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BDS2 CDS Prosthodontics Removable > finishing RPDs > Flashcards

finishing RPDs Flashcards

1
Q

another term for finsihing

A

flasking

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2
Q

why is it important to finish the wax trial correctly

A

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

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3
Q

what technique is used to process the denture

A

lost wax technique

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4
Q

what equipment is used in processing the PMMA denture

A

metal dental flask

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5
Q

what is the purpose of the 2 part closed mould

A

encloses the wax denture in dental plaster

- wax pattern is trapped in the plaster

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6
Q

what happens when the 2 part mould is opened

A

the wax is evacuated from the mould

leaves a space where it was which can be filled by PMMA

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7
Q

the stage ‘investing the denture’ is also known as

A

The waxed denture is sealed onto the duplicate cast and embedded in dental plaster into the deeper half of the denture flasks.
- hooded technique

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8
Q

hooded technique

A

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

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9
Q

what part of the wax denture is left exposed in the flasking stage

A

the wax palate

Light cure/shellac/acrylic base plate – need space to remove
- Leave space as well as acrylic poured in here

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10
Q

after the flasking stage, when the plaster mould is set what is it coated with

A

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
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11
Q

after the mould is set what is the next stage

A

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.

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12
Q

what are held in the investing plaster following flasking in the hooded technique

A

the artificial teeth and clasps

not ideal
- cannot see buccal aspect
need to ensure the wax is removed

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13
Q

filling the mould is also called

A

packing

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14
Q

what material is used to pack the mould

A

PMMA

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15
Q

what are the plaster surfaces and cast coated with prior to packing

A

a ‘mould seal’ to prevent plaster adhering or penetrating the denture
- stop acrylic setting to denture base before acrylic removed

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16
Q

what stage does the mixed PMMA reached when it is packed around the teeth

A

dough stage

- special attention when packing the mould around the teeth

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17
Q

why is the mould closed under pressure after packing

A

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
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18
Q

summary of ‘packing’

A

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.

19
Q

powder component of PMMA

A

polymer

20
Q

liquid component of PMMA

A

monomer

21
Q

characteristics of the liquid component (monomer) of PMMA

A

Highly corrosive

Controlled environment – porcelain or glass jar, extraction, gloves, mask

22
Q

issue is mix too much powder to liquid for PMMA

A

granular porosity

23
Q

issue if PMMA processed under too much pressure

A

contraction porosity

24
Q

issue if heating of PMMA is not controlled

A

gaseous porosity

Holes in acrylic
- Shouldn’t appear in clinic as unhygienic

25
Q

how to remove the denture following plaster and cast after adding PMMA

A

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

26
Q

what should the processed denture be placed on after removal from the dental flask

A

on the duplicate cast

27
Q

cold cure PMMA process

A 
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

28
Q

2 positive of cold cure PMMA

A

fast way of creating denture

easy

29
Q

2 negatives of cold cure PMMA

A

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

30
Q

what system is used to check the occlusion of the finished processed denture

A

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

31
Q

methods technician can use for final occlusal refinement

A

finished and polished after sawn of the denture

acrylic has sharp edges
- hand tools to make as as smooth as possible around periphery

32
Q

what surface should not be polished/abraded

A

the fitting surface

Check for imperfections which could hurt pt but avoid brush in fitting surface/teeth area
- Creates unrealistic flat edges

33
Q

what is the denture fitted to after polishing

A

the definitive cast

34
Q

key thing to check for when finished denture is on the definitive cast

A

any spaces

esp. cingulum and flange

35
Q

why would a denture fit the cast but not the pt

A

imperfections on impression

36
Q

when are denture clasps checked

A

after finishing the denture and it being fitted onto the definitive cast

37
Q

how should the clasp sit on the definitive denture

A

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

38
Q

what should the anterior flange of the finished denture be like

A

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

39
Q

what should the finished denture be fitted to

A

the definitive master cast

40
Q

where should the denture finish above anatomically

A

the high survey line

41
Q

what aspects of the denture need to be thinned to blend the denture to the palate

A

post dam and palatal periphery

  • not a ridge, smooth transition over, helps with peripheral seal
42
Q

what measurement MUST be the same in pt and denture

A

the occlusal vertical dimension

articulator pin on table

43
Q

what is a key feature of PMMA edges of denture to check

A

smooth - not sharp

polish so no harm to pt

44
Q

why should the fitting surface of the denture never be polished

A

compressed under great compression, fitting surface is accurate and has great detail

BDS2 CDS Prosthodontics Removable (10 decks)

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