Die Materials And Technique Of Fabrication

Die Materials And Technique Of Fabrication

What are the requirements of dies? Describe materials used in preparation of dies and few techniques used for preparing dies?

Requirements of Dies

• It must reproduce all surfaces of the prepared teeth accurately without any bubbles or voids
• The remaining unprepared tooth structure 1 mm cervical to the finish line should be readily discernible on the die
• Should be dimensionally stable
• Strong and resistant to abrasion

Read And Learn More: Fixed Partial Denture Short Essay Question And Answers

• Should be easily sectionable and easy to trim
• Should be compatible with the separating agent used
• Should color contrast with the wax used
• Should be easily wettable by the inlay wax
• Must be compatible with the impression material.

Classification

Metallic

• Amalgam
• Metal sprayed
• Electroplated.

Nonmetallic

• Gypsum
• Epoxy resin
• Silicophosphate cement
• Polymer
• Ceramic.

Others

• Divestment.

Gypsum (Type 4-Velmix die stone and Type 5-Suprastone)

Gypsum Disadvantages

• Decreased accuracy
• Decreased resistance to abrasion.

Gypsum Advantages

• Inexpensive
• Easy to use
• Produces consistent results.

Variation of technique

Impregnate the surface of the die with a low-viscosity resin (cyano-acrylate) to improve abrasion resistance.

Epoxy Resin

Epoxy Resin Advantages

• Good strength
• Good abrasion resistance
• Can be cured at room temperature
• No complicated equipment required
• Dimensionally stable
• Retainers adapt better when made on epoxy dies
• Silicone and polyether are compatible with epoxy.

Epoxy Resin Disadvantages

• More expensive than gypsum
• Polymerization shrinkage
• Polysulfide and hydrocolloid are not compatible.

Epoxy Resin Variation

• Epoxy resin, which is heat-treated after setting, is also available.

Electroplated die

Electroplated die Advantage

• Good abrasion resistance.

Electroplated die Disadvantages

• Silicone and polyether impressions are difficult to electroplate
• Polysulfide can be silver-plated, but cannot be copper plated
• Silver plating uses cyanide solution, which is extremely toxic.

Electroplated die Technique

• Finely powdered silver or graphite is brushed onto the impressions to make them conduct electricity
• The impression is then placed in the electroplating bath
• A layer of pure metal is deposited on the impression which is supported with type IV stone or resin.

Methods of Die Preparation

• Working cast with separate die.
• Divestment technique.
• Working cast with a removable die.

Working cast with a separate die

Impression

• Two impressions are made, one for the sectional cast and another for the full arch cast, and poured in hard density stones.

Pouring dental stone for full-arch impression

• The dental stone is filled by gently vibrating until the preparation area fills and then the entire area of impression. An additional base can be added after the initial set has occurred.

Pouring dental stone for sectional impression

• The preparation area is filled without air entrapment and stone is built up to a height approximately 1 inch over the preparation for handle on the die.

Die preparation

• After the cast is removed, a separating agent is applied to the prepared teeth. A handle, larger in diameter than the preparation, octagonal in shape, and parallel to the long axis of the tooth, is formed on the die. Finally prepared die should be smooth and free of ridges with the finish line highlighted with a sharp red pencil.

Divestment technique

• A die is formed from a refractory material on which the restoration is waxed, kept for burnout, and cast directly against the die.

Indications

• For intricate patterns that are not readily removable from the die.

Divestment Disadvantages

• Does not perfectly fit as retainers made of other techniques
• The die is destroyed in the casting process and a second cast and die needs to be made for finishing purposes.

Working cast with removable dies

• Dowel pin technique.
• Curved dowel pin.
• Di-lok tray.
• Pindex system.

Requirements of removable dies

• Must return to their exact original positions
• Must remain stable when inverted
• Must be easily mountable on an articulator.

Dowel Pin Technique

Synonyms

• Straight pin technique
• Tapered pin technique.

Dowel Pin Advantages

• The least amount of inaccuracy in a horizontal direction
• Less vertical deviation.

Dowel Pin Procedure

• An impression is made and the straight dowel pin is centred directly over the preparation
• Bobby pins are placed across the impression buccolingually with the dowel pins placed between the arms of a bobby pin and both are stabilized by straight pins with sticky wax.

Pouring the impression

• Die stone is poured in the impression by filling the prepared teeth and covering the knurled end of the dowel pin
• Paper clips are added to other areas to provide retention for the second pour of stone.

Removing bobby pins and straight pins

• After the first pour sets, the straight and bobby pins are removed
• The tip of each dowel is covered by soft wax
• A V-shaped buccolingual orientation groove is placed on each die
• The area around each die is lubricated.

Removing cast

• After the cast sets, it’s removed and trimmed
• The utility wax is uncovered and a jeweler’s blade is used to cut through the mesial and distal sides of each die
• The die is loosened from the cast by gently tapping on the end of the dowel
• The cuts should taper towards each other slightly from occlusal to gingival.

Mounting the casts

• After the die is removed and ditched, utility wax is placed back into the wells around the tips of the dowels
• The casts are mounted.

Curved dowel pin

Curved Dowel Pin Procedure

• A position bar is used to orient the curved dowel into the impression of the prepared tooth
• The position bar is oriented faciolingually till the dowel tip extends 1.1–2.0 mm into the impression with the tail pointing facially.

Pins placed

• One pin in the facial aspect—Straight pin
• The second pin in the lingual aspect
• Pins are placed for all prepared tooth and pontic region
• A dowel pin is also placed near the center of each segment of the unprepared tooth
• The dowel pin’s head should be parallel to the long axis of the tooth.

Pouring of dental stone

Die stone is poured into the impression until it covers the heads and 1.0–2.0 mm of the thicker hexagonal bodies of the dowels.

Removal of positional pins

• After the die stone has set the two straight pins and the positioning bar is slid off each dowel
• A 2.0 mm deep hole is cut on either side of each dowel
• Lubricate the exposed parts of the dowels
• Boxing wax is placed around the impression and dental stone is filled till the dowels are covered by at least 2.0 mm, except for the tips.

Sawing the cast

• After the stone sets, remove the boxing wax and place vertical saw cuts on either side of each die
• Separate each segment by gently tapping on the protruding tail of the dowel.

Preparing working cast

• A horseshoe-shaped working cast with the base trimmed flat is made
• Holes are drilled with a drill press in the bottom of the cast directly under the center of each prepared tooth, pontic area, and segment containing unprepared teeth
• A curved dowel is tried into the prepared holes till the head seats are completely and luted with cyanoacrylate cement

• After the cement has hardened, a thin layer of petrolatum is applied and a second pour is done.

Di-Lok tray

Requires a specially articulated tray with internal orienting grooves and notches to reassemble the sectioned master cast accurately.

Di – Lok tray Procedure

• Evaluate the fit of the tray on an articulator.

Pouring the impression

• The entire arch impression is poured with die stone to a height of approximately one inch. The U-shaped cast with an open lingual area must be trimmed to fit the di-lok tray
• After the cast is allowed to dry, trim the lingual side of the cast on an arbor band and try the cast in the di-lok tray.

Placing the cast in the tray

• After horizontal grooves are cut in the base of the cast, the tray is filled three quarter with dental stone
• A slurry water-soaked cast is seated into the tray by jiggling it slightly till the cervical lines of the teeth are about 4 mm above the edge of the tray.

Removing cast from the tray

• After the stone sets, the cast is removed from the tray by lifting it back up, and then the buccal facing forward and tapping on the base of the cast with a laboratory knife
• The removed cast is sawed with a taper between the prepared tooth and the adjacent tooth.

Preparation of removable die

• Remove all dies with finger pressure and trim the excess stone gingival to the finish line
• Mark the finish line with a red pencil.

Removable Die Disadvantage

• The large size of the tray makes articulation difficult.

Pindex System

• Preparing the master cast
• The final impression is poured into the stone
• After the stone sets, the retrieved cast is trimmed to a horseshoe-shaped form
• The buccolingual width of the base of the horseshoe is 13–18 mm and thickness is 15 mm between the gingival margins of the preparations and the inferior border.

Pin Placement

• After the undersurface of the cast is trimmed perfectly flat, drill two holes for each removable section as far apart to provide space for the pins and sleeves
• The pins are cemented into holes using low-viscosity cyanoacrylate cement
• The short index pins are cemented in the lingual holes
• Long pins cemented into the buccal holes
• The white sleeves are placed over the long pins and the gray sleeves over the short pins.

The Secondary Base

• A strip of carding wax is placed over the extensions of the long pins and the gray sleeves
• The master cast is boxed or placed in a rubber base former and a secondary base is poured with cast stone.

Removable Dies

• After the secondary base sets, remove the master cast and trim the secondary base on the model trimmer
• Dies are sectioned with a die saw and trimmed carefully to expose the finish line.
• Clean the stone grindings from the dies, pins, base, and pin holes
• Reseat the dies
• The master cast is mounted.