Impression techniques for crowns and bridges

Question 1

name 2 hydrophillic impression materials

Answer 1

alginate
agar

Question 2

name a hydrophobic impression material
give examples of addition and condensation

Answer 2

elastomeric:
addition - affinis
condensation - cured silicones, polysulphides, polyethers

Question 3

what is important to ensure the prep is prior to taking a silicone impression?

Answer 3

that it is dry

Question 4

explain differences between addition and condensation silicones

Answer 4

addition - very accurate and stable, leave more than 1hr before pouring
condensation - less accurate, leave 24hrs before pouring

Question 5

what impression silicone is used in DDH

Answer 5

affinis - addition cured silicone

Question 6

polyethers - what dispenses it? accuracy, taste, undercuts, hydrophobic

Answer 6

pentamix
very accurate
bad taste
stiff on removal - avoid when undecuts, perio pts
less hydrophobic

Question 7

polysulphides - undercuts?

Answer 7

good for big undercuts

Question 8

what kind of tray should be sued for impression for fixed pros? gold standard?

Answer 8

polycarbonate trays - stock trays, rigid
special trays - for difficult arch shapes
rim lock trays - gold standard but cannot cut out of mouth

Question 9

what impression material should not be used w/ special tray?

Answer 9

polyether - as too stiff

Question 10

explain putty/wash 1 stage technique

Answer 10

2 viscosities (putty high and wash low)
syringe washa round tooth whilst nurse loads tray w/ putty
seat putty impression before wash starts to set

Question 11

explain monophase technique

Answer 11

one viscosity (polyether or medium viscosity silicone)
same material in syringe and tray
impression tray inserted over syringed material around tooth

Question 12

explain putty/wash 2 stage technique - is it still used?

Answer 12

2 viscosities (putty and wash)
seat putty impression w/ spacer - allow to set and remove
syringe wash around tooth and reseat putty

rarely used technique as risks compression of putty

Question 13

what condition should prepped teeth be in prior to impression?

Answer 13

dry

Question 14

what is the average biological width? where does it run to/from?

Answer 14

2.04mm

involves gingiva from PDL to tip of bone crest (connective tissue attachment), then up to top of junctional epithelium (epithelial attachment)

Question 15

how far should margins be from alveolar bone crest? what is this the same distance as?

Answer 15

3mm
tip of gingivae ot bone crest

Question 16

what should be considered if it is impossible to avoid biological width?

Answer 16

crown lengthening - removing gingiva w/ scalpel, electrocautery/high speed

Question 17

list symptoms of violating biological width

Answer 17

inflamed gingiva and perio tissues
bone loss
re-establishment of biological width as tissues move apical to original position - leads to gingival recession

Question 18

what should be sorted prior to crown prep?

Answer 18

perio health

Question 19

what can be used prior to impression to keep the gingiva out the way?

Answer 19

retraction cord - absorbs moisture in the gingival sulcus
can be soaked in haemostatic agent - chemically cortorises

Question 20

what chemical and ratio should be used for impression disinfection? how long should object be placed in disinfectant?

Answer 20

10 x 1.7g actichlor tabs per 1 litre water - for 3 mins (1000ppm)

Question 21

when are pick up impressions used and what do they allow?

Answer 21

taking impressions of multiple crown preps in one go can be hard - so pick ups allow you to marry together 2 separate impressions