Pros- Impression and Casting Demonstration 10.12.19
Aim: Cast impressing using Stone and plaster
- 1-stage cast pouring used when there is no dentition. This requires no setting and all materials can be added together
- 2-stage casting pouring technique (used for dentition)
STAGE 1
1) Gather clean equipment
2) Choose accurate impression tray/ assess its fitting; according to patient and if the tray is loss/ doesn’t sit well, use
WAX to have with keeping tray in place and getting better anatomical presentation of the mouth. Addition of wax
is known as BORDERMOULD.
3) Use GREEN alginate impression. Figure of 8 mixing to remove air bubbles and pour into impression tray.
4) Once, removed. Disinfected in clinics and bring to lab
5) In labs, we want to wash it with COLD water to add moisture to it. This reduces surface tension and allows yellow
stone to smoothly run across the surface of impression (negative replica of mouth)
6) Then, we prepare stone (use half a cut in general) and add water incrementally (could be using your hand to
control how much we add. We want to mix by scrapping sides + circular mixing. Do not mix for more than 1
minute. We want to have the thickest possible mixture but flowable.
7) Then, place impression tray onto vibrator, add stone on soft tissue and from one side little by little. And let it run
the water out. Vibrator makes air bubbles come to surface
8) Then, turn off vibrator. Place bulk amounts of stone on the top to over fill it (10mm) and overfill it from around
the impression model (no more than 2mm). Then, add the legs to the model, not excessively. Wipe excess with
finger. Don’t forget tongue spaces as well.
9) Then, let it set for 20 mins, once set, trim legs so it allows the tray to sit parallel to the surface. (we want legs to
allows mechanical retention of plaster with stone)
- Try to not a have RUNNY mixture; thick is better!
- For lower arch, retro molar pad area, we might have had impression outflow so if stone outflows don’t worry, just
don’t leave mould flat on the surface to prevent deterioration.
- Be careful the impression tray is not covered in STONE, it will be very hard to remove it.
STAGE 2
1) Soak plaster mould for 5 minutes, and then add plaster (we don’t want to add plaster moisture to be absorbed by
stone, it will make plaster very brittle)
2) Then, using roughly half a cup and water according to how much we want- make plaster paste
3) Add that to the grooves, cuts of stone and cover the stone with it completely. Don’t forget the tongue spaces
4) Gather rest of plaster from bowl, place into onto table and press the mould onto it; and press down so legs of
mould touches the surface.
5) Then, like icing a cake, using a plaster knife, neat the plaster and remove excess
6) Leave it to dry- it is removable from surface – (come back another day to trim)
TRIMING: using the machine + BUR
- Order: Back, base, sides (for the back we want some angles, nothing sharp all around the cast)
- Using the bur to fine trim so dentition cast can sit well on articulator: we want to hold the hand piece as if we
are to punch someone, keep thumb free and keep it higher than the moving burr.
- Place finger on the cast and use it to start off with trimming higher points/ heels of cast. Then, form an even line,
horizontal to occlusal plane. We don’t want to go lower than sulcus.
- Anatomical features must be very clear and identifiable.
- DO NOT trim lower than sulcus
- POSITIVE AIR BUBBLES in cast are from air bubbles present in IMPRESSION MATERIAL (from alginate)
- NEGATIVE AIR BUBBLES in cast are from air incorporated into stone paste when it was mixed
- Discarding:
Tissues or rubbish into BLACK CLINICAL BIN
Contaminated tissue or things with plaster or stone into PLASTER/ STONE BIN
Wasted PLASTER or STONE into STONE/ PLASTER bucket
Aim: Cast impressing using Stone and plaster
- 1-stage cast pouring used when there is no dentition. This requires no setting and all materials can be added together
- 2-stage casting pouring technique (used for dentition)
STAGE 1
1) Gather clean equipment
2) Choose accurate impression tray/ assess its fitting; according to patient and if the tray is loss/ doesn’t sit well, use
WAX to have with keeping tray in place and getting better anatomical presentation of the mouth. Addition of wax
is known as BORDERMOULD.
3) Use GREEN alginate impression. Figure of 8 mixing to remove air bubbles and pour into impression tray.
4) Once, removed. Disinfected in clinics and bring to lab
5) In labs, we want to wash it with COLD water to add moisture to it. This reduces surface tension and allows yellow
stone to smoothly run across the surface of impression (negative replica of mouth)
6) Then, we prepare stone (use half a cut in general) and add water incrementally (could be using your hand to
control how much we add. We want to mix by scrapping sides + circular mixing. Do not mix for more than 1
minute. We want to have the thickest possible mixture but flowable.
7) Then, place impression tray onto vibrator, add stone on soft tissue and from one side little by little. And let it run
the water out. Vibrator makes air bubbles come to surface
8) Then, turn off vibrator. Place bulk amounts of stone on the top to over fill it (10mm) and overfill it from around
the impression model (no more than 2mm). Then, add the legs to the model, not excessively. Wipe excess with
finger. Don’t forget tongue spaces as well.
9) Then, let it set for 20 mins, once set, trim legs so it allows the tray to sit parallel to the surface. (we want legs to
allows mechanical retention of plaster with stone)
- Try to not a have RUNNY mixture; thick is better!
- For lower arch, retro molar pad area, we might have had impression outflow so if stone outflows don’t worry, just
don’t leave mould flat on the surface to prevent deterioration.
- Be careful the impression tray is not covered in STONE, it will be very hard to remove it.
STAGE 2
1) Soak plaster mould for 5 minutes, and then add plaster (we don’t want to add plaster moisture to be absorbed by
stone, it will make plaster very brittle)
2) Then, using roughly half a cup and water according to how much we want- make plaster paste
3) Add that to the grooves, cuts of stone and cover the stone with it completely. Don’t forget the tongue spaces
4) Gather rest of plaster from bowl, place into onto table and press the mould onto it; and press down so legs of
mould touches the surface.
5) Then, like icing a cake, using a plaster knife, neat the plaster and remove excess
6) Leave it to dry- it is removable from surface – (come back another day to trim)
TRIMING: using the machine + BUR
- Order: Back, base, sides (for the back we want some angles, nothing sharp all around the cast)
- Using the bur to fine trim so dentition cast can sit well on articulator: we want to hold the hand piece as if we
are to punch someone, keep thumb free and keep it higher than the moving burr.
- Place finger on the cast and use it to start off with trimming higher points/ heels of cast. Then, form an even line,
horizontal to occlusal plane. We don’t want to go lower than sulcus.
- Anatomical features must be very clear and identifiable.
- DO NOT trim lower than sulcus
- POSITIVE AIR BUBBLES in cast are from air bubbles present in IMPRESSION MATERIAL (from alginate)
- NEGATIVE AIR BUBBLES in cast are from air incorporated into stone paste when it was mixed
- Discarding:
Tissues or rubbish into BLACK CLINICAL BIN
Contaminated tissue or things with plaster or stone into PLASTER/ STONE BIN
Wasted PLASTER or STONE into STONE/ PLASTER bucket
