Finishing/Flasking RPD's Flashcards
What is the name for the technique used for processing a denture?
The lost-wax technique
What is the ‘lost wax’ technique? (4 points)
- A metal dental flask is used in the processing of the PMMA denture - 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 by the removed wax is filled using PMMA
What is meant by the term ‘flasking’?
- The wax denture is sealed onto the duplicate cast and embedded in the 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 mins to soften the wax inside. The flask is separated and the wax evacuated with boiling water
What is the hooded method of flasking?
The artificial teeth and clasps held in the investing plaster following flasking
What happens when filling the mould - ‘packing’?
- 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 reached 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 pressure to expel excess material which on re-opening is removed
Give a summary of the ‘flasking’ and ‘packing’ stage of producing a denture? (6 points)
- 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 - On opening the flask, the wax is evacuated with boiling water and the mould is cleaned with a detergent to remove any wax residue - The 2 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 2 halves are closed and placed into a spring compress and processed
What is the powder in PMMA?
a polymer
What is the liquid in PMMA?
- A monomer
Why do you need accurate mixing of PMMA (10mls to 24g)?
- To prevent granular porosity (from too much powder)
Why is PMMA processes under pressure?
Why is PMMA processes under pressure?
Why is heating when mixing PMMA controlled?
To prevent gaseous porosity
Why is PMMA bench cooled?
- To avoid internal stresses - If put in cold water will increase internal stresses and cause the PMMA to crack
How is the denture removed from the plaster?
The plaster is removed from the mould and the plaster mould removed form the denture and cast - Need to try to separate without breaking the acrylic
How can we used cold cure to produce a denture?
- Wax trial on cobalt-chrome - use lab putty with an activator and put over wax - Remove the putty and boil off the wax - Stick the teeth to the putty - Can then pour acrylic in - Can cause problems with air blows - Use cols or luke warm water - It is hard enough but softer than heat cure - Acrylic teeth are only half processed so they are softer - Acrylic doesn’t look as natural
How is the occlusion checked following the process of making the denture?
- The split cast system (where can put casts back onto the articulator) - The duplicate model with denture is secured onto the original mounting with plaster bandage - The occlusion is checked and refined as required against the opposing dentition - The incisal post at rest on the incisal table indicates the occlusal vertical dimension
