Impressions for Conventional Dentures Flashcards
What is an impression?
A reverse or negative form of the tissues which is converted into a positive model/cast using plaster or stone or s mixture of both plaster and stone
Describe the stock trays used in primary impressions?
Limited range of size and shape of trays
Perforated
Modification may be required using soft wax/putty/compound/greenstick or by trimming the tray
High viscosity material should be used
How should the fit of stock trays be assessed?
Look inside mouth and guesstimate correct tray size
Try in the tray and look inside mouth:
Too small if flanges hit the ridge
Too large if it stretched mouth or feels uncomfortable or can’t get in the mouth
What are the limitations of stock trays?
Rarely fit the mouth accurately
Often require modification
May be difficult to obtain necessary border seal
Describe technique for impression taking?
Rehearse tray insertion before loading then rotate loaded tray into mouth
Use firm pressure to seat the tray
Border moulding whilst supporting the impression with other hand
Lower - tongue movement
Upper - partial mouth closure
Do not remove until set
Remove and inspect the impression
What should be evaluated in impressions?
General adaptation and surface detail
Appropriate sulcus depth and shape
Tray placed correctly to ensure ridge is in centre of tray
All appropriate landmarks are included
Anterior lingual sulcus - tongue has been protruded
Impression is fixed to tray
What should be done after an impression is accepted?
Remove debris and rinse
Disinfect
Mark extensions in an indelible pencil
Wrap, label and bag
Prescribe for special trays
Take to lab so impression is cast asap
What should be written for stage in the lab card after primary impressions are taken?
Special trays
Please cast impressions and make upper special tray with x handle and lower special tray with x handle
Why are special trays used?
Ensures even thickness of impression material
Minimises tissue displacement
Maximises dimensional stability of impression material
Less bulky so more comfortable for patient
What are tissue stops?
Pre-formed space for the impression material
Why are tissue stops used?
Ensures uniform thickness of impression material
Helps localise tray during impression taking
Where should tissue stops be placed?
Lower tray - place in canine region and over retromolar pads
Upper tray - place in canine region and along post dam area
What are finger rests and why are they used?
Used with lower special trays in region of 2nd premolar and 1st molar
Allows fore finger to be placed on either side of the tray, thumb under mandible for support to ensure it is fully seated posteriorly and ensures more even distribution of pressure to the tissues
Helps stabilise the tray in the mouth
What are spaced trays?
Constructed using material to leave space between the tray and ridge
Usually 3mm spacing
For use with higher viscosity materials eg alginate
What are close fitting trays?
Spacing up to 1mm
For use with light viscosity materials for wash impressions eg light bodied elastomers
Used in resorbed ridges for replicas
