Dental Materials

Question 1

what are the 2 components of fibre reinforced composite?

Answer 1

polymer + fibres

Question 2

what fibres are used in dental materials?

Answer 2

glass fibres E, R and S

Question 3

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

Answer 3

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)

Question 4

what are fibres impregnated with?

Answer 4

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

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

how does number of fibres embedded into comp affect properties?

Answer 7

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

Question 8

how does fibre length affect properties?

Answer 8

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

Question 9

what is silane essential for?

Answer 9

to ensure interfacial bonding between fibres and matrix

Question 10

give a disadvantage of FRC

Answer 10

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

Question 11

list 5 uses for FRC

Answer 11

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

Question 12

how does prefabricated vs individually formed post differ in properties?

Answer 12

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

Question 13

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?

Answer 13

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

Question 14

what happens to hardness as gold content decreases? why?

Answer 14

as gold content decreases hardness increases - due to solution hardening

Question 15

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

Answer 15

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

Question 16

how is heat treatment carried out

Answer 16

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

Question 17

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

Answer 17

risks coring - zones of concentration, may cause corrosion

homogenisation treatment done to eliminate coring

Question 18

how does low gold alloys compare to silver palladium alloys?

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

kaolin & feldspar - form glassy silicate matrix

Question 21

what does compaction do/reduce?

Answer 21

brings particles together - reduces shrinkage of ceramic when fired

Question 22

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

Answer 22

incrementally
cooled controlled to avoid cracking

Question 23

what material can stop crack propagation? downside?

Answer 23

alumina - though is very opaque

Question 24

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

Answer 24

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

Question 25

what are glassy ceramics based from?

Answer 25

feldspar based = feldspathic

Question 26

how does adding filler affect properties?

Answer 26

improves mechanical properties and opalescenece - usually leucite filler

Question 27

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

Answer 27

atoms packed in dense trays - relatively opqaue

Question 28

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

Answer 28

Ziconium oxide based ceramics

Question 29

name 4 types of porcelain and polycrystaline ceramic and give uses

Answer 29

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

Question 30

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

Answer 30

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

Question 31

Milled composite - only what restorations is this used for?

Answer 31

CADCAM mills from a block of composite inlay/onlay restorations only

Question 32

high alumina porcelain - adv and disadv

Answer 32

alumina added to regular feldspathic porcelain adv - inc strength so produces stronger crown disadv - very white

Question 33

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

Answer 33

any type of crown dental bridge work - max 4 units between abutments 1mm axial, 1.5mm incisal/occlusal

Question 34

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

Answer 34

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

Question 35

why is die relief placed?

Answer 35

to accommodate for luting cement thickness

Question 36

explain difference between active & passive luting cement

Answer 36

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)

Question 37

give 2 ideal properties of luting cement

Answer 37

low film thickness - allows for full seating of restoration pseudoplastic - coats restoration's fit surface without slumping, but flows readily under pressure on fitting

Question 38

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?

Answer 38

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

Question 39

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

Answer 39

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

Question 40

how is durability predicted in the lab?

Answer 40

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

Question 41

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

Answer 41

XML - eXtensible Markup Language

Question 42

give 3 types of ceramic blanks

Answer 42

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