Metals in dentistry /certified fixed orthodontic courses by Indian dental academy

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Metals in dentistry
Dental material
www.indiandentalacademy.com
INDIAN DENTAL ACADEMY
Leader in continuing dental education

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Lectures included in midterm exam
 1. Amalgam
 2. Composites
 3. Glass ionomer cements
 4. Adhesive systems and bonding in dentistry
 5. Dental cements

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General information
 Alloy: a mixture of two or more metals
 Pure metals are rarely used in dentistry because
they are weaker than they are when mixed with
other metals.

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All metal casting
 Classification of cast restorations:
 Intra-coronal (e.g. inlay)
 Extra-coronal (e.g. crown)
 Cast metal alloys can be used for bridges,
partial dentures

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Cast metal restorations

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Classification of dental casting alloy
(ADA)
 High noble alloys: What does noble mean?
 Gold-platinum Does not corrode readily
 Gold-palladium
 Gold-copper-silver High noble: at least 60% noble
 Noble alloys: (Au, Pd, Pt). 40% of which is gold.
 Silver-gold-copper The remaining 40% is base metal
 Palladium-copper (precious metals)
 Silver-palladium Noble: at least 25% noble (no gold
 Base metal alloys requirements). 75% base metal
 Ni-based (semiprecious)
 Co-based
 Ti-based

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Gold alloys (Au)
 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:
 Hardness (resistance to penetration)
 Malleability (ability to be shaped by tapping)
 Ductility (ability to be elongated)

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 Platinum is not used much because:
 Too expensive
 High melting point
 Difficult to mix with gold
 Palladium is used more widely because:
 Good corrosion resistance
 Increases hardness of alloy
 Silver is precious but not noble because it
corrodes.

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Base metal alloys
 < 25% noble metal
 Primary base metals (non-precious):
 Copper
 Silver
 Nickel
 Tin
 Zinc: added to decrease oxidation
 Titanium
 Stiffer than gold alloys, higher stress resistance
Added to gold alloy to increase hardness

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Base metal alloys
 Drawbacks:
 Difficult to finish and cut
 More equipment to manufacture
 Higher casting temperature
 Biocompatibility issues

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Crystal formation
 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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Porcelain bonded alloys
 High noble
 Noble
 Base metal
 Composition is slightly modified to make them more
compatible with porcelain. How?
 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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Porcelain bonding alloy
 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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Removable prosthetic casting alloys
Cobalt Iron
Titanium Beryllium
*Chromium Gallium
*Nickel Carbon
Aluminium molybdenum
Vanadium
Base metals used

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Continue,
 Components are attached to prosthesis
(precision and non precision attachments,
bars) made from metal alloys :
 High noble
 Noble
 Base metal

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Biocompatibility
 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
 Seen on free gingival tissue in contact with metal
 Mostly more sever with fixed prosthesis
 Skin response may occur

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Continue,
 Beryllium, added to Ni-Cr to reduce fusion
temperature and create smaller crystals:
 Can also cause allergy.
 Inhalation can cause lung disease called
berylliosis

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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
Close holes from occlusal
adjustment
Solder wire components to
removable ortho. appliances

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Solders
 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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Welding
 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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Wrought metal alloys
 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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Wire
 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
 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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Endodontic files and reamers
 Example of wrought metal alloy which have
been twisted to produce cutting edges
 Stainless steel
 Nickel-titanium (more flexible)
 Reamers are similar to files but with fewer
twists and cut faster

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Endodontic files

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Metals used in orthodontics
 Wires:
 composed of base meta, stainless steel, cobalt-
chrome-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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 Brackets and bands
 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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 Lingual retainer:
 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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Implant materials
 Used as anchors for prosthetic replacement
of missing teeth
 One or more single units as crowns or bridges
 Support for dentures
 Three main types:
 Subperiosteal
 Transosteal
 Endosseous

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A: Subperiosteal
B: Transosteal
C: Endosseous

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Continue,
 These implants are made of titanium or
titanium alloy, used for its biocompatibility:
 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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Placement and restoration
 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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Maintenance

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Endodontic posts
 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:
 Active, engages canal surface with threads
 Passive post, cemented into the canal space
 Classification by shape:
 Parallel
 Tapered

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 Classification by material:
 Metal
 Nonmetal
 Classification by manufacturing method:
 Custom made: made from a wax or resin pattern
made directly on tooth or indirectly in lab. Using
lot wax technique. Core attached
 Preformed:
 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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Lectures included in the midterm exam
next Thursday
 Amalgam
 Composite
 Glass ionomer cements
 Adhesives in dentistry
 Dental cements

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 References:
 Chapter 8 metals in dentistry
 Dental materials, clinical applications for
dental assistants and dental hygienists
End of part one

Thank you
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Metals in dentistry /certified fixed orthodontic courses by Indian dental academy

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