Primary impressions for conventional and complete dentures Flashcards
List the clinical and technical stages we carry out to make a denture
- Primary impressions
- Cast models and create special trays (Lab)
- Secondary impression
- Cast models and create record rims (Lab)
- Jaw registration
- Mount on articulator and set up teeth (LAB)
- Try in
- process to finish
What should a primary impression aim to record
The entire functional denture bearing area to ensure maximum support, retention and stability for the denture during use
List key features seen on a upper impression
- Hauler notch
- Vibrating line
- Fovea paatinae
- Palatal rugae
- incisive papilla
- Labial frenum
- Labial sulcus
- Buccal frenum
- Buccal sulcus
- Mucogingival line
List key features seen on a lower impression
- Retromolar pad
- Lingual sulcus
- Lingual frenum
- Pear shaped pad
- Buccal sulcus
- Buccal shelf
- Labial sulcus
- Buccal frenum
- Labial frenum
What makes a good impression
- Tissues recorded without distortion
- Completed with minimal discomfort to the patient
- must over the maximum denture bearing area
- Should be free of significant defects
What makes a bad impression
- Significant voids
- under extension
- Overextension
- impression material not adhering to tray
- Impression that does not cover full denture bearing area
What things can lead to a bad impression
- Incorrect tray selection eg using edentulous tray for no edentulous patient
- stock tray being under extended so alginate impression being too high
- Impression tray not being seated centrally leading to widening and narrowing of sulcus
What material scan we use for a primary impression
- Impression compound
- Alginate
- Silicone
What impression compound
A thermoplastic material
What do we mean by thermoplastic material
Softens with heat, hardens when cool
What are some advantages of impression compound
Can repeat the impression until the impression is correct
What 3 parts make up impression compound
- Resins
- Filler
- Plasticiser
Give examples of resins in impression compound
- Paraffin wax
- Beeswax
- Shellac
Give examples of fillers in impression compound
- Talc
2. Chalk
Give examples of Plasticers in impression compound
Stearic acid
Why is plaster added to impression compound
To make it more flowable in the mouth
what can happen if impression material is left in the water bath for too long
The plasticiser will leach out meaning the impression won’t be as soft as ti was before
How do we prepare to use impression compound
- Place cloth at Bottom of plastic bowl
- Soften it in a water bath (55-60 degrees)
- Takes couple of minutes to soften
- once completely soft place into impression tray
What are the advantages of impression compound
- Non toxic
- Easy to use
- Can be re softened
- Muco displasive
- Corrects gross tray problems
What are the disadvantages of impression compound
- Poor surface detail
2. Poor dimensional stability so needs to be cast up quickly
How can we correct and improve the poor surface detail achieved from impression compound
Add an alginate wash
What is alginate
An irreversible hydrocolloid
Do we tend to use alginate on its own
no
What do we usually do before taking a primary impression with alginate
Extend the stock tray using compound or silicone