PFM temp crown/impression/prescription

Question 1

5 functions of temp crown

Answer 1

• protecting tooth vitality if not root filled
• prevent movement of teeth
• maintain function
• aesthetics
• diagnostic

Question 2

3 types of temp crown and what each is made from

Answer 2

• preformed crowns 2: plastic (opaque: polycarbonate/acrylic), metal (tin alloy/ aluminium)
• matrices made from 3: impression matrix, vacuum formed matrix, odus pella/ strip crowns
• lab made

Question 3

4 things to check on temp crown

Answer 3

• marginal fit
• occlusion
• contact points
• adequate tooth reduction

Question 4

when is retraction necessary when taking an impression

Answer 4

if finish line of prep is below gingivval margin –> needs to be retracted for access for impression material

Question 5

3 methods of retraction

Answer 5

• retraction cord: cord wrapped around tooth, placed in to sulcus
• electrosurgery: controlled tissue removal using electric current through a tip
• rotary curettage: removal of epithelial tissue within sulcus using diamond chamfer bur

Question 6

4 ways to pack retraction cord

Answer 6

• pre-prep
• post-prep
• one-cord
• two-cord

Question 7

steps of packing retraction cord

Answer 7

• select diameter of cord that fills smallest, most delicate area of sulcus
• 4-5cm cord per crown prep in Astringent soln
• begin packing where sulcular tissue least likely to be damaged
• pack cord around sulcus
• cut off excess, leaving short tag
• wait 5 mins for tissue to be displaced

Question 8

what is the most delicate area of the sulcus in anterior prep?

Answer 8

labial/buccal aspect

Question 9

where is sulcular tissue most likely to be damaged

Answer 9

deepest part of sulcus (palatal part of max preparations)

Question 10

what is astringent soln

Answer 10

causes toughening of epidermis

Question 11

what type of impression material is one stage putty/wash imp

Answer 11

addition cured silicone

Question 12

what is the wash material used to flow over teeth before taking impression for pfm crown

Answer 12

light-bodied silicone

Question 13

steps for injecting impression material for pfm crown impression

Answer 13

1. flow impression material disto-lingual to disto-buccal in to/just above gingival sulcus
2. fill distal interproximal area
3. lingual surface
4. mesial interproximal surface
5. buccal
6. occlusal surface

Question 14

when should the syringe be lifted from the tooth surface during wash stage of impression and why

Answer 14

never- would cause air blows/defects