Primary impressions and primary registration

Question 1

what can you identify in these pictures?

Answer 1

• attrition with exposed dentine on lower teeth
• reduced clinical crown height
• missing lower premolar and molar
• oral soft tissues look healthy
• concern with teeth with largge restorations
• cantilever bridge on 16,17
• root canals 11, 12, 44
• post retained crown 44
• good bone levels except upper left around 28 angular defect
• need to increase occlusal vertical dimension

Question 2

what is the process of taking a primary impression?

Answer 2

1. PPE
2. tray selection and try in - width is critical
3. select impression material
4. take impression
5. decontaminate - perform
6. write laboratory card

Question 3

why do we need primary casts?

Answer 3

denture design
* look at occlusion
* saddles
* undercuts - survey
lab
* make primary models
* construction of special trays / primary bite blocks

Question 4

how do you fit the handles onto a impression tray?

Answer 4

• hold the flat side of the handle
• hold the tray in front of you as you would seat it in a patient’s mouth
• decide which way round gives most space for the lip/soft tissues

Question 5

describe how you would take an impression of a patients mouth who has free end saddles

Answer 5

1. select try and try in
2. record free end saddles using impression compound (do not record teeth)
3. apply alginate adhesion to try and compound
4. apply alginate to wash over compound
5. record impression again
6. decontaminate

Question 5

why would you use impression compound to capture free-end saddles first?

Answer 5

• stabilises the tray and reduces rocking
• supports the alginate

Question 6

how would you inspect an impression? what are you looking for? why do you need a good primary impression?

Answer 6

• in good light - compare to what you see in the mouth
• record edentulous areas
• record sulcus of the denture bearing area
• record teeth and has good detail of occlusal surfaces
• enables lab to make a good special tray

Question 7

what is the process of decontaminating impressions?

Answer 7

• rinse in water
• place in perform for 10 minutes - if in for too long, it will swell
• indicate that impressions have been decontaminated on lab card
• bag with wet cotton wool or paper towel and take to lab ASAP so it doesn’t dry or shrink

Question 8

when do you need a primary jaw registration?

Answer 8

when casts cannot be hand occluded - no index teeth

Question 9

how do you hand occlude?

Answer 9

hold the casts together and they meet together the same way each time ten lab mounts casts on an articulator

Question 10

how can you confirm occlusion for the lab?

Answer 10

use a wax wafer - warm wax piece in pts. mouth and have them bite together (not always needed) - not to used when you cannot occlude

Question 11

what do you use to support the primary jaw registration blocks in the upper and lower jaw?

Answer 11

• upper - shellac baseplate
• lower - wire strengthener

Question 12

how do you record the primary registration?

Answer 12

• bring blocks together to required occlusal level
• ensure heels (back end) of casts are not touching
• add bite registration paste and ask patient to occlude
• or can add wax between blocks
• check index teeth are still in contact

Question 13

why may the index teeth not be in contact when recording primary registration?

Answer 13

• not enough wax removed from the block
• too much bite registration paste used
• wax was too thick
• bite reg paste set before patient occludes

increases occlusal vertical dimension = inadequate freeway space