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Dental Materials > Dental Materials > Flashcards

Dental Materials Flashcards

1
Q

what are the 2 components of fibre reinforced composite?

A

polymer + fibres

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2
Q

what fibres are used in dental materials?

A

glass fibres E, R and S

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3
Q

give 2 aligments of polymer and a term to describe them - which is theroplastic/thermoset?

A

linear - thermoplastic (don’t form chemical bond on cure so can be remoulded)
cross linked - thermoset (forms chemical bond on set so impossable to remould)

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4
Q

what are fibres impregnated with?

A

PMMA dissolved in a high evaporative solvent - solvent is evaporated away and fibres stay impregnated

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5
Q

what are dental fibres always pre-treated with? what does this allow for?

A

silane (silanation)
silanes allow chemical adhesion between the fibres and the matrix
creates bonds not available in nature and benefit adhesion
improves surface wetting of fibres

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6
Q

how does direction of fibres change properties and use of material?
give uses for linera, bidirectional, random and woven

A

Unidirectional - improved strength in direction of fibres but reduced strength in all other directions
improved tensile strength
uses - posts, fixed pros

Bidirectional - improved strength and stiffness in both directions
improved flexural and tensile strength
inc load bearing and fracture resistance
uses - dental bridge frameworks, splints, removable pros

Random - anisotropic (diff properties in diff directions)
uses - provisional restorations

Woven - interlacing of fibres in certain pattern
uses - ortho, indirect restorations

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7
Q

how does number of fibres embedded into comp affect properties?

A

more fibres imbedded = better strength and stiffness
too many fibres impeded = may compromise flowability and affect placement of comp in cavity

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8
Q

how does fibre length affect properties?

A

longer = stress transferred more efficiently, decreased mechanical properties
shorter = help w/ material handling and less risk of clumping together

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9
Q

what is silane essential for?

A

to ensure interfacial bonding between fibres and matrix

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10
Q

give a disadvantage of FRC

A

humidity of oral cavity may weaken bond between matrix and fibres causing failure

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11
Q

list 5 uses for FRC

A

removable dentures
fixed pros (provisional and permanent)
root canal posts
splints
direct restorations

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12
Q

how does prefabricated vs individually formed post differ in properties?

A

individually formed have inc resistance under loading, higher bond strength, higher fatigue resistance and less cement

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13
Q

how does gold content, hardness, proportional limit, strength, ductility and corrosion resistance change as you go from Type 1-4 (low to extra high strength) gold casting alloy?

A

gold content - decreases
hardness, proportional limit and strength - increases
ductility and corrosion resistance - decreases

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14
Q

what happens to hardness as gold content decreases? why?

A

as gold content decreases hardness increases - due to solution hardening

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15
Q

what types (1-4) of gold casting alloys can undergo heat treatments?

A

T 3&4 = heat treatments possible causing further hardening
T 1&2 = heat treatments not possible - due to lack of silver and copper

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16
Q

how is heat treatment carried out

A

rapidly heating (>600 degrees) then rapidly cooling in cold water plunge - creating new crystal structure

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17
Q

what may happen if heat treat alloy containing platinum or palladum? what is done to avoid this?

A

risks coring - zones of concentration, may cause corrosion

homogenisation treatment done to eliminate coring

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18
Q

how does low gold alloys compare to silver palladium alloys?

A

low gold = low cost and good clinical performance
silver palladium = lower ductility and may have porosity

19
Q

what are the high and low fusing temperatures for traditional dental porcelain?

A

high fusing - 1300 to 1400
low fusing - 850 to 1100

20
Q

give 2 constituents of ceramics - what are they heated/cooled to form?

A

kaolin & feldspar - form glassy silicate matrix

21
Q

what does compaction do/reduce?

A

brings particles together - reduces shrinkage of ceramic when fired

22
Q

how is heat introduced in firing? why is cooling controlled?

A

incrementally
cooled controlled to avoid cracking

23
Q

what material can stop crack propagation? downside?

A

alumina - though is very opaque

24
Q

what has been added to porcelain to allow for fusion to metal? what metals often used to bond to porcelain?

A

leucite added to porcelain to allow for PFM (porcelain fused to metal)
silver-palladium or nickel-chromium

25
Q

what are glassy ceramics based from?

A

feldspar based = feldspathic

26
Q

how does adding filler affect properties?

A

improves mechanical properties and opalescenece - usually leucite filler

27
Q

how are polycrystalline ceramics organised? what does this make them?

A

atoms packed in dense trays - relatively opqaue

28
Q

in only what type of ceramic should acid based cements be used?

A

Ziconium oxide based ceramics

29
Q

name 4 types of porcelain and polycrystaline ceramic and give uses

A

High alumina porcelain - DBC
Feldspathic porcelain - regular dental porcelain, can etch and silanate, DBC & MCC, veneers and covering zirconia
Lithium di-silictae glass ceramic - emax (made using CAD CAM), veneers/onlays/inlays/crowns/covering zirconia
Zirconia - stabilised by yttrium using CADCAM, not etchable, crowns and bridges

30
Q

what kind of ceramic is zirconia? what cement is used to place it? why is this?

A

polycrystalline ceramic

luting cement should be used - as cannot etch, bond or silanate zirconia

could fire and glaze w/ feldspathic on fit surface and then etch however

31
Q

Milled composite - only what restorations is this used for?

A

CADCAM mills from a block of composite

inlay/onlay restorations only

32
Q

high alumina porcelain - adv and disadv

A

alumina added to regular feldspathic porcelain

adv - inc strength so produces stronger crown
disadv - very white

33
Q

what restorations can zirconia be used for? how many units between abutments? crown prep measurements?

A

any type of crown
dental bridge work - max 4 units between abutments

1mm axial, 1.5mm incisal/occlusal

34
Q

E-max crown - what kind of ceramic? benefits & uses

A

lithium disilicate

inc strength, excellent aesthetics, can etch and silanate, works in thin section

veneers, onlays/inlays, crowns, canteliever bridges (2 units)

becoming ceramic of choice

35
Q

why is die relief placed?

A

to accommodate for luting cement thickness

36
Q

explain difference between active & passive luting cement

A

active - bonds to tooth and material, role in retention

passive - fills gap between tooth and restoration, no bond between tooth/restoration, places no role in retention (taper, prep height, surface roughness and mechanical interlocking used instead)

37
Q

give 2 ideal properties of luting cement

A

low film thickness - allows for full seating of restoration

pseudoplastic - coats restoration’s fit surface without slumping, but flows readily under pressure on fitting

38
Q

list 4 types of passive luting cement
which should be avoided under all ceramic crowns?
which is used for bonding tooth to metal?
which of the zincs is antibac/not antibac?

A

Passive luting:
zinc phosphate - 3-6 mins working time, not antibac
zinc carboxylate - 30-40 secs working time, antibac, adehsive to enamel/dentine/some metals
GI luting cements - sets 3-6 mins
RMGI luting cements - better properties than GI luting, can undergo hygroscopic expansion so avoid under all ceramic crowns

Active luting:
adhesive resin and self-adhesive resin - silanated filler & resin, conventional or chemically adhesive (for bonding tooth to metal)
self adhesive requires no etch and bond but worse bond strength than adhesive resin

39
Q

explain how luting cement is bonded to tooth and ceramic of restoration

A

to tooth - etch, rinse/dry and bond tooth then apply cement
to ceramic - restoration etched with HF acid, silane coupling agent applied, air dried then apply cement

so HF acid etch and silane coupling agent on fit surface > cement > etched tooth surface and dentine bonding agent

40
Q

how is durability predicted in the lab?

A

fatigue testing - restorations subject to on and off loading may times in function
number of cycles to failure recorded

41
Q

what software language is used to store and transport CAD CAM info?

A

XML - eXtensible Markup Language

42
Q

give 3 types of ceramic blanks

A
  1. green - lowest strength, most porous
  2. partially sintered
  3. fully dense - highest strength, least porous
43
Q
A

Dental Materials (1 decks)

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