Tutorial 4 - secondary impressions Flashcards
Reasons why an impresion may be unsuitable for use?
- Inadequate material coverage, eg if the material doesnt capsure the teeth, gums and other anatomical like hamular notch/tuberosity structures FULLY
- Distortion - removal too early, patient moving, drags
- Air bubbles or voids where they are important, eg abutment teeth or undercuts or cusps.
- Tearing of the material during removal or otherwise.
- Incorrect incorporation of powder to liquid for alginate
- Shrinkage or expansion of impression material
How can we identify an underextender or overextended special tray?
OVEREXTENDED:
- may extend beyond the normal anatomical boundaries, such as covering the soft palate or lips
- may be excessively uncomfortable for the patient, causing gagging
UNDEREXTENDED:
- Doesnt cover anatomical landmarks such as teeth, maxilary tuberosity and hamular notch, retromolar pad, gigniva, palata, frenums
what is the significance of the hamular notch and maxillary tuberosity in dentures?
We need to make sure we capture this so that we can have a defined denture border and know how far to extend the saddle areas.
Why record secondary impressions?
To enable you to pour a very accurate secondary (“working”) cast on which your partial denture will be made
What must you do before recording the impression?
Confirm your design with your teacher and discuss it with your patient
Undertake any necessary tooth preparations
Try in and possibly modify your special trays
What tooth preparations may be required?
Why undertake these preparations?
rest seats - in order for rests to be placed for retension of the denture
tooth dimple tooth preparations for i-bar
guide planes - in order to have a path of insertion
what are tooth dimple tooth preparations?
small notches made in tooth to make I-bar fit in
If carrying out modifications such as rest seat prep, what do we need to do with the patient first?
You must explain to your patient what you are proposing to do and ensure they consent to this.
You can use the primary cast to practice your preparations and to show the patient what you intend to do.
What modifications might we need to make to the tray?
trimming the tray if it has been overextended
adding green stick if the tray has been trimmed too much
When should silicone not be used for secondary impression material?
not good if we have large undercuts which are bony such as maxillary tuberosity
Why is an accurate impression of the lingual sulcus vital when making a lower partial denture?
To capture all the soft tissues. This is especially important to see if we have enough space to fit a lingual bar.
when do we use lingual bar and lingual plate?
lingual bar is when we have 7mm clearance, also has more possibility for cleaning and traps less plaque
what instructions will you write on your laboratory prescription if making a cobalt chromium denture?
“please construct a cobalt chromium framework to design drawn”
what will be done at next clinical appt?
a try in if the metal framework (if making a cocr denture
OR
definitive jaw registration (if making acrylic denture)
