heavy bodied silicone or polyether impression materials  Selection of a compatible die and impression material is very important in case of flexible dies  Advantages over die stone  Rapid setting  Ease to removal 1/1/2023 Comparision of surface detail reproduction of flexible die materials J Prosth Dent 1998; 80:485-9 12 5. AMALGAM DIES Model amalgam is similar to silver amalgam which is used for fillings  Used only with copper bands with impression compound   Advantages:  Very hard die Disadvantages  Dimensionally unstable ( setting expansion)  Long setting time 1/1/2023 Philips (1992) Science of dental materials 13 11th edition W.B Saunders 6) Ceramic (Refractory die)  Ceramic material  withstand very high temperatures  Special for construction of all-ceramics 1/1/2023 14 1/1/2023 15 IDEAL Requirements OF DIE MATERIALS It should be dimensionally accurate. It should have high abrasion resistance, should possess good strength,& have smooth surface . Toughness – to allow burnishing of foil & resist breakage. Ability to reproduce all fine details in the impression. Compatibility with all impression materials. Colour contrast with wax, porcelain & alloys. Easy & quick manipulation & rapid fabrication. Non-injurious to health by touch or inhalation. Economic. 1/1/2023 16 IDEAL REQUIREMENTS OF A DIE SYSTEM The die should be easy to remove and replace in its original position. The die must be stable when placed in the cast. It should be easy to mount on the articulator TYPES OF DIE SYSTEM Based on the design, die systems can be classified into: 1. Working cast with separate die system 2. Working cast with removable die system three commonly used removable die systems a)Dowel pin system -Straight -Curved b)Di-lok tray system c)Pindex system 3. Other systems -DVA (Dental Venture of America) Model system. -Zeiser model system. 1. WORKING CAST With SEPARATE DIE SYSTEM Two casts are poured from a single impression. - Build the height of cast to approx. 1 inch. - One cast is sectioned and used as a die. The other is not sectioned and is used as the working cast. The wax pattern is prepared on the die and later transferred to the working cast. The die is shaped and finished using an acrylic trimmer and the portion of the die below the cervical line is finished using a scalpel. Die contour be approximately like root to facilitate good axial contours in restoration. 1/1/2023 20 Working cast with separate die Easy to fabricate Advantages: Keeps relation between abutments fixed better contours and emergence profile while wax pattern fabrication. Wax pattern must be transferred from die to cast Disadvantages destroy internal adaptation of wax Different impressions Some times difficult to seat wax pattern on the cast Second pour –impression damaged Different thickness of spacers 1/1/2023 21 WORKING CAST WITH A REMOVABLE DIE SYSTEM In this system a special type of working cast is prepared and the dies are carefully sectioned so that the individual dies can be removed and replaced in their original position in the cast. multiple- pourTechnique. Methods of repositioning die in its working cast systems using die pins dowel pin systems straight curved Systems using pre formed plastic trays without die pins a. DOWEL PIN SYSTEMS • They are prepared using two techniques, namely Pre pour technique Devices are oriented in the impression before it is poured 1/1/2023 Post pour technique Attached to the underside of the cast that has already been poured 23 PRE-POUR TECHNIQUE The dowel pin is positioned within the impression. First pour is poured up to the level of the alveolar process Separating medium is applied and the base is poured After the cast is set, the dies are sectioned by placing vertical sections in the interproximal regions using a die sectioner. Since the separating medium was applied before pouring the second half of the cast, the dies can be easily separated with vertical sections alone. 1/1/2023 25 POST-POUR TECHNIQUE Here, the cast is poured up to the level of the crowns of the teeth in the impression. Subsequently, small holes are drilled within the first pour in the required places and the dowel pins are cemented into the holes The remaining part of the cast is poured and the dies are sectioned as described in the pre-pour technique. If dowel pins are improperly placed, the dowels will not allow the die of the prepared teeth to be withdrawn from the cast . 1/1/2023 27 b. PINDEX SYSTEMS This system is similar to the post-pour dowel pin technique. Special drill press equipment is used to do die sectioning. The drill press has a platform with a slot like opening through which the drill pin will project during the procedure. The unit has a red pilot light lamp on top, which will shoot a point exactly on the drill & act as a guide while drilling Base of cast to gingival crest 15-20 mm 1/1/2023 29 After making the drill holes to the required depth, sleeved die pins are placed and cemented using cyanoacrylate adhesive. After cementing the pins, a base is poured over the base of drilled cast. 1/1/2023 30 Dies are sectioned from underside and from occlusal aspect Working cast with removable die mounted on an articulator 1/1/2023 31 Dowel pin and Pindex system It requires less manipulation of wax pattern, thus reducing the chances of breakage during transfer. Advantages: The handling of restorations is easier. Disadvantages The procedures are technically quite difficult. Difficulty also may be encountered in sawing the die 1/1/2023 32 c. DI-LOK TRAY SYSTEMS In this technique to pour the cast, use a specially designed articulated tray for precise reassembly of a sectioned definitive cast. Impression is poured using two-pour technique. The first pour is poured up to the level of the impression and the second or base pour is poured after positioning the rim of the di-lok tray over the impression. Later, the di-lok tray is disassembled and the grooves on the base of the cast formed by the di-lok tray is used as a guide to do die sectioning. Di-lock tray techinque Advantages: The cast and die can be reassembled in the tray , which is then mounted on the articulator . Overall size of the tray can make articulation difficult. Disadvantages 1/1/2023 34 4. DVA(Dental venture of America) Model system Trimmed impression on alignment fixture Drilling holes for dowel pins as marked 1/1/2023 Marking dowel pin locations on clear plate Inserting dowels in the baseplate 35 DVA Model system Impression is poured, stone placed around dowel pins & alignment fixture replaced over poured impression 1/1/2023 Set cast is removed from baseplate 36 DVA Model system Cast is sectioned Trimmed working casts using the DVA Model System 1/1/2023 37 5. Zeiser model system Zeiser Model System Impression is leveled, blocked out with silicone putty,& positioned over baseplate Pin locations are determined & the pinholes drilled in the base. 1/1/2023 38 Zeiser model system 1/1/2023 39 Zeiser model system 1/1/2023 40 CONCLUSION A good impression and accurate die are the first steps towards the fabrication of an accurate restoration. Proper selection of the die material and its manipulation are paramount to achieve accuracy in the die. 1/1/2023 41 References Fundamentals of Fixed Prosthodontics 4th edition. Herbert.T.Shillingburg. Theory and practice of Fixed Prosthodontics. Tylman’s Contemporary Fixed Prosthodontics.5th edition Stephen F Rosenstiel 1/1/2023 42 Have a nice day Keep smiling…….. 1/1/2023 43