alloys for inlays

1. Alloys for Inlays,
Crowns and Bridges

2.  Inlay – indirect restoration; occlusal
surface excluding cusps
 Onlay – indirect restoration; occlusal
surface plus cusp(s)

3.  Crown – usually covers the clinical crown
of the natural tooth
 Full crowns/ ¾ crowns
 Bridge – replaces missing tooth/teeth
 Abutment vs. Pontic
 Cantilever, Maryland

4.  Cantilever Bridge
 Maryland Bridge

5. Materials for Indirect Restorations:
 Dental Ceramics – Porcelains
 Composites
 Alloys

6. materials
 Requirement
 Composition
 Properties
 Clinical usage/application

7. Requirements
 Biocompatibility – non-allergic, not toxic
 Good corrosion + tarnishing resistance

8. Corrosion tarnishing

9.  Suitable mechanical properties
 High yield stress
 Sufficient ductility
 hardness

10.  Ease of casting – high density, good
fluidity
 Cost – inexpensive material/labour

11. 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

12. Gold alloys

14. 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

15. 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

16. Classification and composition
Ty
pe
Descripti
on
Minimum
total
amount of
noble
metals
Au (%) Ag (%) Cu (%) Pt (%) Pd (%) Zn (%)
I
(A)
Soft 83 80-90 3-12 2-5 Little/no
ne
Little/no
ne
Little/no
ne
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

17. Effects of Alloys Components:
(1) Gold (Au) 
(2) Copper (Cu) 
(3) Silver (Ag) 
(4) Palladium (Pd) 
(5) Platinum (Pt) 
(6) Zinc (Zn) 
Corrosion resistance
Hardness
Counteract orange color of
copper
Increase MP and hardness
Increase MP
Prevent oxidation during
melting (O2 getter)

18. Classification and composition
Ty
pe
Descripti
on
Minimum
total
amount of
noble
metals
Au (%) Ag (%) Cu (%) Pt (%) Pd (%) Zn (%)
I
(A)
Soft 83 80-90 3-12 2-5 Little/no
ne
Little/no
ne
Little/no
ne
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

19. Dental uses
 Type I – situations where there is no
great stress
 Cl III
 Cl V

20.  Type II - inlays

21.  Type III
 Crowns & bridges
 Situations where there is great stress

22.  Type IV
 Cast partial dentures clasps

23. Mechanical properties
1) brittle, strong
2) flexible, strong, tough
3) ductile, medium strength
4) ductile, weak, small toughness

24. Hardness (Brinell)

25. Hardness (Knoop)

26. 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 strength
2 - yield strength
3 – proportional limit
4 – fracture point

27. Heat treatment
 Properties of alloy depend on
 Composition
 Mechanical history (work hardened)
 Thermal history (heated T, rate of cooling)

28. Practical precautions
 Melting with air/gas torch
 To heat alloy sufficiently to completely
molten
 Avoid overheating
 Use reducing zone
 Apply flux

30.  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

31. Other alloys
 Medium and low gold alloys
 Au (50%), Pd, Ag, Cu, Zn
 Silver-palladium alloys
 Ag, Pd, Au, Cu, Id, Zn
 Nickle-chromium alloys
 Ni (75%), Cr (20%)
 Miscellaneous materials
 Cu-Zn (brass) + Id, Ni
 Ag-Id+Pd
 Al-Bronze