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Biomaterials 3 (Metal Alloys 1 (Classifications (Hardness (Type I = Soft
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Biomaterials 3
Metal Alloys 1
Definition What is an Alloy?
A metal product containing two or more elements (1) as a solid solution, (2) as an intermetallic compound, or (3) as a mixture of metallic phases.
Classifications
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Colour
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White
(purest, ie before other metals are added)
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Partial Denture Alloys
Chromium containing alloys must not be cleaned with chloride solutions as the passivating chromium layer is disrupted by the chlorides and rapid corrosion may ensues.
Wrought Clasp Assemblies
- The effects of 0.2% Proof Stress vs E-modulus on the abutment teeth
- wrought claps have higher 0.2% proof stress (Flexibility without distortion) and E-modulus (stiffness) than a cast CrCo clasp
- This places less stress on the abutment teeth during insertion and removal of the denture and mastication
Metal Alloys 2
Fabrications Techniques
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Sintering
A densification process where particles are heated in close contact causing them to fuse together
CAD/CAM
Computer aided design and computer aided manufacturing. Digitally designed and milled from solid blocks
PFM
Metal-Ceramic System
Metal Alloy Requirements:
- A high melting temperature
- The coefficient of thermal expansion (CTE) of the metal should be slightly higher than the porcelain
- Adequate stiffness and strength of the metal framework
- Appropriate alloy selection to prevent discolouration and weakening due to thick oxide layer formation
Veneering Porcelain Requirements:
- A low fusing temperature
- Must wet the alloy applied as a slurry
- Aesthetically pleasing
- Low abrasiveness
- Durability in the oral cavity
Bonding Mechanism
- Chemical (primary mechanism responsible for porcelain-metal bonding)
- Oxide in metal covalently bonds with porcelain
- adequate thickness - as too much/little will cause failure
- Micro-mechanical
- Porcelain binds to metal surface irregularities (created through sandblasting)
- increase surface roughness = increase retention
- Compression Bonding
- Porcelain in compression state caused by mismatch CTEs
- The porcelain needs to be under compression and the metal under tension as they cool, which relates back to the importance of a specific CTE difference between the two.
Metal Alloys
Au-Pd (low Ag)
- Porcealin does not discolour, CTE increased, improved castability
- CTE not comatible w/ some porcealins
Pd-Ag
- Favorable elastic modulus/ porcelain bonding/ low cost
- Less favorable castability, Ag-greening, Pd-decreased bonding
Co-Cr
- chromium adds strength/corrosion resistance,
- cobalt adds strength/hardness/elastic modulus
- good for pts w/ nickel allergies
- Unfavourable melting ranges, poor manipulation, darker oxides
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Dental Ceramics 2
Classification
Glass-matrix ceramics
Feldspathic
Examples: IPS Empress Esthetic, Ivoclar Vivadent Vitadur, VITA Mark II
Synthetic ceramics
- Leucite Based
Ex. IPS Empress I (Ivoclar Vivadent), Vita VM7
- Lithium disilicate
Ex. IPS Empress II, IPS e.max CAD, IPS e. max Press
- Fluorapatite-based
Ex. IPS d.SIGN, IPS e.max ZirPress, IPS e.max Ceram
Glass infiltrated
- Alumina
Ex. In-Ceram Alumin
- Alumina and magnesium
Ex. In-Ceram Spinell
- Alumina and zirconia
Ex. In-Ceram Zirconia
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Resin Matrix
- Resin nanoceramics
Ex. Lava Ultimate 3M ESPE
- Glass ceramic in a resin interpenetrating matrix
Ex. Vita Enamic
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CAD/CAM
Materials
Feldspathic ceramics (e.g. VITA Mark II)
= high-glass content
have good aesthetics and polishability, with similar wear properties to enamel, and can be used for veneers, inlays, onlays and crowns.
Zirconia (e.g Vita Siprinity)
Versatile polycrystalline ceramic, has strong mechanical properties and is able to undergo transformation toughening, so is widely indicated for use in dentistry.
Lithium disilicate (e.g. e.max)
Comes partially crystallised and once heat -treated, is fully crystalised, so can be used for veneers, onlays/inlays, crowns and 3-unit bridges
It has been found that e.max press has slightly superior mechanical properties compared to CAD/CAM fabricated crowns.
Leucite-reinforced
ceramics consist of a glass and crystal phase. The addition of leucite particles improves the mechanical properties of the ceramic, so it is indicated for veneers, inlays/onlays and crowns.
Ceramill Sintron
is a Co-Cr material as soft as wax before sintering, allowing an easy, rapid dry milling process and avoiding classic disadvantages of metal milling. Design of the metal alloy copings in PFMs include the computer calculated shrinkage to maximise accuracy. Composite resin can be used for inlays, onlays, veneers and crowns.
VITA Enamic
is a hybrid= composite resin and high glass ceramic
Benefits include having enamel-like wear properties, reducing damage to opposing dentition (indicated for bruxers), require less tooth preparation than some materials, however can have inferior durability with decreased strength
PMMA
is commonly used for temporaries, bite splints and 3D printing, with almost no residual monomer (1% max.), therefore is less likely to cause reactions.
Y-TZP (Polycrystalline)
3-5% Y2O3 and rest ZrO2
Flexural strength of 900MPA
Fracture toughness of 5.9 MPA2
Indicated in multiunit bridges
Performance
Crack Propagation
Glass ceramic: particle-filled glass
Arrow indicating the direction of crack.
Note the crack deflection and dissipation of the crack driving force as the crack plane is repeatedly reoriented away from the applied tensile stresses. In-Ceram Alumina
Zirconium oxide
Transformation toughening
Under an applied tensile stress (concentrated at a crack tip), the tetragonal phase will convert to monoclinic, with 3-4% volume expansion which puts the crack into compression, retarding its growth
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Wear
Y-TZP and alloys have shown to be the most wear-friendly to the antagonist enamel compared
to glass-ceramics and veneering porcelain
Provisional Materials
Definition = materials which are used to fabricated prosthesis which: Enhance aesthetics, stabilizes tooth and maintains periodontal health
Types
Direct
Resin-Based Acrylics
PMMA = good marginal fit and polishability BUT low abrasion resistance, high vol shrinkage
ex. Temp crowns, bridges, veneers and interim dentures
PEMA = good polishability, lower vol shrinkage BUT low fractured toughness/strength and hardness
ex. for restorations closer to the pulp
ZnOE
Polymer Modified (IRM)
Uses: provisional/permanent luting agent, pulp capping (paeds)
GIC
Indications
Temporary restorations on anterior and posterior teeth
Endodontic interim material
Block out undercuts in crown and onlay preps
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Examples:
Fuji VII - Internal remineralization, (pink) endo temp
Fuji IX - Indirect pulp capping
Fuji TEMP LT - Long term temporary cement (inert silica filler component)
Composites
LuxaTemp(Bis-Acryl) Low shrinkage, good transverse strength, ++ marginal fit/abrasion resistance but brittle
Indirect
CAD/CAM
Indicated for occlusal changes - ensures comfortable bite before permanent restoration. However temp materials are cheaper and cost of equipment is high.
SSC
Used in primary(mainly) and permanent dentition
- adv.
- disadv.
- aestheics poor
- occlusal changes
- nickel allergies
Polycarbonate
Preformed Anterior Crown (synethtic matrix + glass filler)
- Adv.
- good wear properties
- translucency
- aesthetics
- low cost
- time efficient
- Disadv.
- polyz shrinkage
- low strength
- difficult handling