finishing RPDs

Question 1

another term for finsihing

Answer 1

flasking

Question 2

why is it important to finish the wax trial correctly

Answer 2

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

Question 3

what technique is used to process the denture

Answer 3

lost wax technique

Question 4

what equipment is used in processing the PMMA denture

Answer 4

metal dental flask

Question 5

what is the purpose of the 2 part closed mould

Answer 5

encloses the wax denture in dental plaster

- wax pattern is trapped in the plaster

Question 6

what happens when the 2 part mould is opened

Answer 6

the wax is evacuated from the mould

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

Question 7

the stage ‘investing the denture’ is also known as

Answer 7

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

Question 8

hooded technique

Answer 8

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

Question 9

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

Answer 9

the wax palate

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

Question 10

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

Answer 10

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

Question 11

after the mould is set what is the next stage

Answer 11

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.

Question 12

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

Answer 12

the artificial teeth and clasps

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

Question 13

filling the mould is also called

Answer 13

packing

Question 14

what material is used to pack the mould

Answer 14

PMMA

Question 15

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

Answer 15

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

Question 16

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

Answer 16

dough stage

- special attention when packing the mould around the teeth

Question 17

why is the mould closed under pressure after packing

Answer 17

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

Question 18

summary of ‘packing’

Answer 18

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.

Question 19

powder component of PMMA

Answer 19

polymer

Question 20

liquid component of PMMA

Answer 20

monomer

Question 21

characteristics of the liquid component (monomer) of PMMA

Answer 21

Highly corrosive

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

Question 22

issue is mix too much powder to liquid for PMMA

Answer 22

granular porosity

Question 23

issue if PMMA processed under too much pressure

Answer 23

contraction porosity

Question 24

issue if heating of PMMA is not controlled

Answer 24

gaseous porosity

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

on the duplicate cast

Question 27

cold cure PMMA process

Answer 27

``` 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

Question 28

2 positive of cold cure PMMA

Answer 28

fast way of creating denture easy

Question 29

2 negatives of cold cure PMMA

Answer 29

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

Question 30

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

Answer 30

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

Question 31

methods technician can use for final occlusal refinement

Answer 31

finished and polished after sawn of the denture acrylic has sharp edges - hand tools to make as as smooth as possible around periphery

Question 32

what surface should not be polished/abraded

Answer 32

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

Question 33

what is the denture fitted to after polishing

Answer 33

the definitive cast

Question 34

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

Answer 34

any spaces | esp. cingulum and flange

Question 35

why would a denture fit the cast but not the pt

Answer 35

imperfections on impression

Question 36

when are denture clasps checked

Answer 36

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

Question 37

how should the clasp sit on the definitive denture

Answer 37

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

Question 38

what should the anterior flange of the finished denture be like

Answer 38

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

Question 39

what should the finished denture be fitted to

Answer 39

the definitive master cast

Question 40

where should the denture finish above anatomically

Answer 40

the high survey line

Question 41

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

Answer 41

post dam and palatal periphery - not a ridge, smooth transition over, helps with peripheral seal

Question 42

what measurement MUST be the same in pt and denture

Answer 42

the occlusal vertical dimension articulator pin on table

Question 43

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

Answer 43

smooth - not sharp polish so no harm to pt

Question 44

why should the fitting surface of the denture never be polished

Answer 44

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