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BDS2 - prosthetics > finishing/flasking > Flashcards

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

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2
Q

what type of technique is used for processing the denture

A
  • a ‘lost-wax’ technique
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3
Q

what is used in the processing of a PMMA denture

A
  • metal dental flask is used
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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
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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
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6
Q

what is a separating medium often used

A
  • sodium silicate
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7
Q

what type of technique is used during investing the denture

A
  • hooded technique
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8
Q

why must you ensure you font have any air blows

A
  • as acrylic will fill this
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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
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10
Q

what is another method of investing the denture

A
  • plaster over plaster dentate
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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
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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
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13
Q

why is a trial of the packing stage conducted

A
  • to ensure the mould is completely filled
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14
Q

what is used to mix PMMA

A
  • powder = polymer
  • liquid = monomer
  • hydraulic press
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15
Q

what must you be careful of with the monomer

A
  • it is very corrosive so needs to be in a controlled environment
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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
Q

what is good about cold cure method

A
  • very fast way of creating a denture

- 5-10 min set

26
Q

what are the negatives of cold cure method

A
  • 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
Q

how is occlusion check following processing

A
  • 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
Q

why might occlusion need altered

A
  • processing can sometimes alter the occlusion and the pin may not be on the table
  • it may have been raised
29
Q

what is done after the occlusion is adjusted

A
  • the duplicate model is removed from the denture by sawing the model from the denture
  • the denture is finished and polished
30
Q

what can be done following polishing

A
  • denture can be fitted to the definitive cast
31
Q

why must acrylic be finished

A
  • it has lots of sharp corners and angles

- use hand tools

32
Q

why don’t you do much finishing and polishing on the fitted surface

A
  • this could affect the fit of the denture

- just need to remove any bits that may irritate the patient

33
Q

what must you do if the clasp scrapes or damages the cast

A
  • needs changes as this will damage patient’s tooth

- need to remove the sharp edges

34
Q

how should clasp arm sit

A
  • 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
Q

what is the finishing process in brief

A
  • 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

BDS2 - prosthetics (10 decks)

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