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Inlay – indirect restoration; occlusal surface excluding cusps
Onlay – indirect restoration; occlusal surface plus cusp(s)
Crown – usually covers the clinical crown of the natural tooth Full crowns/ ¾ crowns
Bridge – replaces missing tooth/teeth Abutment vs. Pontic Cantilever, Maryland
Gold alloys with at least 75% noble metals Proportion of gold in alloy
Carat rating – number of 24th parts of gold
Finess rating – parts/thousand of gold
Alloy Composition: Noble Metals
Gold (Au) * Platinum (Pt) * Palladium (Pd) * Iridium, Ruthenium, Niobium, Osmium
Resistant to corrosion and tarnish Gold was the first metal successfully used
copper & silver added to enhance it
Precious Metal = containing metals of high economic value such as gold, platinum, palladium, silver, (rhodium), (iridium), (rhuthenium), and (osmium).
Noble Metal = a precious metal that is resistant to tarnish. This excludes “silver” by definition
Classification and compositionType
Description
Minimum total
amount of noble metals
Au (%) Ag (%) Cu (%) Pt (%) Pd (%) Zn (%)
I (A)
Soft 83 80-90 3-12 2-5 Little/none
Little/none
Little/none
II (B)
Medium 78 75-78 12-15 7-10 0-1 1-4 0-1
III (C)
hard 78 62-78 8-26 8-11 0-3 2-4 1
IV (D)
Extra hard
75 60-70 4-20 11-16 0-4 0-5 1-2
Effects of Alloys Components:
(1) Gold (Au) (2) Copper (Cu) (3) Silver (Ag) (4) Palladium (Pd) (5) Platinum (Pt) (6) Zinc (Zn)
Corrosion resistanceHardnessCounteract orange color of copperIncrease MP and hardnessIncrease MPPrevent oxidation during melting (O2 getter)
Classification and compositionType
Description
Minimum total
amount of noble metals
Au (%) Ag (%) Cu (%) Pt (%) Pd (%) Zn (%)
I (A)
Soft 83 80-90 3-12 2-5 Little/none
Little/none
Little/none
II (B)
Medium 78 75-78 12-15 7-10 0-1 1-4 0-1
III (C)
hard 78 62-78 8-26 8-11 0-3 2-4 1
IV (D)
Extra hard
75 60-70 4-20 11-16 0-4 0-5 1-2
Mechanical properties
1) brittle, strong2) flexible, strong, tough3) ductile, medium strength4) ductile, weak, small toughness
type Proportional limit (MN/m2)
Ultimate tensile strength (MN/m2)
Elongation (%) Hardness (BHN)
I (as cast) 85 200 25 40-75
II (as cast) 160 345 24 70-100
III (softened) 195 365 20 90-140
III (hardened) 290 445 10 120-170
IV (soft) 360 480 15 130-150
IV (hard) 585 790 10 210-230
1 – ultimate tensile strength2 - yield strength3 – proportional limit4 – fracture point
Heat treatment Properties of alloy depend on
Composition Mechanical history (work hardened) Thermal history (heated T, rate of cooling)
Practical precautions Melting with air/gas torch
To heat alloy sufficiently to completely molten
Avoid overheating Use reducing zone Apply flux
Re-use of surplus alloy
Don’t mix surplus alloys of different types
Don’t melt alloy > 2-3 times (Zn lost)
Mix with new alloy