RPD LAB - FINISHING/FLASKING

Question 1

What happens in ‘flasking’

Answer 1

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

Question 2

Why is the palate left exposed in ‘flasking’

Answer 2

o This is where the light cure base gets placed so we need to make sure that there is space to remove that
o It is also because this is where we place the acrylic manually

Question 3

On setting in the ‘flasking’ stage what is the plaster mould coated in

Answer 3

a separating medium (sodium silicate)

Question 4

In the ‘flasking’ stage what is the mould completed with

Answer 4

with a 50/50 plaster/stone mix

Question 5

What is done following the setting of the completed mould in ‘flasking’

Answer 5

The dental flask is immersed in hot water for 10 minutes to soften the wax inside.

Question 6

When the flask is separated after ‘flasking’ what is the wax evacuated with

Answer 6

with boiling water

Question 7

What happens in the hooded method of flasking

Answer 7

the artificial teeth and clasps are held in the investing plaster following flasking.

Question 8

What are the plaster surfaces and cast coated with in ‘packing’

Answer 8

a ‘mould seal’ to prevent plaster adhering or penetrating the denture.

Question 9

When should the mixed PMMA be packed

Answer 9

when it has reached the dough stage

Question 10

When packing the mould where should special attention be paid to

Answer 10

packing the mould around the teeth.

Question 11

Why is the mould closed under pressure

Answer 11

To expel excess material which on re-opening is removed

Question 12

After the excess PMMA is removed what is done

Answer 12

The two halves are closed and placed into a spring compress and processed

Question 13

What is the powder in PMMA

Answer 13

the polymer

Question 14

What is the liquid in the PMMA

Answer 14

the monomer

Question 15

What is the ratio for PMMA

Answer 15

10mls to 24g

Question 16

What happens if too much powder is used

Answer 16

can result in granular porosity

Question 17

What should the PMMA be processed

Answer 17

under pressure in a hydraulic flask

Question 18

Why should the PMMA be processed under pressure

Answer 18

otherwise the acrylic will expand and pull the acrylic apart resulting in contraction porosity

Question 19

What else can result in contraction porosity

Answer 19

Having too little acrylic can also result in contraction porosity as well

Question 20

Why should the heat be controlled when mixing PMMA

Answer 20

– it should not be too hot as this will cause it to boil too quickly and this will cause holes in the acrylic which will result in gaseous porosity

Question 21

Why should the PMMA then be bench cooled

Answer 21

to relieve internal stress

Question 22

How is the denture removed following processing

Answer 22

 The plaster is removed from the mould and the plaster mould removed from the denture and cast

Question 23

What are the advantages of cold cure

Answer 23

o very easy to do

o quick

Question 24

What are the disadvantages of cold cure

Answer 24

o it is not processed properly so it is not polymerized properly meaning that the acrylic is softer than it would be in heat cure
o also means acrylic teeth aren’t fully processed and so if there is any heavy occlusal contacts these teeth will wear down quicker than in the heat cure process
o heat cure acrylic looks more natural than cold cure

Question 25

How is the occlusion checked

Answer 25

 This is done using the split cast system

Question 26

Describe the process of checking the occlusion

Answer 26

 The duplicate model (with denture) is secured to the original mounting with plaster bandage
 The occlusion is checked and refined as required against the opposing dentition

Question 27

What indicates the occlusal vertical dimension on checking the occlusion

Answer 27

 The incisal post at rest on the incisal table indicates the occlusal vertical dimension

Question 28

How is the duplicate model removed from the denture following occlusal refinement

Answer 28

by sawing the model from the denture

Question 29

What happens following occlusal refinement and removal

Answer 29

 The denture is finished and polished

Question 30

What can be done following polishing of the denture

Answer 30

the denture can be fitted to the definitive cast

Question 31

What do the denture on the definitive cast show regarding the clasps

Answer 31

 The denture on the definitive cast shows the space between the clasp arm and the cast

Question 32

What do we want to see with the clasp

Answer 32

 Want a close adaptation of the finished clasp on the cast and want to ensure arm of the clasp is not anywhere near tissue or undercut and only the terminal end will be on the selected undercut