impressions Flashcards
what is an impression?
-ve imprint of an oral structure used to produce a +ve replica of the structure used as a permanent record or in the production of a dental restoration or prosthesis.
what is a study model?
+ve life size production of the teeth and adjacent tissues formed by pouring dental plaster into an impression.
Used to study patients oral condition
what is the clinical procedure for taking an impression?
Prepare the patient (MH,explain, position, remove appliances and debris)
Assemble materials and equipment
Alginate (gelation 3-4 mins, spatulation 1 min, 30s working time)
Trays
Fixative
Wax
Disinfectant (5 tabs to ½ jug)
Plastic bag and lab card
Retract and insert with a rotary motion, centre and seat.
Mandibular- work in front of patient maxillary- work from behind the patient.
how and why would you disinfect an impression?
Prevent cross infection during laboratory procedures
Sodium hypochlorite 5-10 mins
Actichlor- 10 tabs for 1 litre for 2 mins
what is an interocclusal record?
Registration of normal positional relationship of the opposing teeth or dental arches
Relates cast correctly
describe alginate
Irreversible hydrocolloid
Carboxylated polysaccharide based on alginic acid
Gels by cross-linking formation with calcium ionsSodium alginate
Calcium phosphate
Sodium phosphate (retarder)
Fillers eg. Zinc carbonate
pH indicators: change colour - pH drops as gels
what is the gelation, spatulation and working time for alginate?
gelation- 3-4mins
spatulation- 1min
working- 30s
