irs-t models for indirect restorations

Question 1

What is a die?

Answer 1

Removable, separate component on sectional model w access to margin of tooth

Question 2

What are the types of sectional models?

Answer 2

Pinned systems- technically difficult, v accurate, time consuming
Tray systems- quick, simple, cheap, less accurate but perfectly acceptable
Digitally produced

Question 3

How are sectional models produced?

Answer 3

Pinned/tray- produced in hard material (Class IV die stone)
Digital- milled from plastic or 3D printed in photo curing resin

Must withstand production process

Question 4

How is a tray system sectional model made?

Answer 4

1. Impression trimmed to leave teeth and 2-3mm of gingivae
2. Sulcus and palate not required, keeps model compact and minimises inaccuracies due to die movement
3. Centre marked to allow ease of positioning
4. Surface tension reducing solution applied to allow die to flow readily into detail
5. Plastic tray forms base which incorporates locating grooves and retaining lugs
7. Vacuum mixed die storm is vibrated into impression
8. Tray base is filled
9. Impression turned into base, aligned and left to set
10. Once set, impression is removed and model is left due dry before sectioning and ditching
11. Sectioning- 2 parallel cuts using hand saw either side of tooth
12. Removal of gingival tissue using bur (rose head or flame shaped) due to allow margin to be seen and accessed clearly
13. Use die hardener to increase abrasion resistance when using blade near margin
14. Use die spacer (~50 microns thick) to surface of die as a mock up of cement (allows room between tooth and restoration for cement)

Question 5

How are digital models produced?

Answer 5

Design
Arrange and process files
Print
Wash
Cute

Cost effective, moderate resulted needed, quick
Indirect- high resolution needed so slower and more expensive