working cast and dies Flashcards
What is the relevant soft tissue that should be reproduced?
part of palatal and facial mucosa
Do we have to take impression of the vestibule?
no
What is the most commonly used material for making dental die
gypsum
What are the most commonly used types of gypsum?
dental stone type 3 and high-strength type 4
Which type of gypsum is used for mounting on articulator?
model plaster type 2
How is gypsum supplied?
in the form of powder mixed with water in certain ratios
Why can’t ceramic restoration be used with gypsum die?
gypsum can’t withstand high temperatures so it’s used with refractory dies
What are refractory dies used for?
all ceramic restoration and laminate veneers
Is the dowel pin technique used nowadays?
no
Is the di-lock tray technique used nowadays?
rarely
Is the pendix system technique used nowadays?
yes, it is the most commonly used method for a working cast with a removable die
What does the dowel pin consist of?
head and tail
Where does the head enter in the dowel and pin technique?
inside coronal part of the die
What does the tail look like in dowel and pin technique?
all sides are circular except one side is flat to provide stability
Why do we use 2 pins in dowel and pin technique?
more accurate than using one pin
Is long dowel pin more retentive than short dowel pin?
yes
How is the sawing technique made?
parallel or slightly diverging but never converging
What happens if there is insufficient opening of contact?
incorrect crown and bridge as it can affect the finish line during sawing technique
What does the dental cast have to look exactly like?
the patient
Why do we take upper and lower cast impression if the dentist is working only on the upper arch?
for the lab to know how the teeth are in occlusion , how tall the teeth are and their contact
What are the requirements of a working cast?
- must produce both prepared and unprepared tooth surface and should be free of voids (air bubbles)
- all surfaces of teeth involved in anterior guidance and occlusal surface of all unprepared teeth must allow for precise articulation of opposing casts
- all relevant soft tissues should be reproduced
What are the requirements of die material?
- reproduction of surface details accurately (cusps, fissures, contact)
- high hardness to resist scratching
- dimensionally accurate (no shrinkage)
- high mechanical properties (not break easily)
- compatible with impression material and separating medium
- colour contrast
- easy to section and easy to trim (even if its strong)
What are the types of die materials used?
- amalgam (historical and not used anymore)
- electroplated discs (historical and not used anymore)
- resin (not used anymore)
- gypsum
- refractory die
- flexible die material
- 3D printed casts
- virtual casts (CAD software)
Why is resin not used anymore?
shrinkage problem
