complete dentures Flashcards
What does alveolar resorption involve?
Magnitude Site and pattern Time relations Influencing factors Problems
What is the magnitude of resorption in mandible compared to the maxilla?
4x greater in the mandible than the maxilla
How does the residual ridge change as a result of mandibular resorption?
More lingually placed anteriorly More buccally placed posteriorly In at the front and out at the back Labial plate is weaker in front Lingual plate is weaker in back
Where should mandibular denture teeth be placed in relation to the residual ridge?
Lower anteriors- on or slightly ahead
Canines and premolars- on
First molar- on or just inside
Second molar- on or just outside
How does the residual ridge change as a result of maxillary resorption?
More palatial in all regions
Where should maxillary denture teeth be placed in relation to the residual ridge?
All slightly buccally/labially rather than on
How quick is mandibular resorption over time?
Rapid bone resorption initially when teeth are taken out which then slows over time Eg. 2.5mm in 4 months 3.5mm in 8 months 4mm in 12 months 4.25mm in 16 months
What influences the rate of resorption?
Systemic=quicker eg. Osteoporosis
Local=slower eg. Retained roots and implants preserve bone
Denture induced=quicker (limited evidence)
What are the benefits of retained roots and artificial implants?
They preserve the bone around them so the dentures are more stable
What is the ‘neutral zone’?
The teeth are placed in balance so that the forces of the tongue and cheek work together to keep the dentures in place
What are immediate dentures?
Relates to rapid initial resorption
What should happen if the patient has a class 3 molar occlusion?
Lower molar teeth must be placed correctly over the ridge
May have to allow cross-bite for aesthetic purposes
Why might patients get a molar crossbite?
Often due to the palatial resorption of maxilla and buccal change of mandible- resorptive pattern
How might the mucosa be affected by bone resorption?
It might get compressed between the denture base and the sharp bone ridges leading to pain
How might the mental nerve be affected by bone resorption?
May become compressed leading to shooting pain or numbness and paresthesia
What happens if there is irregular resorption?
The mucosa might become sandwiched between sharp bony spicules and the denture base- painful
How might the patients appearance be affected?
Lack of support of soft tissues may lead to angular cheilitis (fungal infection at corners of mouth) and ages patient significantly
What kind of impression would you do with a ridge with minimal/without undercuts?
Rigid impression material in close fitting special tray
What kind of impression would you do with a ridge with large undercuts?
Elastic impression material in spaced special tray
What is an undercut?
The area between the maximum bulbosity of the ridge compared to the deepest part of the sulcus beneath
The contour that would prevent the placement of a prosthesis
Why is zinc oxide-eugenol used?
Cheap, easy to modify and accurate
Mucostatic but if in non-spaced, non-perforated tray= mucocompressive
Sometimes used with one spacer
Mucostatic, two spacers and wide perforations in mild flabby areas
What does a close fitting special tray look like?
1-2mm short of final denture border
Minor to moderate undercuts
Mucocompressive impression
What does a spaced special tray look like?
Use alginate instead
2-3mm short of final denture border
Moderate to severe undercuts
Mucostatic impression
Why might you use tissue stops?
Use for anything but ZnO
Silicone- 1.5-2mm TS
Alginate- 3mm TS
Ask lab to create
For areas that are relatively noncompressive
Stops tray showing through if excessive pressure
How do you adjust your tray?
Before taking impression, check tray- cheek traction to see if moves
Overextended- trim back so frenae etc. aren’t impeded and can be recorded
Underextended- add greenstick
How far should the tray extend?
Must be short of the deepest part of the sulcus
How do you use Zinc Oxide Euganol?
2 tubes- the red and white quantities should be the same to control the setting times
Mix evenly and don’t overload tray
What should you tell the patient before taking a ZnO impression?
There is often a burning sensation, it’s sticky and has a strong taste
Let them know that it will get quite warm in their mouth, don’t worry, it’ll set quickly
What precautions should you take with ZnO impressions?
If dry mouth, patient should rinse
Elastoplast allergies*
*shouldn’t use ZnO if so
How do you record the impression?
Lift the tongue
Must border mold the periphery so that the denture isn’t overextended
Why might finger rests be made?
Prevents fingers from distorting the periphery
What might you be able to do if the tray penetrates a ZnO impression?
You could add a bit of material to correct this rather than retaking it
Why might you want to use a combination of materials?
Selective pressure impression
Eg. Monophase silicone anteriorly for fibrous ridges
ZnO posteriorly for firm tissues
What is a flabby/fibrous ridge?
Displaceable/mobile ridge usually in upper anterior region
Often when lower teeth retained against upper edentulous ridge
What is the implication of a flabby/fibrous ridge?
Causes instability of denture due to lack of underlying bone
How should you record a fibrous ridge?
Should be done in a mucostatic way
Use a ZnO tray with a window box anteriorly to inject light bodied silicone to avoid compression
What is an Alma Gauge?
Can give lab a vertical and horizontal reading if there is a good old denture
This is so the bite blocks can come back at the correct dimensions
The plunger should be at the indentation of where the incisive papilla is
How should you instruct the lab?
Eg. Please make upper and lower registration rims
Specify- eg. Alma gauge of old upper using incisive papilla as fixed point V12 H7
If not- rough guide 22mm upper and 18mm lower from deepest area of sulcus
