‫‪Alloys‬‬
‫أحمد عبد العزيز الحسين‬
‫أخصائي تركيبات سنيه في وزارة الصحة األردنية‬
‫محاضر غير متفرغ في جامعة العلوم والتكنولوجيا األردنية‬
‫‪Ahmad Abdul Aziz Alhussien‬‬
‫‪Prosthodontist at M.O.H‬‬
‫‪Part time lecturer at J.U.S.T‬‬
‫‪BSc , MSc, Jor. Board/ prosthodontics‬‬
Introduction
• 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.
• Cast metal alloys can be used for bridges, partial
or complete denture bases
Classification of dental casting alloy
(ADA)
• High noble alloys “precious metals”
– at least 60% noble. 40% of which is gold. The
remaining 40% is base metal
• Noble alloys(semiprecious)
– at least 25% noble (no gold requirements). 75% base
metal
• Base metal alloys
– Less than 25% noble
• What does noble mean?
– Does not corrode readily
• Noble metals are: Au, Pd, Pt
Noble Alloys
• Gold alloys
– Most corrosion resistant
– Pure gold is 24 karat, 100%
– Properties:
• Low Hardness (resistance to penetration)
• High Malleability (ability to be shaped by tapping)
• High Ductility (ability to be elongated)
Noble alloys
• 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.
Base metal alloys
• < 25% noble metal
• Primary base metals (non-precious):
– Copper .. Added to to increase hardness
– Silver .. Added to increase hardness
– Nickel .. Biocompatibility issues
– Tin .. Added to increase flowness
– Zinc .. added to decrease oxidation
• Stiffer than gold alloys, higher stress
resistance
Base metal alloys
• Drawbacks:
– Difficult to finish and cut
– More equipment to manufacture
– Higher casting temperature
– Biocompatibility issues
Base metal alloys
• Small crystals produce better qualities than
larger ones “malleability and ductility”
• Some alloys such as gold maybe reheated
(annealing) to improve properties “hardness”
• Reheating base metal alloys is not
recommended “corrosion”
Biocompatibility
• 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
• Beryllium, added to Ni-Cr to reduce fusion
temperature and create smaller crystals:
– Can also cause allergy.
– Inhalation can cause lung disease called berylliosis
Base metal alloys
• stainless steel alloy (18/8)
– (18% chromium, 8% nickel)
Concepts
• Solder Alloys that are used to join metals
together or repair cast restorations
• Welding : Process of fusing two or more metal
parts through the application of heat,
pressure, or both, to produce a localized union
across an interface between the parts.
Implant materials
• Used as anchors for prosthetic replacement of
missing teeth
• Three main types:
– Subperiosteal
– Transosteal
– Endosseous
Implant materials
• 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