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
Why is electroplated disc not used anymore?
- toxic
- very expensive
- takes a very long time
What are the 5 forms of dental gypsum?
- impression plaster type 1
- model plaster type 2
- dental stone type 3
- high strength type 4
- high strength high expansion type 5
Is impression plaster type 1 used nowadays?
no
What are the advantages of gypsum?
- inexpensive
- easy to use
- consistent results
What are the disadvantages of using gypsum?
relatively poor abrasion resistance
What are refractory dies?
special type of ceramic supplied in powder and liquid, mixed and fired according to manufacturer construction to form the die
What is the property of refractory dies?
can withstand high temperatures
What are flexible die materials?
similar to heavy body silicon and polyether material in consistency
What are flexible die materials used to make?
temporary restorations and indirect composite resin inlay or onlay
What are the advantages of flexible die materials?
- body light consistency
- more rapid setting
- easy to remove restoration or onlay
What do we need to do to get 3D printed casts?
- intra-oral scanner
- scanning of teeth
Which type of impression is more accurate: physical or digital?
digital
What are the properties of virtual cast
- scanning
- quicker and easier
What is the classification of working cast and die system?
- working cast with separate die (warpage and distortion may happen)
- working cast with removable die
What are the types of working cast with removable die?
- dowel pin technique
- pindex system
- di-lock tray
What does the dowel pin technique require?
sawing technique (between teeth’s contacts) and it consists of first pour (head is found) and second pour (tail is found)
What is the pindex system?
- forms a pinhole and then add super glue until it dries
- head of dowel pin is inserted to have a removable die
Is using double pins better than using a single dowel pin?
yes
What is the name of the super glue used in pindex system?
cyanoacrylate or amir alpha glue
What is the function of a die spacer?
- allows space for the luting cement
- allows space for easy removal of wax pattern from the die after its construction
- creates space between internal surface of casting and of prepared surface of the tooth everywhere except immediately adjacent to the margin (1mm short of finish line)
- one or two coats are applied
Where is the die spacer applied?
all the die except that finish line to allow adaptation of the margin to the finished line
Why do we add grooves in the di-lock tray?
help to put back the sawed die in the correct place
What is used for die preparation?
- a bur is used to trim under the finish line area to accentuate the finish line
- a marker is used t define the finish line
- a red pencil (non-carbon) could attach to the wax and contaminate the future casting
What is ditching?
removing fine details using a fine instrument (it makes a ditch)
What is a die hardener?
- painted on the die to increase its surface hardness
- placed all over the die (extends beyond finish line)
- allow time to harden and set
- prevents scratching
