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1. Metals in dentistry
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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Dental material
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2. Lectures included in midterm exam
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1. Amalgam
2. Composites
3. Glass ionomer cements
4. Adhesive systems and bonding in dentistry
5. Dental cements
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3. General information
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Alloy: a mixture of two or more metals
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Pure metals are rarely used in dentistry because
they are weaker than they are when mixed with
other metals.
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4. All metal casting
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Classification of cast restorations:
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Intra-coronal (e.g. inlay)
Extra-coronal (e.g. crown)
Cast metal alloys can be used for bridges,
partial dentures
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5. Cast metal restorations
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6. Classification of dental casting alloy
(ADA)
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High noble alloys:
 Gold-platinum
 Gold-palladium
 Gold-copper-silver
Noble alloys:
 Silver-gold-copper
 Palladium-copper
 Silver-palladium
Base metal alloys
 Ni-based
 Co-based
 Ti-based
What does noble mean?
Does not corrode readily
High noble: at least 60% noble
(Au, Pd, Pt). 40% of which is gold.
The remaining 40% is base metal
(precious metals)
Noble: at least 25% noble (no gold
requirements). 75% base metal
(semiprecious)
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7. Gold alloys (Au)
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Most corrosion resistant
Pure gold is 24 karat, 100%, or 1000 fine
(percentage * 10)
Pure gold is too soft, so, gold alloys were mostly
used
Gold alloys classified:

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Hardness (resistance to penetration)
Malleability (ability to be shaped by tapping)
Ductility (ability to be elongated)
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8. 
Platinum is not used much because:
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Palladium is used more widely because:
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Too expensive
High melting point
Difficult to mix with gold
Good corrosion resistance
Increases hardness of alloy
Silver is precious but not noble because it
corrodes.
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9. Base metal alloys
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< 25% noble metal
Primary base metals (non-precious):
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Copper
Added to gold alloy to increase hardness
Silver
Nickel
Tin
Zinc: added to decrease oxidation
Titanium
Stiffer than gold alloys, higher stress resistance
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10. Base metal alloys
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Drawbacks:
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Difficult to finish and cut
More equipment to manufacture
Higher casting temperature
Biocompatibility issues
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11. Crystal formation
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Alloys start to form crystals as they cool down
after being poured into molds.
Small crystals produce better qualities than
larger ones
Some alloys such as gold maybe reheated
(annealing) to improve properties
Reheating base metal alloys is not
recommended.
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12. Porcelain bonded alloys
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High noble
Noble
Base metal
Composition is slightly modified to make them more
compatible with porcelain. How?
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Blended and mixed to withstand high temperature when
porcelain is fired (850-1350 C)
Small amounts of indium and tin are added to form oxides
on metal surface to which porcelain is bonded
Silver and copper is not used to avoid green staining of
porcelain
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13. Porcelain bonding alloy
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When PFM restorations are constructed,
layers of porcelain are fired in an oven on the
metal base to cover the metals’ dark color
Body and incisal porcelain are added in
layers to simulate enamel and dentine colors
and translucency.
Porcelain and metal should have compatible
rates of thermal expansion or porcelain will
crack.
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14. Removable prosthetic casting alloys
Base metals used
Cobalt
Iron
Titanium
Beryllium
*Chromium
Gallium
*Nickel
Carbon
Aluminium
molybdenum
Vanadium
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15. Continue,
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Components are attached to prosthesis
(precision and non precision attachments,
bars) made from metal alloys :
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High noble
Noble
Base metal
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16. Biocompatibility
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Noble metals are more biocompatible than
base metals because they corrode less
(corrosion products can cause allergy):

Nickel is associated with allergy (9-12% of
population), especially in women
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Seen on free gingival tissue in contact with metal
Mostly more sever with fixed prosthesis
Skin response may occur
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17. Continue,
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Beryllium, added to Ni-Cr to reduce fusion
temperature and create smaller crystals:
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Can also cause allergy.
Inhalation can cause lung disease called
berylliosis
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18. Solders
Alloys that are used to join metals together or repair
cast restorations
Gold solders
Silver solders
Join bridge units
Used in ortho., paedo.
Add contacts
Solder fixed space maintainer
components
Correct marginal deficiencies Solder wire components to
removable ortho. appliances
Close holes from occlusal
adjustment
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19. Solders
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The solder alloy should have a lower melting
temperature than the cast restoration.
For gold solders, the higher the gold content
the lower the melting range.
For silver solders, tin is added to lower
melting temperature and improve flow. Silver
solders produce stronger joints and need
lower heat to melt so they do not weaken the
wire adjacent to solder joint.
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20. Welding
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Process of fusing two or more metal parts
through the application of heat, pressure, or
both, with or without a filler metal, to produce
a localized union across an interface between
the parts.
The welded point is susceptible to corrosion
In soldering no fusion occurs, the gap
between the two joint parts is filled with
molten metal.
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21. Wrought metal alloys
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Are alloys that have been mechanically
changed into another form (can be shaped as
a flat plate, or wire).
The resulting alloy, is harder and has a
greater yield strength (point at which a force
produces permanent deformation).
Resistance to deformity can be modified by
heating, annealing.
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22. Wire
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Is a wrought metal which can be soft and easily
shaped or may resist bending as does as spring.
Used for clasps in partial dentures
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Stainless steel (iron, carbon and traces of Mn, Cr, Ni to
resist tarnish and rust)
Platinum-gold-palladium (PGP)
Arch wires and ligature used in orthodontic
appliances
Arch bars and ligature wires used in oral surgery for
fracture stabilization
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23. Endodontic files and reamers
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Example of wrought metal alloy which have
been twisted to produce cutting edges
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Stainless steel
Nickel-titanium (more flexible)
Reamers are similar to files but with fewer
twists and cut faster
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24. Endodontic files
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25. Metals used in orthodontics
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Wires:
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composed of base meta, stainless steel, cobaltchrome-nickel, titanium, titanium-nickel.
Able to resist deformity. This resistance creates
‘memory’ in the wire, so it tries to reassume its
original shape. That enables the wire to move
teeth.
Wires have different diameters (gauge), the
thicker the wire the smaller the gauge
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26. 
Brackets and bands
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Cemented on teeth with bonding resin
Retain the arch wire that has been shaped by the
orthodontists to guide the teeth into new position.
The wire is held to brackets and bands by ligature
wire or elastics
Made from stainless steel, the bracket has a slot
into which the wire fits and 4 wings to hold the
ligature or elastics
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28. 
Lingual retainer:
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Used to maintain the position of teeth after orthodontic
treatment
Adapted to the lingual surface of anterior teeth and bonded
with composite.
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29. Implant materials
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Used as anchors for prosthetic replacement
of missing teeth
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One or more single units as crowns or bridges
Support for dentures
Three main types:
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Subperiosteal
Transosteal
Endosseous
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31. A: Subperiosteal
B: Transosteal
C: Endosseous
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32. Continue,
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These implants are made of titanium or
titanium alloy, used for its biocompatibility:
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Pure titanium is not as rigid as the alloy
These implants are retained by intimate
contact with bone (osseointegration)
Some implants are coated with Calcium
phosphate (hydroxyapatite) or plasma
proteins to improve osseointegration
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33. Placement and restoration
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Incision and bone exposure
A hole is drilled that is slightly smaller than
implant cylinder size so when implant is
placed it will have a frictional fit with bone.
Excessive heat should be avoided
Permanent restoration is attached to implant
core with a screw made of gold alloy
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35. Maintenance
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36. Endodontic posts
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Posts are metal or nonmetal rods placed in
root canal
The purpose of a post is to retain the core
build up over which the crown is placed
Classification:
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Active, engages canal surface with threads
Passive post, cemented into the canal space
Classification by shape:

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Parallel
Tapered
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37. 
Classification by material:
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Metal
Nonmetal
Classification by manufacturing method:
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Custom made: made from a wax or resin pattern
made directly on tooth or indirectly in lab. Using
lot wax technique. Core attached
Preformed:
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They rely for retention on shape, diameter, length, and
cementation.
Come in kits with drills specific to size of post
Core not attached, need to be made from amalgam,
composite, hybrid GIC
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38. www.indiandentalacademy.com
38

39. Lectures included in the midterm exam
next Thursday





Amalgam
Composite
Glass ionomer cements
Adhesives in dentistry
Dental cements
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39

40. End of part one
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References:
Chapter 8 metals in dentistry
Dental materials, clinical applications for
dental assistants and dental hygienists
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41. Thank you
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