Die Materials And Die System

Die Materials And Die System

Write a short note on the die and die materials.
Or
Write a brief on die materials.
Or
Write a short note on dies. (Mar 2001, 6 Marks)
Or
Classify die materials.
Or
Write in brief on die and die materials.
Answer:

Die is a positive replica of a prepared tooth or teeth in a suitable hard substance on which inlay, crown, and other restorations are made.

Ideal Requirements of Die Material:

An ideal die material should be:

• It should be dimensionally stable and accurate.
• It should have high strength, high abrasion resistance, and toughness to allow burnishing of foil and resist breakage.
• It should have a smooth surface.
• It should be able to reproduce all fine details in the impression.
• It should be compatible with all impression materials.
• It should have color contrast with wax, porcelain, and alloys.
• It is easy to manipulate and quick to fabricate.
• It should be non-injurious to health by touch or inhalation.
• It should be economical.

Types/Classification of Die Materials;

• Gypsum:
  • Type IV: dental stone.
  • Type V: dental stone, high strength, high expansion.
  • Type V: dental stone and lignosulphonates.
• Metal and metal-coated dies:
  • Electroformed
  • Sprayed metal
  • Amalgam.
• Polymers:
  • Metal or inorganic filed resins.
  • Epoxy.
• Types of cement: Silicophosphate or polyacrylic acid bonded cement.
• Ceramic or Refractory Materials:  Investments and Divestment.

Description of Die Materials:

Type IV and Type V Gypsum Materials:

• Type IV and type V gypsum materials are very commonly used materials for the fabrication of dental dies. The properties of these materials provide an economical and ease of usage.

The following are the advantages of gypsum die materials:

• Lead to the accurate reproduction of fine details
• They provide relative dimensional accuracy and stability
• Good color contrast with impression material and casting waxes
• These materials are inexpensive and easy to use.

Amalgam: 

Silver-tin amalgam or copper amalgam can be packed into compatible impressions, i.e. rigid impression materials such as compound to produce a hard die with fine details and sharp margins.

But this has a disadvantage, i.e. there is potential mercury toxicity. Amalgam needs rigid impression materials, and it also takes a longer time to get hardened into set mass. Its high thermal conductivity leads to cooling of the wax causing distortion of the wax pattern.

Metallic:  Such dies may be produced either by direct spraying or electroplating the impression.

Metal-sprayed Dies:

Low-fusing metal alloys, i.e. bismuth-tin alloy having a melting point of l38°C can be directly sprayed on the compatible impression which creates a shell of metal in which dental stone can be filed.

Bismuth-tin alloy has the disadvantage of being soft with poor abrasion resistance. Metals and alloys can be melted with oxyacetylene or another flame. This method applies to elastomers and with care to impression compounds.

Electroplated Dies:

• The surface of the impression is made electroconvulsive by depositing file metal or graphite with the help of a camel hairbrush, this process is called metalizing.
• The coated impression becomes the cathode or the negative electrode.
• Here anode or the positive electrode is formed by the pure metal.
• The electrolyte is either an acid solution or an alkaline solution.
• Now a low voltage direct current (DC) of 5 to 50 mA/cm2 is passed for 10 hours which leads to slow dissolution of the anode with the movement of metallic ions from the anode to the cathode.
• As a shell of metal is formed, the rest of the impression is poured with dental or die stone.
• Metals commonly used for electroplating are copper or silver.

Polymers and Filled Polymers:

Acrylic as well as epoxy resins, polyesters, and epimines with ceramic or metallic filers can be used to produce dies with good abrasive resistance. The autopolymerizing reaction of these materials has inherent disadvantage of shrinkage leading to inaccuracy in the die produced.

Epoxy Resin Die Materials:

• Dies manufactured from epoxy resin or polyurethane has high strength and abrasion resistance as compared to die stone.
• Epoxy resin dies are also compatible with polyether and polyvinyl siloxane impression materials but they are not compatible with hydrocolloid impression materials since water present leads to the retardation of the polymerization of resin.
• Main disadvantage of these materials is their polymerization shrinkage which is about 0.1-0.3%. So this means they are not dimensionally stable.
• Shrinkage can be reduced to a larger extent by using either a centrifugal machine or auto mixing system.

Silicophosphate Cement:

Silicophosphate cement produces a hard die as compared to gypsum products but has higher shrinkage because of loss of water. Cement may shrink and become brittle with a tendency to crack due to dehydration affecting the accuracy of the die.

Ceramic Die Materials:

Ceramic slurry (powder and liquid) is mixed to a putt-like consistency and packed into the impression of the prepared tooth. Now the fabrication is removed from the impression after an hour and fired at 600°C for 8 minutes which produces a hard strong die. These ceramic dies are used to fabricate porcelain restorations.