Finishing and Delivery

Question 1

What technique is used to process the denture?

Answer 1

Lost wax

Question 2

What tool is used to process the PMMA denture?

Answer 2

Metal flask

Question 3

How is the metal flask used to process the denture?

Answer 3

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 using hot water

The space left (with teeth) by the removed wax is filled
using PMMA dough

Question 4

What is the most difficult part of flasking?

Answer 4

Elimination of all undercuts usually found on the labial/ buccal aspect before adding plaster

Question 5

How are the undercuts minimised at the initial stages?

Answer 5

Using dental plaster to block out

Question 6

Describe the hooded method of flasking?

Answer 6

The waxed denture is sealed onto the
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 (sodium silicate) and the
mould is completed with a 50/50
plaster/stone mix.

Following the setting of 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.

The mould prior to ‘packing’ the PMMA. 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 a 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 hydraulic pressure to expel excess material which on re-opening is removed.

Question 7

What is the procedure for packing?

Answer 7

*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.

*THE FLASK IS OPENED AND EXCESS IS REMOVED.

*THE TWO HALVES ARE CLOSED AND PLACED INTO A SPRING COMPRESS AND PROCESSED.

Question 8

Why does granular porosity happen?

Answer 8

Too much powder resulting in dry mix due to a lack of monomer

Question 9

What two components make up PMMA?

Answer 9

power (polymer)
liquid (monomer)

Question 10

Why does contraction porosity occur?

Answer 10

insufficient acrylic is packed into flask
OR
insufficient pressure is applied during processing

Question 11

Why does gaseous porosity occur?

Answer 11

premature rise in temperature during the curing of PMMA (allow slow and controlled rise in temperature)

Question 12

Why do internal stresses occur?

Answer 12

if the cast is cooled too quickly after boiling

Question 13

Why is porosity bad?

Answer 13

undesired appearance and voids which compromise strength of material

Question 14

Where does porosity usually occur?

Answer 14

on the thickest part of the acrylic and and be solved by rebasing the denture

Question 15

After processing, how can the occlusion of the acrylic denture be checked?

Answer 15

split cast system

• 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 16

What does the incisal pin at rest on the articulator on the incisal table indicate?

Answer 16

occlusal vertical dimension

Question 17

After checking the occlusion, what is done?

Answer 17

finished and polished using handpiece and burr

Question 18

What is the final checklist?

Answer 18

• THE DENTURE IS FITTED TO THE DEFINITIVE (MASTER) CAST
• THE ANTERIOR FLANGE SHOULD HAVE A THIN EDGE TO BLEND WITH THE SURROUNDING SOFT TISSUE
• THE DENTURE IS FINISHED ABOVE SURVEY LINES
• THE POST DAM AND PALATAL PERIPHERY IS THINNED TO BLEND WITH THE PALATE
• THE OCCLUSAL VERTICAL DIMENSION MUST BE THE SAME AS THE ORIGINAL REGISTRATION
• THERE SHOULD BE NO SHARP EDGES
• THE DENTURE SHOULD BE POLISHED ONLY ON THE NON- IMPRESSION SURFACE