Week 2

• Calcination


  Heating gypsum and driving off part of the water of crystalization
• Casts


  • Diagnostic casts
  • Working casts
  • Dies
• Diagnostic cast
• Working casts
• Gypsum products


  • Plaster
  • Die stone
• Calcination


  • Less water
  • Higher density
• The control of setting expansion is critical for accurate models and dies
• Setting expansion occurs only during the hardening of the gypsum product
• Gypsum products


  • Type I Impression plaster
  • Type II Model plaster
  • Type III Dental stone
  • Type IV Dental stone high strength
  • Type V Dental stone high strength & expansion
• Model plaster requires 45 ml of H2O
• Dental stone requires 30 ml of H2O
• High strength stone requires 23 ml of H2O
• High strength/expansion stone requires 20 ml of H2O
• Gypsum setting is an exothermic reaction that generates heat
• For regular-set products, the initial set occurs within 8 to 10 minutes from the beginning of the mix
• Separation of impression from cast should occur 45-60 minutes after pouring
• Before separating the impression from the cast, ensure that no part of the impression tray is connected to the gypsum. Do not pry or rock in one direction too far or the cast will likely break
• If an alginate impression has dried out before the cast has been separated, soak the impression and cast in water for 15 minutes. The alginate will soften which allows removal of the cast without breaking anatomic structures
• Pouring casts methods


  • Double-pour method
  • Single-step method
  • Boxing method
• The anatomic portion and art portion (base) should be poured separately
• The anatomic portion forms a point at the midline for maxillary casts, while mandibular casts are rounded from cuspid to cuspid
• How are dental waxes used in clinical dental procedures?


  • 1.
  • 2.
  • 3.
  • 4.
• Dental waxes


  • Natural
  • Synthetic
• Dental waxes


  • Melting range
  • Flow
  • Excess residue
  • Dimensional change
• Dental waxes

  • Pattern waxes
  • Processing waxes
  • Impression waxes
• Pattern waxes


  • Inlay
  • Casting
  • Baseplate
• Processing waxes


  • Boxing
  • Utility
  • Sticky
• Impression waxes


  • Corrective
  • Impression
  • Bite registration
• Diagnostic cast


  Poured in plaster
• Working Cast


  Poured in dental stone
• When the gypsum looses its glossy ?

  Initial set has reached
• Plaster


  More water + air voids
• Die Stone


  Less water + less air voids
• What is the strength of the gypsum depends on ?


  The amount of water used in producing the “model”
• A product with less water

  Has a higher density of crystals (denser and stronger)
• 2 Factores that contributes to the strength and abrasion resistance of the final product

  Shape of particles

  Porosity
• High strength stone


  • Expends the least @ 0.10%
• Setting expansion


  Occurs only during the hardening of the gypsum
• Control of setting expansion


  • Critical for accurate models and dies
• Expansion has to be held to a minimum

  More expensing = oversized