Diagnostic Impression & Cast Diagnostic Mounting

Question 1

What is a survey cast for?

Answer 1

– Analysis of contour of hard & soft tissue
– Determine path of insertion
– Determine if abutment restorations required
– Determine if surgical intervention needed
– Design RPD
– Develop plan for tooth modifications

Question 2

What is a diagnostic cast?

Answer 2

Accurate reproduction of teeth & adjacent tissues

Question 3

What are the characteristics alginate?

Answer 3

– Ease of use
– Inexpensive
– Less surface detail than elastomeric materials
– Adequate accuracy/precision for Dx cast

Question 4

How can you control the setting time of alginate?

Answer 4

water temp

Question 5

What does changing the water/powder ratio of alginate do?

Answer 5

– Not affect accuracy
– Affect consistency
– Affect strength
– Affect setting time

Question 6

What are the diagnositc impression techniques?

Answer 6

• Stock tray: rim lock, perforated metal, plastic
• Maxillary Tray width:
  – 5-7mm buccal clearance
  – Material thick enough to spring over undercuts
  – Inadequate length, extend with wax
• Mandibular Tray width:
  – 5-7 mm buccal & lingual clearance
• Tray adhesive
• Mixing material: bubble-free
• Load tray level with flanges
  – Small increments, prevent air entrapment
• Load syringe
• Seat tray: do not overseat
• Impression left in mouth 2-3 min after loss of surface tackiness
• Removal of impression
  – “Snap” removal of tray

Question 7

What are potential problems with diagnostic impressions?

Answer 7

– Alginate sticking to teeth
– Alginate pulling away from tray: adhesive not used
– Voids in critical areas
– Inadequate extension to soft tissue areas
– Layered impression: material on teeth/tissue set before tray seated
– Granular impression: inadequate spatulation, premature removal
– Contact between cusp tips & tray

Question 8

How do you pour a diagnostic cast?

Answer 8

• Rinse off saliva, Spray with disinfectant
• Wrap with moist towel
• Suspend tray by handle
• Impression should be poured within 12 min.
• Pour with dental stone (yellow)
  – Master cast poured with improved (die) stone (green)
• Difficult to box without distorting impression

Question 9

What is the two-stage pour technique?

Answer 9

1st stage pour
– Impression filled with dental stone
– Suspend filled tray by handle for 10-12 minutes until initial set of stone

2nd stage pour
– Impression with set stone inverted into base patty
- separate impression from cats after 45-60 minutes

Question 10

What is the purpose of the face-bow transfer?

Answer 10

Relate MX cast to articulator condylar elements at the same orientation of maxillary teeth to patients’ condyles