finishing/flasking Flashcards
1
Q
why must a wax trial look presentable
A
- as its goingto be tried in the patient’s mouth
- it won’t have good retention however as it is wax
2
Q
what type of technique is used for processing the denture
A
- a ‘lost-wax’ technique
3
Q
what is used in the processing of a PMMA denture
A
- metal dental flask is used
4
Q
what happens during finishing/flasking
A
- a two part closed mould is made, enclosing the wax denture using dental plaster
- the two part mould is opened and the wax is evacuated from the mould
- the space left is filled using PMMA
5
Q
what happens during investing of the denture
A
- the waxed denture is sealed onto he duplicate cast and embedded in dental plaster into the deeper half of the denture flasks
- the wax palate is left exposed
- on setting the plaster mould is coated with a separating medium and mould completed
- following setting the dental flask is immersed in hot water for 10 mins to soften wax
- the flask is separated and the wax evacuated with boiling water
6
Q
what is a separating medium often used
A
- sodium silicate
7
Q
what type of technique is used during investing the denture
A
- hooded technique
8
Q
why must you ensure you font have any air blows
A
- as acrylic will fill this
9
Q
what is not good about the hooded technique
A
- not ideal as can’t see the buccal surface so don’t know if all the wax is gone or not
- need to make sure that when you add the acrylic its pushed as buccally as it can be
10
Q
what is another method of investing the denture
A
- plaster over plaster dentate
11
Q
how is the mould filled/packed
A
- the plaster surfaces and cast are coated with a ‘mould seal’ to prevent plaster adhering or penetrating the denture
- when the mixed PMMA has reach dough stage it is packed into the mould with special attention being paid to packing the mould around the teeth
- the mould is closed under pressure to expel excess material which on re-opening is removed
- trial packing
12
Q
what is the procedure for packing
A
- on setting the mould is placed in hot water for 10 mins to melt the wax inside the flaks and to assist the opening of the mould
- on opening the flask the wax is evacuated with boiling water and the mould cleaned with a detergent to remove any wax residue
- the two halves of the mould are coated with a mould seal and PMMA is packed into the mould at appropriate dough stage
- flask opened and excess removed
- two halves removed and placed into a spring compress and processed
13
Q
why is a trial of the packing stage conducted
A
- to ensure the mould is completely filled
14
Q
what is used to mix PMMA
A
- powder = polymer
- liquid = monomer
- hydraulic press
15
Q
what must you be careful of with the monomer
A
- it is very corrosive so needs to be in a controlled environment
16
Q
what is the ratio for mixing of PMMA
A
- 10mls to 24 grams
17
Q
what can happen is there is too much powder used in mixing of PMMA
A
- granular porosity
18
Q
what is contraction porosity
A
- when there is not enough pressure applied or when there is not enough acrylic as it expands to fill the spaces and then contracts
19
Q
what happens if the temperature is too high during PMMA mixing
A
- if the temperature is too high then the monomer boils too quickly and causes bubbles leading to gaseous porosity
- needs to be heated slowly
20
Q
why must you bench cool when mixing PMMA
A
- if try to cool it by placing it in cold water then the internal stresses will cause it to fracture or crack
21
Q
why is it unacceptable for patient to go away with porosity dentures
A
- unhygienic
22
Q
Where is porosity most common
A
- thicker areas of the denture
23
Q
how is the denture removed following processing
A
- can be tricky and messy
- the plaster is removed from the mould and the plaster mould removed from the denture and cast
- can saw away the mould from cast
24
Q
what is the cold cure method
A
- use lab putty with an acirttvaot and mould over the wax trial on the denture
- then remove putty and boil off the wax
- stick the teeth to the putty
- now have a cavity for space to pour acrylic into
- place flask under pressure and cold water
25
what is good about cold cure method
- very fast way of creating a denture
| - 5-10 min set
26
what are the negatives of cold cure method
- acrylic is often softer this way then heat cure
- not polymerised correctly
- will wear down quicker then heat cure denture
- acrylic doesn't look as natural this way as just one single colour
27
how is occlusion check following processing
- the duplicate model with denture is secured to the original mounting with plaster bandage
- the occlusion is check and refined as required against the opposing dentition
- the incisal post at rest on the incisal table indicated occlusal vertical dimension
- need to use articulating paper to find high points
28
why might occlusion need altered
- processing can sometimes alter the occlusion and the pin may not be on the table
- it may have been raised
29
what is done after the occlusion is adjusted
- the duplicate model is removed from the denture by sawing the model from the denture
- the denture is finished and polished
30
what can be done following polishing
- denture can be fitted to the definitive cast
31
why must acrylic be finished
- it has lots of sharp corners and angles
| - use hand tools
32
why don't you do much finishing and polishing on the fitted surface
- this could affect the fit of the denture
| - just need to remove any bits that may irritate the patient
33
what must you do if the clasp scrapes or damages the cast
- needs changes as this will damage patient's tooth
| - need to remove the sharp edges
34
how should clasp arm sit
- nowhere near the tissue or undercut as will have difficulty getting denture in and out if it sits below the undercut
- clasps should be closely adapted to the cast = hugging the tooth
35
what is the finishing process in brief
- the denture is fitted to definitive cast
- the anterior flange should have a thin edge to blend with the surrounding soft tissue
- the denture is finished above the surgery line
- the post dam and palatal periphery is thinned to blend with the plate
- the occlusal vertical dimension must be the same as the original restoration
- there should be no sharp edges
- the denture should be policed only on the non-impression surface
