Surveying Of A Cast Flashcards
List the 4 tools that are used to survey a cast
Analysing rod
Graphite marker
Undercut gauge
Trimming knife
Explain how and why 1st tool is used
- Analysing rod:
- Metal rod placed against teeth and ridges to identify undercut areas and identify parallelism (no triangles of light), identify paths of insertion and guide planes
- Should be in contact with maximum bulbosity of the tooth
Explain how and why 2nd tool is used
- Graphite marker
- marks lines on teeth and ridges
- Side of marker→ contact most bulbous part of tooth = max convexity (hence determines undercut area → upper survey line
- Tip of marker → contact with the cast→ extent of undercut→ Iower survey line
- Area between 2 lines= undercut areas
Explain how and why 3rd tool is used
- Undercut gauge
- Measure depth of undercut
- Allows positioning of tip of retentive clasp arms on tooth to be determined
- Different clasp materials can engage different depths of undercut depending on their flexibility (elastic modulus) and cross section
- Deeper undercut needs more flexible material to engage and disengage effectively
0.25 - Cast CoCr (least flexible)
0.5 - Wrought Stainless steel
• 0.75 - Gold (most flexible)
• Shank and head of gauge should contact the tooth at the same time
• Colour pencil then used to mark position where head of gauge touches tooth, indicating where retentive clasp can terminate
Explain how and why 4th tool is used
- Trimming knife
- Used to eliminate unfavourable undercuts on master cast/ secondary cast
“blocking out”→ Wax placed and then cut off parallel to path of insertion
• Duplicate cast then made on which the denture is manufactured
• Also used to prepare guide surfaces on teeth
What does a low survey line mean in terms of undercuts
- Little or no useable undercut therefore clasp tip would be too close to soft tissue
SOLUTION:
- add composite to create an undercut area
OR create a dimple preparation
What does a medium survey line mean
Literally situated in between high and low points
- suitable for occlusally + gingivally approaching clasps
What does a high survey line
- very deep undercut
- requires highly flexible clasp type
- OR modification of survey line
What does a diagonal survey line
Suitable for either type of clasp (gingival or occlusal)
Where are the usual favourable undercuts found on upper and lower teeth
BULL rule - buccal for uppers, lingual for lowers
List types of maxillary major connectors (4)
Palatal plate
Anterior posterior bar
Mid palatal bar
Horse shoe connector
Palatal plate - pros and cons
Pros:
- good rigidity
- max support
cons:
- unhygienic
- heavy
Anterior and posterior bar
Pros:
- reduction in palatal coverage
- better tissue sensation
- more comfortable - patients do not like to have their palate covered
Cons:
- less denture support
- not suitable for deep vaulted palate (the denture already more prone to fold in on itself- with this less strong denture cannot use this type)
-
