DENTURES2 Flashcards
What is an Impression?
Negative replica of tissues which is converted into positive model cast in stone or plaster
What are the main impression materials used in denture making?
Alginate
Impression compound
Silicone
Polyether
What other impression materials may be used to aid denture construction?
ZOE- not elastic
Agar (reversible hydrocolloid)- duplication of casts
Impression plaster
Impression waxes
What are the advantages/disadvantages of alginate?
ADV- cheap, easy to use, elastic, accurate
DIS- messy, poor dimensional stability (but ok for dentures)
What are the features of impression compound?
Non-elastic (only used for free end saddles)
Poor surface detail
Expensive
Messy
Only used for primary impressions
Can burn patient
What are silicones and polyethers used for?
Master impressions- more accurate than alginate
What are the features of silicones
Dimensionally stable
Hydrophobic
Variety of consistencies
Can be messy to use
Very accurate
What are the features of polyethers?
Dimensionally stable
Hydrophilic (better)
No variety of consistencies (always medium body)
Can be messy to use
Very accurate
What is the clinical relevance of impressions?
Allows link and communication between dentist and technician
What tray should be used in complete dentures?
Edentulous tray- shallower
Should engage over alveolar ridge and engage full depth of sulcus
How do you choose the right tray?
Look and estimate correct size
Try it in:
Too small if flanges hit ridge
Too large- stretches mouth
When do you sue elastic impression materials like alginate?
If there are undercuts
Use non-elastic if no undercuts
Where should you stand when taking an impression?
Upper- behind
Lower- in front
What are the steps in taking an alginate impression?
Rotate the tray in
Position the tray before seating it
Manipulate the tissues (pull lip over etc)
Keep holding the tray until it is set
What are the steps in preparing impression compound?
Immerse in water bath at 55-60°C for 4-5 mins- ensures complete softening
Place gauze/paper towel at bottom of bath to prevent sticking
Handle with vaseline on gloves
What happened if you knead compound?
Water is incorporated and acts as plastciser
What happens if you leave impression compound in bath too long?
Becomes difficult to handle- components leach out and affect properties
How do you take an impression using compound?
Rotate the tray into patients mouth
Use firm pressure to seat tray
Tissuemoulding
Remove the impression
What should be checked when inspecting impressions?
Is denture bearing area covered
Peripheral seal (should be difficult to remove)
Surface detail- accurate
Can a satisfactory cast be produced
How are impression decontaminated in GDS?
Rinse under tap to remove gross debris or saliva
PERFORM- 10mins
What should be detailed in the stage and date sections of the prescription card?
Stage- what you want done
Date- when is work required
Following a primary impression what should you ask the lab to provide?
Light cured special trays with handles (IO or EO) with spacing
Casts
How much spacing is required for different materials?
Alginate- 3mm
Silicone or polyether:
Upper- 2mm
Lower- 0.5-1mm
How do you correct an under/over-extended special tray
Over- trim extension
Under- border moulding
What is border moulding? (may not be needed for alginate)
Addition of material (greenstick/silicone or wax) to the outside of the periphery of the trays to fill the functional sulcus
Where are stops prescribed to be positioned to create space in the upper tray?
In canine and post dam regions (whole posterior border)
What are the purposes of occlusal stops?
Allows accurate correction of posterior borders of tray
Preform space for impression material
Help stabilise special tray
How thick should the occlusal stops be for different impression materials?
Alginate- 3mm
Light body silicone- 1mm
Where are occlusal stops prescribed to create space in the lower tray?
Retromolar pad
Ridge in canine areas
What do we look for upon inspection of master impression?
Coverage of denture bearing area
Good functional sulcus
Good surface detail
Suitability for master casting
What does the replication of the functional sulcus help the technician with?
Getting right flange width
What do we want the lab to produce for the next visit?
Master casts
Wax record blocks
When making replica dentures why is it helpful to modify them temporarily with green stick?
Checks assessment is correct
Makes later stages easier
What are the steps in modifying a denture with green stick
Heat slowly- wait until it goes matt
Place large piece
Shape approximately
Mould in mouth (finger pressure and swallowing)
When temporarily modifying a denture where should green stick not be placed?
On fitting surface
Modification should be done on polished surface (often in mylohoid space)
What are the objectives when taking replica dentures?
Replica should be dimensionally accurate, have a solid base for recording working impression and have easily modifiable occlusal and polished surfaces
What should you ask the lab to produce following replica impression?
Replica blocks in wax or shellac
Ready for second impressions and occlusion
