Dental Models and Die Materials

Model and Die Materials

• A dental model is a positive replica of the teeth and adjacent structures.
• A dental die is a positive replica of the individual prepared tooth on which inlays and crowns are made.

Ideal Properties of Model and Die Materials

• Ability to reproduce all fine details in the impression
• Dimensional stability
• High abrasion resistance to resist scratching during carving of wax pattern
• Good strength and smooth surface
• Compatibility with all impression materials
• Reasonable setting time
• Color contrast with wax pattern to easily distinguish between them

Types of Cast and Die Materials

• Gypsum
  • Type II dental plaster
  • Type III dental stone
  • Type IV dental stone, high strength
  • Type V dental stone, high strength, high expansion
• Metals
  • Electroplated dies
  • Low fusing metals
  • Amalgam
• Polymers
  • Epoxy resin
• Cements
  • Silicophosphate cements
• Ceramics

Gypsum Products

• Gypsum is a mineral found in nature, formed of calcium sulfate dihydrate (CaSO4.2H2O) known as Alabastar.
• Production of gypsum products involves a process called "Calcination", where CaSO4.2H2O is ground and heated, leading to water loss and the formation of Ca sulphate hemihydrate (CaSO4.1/2H2O).
• Gypsum products are chemically the same (CaSO4.1/2H2O) but differ in:
  • Method of manufacturing
  • Particle size and shape
  • Water/powder ratio
  • Physical and mechanical properties
  • Uses

Types of Gypsum Products

• Type I: Impression plaster, used as secondary impression material
• Type II: Model plaster
• Type III: Dental stone (Hydrocal)
• Type IV: High strength Dental stone (Densite)
• Type V: High strength, high expansion dental stone

Properties of Gypsum Products

• Particle size and shape:
  • Type II: Large, irregular, and porous
  • Type III: Smaller, more regular, and less porous
  • Type IV: Smallest, most regular, and least porous
  • Type V: Smallest, most regular, and least porous
• Water/powder ratio:
  • Type II: 0.5
  • Type III: 0.35
  • Type IV: 0.22
  • Type V: 0.22
• Porosity:
  • Type II: High
  • Type III: Moderate
  • Type IV: Low
  • Type V: Low
• Compressive strength:
  • Type II: Low
  • Type III: Moderate
  • Type IV: High
  • Type V: High
• Abrasion resistance:
  • Type II: Low
  • Type III: Moderate
  • Type IV: High
  • Type V: High
• Setting expansion:
  • Type II: High
  • Type III: Moderate
  • Type IV: Low
  • Type V: High
• Uses:
  • Type II: Diagnostic cast, articulation of stone cast, and flasking procedure for acrylic dentures
  • Type III: Full or partial denture master casts, orthodontic models, and flasking procedure for acrylic dentures
  • Type IV: Used in dies for fabricating wax patterns of cast restorations (crowns and bridges)
  • Type V: Used for construction of dies on which base metal alloys will be cast