def cast and dies Flashcards
Definitive (Master or Working)
Cast
Definitive (Master or Working)
Cast: A replica of the tooth surfaces,
residual ridge areas, and/or other
parts of the dental arch and/or facial
structures used to fabricate a dental
restoration or prosthesis.
Die:
Die: Positive reproduction of the
individual prepared tooth; used for
wax pattern fabrication.
A good cast must be:
Bubble free
Distortion free
cast must reporduce which surfaces?
*Reproduce both prepared and unprepared tooth surfaces, and be free
of voids.
occluding surfaces of casts must allow for
All occluding surfaces must allow for precise articulation of the opposing casts.
soft tissues of cast
*All relevant soft tissues should be reproduced.
*Edentulous spaces and ridge contours involved in FPD
Requirements for the Die:
*Reproduces?
*All surfaces must be?
*bubbles or voids?
*The apical unprepared tooth structure?
*Adequate access for?
*Establish correct?
*Reproduces the prepared tooth exactly.
*All surfaces must be accurately duplicated.
*No bubbles or voids especially along the finish line.
*The unprepared tooth structure apical to the finish line should be
easily visible (0.5 – 1mm).
*Adequate access for carving wax pattern margin.
*Establish correct cervical contour of the restoration.
Advantages of the FULL ARCH CAST:
*Guide to?
*Ease of?
*Development of?
*Guide to occlusal surfaces and contours
*Ease of articulation
*Development of optimum occlusion
*(Development of optimum pontic adaptation and esthetics)
Classification of gypsum products according
to ADA Specification No-25
*ADA Types I -V
*Type I and II: impression plaster / model and
mounting plaster
*Type III: dental stone (general purpose casts)
*Type IV: high strength / lowest expansion (die
stone)
*Type V: high strength / high expansion (die stone)
Desirable Properties of Cast / Die Materials
*Accuracy
*Reproduce fine detail (20μ-wide-line)
*Strong and durable
* color
*Strong and durable cast qualities
*Strength (wet strength / dry strength)
*Resistance to shearing forces (edge strength)
*Abrasion resistance
*Color of cast
*Contrast to wax
*Scanning visibility
(CAD-CAM)
Water : Powder Ratio
*Least amount of water necessary to obtain proper manipulation of stone
*Manufacturer’s recommendation
*Add powder to liquid in mixing bowl for proper wetting.
Properties related to water:powder ratio
*Directly proportional: setting times / manipulation
*↑water = ↑ setting time; ↑ fluidity
*Inversely related: strength and setting expansion
*↑water = ↓ compressive strength
*↑water = ↓ setting expansion
*(important in gypsum investment)
set gypsum? disinfectant? alc?
Beware of Interactions when pouring cast
*Gypsum that has already set acts as a catalyst when in contact with unset gypsum and can cause changes in the set and working times.
*Excessive disinfectant solution or water can give you unset or powdery gypsum at the surface.
*Make sure that your impressions are clean and only slightly damp before you pour.
*Excessive use of alcohol based surfactants or debubblizers can also create surface issues like softness or chalkiness
Mechanical-Vacuum Mixing of Gypsum
*Helps eliminate porosity
*Strengthens the cast
*20 seconds / 425 rpm / >25mmHg
*Over-spatulation → decreased
working time
Dimensional Accuracy and Strength
*Minimal expansion for procedure
*Surface should be hard and smooth when removed from impression
*Wet strength – Dry strength
*Strength doubles 1H → 24H
*Set in an upright position
*Prevents stone slumping from cusps
Alginate Impressions: 2-Pour Technique
*Anatomic pour with Type III Stone: cover vestibule; stack up stone; add
nodules
*Base: 2omix after initial set of anatomic pour or after separation from
impression (45 min).
Solubility: Gypsum immersion in water effect on linear deminsion
Linear dimension ↓ per every 20 minutes of immersion
Immersion in water saturated with calcium sulfate (slurry) will decrease what quality?
Immersion in water saturated with calcium sulfate (slurry) will decrease
solubility