Download - Dental base metals and PFM alloys
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UTHSCSA Dental School
H. Ralph Rawls Spring 2012
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UTHSCSA Biomaterials 2
for Casting Alloys
: noble metal ≥ 60 wt % & gold ≥ 40 wt %
: noble metal ≥25 wt % (with or w/o gold)
: noble metal
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UTHSCSA Biomaterials 3
for Dental Alloys
• Biocompatible • Adequate physical and mechanical properties • Corrosion resistant • Fabrication requirements feasible for trained
dental personnel • Inexpensive
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UTHSCSA Biomaterials 4
Examples
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UTHSCSA Biomaterials 5
Dental of Metal Alloys
• Inlays
• Onlays
• Crowns
• Bridges
Increasing require-ment for hardness & rigidity Decreasing
ease of casting and burnishing
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UTHSCSA Biomaterials 6
Crown & Bridge Alloys
Properties and Characteristics
Type Noble conc. Castability Adjust-
ability Durability Appearance
(%) Melt oC
Density g/cm3
Shrink Vol% Elong% Hard
VHN Yield MPa Tarnish Color
PFM 0 1400 7 2.3 8 380 700 Low Silver
Base <25 1300 7-8 7 600 White
Noble 25-60 1000 11-12 8-12 250 500 Mod white High
Noble >60 900-1000 14-18 1.5 25 50 400 None varies
24k Au 100 1064 19 30 28 10 None yellow
(Burnishability)
Difficult to Impossible Difficult
Easy
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UTHSCSA Comprehensive Dentistry 7
Common Types of Base-Metal Dental Alloys • Cobalt, chromium, nickel (Co-Cr-Ni) Co-Cr Alloys Ni-Cr Alloys • Stainless steel (Fe-C) alloys • Titanium & Ti alloys
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• Co-Cr Alloys: Partial denture framework Porcelain-metal restorations (PFM) Implants • Ni-Cr Alloys: Partial denture framework Porcelain-metal restorations (PFM) Crowns and bridges
Cobalt-Chromium-Nickel (Co-Cr-Ni) Alloys
Cobalt: Hard, strong
and rigid
Elastic modulus 2x gold alloys
Low density
Cr: passivating effect
UTHSCSA Comprehensive Dentistry
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Hardness of Co-Cr-Ni Alloys
Due to extreme hardness, special polishing and finishing techniques are required • Sand blasting Smoothes the surface of the cast Removes adherent investment
material • Electrolytic polishing Removes high spots, fills in the low
UTHSCSA Comprehensive Dentistry
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UTHSCSA Biomaterials 10
Composition of Typical Co-Cr-Ni Alloys
Components
Ticonium™
(Ni-Cr)
Vitallium™
(Co-Cr)
Jelenko LG ™
(Co-Cr-Ni)
Stellite 1™
(Co-Cr-W) Cobalt 62.4 53.7 48.5 Nickel 65.9 13 Chromium 17 30 27 33 Molybdenum 5 5 4 Aluminum 5 Iron 0.5 1 1 Carbon 0.1 0.5 2.5 Beryllium 1 Silicon 0.5 0.6 0.6 Manganese 5 0.5 0.7 Tungsten 13
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Characteristics of Non-Noble PFM Alloys*
Ni - Cr(no Be)
Ni - Cr(with Be)
Co - CrCasting
Temperature (oC)
1430 – 1540°C2600 – 2800°F
1370 – 1480°C2500 – 2700°F
1430–1590°C2600–2900°F
Castability acceptable excellent acceptable
Fit good good good
Hardness(VHN)
175 - 350 300 - 350 300 - 500
Grinding /polishing
difficult difficult very difficult
SagResistance
excellent excellent excellent
Typical values and characteristics Compare to the “high noble” gold alloys: 50 – 150 VHN(Vicker’s hardness number – an indentation hardness test)
Beryllium (Be) lowers melting temp. & improves castability
UTHSCSA Comprehensive Dentistry
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Co-Cr-Ni Alloys Biocompatibility
14 patients: 8 sensitive to Co 1 sensitive to Cr 1 sensitive to Ni
Patients usually complain of pain
Co, Ni & Cr contact
hypersensitivity
vapor toxicity UTHSCSA Comprehensive
Dentistry
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Applications of Stainless Steel • Endodontic instruments • Other hand instruments • Orthodontic wires & brackets • Preformed crowns
(pedodontics) • Implants
UTHSCSA Comprehensive Dentistry
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UTHSCSA Comprehensive Dentistry
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UTHSCSA Biomaterials 15
Ti & Ti Alloys • Biocompatibility • Low density = 4.5 g/cm3 Very light metal
• Melting point = 1,665°C (higher than others) • Difficult to cast • Lowest elastic modulus (i.e., least
rigid) of base metal alloys
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Applications of Ti and its Alloys
• Implants • Crowns • Bridges • Partial Dentures
UTHSCSA Comprehensive Dentistry
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Aluminum - Vanadium Alloy
Ti-6Al-4V • Most common Ti alloy • Dental implants Implants in other areas of the body
• Biocompatible • Harder & less ductile than cp-Ti • More wear resistant than cp-Ti • Less rigid (lower elastic modulus) than
cp-Ti UTHSCSA Comprehensive Dentistry
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Dental implants
Ti alloy
UTHSCSA Comprehensive Dentistry
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“Commercially Pure” Titanium (cp-Ti)
• Dilute oxygen alloy
Oxygen is in solid solution with Ti
• β-Titanium - above 882.5oC
Malleable, used for orthodontic wires
• α-Titanium - below 882.5oC
difficult to form and work UTHSCSA Comprehensive Dentistry
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Commercially Pure Titanium (cp-Ti)
• Biocompatible
• Inexpensive
• Lightweight
• Strong BUT ! !
• Casting is difficult
Partial Denture Framework
UTHSCSA Comprehensive Dentistry
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Overview: Features of Co-Cr-Ni Base Metal
alloys • Cobalt-chromium alloys (Co-Cr) Rigid and strong in thin section Major connector in partial dentures Low density, thus a denture will be light weight Difficult to adjust and clasps may fracture even
on minor adjustment
Nickel-chromium alloys (Ni-Cr) Strong in thin section and so can be used for
long-span bridges They can be cast to very fine margins
Produce a grey discoloration in abutment teeth UTHSCSA Comprehensive Dentistry
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UTHSCSA Biomaterials 22
Overview: Features of Steel
• Iron-carbon-chromium alloys (stainless steel)
Cr-oxide provides a passive, corrosion-resistant surface
Low cost is main advantage
Main uses:
orthodontic bands & wires
Pediatric dentistry crowns
Mechanical properties slightly inferior to other alloys
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Overview: Features of Ti Alloys
Commercially pure titanium (cp-Ti) Biocompatible Dentures and overdentures Fixed and removable crown and
bridgework Implant-borne restorations
(crowns, bridges) Implants (as Ti-6Al-4V) Difficult to cast - low density, high mp,
oxidizable UTHSCSA Comprehensive Dentistry
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UTHSCSA Biomaterials 24
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UTHSCSA Biomaterials 25