Primary Impressions and Primary Jaw Registration

Question 1

Why do you need primary casts?

Answer 1

saddles (what do the saddles look like and what are you going to put to replace?)
look at the occlusion (hand articulation to test or use an articulator)
undercuts - survey (see if there are undercuts for clasps to engage in)
lab (make primary models and to construct special trays)

Question 2

What are the blue and clear trays used for?

Answer 2

deeper trays for patients with teeth (dentate)

Question 3

What are the green trays used for?

Answer 3

for edentulous teeth

Question 4

How should you hold the 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 with the fitting
  surface facing the teeth
• Then decide which way round gives most
  space for the lip/soft tissues

Question 5

How can you modify the length and depth of the tray? (width is critical)

Answer 5

• Add ribbon wax (red soft wax) /greenstick (impression compound material)
• Remove overextensions with acrylic bur on straight handpiece

Question 6

What impression material is normally used and what material should not be used on teeth?

Answer 6

alginate is used
impression compound should not be used on teeth only edentulous

Question 7

Where can impression compound be used and why?

Answer 7

• Can use impression compound to capture the free-end saddle areas before taking impression in alginate
• Stabilizes the tray – reduces rocking

Question 8

After compound is used, what should be applied?

Answer 8

Record free end saddle areas using compound.

Then apply alginate adhesive to tray and compound

Apply alginate to wash over compound to fill the tray

Question 9

Why should alginate flow over the tray?

Answer 9

to capture sulcus area and avoid denture being overextended/underextended

Question 10

How should the tray be inserted?

Answer 10

rotate the tray at 90 degrees to avoid patient gagging

Question 11

What should be inspected in the impression?

Answer 11

it record edenulous areas

records sulcus of the denture border area

records teeth and has good detail of occlusal surfaces – occlusion

enables lab to make a good special tray

Question 12

How should you decontaminate your impressions?

Answer 12

• Rinse
• Place in Perform for 10 minutes
• Indicate that impressions have been decontaminated on lab card
• Bag with wet cotton wool or paper towel and take to lab as soon as possible

Question 13

Why is a wet cotton wool added?

Answer 13

minimise the resorption of the cast

Question 14

When would you need a primary jaw registration?

Answer 14

if you casts can’t be hand articulated

Question 15

What are index teeth?

Answer 15

The teeth that contact each time are called “index teeth”

Question 16

What is hand articulation and does it require a primary registration?

Answer 16

• Can hold the casts together and they meet together the same way each time
• Reflective of what’s in patient’s mouth
• There are enough index teeth present
• You don’t need to record the occlusion and you don’t need a primary record block
• Lab will mount casts on an articulator

Question 17

What is a wax wafer used for?

Answer 17

• You may wish to place a piece of warm wax into the patient’s mouth and have them bite together to confirm the occlusion to the lab
• This is referred to as a wax wafer and is an inter-occlusal record
• Where teeth contact, the wax should be pierced
• It is not always needed

Question 18

If your casts can’t be Hand Articulated, what do you need?

Answer 18

• You need primary record blocks (rocking teeth - unstable)
• Upper shellac baseplate
• Lower wire strengthener
• Casts then mounted on articulator after registration is provided to lab

Question 19

What is the most important thing when recording primary registration?

Answer 19

teeth still touching the same way they were with old dentures/ normal dentition

Question 20

What might the index teeth not touching cause?

Answer 20

anterior over-bite

Increased occlusal vertical dimension

Inadequate freeway space

Question 21

How is the primary regisration recorded?

Answer 21

• Bring primary record blocks to required occlusal level
• Add bite registration paste and ask the patient to occlude
• Check index teeth are still in contact

Question 22

What could be the issues affecting index teeth in primary blocks?

Answer 22

Not enough wax removed from block?

Too much bite reg paste used?

Bite reg paste set before
patient occludes?

Question 23

What step is added in casts that can’t be hand articulated?

Answer 23

primary jaw registration

Question 24

What should you do before taking master impressions?

Answer 24

Design the denture
* Identify any teeth that may require modification eg rest seats/guide planes
* If planning a CoCr denture ask the lab to survey your primary casts and, following your primary jaw registration (if needed), mount on articulator and return to you along with special trays
* You can now design your denture prior to taking the master impression

Question 25

In casts that can be hand articulated, what step is added for chrome dentures?

Answer 25

framework trial

Question 26

What are record blocks made for?

Answer 26

where insufficient natural teeth are present to define the occlusion, blocks aid the articulation of models