finishing RPDs Flashcards
another term for finsihing
flasking
why is it important to finish the wax trial correctly
Fitted in pt mouth needs to look presentable so happy with appearance
Not retentive - because in wax
Finished under high pressure - pressed together
- Colour is realistic here - but sometimes high stability wax is darker reassure will be different colour
Use flamer to go over wax to give smoothness to bulbosity of wax
what technique is used to process the denture
lost wax technique
what equipment is used in processing the PMMA denture
metal dental flask
what is the purpose of the 2 part closed mould
encloses the wax denture in dental plaster
- wax pattern is trapped in the plaster
what happens when the 2 part mould is opened
the wax is evacuated from the mould
leaves a space where it was which can be filled by PMMA
the stage ‘investing the denture’ is also known as
The waxed denture is sealed onto the duplicate cast and embedded in dental plaster into the deeper half of the denture flasks.
- hooded technique
hooded technique
The waxed denture is sealed onto the duplicate cast and embedded in dental plaster into the deeper half of the denture flasks.
need the extra depth so opposite side is not too high
reducing all the air that could possibly be trapped by tapping
what part of the wax denture is left exposed in the flasking stage
the wax palate
Light cure/shellac/acrylic base plate – need space to remove
- Leave space as well as acrylic poured in here
after the flasking stage, when the plaster mould is set what is it coated with
plaster mould is coated with a separating medium/agent (sodium silicate) and the mould is completed with a 50/50 plaster/stone mix.
- Allows for it to come apart
- No undercuts mean cast will not break
after the mould is set what is the next stage
the completed mould, the dental flask is immersed in hot water for 10 minutes to soften the wax inside.
The flask is separated and the wax evacuated with boiling water.
what are held in the investing plaster following flasking in the hooded technique
the artificial teeth and clasps
not ideal
- cannot see buccal aspect
need to ensure the wax is removed
filling the mould is also called
packing
what material is used to pack the mould
PMMA
what are the plaster surfaces and cast coated with prior to packing
a ‘mould seal’ to prevent plaster adhering or penetrating the denture
- stop acrylic setting to denture base before acrylic removed
what stage does the mixed PMMA reached when it is packed around the teeth
dough stage
- special attention when packing the mould around the teeth
why is the mould closed under pressure after packing
to expel excess material which on re-opening is removed.
Plastic sheet over the top gives opportunity to open
- Assess whether enough material
- Not any excess wedging open the flask – trim back
summary of ‘packing’
On setting, the mould is placed in hot water for 10 minutes to melt the wax inside the flask and to assist the opening of the mould.
- Allow the wax to soften
On opening the flask, the wax is evacuated with boiling water and the mould cleaned with a detergent to remove any wax residue.
- Some can be premixed water and detergent
The two halves of the mould are coated with a mould seal and PMMA is packed into the mould at the appropriate ‘dough’ stage.
A trial of the packing stage is conducted to ensure the mould is completely filled.
- Although not necessary
The flask is opened and excess is removed.
The two halves are closed and placed into a spring compress and processed.
powder component of PMMA
polymer
liquid component of PMMA
monomer
characteristics of the liquid component (monomer) of PMMA
Highly corrosive
Controlled environment – porcelain or glass jar, extraction, gloves, mask
issue is mix too much powder to liquid for PMMA
granular porosity
issue if PMMA processed under too much pressure
contraction porosity
issue if heating of PMMA is not controlled
gaseous porosity
Holes in acrylic
- Shouldn’t appear in clinic as unhygienic
how to remove the denture following plaster and cast after adding PMMA
the plaster is removed from the mould and the plaster mould is removed from the denture and cast
Use saw to take away small chunks at a time
what should the processed denture be placed on after removal from the dental flask
on the duplicate cast
cold cure PMMA process
Wax trial on CoCr - Use lab putty with activator - Place over saddles and teeth - Make matrix Remove putty when set
Sticky wax round the sides can help
- Issue with air blows
Boil off wax
- Cavity for space to fill acrylic in matrix with acrylic teeth
Cold cure acrylic filled up
- Place in tank under pressure in cold/lukewarm water for 10-15mins
2 positive of cold cure PMMA
fast way of creating denture
easy
2 negatives of cold cure PMMA
Not polymerised properly
- Acrylic softer than heat cure
- — Grinding or heavy contact teeth wear down quickly than if use heat cure
- —-Lifespan of denture is 5 years approx.
Acrylic doesn’t look as natural esp. anterior
- Heat cure - has vein like appearance
Specify type wanted
what system is used to check the occlusion of the finished processed denture
the split cast system
The duplicate model (with denture) is secured to the original mounting with plaster bandage
Rear location notches used to place denture back on articulator, no glue used
The incisal post at rest on the incisal table indicates the occlusal vertical dimension
Guarantee that when process get a raised bite
- Pin off the table
Technician should use articulating paper to id heavy contact high points so get pin back on table
If cast been broken during casting or finishing stage - technician should advise and then alter chairside
methods technician can use for final occlusal refinement
finished and polished after sawn of the denture
acrylic has sharp edges
- hand tools to make as as smooth as possible around periphery
what surface should not be polished/abraded
the fitting surface
Check for imperfections which could hurt pt but avoid brush in fitting surface/teeth area
- Creates unrealistic flat edges
what is the denture fitted to after polishing
the definitive cast
key thing to check for when finished denture is on the definitive cast
any spaces
esp. cingulum and flange
why would a denture fit the cast but not the pt
imperfections on impression
when are denture clasps checked
after finishing the denture and it being fitted onto the definitive cast
how should the clasp sit on the definitive denture
clasp has been adjusted to the shape of the cast.
- Arm is not near the tissue or undercut
- —-If it does then trouble in insertion/removal
mark made on the cast.
- Although a mark can be anticipated, this has scraped the cast indicating a sharp edge that requires refining.
- Minor adjustments done in lab not with pliers
Hugging the tooth – close adaptation
- Not large gaps
what should the anterior flange of the finished denture be like
should have a thin edge to blend with the surrounding soft tissue
Disguised well, looks natural
Not usually into soft tissue undercut
- Hard to remove
Some soft tissue undercuts can be useful if compressible – request for them not to be removed
what should the finished denture be fitted to
the definitive master cast
where should the denture finish above anatomically
the high survey line
what aspects of the denture need to be thinned to blend the denture to the palate
post dam and palatal periphery
- not a ridge, smooth transition over, helps with peripheral seal
what measurement MUST be the same in pt and denture
the occlusal vertical dimension
articulator pin on table
what is a key feature of PMMA edges of denture to check
smooth - not sharp
polish so no harm to pt
why should the fitting surface of the denture never be polished
compressed under great compression, fitting surface is accurate and has great detail
