Master Cast and Die Prepearation.pdf

Master Cast and Die Prepara/on • Defini&ve/Master/Working Cast: The replica of the prepared teeth, ridge areas, and other parts of the dental arch o It must reproduce both prepared and unprepared tooth surfaces. o The unprepared teeth should be free of voids that are adjacent to the prepara/on o All...

Master Cast and Die Prepara/on • Defini&ve/Master/Working Cast: The replica of the prepared teeth, ridge areas, and other parts of the dental arch o It must reproduce both prepared and unprepared tooth surfaces. o The unprepared teeth should be free of voids that are adjacent to the prepara/on o All surfaces of any teeth involved in anterior guidance AND the occlusal surfaces of all unprepared teeth must allow for precise ar/cula/on of the opposing casts. o All relevant so< &ssues should be reproduced in the defini/ve cast, including all edentulous • Master Die: Posi&ve reproduc/on of the prepared tooth and consists of a suitable hard substance of sufficient accuracy o It must reproduce the prepared tooth exactly. o All surfaces must be accurately duplicated (no bubbles or voids) o The unprepared tooth structure immediately cervical to the finish line should be easily discernible on the die, ideally with 0.5 to 1 mm visible (must be present to help the technician establish correct cervical contour of the restora/on) o Adequate access to the margin is important. • Gypsum: 5 types o Plaster: I, II o Dental Stone: III o Die Stone: IV, V Plaster (b calcium/sulfate hemihydrate crystals) o Type I Impression Plaster o Type II Model Plaster (for use in lab to mount casts) o Plaster is WEAKER than stone due to: 1) porosity of the par/cles, requiring MORE water to mix 2) irregular shapes of par/cles PREVENT /ght fiUng Stone (µ hemihydrate form) o Type III Dental Stone o Type IV High-strength stone, Low-expansion stone (die stone) o Type V High-strength, High-expansion dental stone (die stone) o Stone is widely used: § Makes casts and molds § High crushing strength § Abrasion resistance o Approximately 2.5 /mes stronger than plaster 1) Non-porous cuboidal crystal material, requiring LESS water to mix 2) Dense, regularly shaped • Die Stones (modified µ calcium hemihydrate crystal) o Vacuum mixing required (make sure vacuum mixer is in green zone) o High-strength, Low-expansion stone: (Type IV) § Used for inlay, and crown/bridge casts due to increased strength and resistance to abrasion § harder cast material than dental stone § crystals are slightly larger and more dense than those of dental stone o High-strength, High-expansion stone: (Type V) § Best for polyether or polyvinyl impression materials due to high expansion • Two Stage Pour o First Pour for Impression o Second Pour for base