Working Cast & Die PDF

Working Cast & Die Working cast - It is the positive representation or replica of the prepared teeth, ridge areas & other parts of dental arch Opposing cast - It is the positive representation or replica of the non-prepared teeth & ot...

Working Cast & Die Working cast - It is the positive representation or replica of the prepared teeth, ridge areas & other parts of dental arch Opposing cast - It is the positive representation or replica of the non-prepared teeth & other parts of non-working dental arch (opposing arch) Single Die - It is the positive replica of a single prepared tooth only, it is obtained from single copper band impression made from either impression compound or rubber base Removable Die - It is an accurate positive replica of prepared abutment tooth, made to be removable to adjust & establish correct proximal relationship Requirements of ideal cast 1- Accurately reproduces prepared & unprepared teeth 2- Accurately reproduces of edentulous areas 3- All portions of cast should be free of distortions or voids 4- Properly trimmed to insure access for carving wax pattern margins N.B: Recording unprepared teeth is important for:  Proper occlusion  Proper proximal contact  Proper contour  Proper anatomy following the contralateral tooth ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬1‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  Requirements of ideal die 1- Accurately reproduce the prepared tooth only 2- Free from bubbles or defects especially at finish line 3- Accurately reproduce the finish line Requirements of ideal die material 1- Strength >> High strength to withstand handling without being fractured or distorted 2- Hardness >> High to resist scratching & abrasion during wax pattern carving 3- Accuracy & Stability >> High dimension accuracy & dimension stability 4- Color >> Good color contrast with other materials so preparation margins could be easily detected 5- Compatibility >> - Compatible with impression material 6- High wettability with wax >> allow high flow of wax Classification of working cast & die according to construction technique I- Single die II- Working cast with removable die III- Working cast with separate die IV- Virtual cast & die Classification of single die according to material 1- Dental stone die (type IV or V) 2- Resin or epoxy die 3- Electroplated die (silver-plated or copper-plated) 4- Flexible die ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬2‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  I- Single die A) Stone die - Improved stone (type IV or V) is used as it has high mechanical properties - CAD/CAM stone is a scannable type that can be scanned by an extra-oral scanner Advantages 1- Adequate dimensional stability 2- Good flow that reproduce fine details 3- Compatible with impression compound or rubber base 4- Not expensive 5- Easily fabricated Disadvantages 1- Low abrasion resistance (gypsum hardener increases abrasion resistance) 2- Low strength (brittle) 3- Needs careful handling B) Resin die (used in researches) - Self-cured epoxy resin or polyurethane resin is used Advantages 1- High abrasion resistance 2- High strength 3- Compatible with impression compound & majority of rubber base Disadvantages 1- Dimensional instability (Polymerization shrinkage) >> undersized die >> Tight cast 2- Expensive & more time consuming 3- Incompatible with hydrocolloids & polysulphide (due to H2O byproducts) ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬3‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  C) Electroplated die - This technique involves the deposition of metal layer by layer on the impression surface by electroplating process - Silver & Copper are the most used materials D) Flexible die - It is constructed from heavy body silicone impression material - Used for chairside inlays, onlays or temporary restorations to allow easy removal of the pattern from the die Advantages 1- Fast setting (2 minutes) 2- Good flow >> produce fine details 3- Easier removal of the pattern or the restoration ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬4‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  II- Working cast with separate die - It is also called Double pour technique or Solid cast with individual die technique - It is a die separated from master cast, the wax pattern is constructed on this separate die then transferred to another uncut master cast to adjust contact, occlusion & contour - It can be obtained from 2 separate impressions or just one impression that poured twice (usually rubber base) the 1st pour is more accurate & used to fabricate the separate die while the 2nd pour is less accurate & used to fabricate the master cast Advantages 1- Simple technique 2- Keep the relationship between the abutment fixed & immovable 3- Keep the gingival tissues >> affect crown contour Disadvantages 1- Distortion of the wax pattern during transferring from separate die to working cast 2- Second pour of is usually not accurate as the 1st one (2nd is usually less accurate) 3- Used only with elastomeric impression material that can be poured twice ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬5‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  III- Working cast with removable die “It is the positive replica of the prepared tooth, which is made removable from the cast for better accessibility. It can be replaced in the same position for proximal contact & occlusal adjustment” Requirements of ideal removable die 1- It should exactly return to its original position 2- Stable with no movement in any direction even when inverted 3- Maintain fixed relationship with the adjacent teeth 4- The cast with the removable dies can be easily mounted on the articulator Advantages 1- Convenient for use 2- No distortion of wax pattern as it is not transferred 3- More standardized as it needs only 1 impression with 1 cast Disadvantages 1- The risk of changing the relationship between the abutments 2- The gingival tissues & other landmarks are destroyed due to sawing Techniques of working cast with removable die A) Dowel pin technique B) Pindex system C) Di-lock tray D) DVA system E) Zeiser system ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬6‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  A) Dowel pin technique (Pre pour system) - Dowel pin is a 2 cm tapered brass or stainless steel post with constricted head to provide mechanical interlocking with the stone - It is rounded with minimum one flat surface to prevent die rotation Steps >> 1- The dowel pin is positioned over each prepared tooth in the impression accurately parallel to long axis & 1 mm short to the occlusal surface (not touching the impression) otherwise: - It may impinge in the margin - It may weaken the die - Prevent the die from easily removal from the cast 2- The dowel pin is positioned by Bobby pins, straight pins & Sticky wax 3- 1st pour of the Working cast (10mm thickness) using vacuum mixer & under vibrator >> put paper clips are put in the stone before it sets >> to provide retention for the base which will be placed later 4- Lubricate the area around each dowel pin with a separating medium >> to permit easy separation of the dies from the working cast >> then 2nd pour is done with contrast color >> to form the base 5- After setting >> cast is removed from the impression >> trim the excess on a model trimmer 6- Dies are separated from the cast by using a saw frame >> which cut mesial & distal of each die & the 2 cuts should converge apically to avoid locking of the die ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬7‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  B) Pindex system (Post pour system - Reverse Drill) It consists of: - Base - Light indicator at the top of the machine (Pilot light) - Drill at the base Steps >> - 1st Pour the impression using extra-hard stone under mild vibrations to prevent air bubbles entrapment >> working cast (10-15mm thickness) - After complete setting, using a pencil to mark the position of the pin on the occlusal surface of the prepared tooth - The cast is put on the table of the machine & moved until the pilot light is exactly over the mark - Hold the cast in place while lifting the handles of the machine to allow the drill to create a hole at the base of the cast - The pin is cemented in place by a special adhesive (cyano-acrylate) ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬8‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  - Lubricate the area around each dowel pin with a separating medium >> to permit easy separation of the dies from the working cast >> then 2 nd pour is done with contrast color >> to form the base N.B: Dowel pins should be placed bilaterally to allow stability of the cast during pouring the base - Dies are separated from the cast by using a saw frame >> which cut mesial & distal of each die & the 2 cuts should converge apically to avoid locking of the die ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬9‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  E) Di-Lock tray technique The Di-Lock tray consists of - The base with elevated middle portion - The surrounding side portion with orienting grooves - The key portion which connects the above 2 portions Steps >> - Pour the impression with extra-hard stone >> working cast >> Trimming to be 10- 15mm thickness >> make it U-shape - Pouring of the base inside the Di-lock tray - After setting of the stone, unlock the tray & get the new cast (the original master cast with its new base) ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬10‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  - For each die 2 vertical cuts are done by a saw blade until 3/4 of the base - By finger pressure, the remaining part of the base is fractured, thus you get a removable die (repeat the procedures with each die) - The tray is mounted on suitable articulator N.B: Method preventing die rotation A- The flat side/sides of the dowel pin B- Using curved dowel C- Using 2 dowel pins with common head D- Using 2 separate dowel pins E- The vertical ribs of Di-lock tray N.B: Di-Lock tray is the only technique that does not depend on dowel pins ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬11‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  Die Preparation 1- Die trimming - Using a lancet blade or trimmer, the parts of the cast mesial & distal to the prepared tooth (or teeth) is removed - The handle of the die is then prepared, it is about one inch long & should be slightly tapered toward the base & parallel to the long axis of the tooth 2- Ditching - The die is then trimmed gingival to the finish line by removing the gingival portion of the die & make a circumferential groove (undercut) just below the finish line by a pear shaped acrylic bur, this are should be treated with sharp blade & tanner carver to be smooth & free from any irregularities Aim of ditching:  It makes the finish line more clear on the die  Better accessibility to carve the wax pattern at the finish line & prevent over- extended wax margin - The contour of the die gingival to the finish line should approximate that of the root to facilitate proper axial contouring + allow easier wax carving ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬12‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  3- Drawing the finish line - The finish line should be lightened with bright red pencil N.B: Avoid pencil containing carbon (graphite) - Avoid contamination of the wax which will affect the alloy - Ignore color contrast - Act as anti-flux at the finish line (leads to improper margin adaptation) 4- Die relief = Die spacer - The preparation area is then painted with die relief material (die spacer) to provide a space of 20-40 microns for the cement >> to allow complete seating of the restoration - It should not coat the entire preparation, a band of 0.5-1 mm must be left uncoated at margins to insure adequate marginal fit N.B: If insufficient die relief >> hydraulic pressure during cementation >> incomplete seating of the restoration - If over relief >> inadequate internal adaptation >> loose restoration 5- Die hardening - The finish line is painted with a die hardening agent as cyano-acrylate to increase die hardness to resist abrasion or scratching during carving ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬13‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  IV- Virtual Cast & Die "Computer-Aided-Imaging/ Computer-Aided-Designing/ Computer-Aided-Manufacturing" Consisted of 3 steps: 1-Scanning 2- Design on software 3- Manufacturing 1) Scanning (imaging or acquisition) it may be  Extra-orally for study models, dies, patterns (wax or resin), bite registration, impression or articulators  Intra-orally for prepared teeth, adjacent, opposing teeth or gingival tissues I.O Scanner E.O Scanner 2) Designing - A special computer software is used to mark the restoration margins, select optimum insertion axis, axial contour, proximal contact & occlusion 3) Manufacturing - May be subtractive >> using milling machines (more waste of material) - May be additive >> using 3D printers (less waste of material) ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬14‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  CAI/CAD/CAM systems a) Direct Chair-side system: Using Intra-oral scanner >> scan the prepared tooth, creates restorations chair-side, and then seats it within a single appointment b) Indirect Lab-side system: Physical impression >> sent to the lab >> extra-oral scanning >> the lab designs & produces the restoration using CAD/CAM c) Integrated system: Using intra-oral scanner >> scan the prepared tooth >> then sent data via the internet to the laboratory for designing & milling (in-lab design & in- lab milling) Advantages of CAD/CAM systems: Disadvantages of CAD/CAM systems: 1- Introduction of new material as zirconia 1- High relative cost 2- Decrease time & effort 2- Need training 3- No need for physical impression 3- Waste of material in case of milling 4- Easy documentation (while 3D printing has less waste) Uses of CAD/CAM system: 1- Construction of fixed restorations (crown, bridge, veneer, inlay) 2- Construction of removable restorations (removable partial denture) 3- Construction of orthodontic appliance ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Working Cast & Die ‫ـــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬15‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬