5. Impressions Flashcards
What is the ideal thickness of alginate in a tray
5mm
What is the ideal thickness of elastomeric impression material in a tray
3mm
Compare the goals of obtaining an impression of a dentate arch compared to a partially edentulous arch
Dentate
- Capture teeth
- More tolerant to impression errors
Partially edentulous
- Capture all teeth (esp abutments)
- Surrounding tissue
- Edentulous areas
- Less error tolerant
Poor fit for stock trays is typically expected where
edentulous areas
regions where the stock tray is often under-extended is where
- Hard palate height
- Post dam distal edge of maxilla (hamular notch)
- Lingual extent of mandibular tray (FOM)
Where should you use your finger to wipe alginate
- Occlusal surfaces of teeth
- Proximal surfaces of teeth adjacent to edentulous areas
- Retromylohyoid fossa (syringe)
Correct W:P ratio for alginate is
dimensional accuracy
Dx casts are used to
- Evaluate occlusion and available space
- RPD survey and framework design
- Dx wax up if needed
- Construction of custom tray for secondary impression
What direction should the cast be moved on a survey table to alter the angulation of the guide planes
-anteroposteriorly
What direction should the cast be moved on a survey table to alter the angulation of the retentive areas
laterally
Latticework should extend how far buccally
1-2 mm beyond the crest of the ridge
Finish lines extend onto
proximal plates
Lateicwork joins the lingual bar where
at the midpoint
Minor connectors are _ to the major connector
pependicular (90 degrees)
The distance between the approach arm for an infrabuldge clasp and the gingival margin is
4mm
Retentive clasps are how wide… reciprocal
-1.5mm taper to 1mm when engaging the undercut …1.5 mm
Sequence for tooth mods
- guide planes
- HOC (acial surfaces aka B and L)
- Rest preps
How is a custom tray made for a partial denture
- 1 layer of wax over the edentulous regions and 2 over the teeth
- 1 layer over hypermobile tissue, thin and narrow crest of alveolar ridge (alternative is just 1 layer of wax over entire edentulous area)
Overall thickness of the custom tray should be
2-3 mm
Why should you vent the tray and where should you do it
- Why= relief area
- Primary v.s secondary support area (do in regions of tissue compressibility, sensitivity and resistance to resorption)
Hard prominent areas to relief on the maxilla
- median palatine raphe
- torus palatinus
Hard prominent areas to relieve on the mandible
- Torus mandibularis
- Genial tubercles (if prominent)
- Prominent mylohyoid ridge
Sensitive areas on the maxilla that require relieving
- Incisive papilla
- Rugae
- Flabby ridge
- Sharp bony spicules
Sensitive areas on the mandible to relieve
- Mental forame in resorbed ridges
- Flabby tissue
- Sharp bony spicule
T/F You don’t need to boarder mold an impression for a partial
f- need to boarder mold the edentulous areas, abutment areas, and lingual bar/plate area
The depth of the FOM should be verified how
measuring intraorally with a perio probe
How much wax due to place for relief
1 layer
What are the maxillary and mandibular primary support areas
Maxillary
- Hard palate
- Tuberosities
Mandibular
- Buccal shelf
- Retromolar pad
What are the maxillary and mandibular secondary support areas
Residual ridges!!
+ maxillary rugae
Will the custom tray have retention? why or why not
no because there are teeth
Temperature for green stick compound
135-140 degrees F (5 min water bath)
Where can’t you blockout undercuts
any partial RDP framework area
What can be used to block out undercuts
- Teflon tape
- OraSeal Putty
- Wax
Characteristics of polysulfide impression material
- Highest tear strength
- Less rigid than PVS
- Easier to recover (cautious of deformation)
- Ideal thickness= 3 mm
- Working time= 8-10 mins
- Pour 15-30 min after removal from mouth
- Can’t be re-poured
Characteristics of PVS
- Very accurate
- Very dimensionally stable (can pour 1 week after removal)
- Can re-pour
- 3-5 min working time
- Ideal material thickness= 3 mm
- Better recovery from deformation than polysulfide
What should you do after placing in the tray to take the secondary impression
boarder movements
How can you prevent fracture of the cast during separation
- Cast should be damp
- Heat tray to soften (torch)
- Cut tray if necessary
Which is done first the survey crown prep or rest preps
rest preps
T/F The impression used for the survey crown impression can be used for the RPD framework fabrication as well
f- need 2 impressions
What should you do before cementing a survey crown
survey it make sure the contours are what you want
What must you do to your pindex for your survey crown
tripod it
What is drawn in red for the framework drawning
- finishlines
- retentive clasps
- tripod marks
What is required to submit to the lab when a post is desired
matric
