Partial denture 4 Flashcards
What is the aim of primary impressions
Create cast for further denture construction work
Design denture
Surveying the teeth
Using general treatment planning to decide which teeth will need to be replaced
Special tray - impression tray
We need impression to cover entire denture area
Accurate impression of all standing teeth and buccal and lingual surfaces
what are the arrows representing
Indication of full denture bearing area
Upper arch - whole of hard palate
Vibrating
Good impression of any sulcus areas where teeth are missing
No posterior teeth
Good recording of maxillary tube veracity
what are the arrows representing
Lower arch - no palate - record well any areas where teeth are missing
Record sulcus areas buccally
Good impression of lingual sulcus all the way round
No posterior teeth - extend impression all the way around
Retomolar pad- thickened area of mucosa
What are the problems with the retromolar pad
Sometimes retromolar pad isn’t easy to see
Should be in these regions
Can’t sometimes see retromolar pad
Impressions of models show the retromolar pad
Name different types of elastic impression materials
Name different types of inelastic impression materials
what do we consider when taking a impression of objects with undercuts
Elastic material - needs to cover teeth with undercut area and interproximal spaces
Elastic material able to come out of those areas and spring back to shape
How are primary impressions usually taken
Describe the chemicals aliginate contains
Irreversible hydrocolloid
Don’t need to learn chemical processes
Just need to be aware of what material it contains
What are the advantages of alginate
Well tolerated- too hot or cold
Add flavours to it
Flows well over the surface
Mucostatic- doesn’t distort tissues too much
What are the disadvantages of alginate
If left open to atmosphere - will dry out
syneresis= long polysaccharide chains in alginate material will coil up and squeeze water out
Seal in plastic bag
Swells up in water - through process call imbibition
Poor tear resistance - might tear when taking impression back out
Require adhesive to stick to impression tray
what are the 4 stages in impression taking
Modify with various materials
Alginate needs to be supported by rigid
Put adhesive on tray
Check impression to make sure it fulfils requirement
How do we select trays
Select try
Usually medium and see if it goes over teeth and hope to see couple mm of space on either side
Should cover all teeth
Teeth behind impression tray
Should extend to short of 2 mm
What are the common problems of selecting trays
Why is tray modification needed
May need to add material if short of sulcus depth
If excessive amount of spaced between tray and mucosa
name the problem and how to modify
- tray is short of sulcus depth
Alginate material may get there but would be unsupported and floppy
Avoid any parts of impression where the alginate might be sticking up without being supported
3 materials used to modify tray to make it more suitable to take impression for partial dentures
Describe this
Larger edentulous areas, big bulk of alginate unsupported
Large height of alginate material - like a gel - take a impression of it and tend to slump in the area afterwards
Describe this
Modify tray by adding material in the area to take up some of the space
Silicone putty or wax
Alginate is now supported
what do you need to make sure when taking impressions and alginate
Load tray with alginate making sure it completely covers entire tray
How do we position when taking lower impressions from a patient
Stand in front of patient
Patient mouth about level with elbows
How do we position when taking upper impression from the patient
Stand behind patient- chair leaning back slightly
Mouth adjusted so same height as elbow
Upper impression in front - end up having to stoop down - twist spine or hurt back
Describe border moulding labial and lingually
While the impression material is soft - stimulate normal function of the mouth
Ask patient to move tongue around
Tongue into one cheek or the other
How do we assess completed impressions
what is the issue with this impression
Same patient on same day
1st impression
Okay impression of teeth but massively underdeveloped edentulous area
Make sure teeth are fine and covered entire denture bearing area
How do we mark the extent for special tray
Once happy with an impression
Draw a line 2mm short of incisal
Technician makes plaster model - the line will come out on that model
what are the aims of SECONDARY IMPRESSIONS
What are the stages of secondary impressions
Greenstick
Take impression - alginate or silicone
Rest / impression needs to be accurate
Fits snugly into that seat
Clasps need to be in a undercut area - esp cobalt chrome 2.2.5 mm depth
Sometimes teeth don’t have a natural undercut
Changing the survey lines
Survey lines higher up
What additive techniques can we use to modify the secondary impression
Anterior
Cingulum rest
Much more likely to create a flat surface to create a rest seat for us
What are special trays
Made specifically for a patient
So they fit the patient’s mouth
Describe the special trays specification
Using alginate
Need a spec fo 3mm around teeth to be flexible
Large edentulous areas- no undercuts there
Get trayed without any space- close fitting
Special tray to be within 2 mm of full depth beneath sulcus
How do you perforate special trays
Ideal
3mm space between trya and tooth in all dimensions
Push it down too far and loose the space occlusally
Lost the space
Once we pushed it too hard
Include stops within the special tray
Raised areas of acrylic that rest on the teeth
3 mm above teeth all the way around
What are stops
Little bits of acrylic / greenstick to a tray to prep the tray up
What is special trays - border moulding
describe the sulcus at rest and sulcus during function
Displace denture
Need to do impression of functional depth of width of the sulcus
Describe the clinical technique of border moulding
- Set up warm water bath (50 degrees)
Impression compound comes as pink or green stick - pink stays softer for longer (thermoplastic materials) - Keep moving the impression compound in and out of the flame for a few seconds each time until it starts to droop.
Drape it onto the tray border staying more to the outside for eh tray. The tray must be dry for it to stick. - Always insert into warm water for a couple of seconds before putting it into patients mouth otherwise can cause a burn
- The impression compound must look as if it has moulded to the shape of the sulcus, Folds and voids should be eliminated by further muscle trimming after re heating the compound
- Finally excess impression compound must be removed form the fitting surface with a hot wax knife, leaving only the depth and buccal surface remaining,
What do we need to be aware of inside the tray
What would happen if we left green stick to pink stick inside of tray
Area of impression material , when we remove has to squeeze through space
Compressed
Spring back to original shape
Area know squeeze through is less
Hw would you remove green stick from inside of tray
Remove greenstick or pink stick on inside of tray
But still record depth and width of sulcus
Apply adhesive to tray
Take our final impression
Draw line on outside of tray - 2mm form depth to guide technicion when trimming model.
Make sure no damage is done to flanges
Impression fro complete denture
what occurs after all impression taking
What do we need to check when trying in metal framework
How do we check the accuracy of fit of the components
also check the position of the retentive and bracing arm
- Inspect all components which are designed to be clear of the gingival margin area, and check that the clearance is adequate
- Check the stability of the framework
-Finally check the occlusion for clearance of all components
How do we examine the framework in the mouth
- If upper and lower frameworks are to be tried in, try each independently
- Check the occlusion of each separately and then together to ensure that there are no premature contacts.
This should be done by visual examination, comments from the patient and the use of articulating paper or occlusal indicator wax - Adjusting the framework
disclosing paste used to determine areas of metal work that need adjustment to aid seating
What does recording the occlusion mean
Using wax blocks in patient mouth
Close together and trim those blocks
Learn more in practice
What are we trying to achieve at this clinical visit
What do we have to do after recording the occlusion: 3 scenarios -
Look at lectures for case
What can be used to record the patients occlusion
Blue mousse - pick up impression of opposing teeth
