lab 5- tooth modification Flashcards
Why might we need to modify teeth
- Create space for occlusal rests
- Create undercuts where none exists
- Block out undercut where it is inconvenient
- Create guide planes
Why might we need to create space for occlusal rests
so that they don’t cause an interference to the bite
How can we create undercuts on a tooth
By adding composite
What is another name for secondary impressions
Major or working impressions
What are the aims of a secondary impression
- Accurately record the denture bearing area
- Record the functional depth and acceptable width of the sulk where a denture flange or major connector will extend
- Record the abutment teeth and tooth preparation in sufficient detail
What are secondary impressions taken with
A special tray
Medium and light bodied silicone or alginate
When would we use alginate to take a secondary impression
When there a lone tooth standing
Which material is more accurate: silicone or alginate?
Silicone
Which material do technicians prefer: silicone or alginate? Why
Alginate as it is easier to remove off the tray and is harder to break
What are some qualities of special trays
- They extend 2mm short of the sulcus depth
- 3mm space where there are teeth
- Is close fitted in edentulous areas
- Has stops
Why do special trays need to extend 2mm short of the sulcus depth
To allow space to add greens tick for border moulding
Why do we have stops on special trays
To create space and ensure the impression material is of even depth the whole way round the mouth
Where do we want stops to be on partial dentures
On teeth
Describe how we create a special tray
- Put tray in position in the patients mouth
- Carry out muscle trimming and see if there are any over extensions
- Use greens tick or heavy bodied silicone on borders of tray
- Trim border material from inside of tray
- Apply adhesion
- Take final impression in silicone or alginate
When would you add green stick to a special tray
Only needs to be placed in areas where we are putting components onto the denture eg flanges or gingival ally approaching clasps
Name the step we need to carry out to ensure we take a good prosthetic impression
Border moulding
Why is border moulding important
To record the functional sulcus for correct flange extension and major connector position
What can we use to carry out border moulding
- Green stick
2. Heavy bodied silicone
How to we carry out border moulding using green stick
- Set Bunsen burner and
warm water bath - Heat green stick in fire by constantly moving it and waiting for it to droop
- Drape the green stick onto the borders staying more to the outside of the tray
- Always insert the tray into warm water for a couple of seconds before putting it into the patients mouth
- Trim any excess
- Remove excess impression compound from the fitting surface with a hot wax knife
Why should we place the impression tray into warm water before placing it into the patients mouth?
To cool the impression down a little so it doesn’t burn the patient
How should the impression compound look after you have placed it into the mouth
The impression compound must look as if it has moulded to the shape of the sulcus
You should be able to see the depth and buccal surface
How should we get rid of folds and voids on an impression
By muscle trimming after re heating the compound
What is a perforation on a special tray
Holes greater than 2mm in diameter
When are perforations needed on a special tray
When using alginate
Why do we need to put perforations on a special tray when using alginate?
To reduce the impression pressure
What happens if you need perforations on a special tray but have forgotten to ask for them
You can create perforations chair side using a rose head burr in a straight handpick
What can be a potential problem if you make a special tray with perforations
Perforations reduce impression pressure unevenly which can cause a potential theoretical problem for imps of mucosa
What is the preferred material for definitive secondary impression
Medium bodied silicone with a light bodied silicone wash
How do we use medium bodied silicone
- Block out any visible embrasures with carding wax
- Light bodied silicone is then syringed intra orally onto any tooth surface the cobalt chrome will touch
- Tell you assistant to full the special tray with medium bodied silicone
- Insert position and seat the filled tray into the patients mouth
- Border mould the soft tissues until the silicone sets
How do we tell the technician how much we want to trim the model
Draw a line 2mm from the depth on the outside of the impression to guide the technician when trimming models
