Theory of dentures 2 Flashcards
4 common impression material
- alginate
- impression compound
- silicone
- polyether
alginate basic properties
- Cheap
- Easy to use
- Can be messy - easy to wipe off
- Elastic
- Poor(ish) dimensional stability – satisfaction for complete denture as long as handle material well and poor models soon
- Accurate(ish)
impression compound
- Non-elastic – cannot be used for dentate (unless for free end saddle)
- Poor surface detail (disadv)
- Not that cheap (anymore)
- Can be messy to use, can burn pt if too hot
- Only for primary impressions as poor surface details
silicones and polyethers only used for
master impressions (as £££)
silicones
- Dimensionally stable
- Hydrophobic
- Variety of consistencies (lighr – medium- putty)
- Can be messy to use
- Very accurate
- Expensive
only for master impressions
polyethers
- Dimensionally stable
- Hydrophilic (better)
- No variety of consistencies (only medium)
- Can be messy to use
- Very accurate
- Expensive
only for master impressions
4 rarer impression materials
- Zinc oxide eugenol – thick and not elastic (undercut issue)
- Reversible hydrocolloid (agar) (duplicating casts in labs)
- Impression plaster
- Impression waxes
impression definition
a reverse or negative form of the tissues which is converted into a positive model/cast using plaster or stone.
clinical relevance of choosing impression material
- The impression material is the vital link between the skills of the dentist and those of the technician
how to choose impression tray
- Look inside the and decide (guess) the correct tray size.
- Try it in (and look in the mouth)
- too small – flanges hit the ridge
- too large – stretches the mouth or feels uncomfortable
tray needs to cover the alveolar ridge and go right to the depth of the sulcus
key point for complete denture trays
make sure it is an edentulous tray
- Dentate – rounded
- Edentulous – flanges at right angles to the occlusal surface
when to use elastic Vs non-elastic impression materials
Elastic or Non-elastic Impression material – are there undercuts?
- Yes -> elastic (alginate)
- No -> non-elastic (impression compound)
- Non-elastic materials can get caught in undercuts and be difficult to remove- be careful
basic points of doing an impression
- Rotate the tray in
- Position the tray before seating it - heels first than anterior
- Manipulate the tissues
- Keep holding the tray until it is set
alginate consistency
can alter
Runny – more water
Less runny – warm water and less (good for pts who gag)
heating impression compound
- Immerse in water bath at 55-60oC for 4-5 mins to ensure complete softening
- Gauze/paper towel at bottom of bath to prevent it sticking
- If you knead it water will be incorporated and act as plasticiser
WARNING: If it is left too long it becomes difficult to handle and some of its constituents may leach out, altering the material properties (often the plasticiser stearic acid).
loading tray with heated impression compound
cover gloves with vaseline to prevent impression compound sticking
where to stand for upper impressions
behind
where to stand for lower impressions
in front
common mistake with impression compound
not softening the compound enough
4 points of inspection of primary impression
- Have you covered the denture bearing area?
- Have you achieved a good peripheral seal? – do you get noise when remove? Is it hard?
- Have you recorded adequate surface detail?
- Suitable to produce a satisfactory primary cast?
Yes -> Cast
No -> Retake (always check with supervisor before disgarding an impression)
decontamination of impression
- Rinse under the tap to remove gross debris and saliva
- Follow GDS recommended procedures currently “Perform For 10 minutes”
- Show to staff first
prescription guard sections
Pt sticker, tx, clinic it is from, your name and email, date of primary impressions and supervisor
Stage – what you want done (not what you have done)
- E.g. taken primary so want master impressions
Date – date you want the work for
Guide
- What do you want done with the work you give - ? cast
- What do you want back – special trays?
prescription card for after taking primary impressions
- Light cured acrylic special trays
- What type of handles (intra-oral or extra-oral handles)
- Spacing – depends on material for master impressions
- Alginate 3mm
- Silicone/polyether
- spaced 2mm (often upper)
- Close fitting 0.5-1mm (often lower)
- Mark on impression outline for special tray? – inedible pencil to extension of tray
what are these and what are they for
special trays used to take master impressions
importance of special tray handle position
- if handle is proclined and could impinge on the upper lip affecting the stability of the tray
- should be made to consider the angle of the muscles to help hold the special tray in place
pro of this special tray handle position
Made to consider the angle of the muscles to help hold the special tray in place
what to do once have special trays back from lab
try in upper special tray first then lower
- Stand behind the patient (for upper)
- Gently rotate tray into the mouth
- Check the fit and extension
- If overextended reduce the extension
- If underextended correct during border moulding
border moulding
Addition of material (greenstick/silicone or wax) to the outside of the periphery of the trays to fill the functional sulcus.
- Needed for lighter materials (silicone or polyether)
- Get width and depth of sulcus
- Arrow shows as the greenstick has exposed the tray, maybe overextended in that area
- Greenstick do a third of tray in one go (e.g. 3-3, then buccal areas another time)
- Massage and manipulate the tissues when soft material in mouth to get width the tissues
what is this
tracing compound (greenstick) used for border moulding special trays
Moodle video
- Heat slowly
- Don’t burn the patient (warm but not cold water)
how to make space in special tray
use ‘(occlusal) stops’ - make tray more stable
‘stops’ in upper special tray
‘Stops’ to the space prescribed in the canine and post dam regions
- These will allow accurate correction of the posterior borders of the tray and will pre-form space for the impression material
- The stops should involve the whole of the posterior border of the tray.
‘occlusal stops’ in lower special tray
‘Stops’ to the space prescribed on the retromolar pad and on the ridge in the canine areas
- These will allow space for the impression material
tip if using a light bodied silicone impression material from a gun
put some on glove to check when set
what is the red anteriorly on this master impression
Red wax used anteriorly for border moulding to get satisfactory border sulcus
4 check points for master impression
- Have you covered the denture bearing area?
- Have you achieved a good functional sulcus?
- Have you recorded good surface detail?
- Suitable to produce a master cast?
Yes -> Cast
No -> Retake
consider the fitting surface – if voids small and not on it then should be ok
master impression ->
casts (Intended result)
Ideal is width of sulcus is clearly defined on model
- Ensure right width of flange
prescription card for master impressions
Stage – what you want done (not what you have done)
Date – date you want the work for
Guide
- What do you want done with the work you give - ? cast
- What do you want back – ? wax record block
(ADD)
replica denture assessment consists of
Decide what is wrong with old denture and make sure you change it
Denture modification
I like to temporarily modify the old dentures (with greenstick)
Why?
- Check assessment correct
- If pt notices an improvement with modifications then know on right track
- Make later stages easier
how to do denture modification of old dentures to see if assessment correct
- Heat greenstick slowly
- Initially shiny, wait till matte that is working temperature
- Wait until it goes matt
- A big “dod” on polished surface (not on fitting surface)
- Shape approximately
- Mould in mouth and get pt to swallow – aim to get better extension distally
replica impression objectives (3)
- Create a replica prosthesis that is dimensionally accurate
- Replica should have a solid base for recording the working impression
- Replica should have occlusal and polished surfaces that can be easily modified
Video Technique on Moodle
replica impression summary
Edentate tray with laboratory putty (not safe to use in humans)
Pushed lower denture fully into lab putty, made a smooth margin between putty and denture
- Because when technicians place shellac on if not level more difficult for technician
Once taken initial impression of the polished surfaces get another amount of lab putty, push into fitting surface of allow us to get the impression fitting surface
Once set lever out denture using a wax knife, always at heel (less likely to break)
Combined will be void – technician can pour wax in, will have record block of wax teeth and polished surfaces and more solid base
prescription card after denture modification of replicas stage
Stage - “Second impression and occlusion”
- as with replica technique not have to do occlusion and impression separately
Disinfect and date of next appt
Fill in
- Nothing want done as will work with impression on lab putty
- Want back – replica blocks with shellac base and wax polished teeth and surfaces
