4. metal alloys and casting

alloy

• mixture of 2+ metals or metalloids that are mutually soluble in the molten state

• mixture of different elements mixed together

Alloying elements are added to alter the (BLANK x3) of a metallic element, thus obtaining properties not found in a pure metal

hardness, strength, and toughness

may be classified on basis of their metal composition as what three categories?

base metal alloy, noble metal alloy, and high noble metal alloys

what are the general requirements of a dental alloy? (5)

• Not produce harmful toxicologic or allergic effects

• Chemical properties should provide resistance to corrosion and physical changes when in the oral cavity

• Physical and mechanical properties (thermal conductivity, melting temperature, coefficient of thermal expansion, and strength) should meet certain minimum values*

• The technical expertise needed for fabrication and use should be feasible for the average dentist and skilled technician

• The metals, alloys, and companion materials should be plentiful, relatively inexpensive, and readily available

dental metallic material ISO 22674 classification

0–5 based on mechanical properties like strength (proof stress) and elongation. Its purpose is to ensure, through standardized requirements, that alloys have suitable, reliable strength, corrosion resistance, and ductility for specific clinical uses, such as inlays, crowns, or dentures

which type of dental metallic material ISO 22674 classification?

• intended use: low stress, single-tooth fixed restorations (small)

• example: small one-surface inlay

• minimal proof strength w 0.2% non-proportional extension (MPa): N/A

• minimum percent elongation after fracture: N/A

• minimum young’s modulus (GPa): N/A

type 0

which type of dental metallic material ISO 22674 classification?

• intended use: low stress, single-tooth fixed restorations

• example: crown w minimal occlusal force

• minimal proof strength w 0.2% non-proportional extension (MPa): 80

• minimum percent elongation after fracture: 18%

• minimum young’s modulus (GPa): N/A

type 1

which type of dental metallic material ISO 22674 classification?

• intended use: single tooth, fixed restorations

• example: crown w normal occlusal force

• minimal proof strength w 0.2% non-proportional extension (MPa): 180

• minimum percent elongation after fracture: 10%

• minimum young’s modulus (GPa): N/A

type 2

which type of dental metallic material ISO 22674 classification?

• intended use: multiple tooth, fixed restorations

• example: fixed partial denture (bridge)

• minimal proof strength w 0.2% non-proportional extension (MPa): 270

• minimum percent elongation after fracture: 5%

• minimum young’s modulus (GPa): N/A

type 3

which type of dental metallic material ISO 22674 classification?

• intended use: thin sections under high force

• example: precision attachment

• minimal proof strength w 0.2% non-proportional extension (MPa): 360

• minimum percent elongation after fracture: 2

• minimum young’s modulus (GPa): N/A

type 4

which type of dental metallic material ISO 22674 classification?

• intended use: high stiffness and high stress

• example: removable partial denture clasp

• minimal proof strength w 0.2% non-proportional extension (MPa): 500

• minimum percent elongation after fracture: 2%

• minimum young’s modulus (GPa): 150

type 5

what are the noble metals? (8 of relevance)

gold, silver, platinum, palladium, rhodium, ruthenium, iridium, and osmium

what are the base metals? (13

• definition: common and inexpensive metal, as opposed to a precious metal such as gold or silver

• nickel, cobalt, chromium, titanium, iron, and copper

  • also: carbon, silicon, aluminum, gallium, ruthenium, manganese, molybdenum, tungsten, tantalum

noble metals are defined on the basis of their

chemical properties

precious metals are defined based on

cost

(?) was originally used for noble metal alloys containing significant amounts of silver

semiprecious

(?) alloys are composed of (?) ingredients, with most being based on a combo of nickel and chromium

non-precious

which class has this requirement: total noble content ≥60% where ≥40% is gold (IMPORTANT)

high noble alloys

which class has this requirement: titanium content ≥85%

titanium and titanium alloys

which class has this requirement: total noble content ≥25%

noble alloys

which class has this requirement: ≥25%

predominantly base metals

what are five important considerations when choosing a cast alloy? (important to me)

noble metal content → corrosion resistance, internal properties, tarnish resistance, biocompatibility, and classification

hardness → wear resistance, surface

yield strength → load; maximum stress a material can withstand before undergoing permanent deformation

elongation → margin

fusion temperature → soldering

what three properties are important to consider when choosing alloys for PFM restorations?

Thermal expansion, bond strength, and composition

T or F: there should be a slight mismatch between porcelain and metal (porcelain being slightly lower)

true, this is the porcelain-metal compatibility property of thermal expansion

what does porcelain-to-metal bond strength measure?

ensures retention of porcelain to metal in both the oral environment and during thermal processing

composition is important bc some components can affect the (?) of porcelain

color

why is yield strength crucial?

bc of small cross section

what controls the minimum allowable dimensions of critical areas?

stress

what affects the flexibility of a metal framework?

elastic modulus

what affects tarnish resistance, corrosion resistance, and thermal stability?

chemical stability

ANSI/ADA Specification No. 5 for Dental Casting Alloys (!)

stablishes standardized requirements, classification (Types I-IV), and testing methods for noble metal alloys—primarily gold—used in dentistry. It ensures the quality, biocompatibility, composition, and physical properties (hardness, yield strength) of materials used for crowns, bridges, and inlays.

ANSI/ADA Specification No. 5 for Dental Casting Alloys: which class? (!)

85% 20K

• description: soft

• usage: inlays: low stress applications

• yield strength: <140 MPa

• elongation (annealed): 18%

• vickers hardness: 60-90 VHN

type I

ANSI/ADA Specification No. 5 for Dental Casting Alloys: which class? (!)

75% 18K

• description: medium

• usage: inlays and onlays: increased stress applications including cusp replacement

• yield strength: 140-240 MPa

• elongation (annealed): 18%

• vickers hardness: 90-120 VHN

type II

ANSI/ADA Specification No. 5 for Dental Casting Alloys: which class? (!)

70% 17K

• description: hard

• usage: crowns and short-span bridge: high stress applications

• yield strength: 201-340 MPa

• elongation (annealed): 12%

• vickers hardness: 120-150 VHN

type III

ANSI/ADA Specification No. 5 for Dental Casting Alloys: which class? (!)

65% 15K

• description: extra hard

• usage: long-span bridges, removable partial dentures; high stress, high flexural resistance

• yield strength: >340 MPa

• elongation (annealed): 10%

• vickers hardness: <150 VHN

type IV

what is density effect of alloy elements in dental gold alloys?

how adding metals like copper, silver, or palladium alters the high density of pure gold (specific gravity 19.3 g/cm³) to achieve desired physical and casting properties. Generally, adding base metals or lower-density precious metals reduces the overall density of the alloy, which impacts casting, strength, and tarnish resistance

• Specific gravity: 19.32

• Melting point: 1063°C (1945°F)

• Atomic diameter: 2.88 Å

• Space lattice: Face-centered cubic

• Chemical activity: Inert

• Color: yellow

• Approximate content: 50–95%

• Density effect: Increases markedly

• Effect on color: Lends yellow color

• Effect on melting: Raises melting point mildly

• Tarnish resistance: Essential to good tarnish resistance

• Heat hardening: Contributes importantly with Cu

• Gas absorption: —

• Castability: —

gold

• Specific gravity: 21.45

• Melting point: 1769°C (3224°F)

• Atomic diameter: 2.77 Å

• Space lattice: Face-centered cubic

• Chemical activity: Inert

• Color: white

• Approximate content: 0–20%

• Density effect: Increases markedly

• Effect on color: Whitens slowly; ~12% required; not pure white

• Effect on melting: Raises melting point fairly rapidly

• Tarnish resistance: Contributes importantly

• Heat hardening: Increases with Cu

• Gas absorption: —

• Castability: —

platinum

• Specific gravity: 12.0

• Melting point: 1552°C (2829°F)

• Atomic diameter: 2.74 Å

• Space lattice: Face-centered cubic

• Chemical activity: Mild

• Color: white

• Approximate content: 0–12%

• Density effect: Lowers slightly

• Effect on color: Whitens rapidly; as little as 5%

• Effect on melting: Raises melting point rapidly

• Tarnish resistance: Increases but less than Au/Pt

• Heat hardening: Some increase with Cu

• Gas absorption: High for hydrogen

• Castability: Effects not critical

pallidum

• Specific gravity: 8.96

• Melting point: 1083°C (1981°F)

• Atomic diameter: 2.55 Å

• Space lattice: Face-centered cubic

• Chemical activity: Very active

• Color: red

• Approximate content: 0–17%

• Density effect: Lowers

• Effect on color: Lends red color; dark plate high in Cu

• Effect on melting: Lowers melting point (even below its own)

• Tarnish resistance: Contributes to tarnish (flame/sulfur)

• Heat hardening: Essential if alloy heat hardens

• Gas absorption: —

• Castability: Effects not critical

copper

• Specific gravity: 10.49

• Melting point: 961°C (1761°F)

• Atomic diameter: 2.88 Å

• Space lattice: Face-centered cubic

• Chemical activity: Active

• Color: white

• Approximate content: 0–20%

• Density effect: Lowers

• Effect on color: Whitens slowly; counteracts Cu redness; green gold

• Effect on melting: Slight effect; may raise or lower mildly

• Tarnish resistance: Tarnishes with sulfur

• Heat hardening: Increases with Cu

• Gas absorption: High for oxygen

• Castability: —

silver

• Specific gravity: 7.31

• Melting point: 420°C (787°F)

• Atomic diameter: 2.66 Å

• Space lattice: Close-packed hexagonal

• Chemical activity: Very active

• Color: white

• Approximate content: 0–2%

• Density effect: Lowers

• Effect on color: Minimal (too low %)

• Effect on melting: Lowers melting point rapidly (solders)

• Tarnish resistance: Minimal effect in low %

• Heat hardening: Slight with Cu

• Gas absorption: Good deoxidizer

• Castability: Decreases surface tension; increases fluidity

zinc

• Specific gravity: 22.4

• Melting point: 2443°C (4429°F)

• Atomic diameter: 3.32 Å

• Space lattice: Face-centered cubic

• Chemical activity: Active

• Color: white

• Approximate content: 0.005–0.1%

• Density effect: Increases slightly

• Effect on

• Effect on melting: No effect

• Tarnish resistance: Increased

• Heat hardening: No effect

• Gas absorption: No effect

• Castability: No effect

iridium

PFM compositions of

high gold

PFM composition of gold-palladium (no silver)

PFM composition of gold-palladium-silver

PFM composition of

palladium-copper

PFM composition of

palladium-silver

the concentrations of the following alloys:

• nickel-chromium

• nickel-chromium-beryllium

• cobalt-chromium

• titanium

• titanium alloys

which alloy?

• Gold content between 78% to 87% by weight

• Total noble metal content about 97%

• Light yellow in color

• Excellent hardness, tensile strength, and corrosion resistance

high gold

what three things are added to high gold alloys for strength and to promote good porcelain bond to metal oxide?

tin, indium, iron

which alloy?

• 20% to 30% palladium content

• 10% to 15% silver content

• Higher elastic modulus and less susceptibility of dimensional change during the porcelain baking when compared to high-gold alloys

• Good clinical working characteristics and corrosion resistance

• Silver can change the color of porcelain

gold-palladium-silver

which alloy:

• 50% to 60% palladium, with the most of the balance being silver

• Physical and chemical properties are comparable to other noble metal alloys

• Good corrosion and tarnish resistance

• Can affect the color of porcelain

palladium-silver

which alloy?

• 50% gold

• 40% palladium

• Favorable yield strength and hardness

• Higher elastic modulus when compared to high-gold alloys

• Excellent corrosion resistance

• Thermal expansion is incompatible with some higher-expansion porcelains

gold-palladium alloys

which alloy?

• 70% to 80% palladium

• Up to 15% by weight of copper

• 9% gallium

• High hardness and low elastic modulus

• Sag resistance is a contra-indication for large-span fixed partial dentures

palladium-copper

(blank) resistance is a contraindication for large-span fixed dentures

sag

which alloy:

• 88% palladium

• 4% to 5% cobalt by weight

• Have high coefficient of thermal expansion

• Forms a dark oxide that may be difficult to cover

• More susceptible to hot tearing and embrittlement from carbon when no silver is present

palladiumj-cobalt

palladium-cobalt alloys are (less/more) susceptible to hot tearing and embrittlement from carbon when there is NO silver present

more

base metal alloys are based mostly on what two metals?

nickel and chromium, with a few cobalt- chromium and iron-based alloys available

Corrosion resistance is based on chemical properties

can check for allergies, recalls. not necessarily for PFM but other materials even implants

what is this:

• combinations of various types of waxes compounded to provide the desired physical properties. uses include patterns for inlays, crowns, pontics, partial and complete dentures, and for bite registrations

• one of several esters of fatty acids with higher alcohols (usually monohydric alcohols)

• classified according to their applications into pattern, processing, and impression waxes

dental waxes

what are the three applications of dental waxes?

pattern, processing, impression

what are the four types of pattern waxes?

• (blue) inlay for crowns → type I and II

• resin

• casting

• base plate

what are the six types of processing dental waxes?

• boxing

• sticky

• carding

• blockout

• white

• utility

what are the two impression dental waxes?

corrective and bite registration

define:

• channel or hole through which plastic or metal is poured or cast into a gate or reservoir and them into a mold

  • forms a mount for the wax pattern and fix the pattern in space so a mold can be made

  • creates a channel for elimination of wax during burnout which allows for molten metal to enter such mold

spruing

define: the excess material remaining at the base of the mold after dental casting

sprue button

the sprue should be small and long OR large and short?

the sprue must be large enough so it remains open until the casting solidies and short enough to allow rapid filling of the mold

sprue should always attach to the (bulkiest/slimmest) part of the pattern?

bulkiest