irs-t metal restorations Flashcards
What are different metal alloys?
High gold content (types I-IV)
Medium gold (40-60%)
Low gold (15-20%)
Ag-Pd
Ti alloys
Non precious alloys
What are different metal restorations?
Crown
Inlay
Onlay
3/4 crown
Bridge
What are advantages?
Conservative prep
Robust
Easy to adjust chairside
Support for RPD
Retainer for bridge
Simple production
Accurate fit
What are disadvantages?
Aesthetics
Biocompatibility
Thermal conductivity
What is the conventional production?
Lost wax process
Separator applied to die
Wax pattern produced via dipping and addition of wax
Contacts established
Pattern shaped to match adjacent teeth
What are design considerations?
Thickness of material (0.5mm minimum)
Emergence profile- protect periodontium
Contact- maintain tooth position
Shape- maintain hygiene
Why is refractory investment material expansion deliberate?
Compensates for contraction of metal on cooling
What are the casting temps?
1050C for golds
1450C for CoCr
What is the conventional lost wax casting process?
Mould of wax pattern (refractory investment material-expands when heated)
Sprue channel connects pattern to outside of mould so wax is removed and metal casted
Heated in burnout furnace to 650-950C to burn out wax, expand mould and ensure metal doesn’t freeze on entering mould
Centrifugal/vacuum/air pressure to push alloy into mould
May need heat tx after casting to attain optimum mechanical properties
What is the conventional finishing process?
DEVESTING- removal of refractory investment material
PICKLING- precious metal alloys cleaned in acid 
Non precious metals- shot blasted w AlO2 particles
Series of abrasives and polishing compound
Prepped for cementation
Fitted to a solid model to prevent damage
What is digital production?
CAD
SCAN (IO/EO)
DESIGN (CAD package- 3Shape, Exocad, Cerec)
MANUFACTURE (additive- 3D printing/sintering OR subtractive- milling)
Design can print/mill in wax
Restoration can mill in metal ingot/selective laser melting
How do you do a digital design?
Die is scanned
Margin is defined
Cement lute is defined
Library of tooth morphologies approximates restoration
Export file as .stl
Wax print
What is wax printing?
Produces pattern for casting
V accurate (5 microns)
Slow production
Jewellery production
What is wax milling?
Produces pattern for casting
Accurate 20 micron
Quick production
What is metal milling?
Produces definitive
Accurate <10 micron
Quick production
Expensive
