Dental base metals and PFM alloys

UTHSCSA Dental School

H. Ralph Rawls Spring 2012

UTHSCSA Biomaterials 2

for Casting Alloys

: noble metal ≥ 60 wt % & gold ≥ 40 wt %

: noble metal ≥25 wt % (with or w/o gold)

: noble metal


for Dental Alloys

• Biocompatible • Adequate physical and mechanical properties • Corrosion resistant • Fabrication requirements feasible for trained

dental personnel •  Inexpensive


Examples


Dental of Metal Alloys

• Inlays

• Onlays

• Crowns

• Bridges

Increasing require-ment for hardness & rigidity Decreasing

ease of casting and burnishing


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

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



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


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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


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.



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


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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


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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


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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


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

Dental base metals and PFM alloys

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