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dm (all topics) Flashcards

1
Q

NiTi in endo ratio

A

56% Ni
44% Ti
1:1 atomic ratio

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2
Q

properties of NiTi that makes it suitable for endo

A
  • martensite / austenite phase
  • phase tf under stress
  • twinning + superelasticity
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3
Q

what is austenite phase

A
  • parent phase

- simple cubic structure

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4
Q

what is martensite phase

A
  • mono clinic crystal struucture allows NiTi to undergo limited deformation wo breaking atomic bonds
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5
Q

reasons for NiTi fracture in endo

A
  • torsional load (plastic deformation -> fracture)

- cyclic fatigue (instrument is work hardened at same location until it becomes brittle and fractures)

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6
Q

common solutions used in endo chemical disinfectants

A
  • sodium hypochlorite (>0.5%)
  • chlorhexidine (2%)
  • EDTA
  • MTAD
  • chloroform
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7
Q

what is ceramic

A

rigid material of metallic & non metalllic elements inlcuding oxides, nitrides, carbides, sillicates that are organised in a crystalline / vitreous mixture

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8
Q

properties of ceramics

A
  • translucency
  • chromatic stability
  • biocompatible (insoluble)
  • chemically inert
  • low thermal conductivity
  • high compressive strength
  • decent tensile strength, fracture toughness
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9
Q

how does porcelain solidify

A

Vitrification - porcelain solidify w a liquid structure instead of crystalline structure -> this creates a more stable structure

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10
Q

what is the mechanism of failure for ceramics

A

brittle fracture

- single crack extends around a pre existing flaw

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11
Q

how does ceramic break down

A

ceramics completely non ductile & is v brittle -> doesn’t allow any distortion
fracture occurs suddenly wo prior plastic deformation
so the entire structure just break

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12
Q

what is fatigue

A

fatigue = damage caused by alternating application of load. repeated cyclical damage OVER TIME causes crack growth over microstructural elements

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13
Q

define fracture toughness

A

fracture toughness = ability of a material to withstand crack propagation

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14
Q

what is usually the cause of failure:

a) load
b) compression
c) tension / tensile stresses

A

tension & tensile stresses

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15
Q

what is the purpose of fillers in ceramics

A

fillers are added to resist & inhibit crack propagation

  • the more dispersed the fillers the better
  • the smaller the filler size the better
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16
Q

ideal properties of fillers for ceramics

A
  • bond to matrix (glass)
  • liner coefficient of expansion same as matrix so no stress during cooling
  • small and well dispersed fillers
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17
Q

how does brittle fracture occur in ceramics

A

conc stress from surface defects more than strength of ceramic body hence resulting in brittle fracture
fatigue crack growth caused by repeated cyclical damage to microstructural elements

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18
Q

consequences of surface defects on ceramics

A
  • lower colour stability

- higher chance of fracture

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19
Q

purpose of glazes on ceramics

A

glaze = a ceramic veneer added to porcelain resto after it has been fired

  • seals pores on surface so that surface becomes poreless
  • produce glossy surface
  • induce compression to increase strength
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20
Q

what is the strongest dental material

A

zirconia

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21
Q

what is used to colour ceramics

A

metal oxides

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22
Q

define fluorescence

A

material absorb light at high energy, short wavelength, and emits light at lower energy, typically visible wavelength

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23
Q

what is the function of leucite in ceramics

A

leucite is a reinforcement particle to inhibit crack propagation

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24
Q

what does a solid solution metal mean

A

metals are soluble in each other in the solid state
meaning atoms interspersed randomly in a common space lattice, single phase
*size diff of atoms within 15%

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25
Q

substitutional solid solutions

A

solute atom occupy space normally occupied by solvent atoms

- atoms have similar diameters

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26
Q

interstitial solid solutions

A

solute atoms positioned in interstitial spaces of solvent atoms
- solute much smaller than solvent

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27
Q

effects of alloying

A
  • increase strength, proportional limit, hardness

- decrease ductility

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28
Q

in a binary phase diagram, what does the area between liquidus & solidus represent

A

represents solid solution and liquid solution present at thermal eqm
liquidus and solidus represents the limits of solubility at each composition

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29
Q

what are eutectic alloys

A

alloys that show complete liquid solubility but limited solid solubility

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30
Q

in a eutectic alloy phase diagram graph, what does the liquidus and solidus line represent

A

when liquidus and solidus meet = eutectic composition
this is the lowest temp in which any alloy composition of 2 metals can be entirely liquid.
at this point, the alloy solidifies at a constant temp

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31
Q

properties of eutectic alloys

A
  • brittle
  • increase strength and hardness
  • poor resistance to corrosion
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32
Q

why is CoCr corrosion resistant

A

Cr on surface forms CrO, an inert layer that is tarnish resistance and has stainless properties

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33
Q

what does adding Be do to CoCr

A

smoother casting

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34
Q

MOE of CoCr

A

v high MOE = req lotsa force to deform -> less thickness of material required to achieve the same strength -> denture base can be thinner and lighter

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35
Q

CoCr vs gold shrinkage

A

CoCr has higher shrinkage

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36
Q

ductility of CoCr

A

low ductility -> fracture easily

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37
Q

impt things abt CoCr

A

CoCr cannot use hypochlorite cleansers / chlorine stuff bc it will corrode
oxygenating denture cleansers also tend to stain CoCr

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38
Q

constituents of gold alloys & its purpose

A

gold - tarnish and corrosion resistant, ductile, yellow
platinum - hardens alloy, white
palladium - tarnish and corrosion resistant, hardener, white
copper - increase strength and hardness, increase ductility (decreases tarnish resistance)
zinc - oxide scavenger, improve castability
indium - oxide scavenger, casting fluidity

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39
Q

what are the 4 types of gold alloys

A

type 1 - soft
type 2 - medium
type 3 - hard
type 4 - extra hard

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40
Q

summary of type 1-4 gold

A

type 1 -4
gold content high - low
MOE, strength, hardness, low - high
ductility, melting range high - low

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41
Q

how to compensate for alloy shrinkage

A

controlled expansion of investment so final cast before cooling will be slightly bigger, after cooling will be just right

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42
Q

tarnish vs corrosion

A 
tarnish = staining
corrosion = when metals degrade into oxides/hydroxides through chem rxn
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43
Q

what are wrought metal alloys

A

wm = cold worked metals that are plasticly deformed to change its structure & mechanical properties

a pure metal/alloy that is permanently deformed = wm

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44
Q

define

a) malleability
b) ductility
c) joinability

A

a) malleability - ability to form thin sheets by hammering or rolling
b) ductility - ability to be stretched into a wire
c) joinability - ability to be joined via soldering/welding

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45
Q

outcome of work hardening

A

metal become stronger harder more ductile less ductile, lower corrosion resistance

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46
Q

NiTi composition

A

54% Ni

44% Ti

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47
Q

definition of twinning

A

twinning = an atomic arrangement within a crystal where a region of crystal takes on a different crystallographic axis orientation from the rest of the crystal without breaking atomic bonds

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48
Q

define shape memory

A

shape memory = the ability to return to previously manufactured shape when it is thermally induced

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49
Q

important property of NiTi

A

v high fatigue strength - can take on low loads but at very high frequency

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50
Q

composition of ss implants

A

ss (316L)
Fe - 60-65%
Cr - 17-19%
Ni - 12-14%

18/8 SS
18% Cr 8% Ni 0.2% C

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51
Q

composition of Ti

A

Ti-6Al-4V
6% Al
4% V

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52
Q

although Ti fracture is uncommon, what is the cause

A

metal fatigue from high cyclic ocl loading

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53
Q

Ti casting

A

must be done in vacuum / inert atmp bc Ti itself is v reactive

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54
Q

passivation definition

A

passivation = enhancement of oxide layer to minimise release of metallic ions
- done by immersing in 40% nitric acid / anodisation

INCREASES CORROSION RESISTANCE

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55
Q

self healing properties of YTZP

A

when crack is present, localised stress at the crack tip causes crack propagation
when stress at crack tip reaches a certain level, metastable tetragonal crystal structure transform into a stable monoclinic form
this stress induced change in structure leads to large increase in volume = induce surface compression strength and close up crack, prevent propagation

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56
Q

phase transformation of YTZP

A

tetragonal (more stable) -> monoclinic

leads to substantial increase in volume that induces surface compressive strength

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57
Q

fun facts abt zirconia

A
  • strongest dental material
  • zirconia is 2x stronger than alumina based ceramics
  • 3% of yttria is added to pure zirconia to form YTZP
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58
Q

gypsum bonded investment used for what alloys

A

only gold

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59
Q

type 1 vs type 2 gold alloy shrinkage compensation during casting?

A

type 1 - shrinkage compensated by thermal expansion

type 2 - shrinkage compensated by hygroscopic expansion

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60
Q

purpose of silica in gypsum bonded investment

A
  • refractory material
  • regulates thermal expansion
    cristobalite expands more than quartz but at a lower temp
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61
Q

what is thermal expansion affected by

A

lower w/p ratio, increase thermal expansion

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62
Q

when does thermal expansion occur

A

occurs during setting

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63
Q

when does hygroscopic expansion occur

A

occurs when setting in contact w water

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64
Q

what is hygroscopic setting expansion

A

it is a continuation of ordinary setting expansion when investment is allowed to set in contact w water -> surface tension of water is no longer a limiting factor

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65
Q

when is hygroscopic setting used

A

used to provide extra expansion esp for casting alloys of high COTE or higher contraction upon solidifcation

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66
Q

factors influencing hygroscopic expansion

A
  • more silica = more expansion
  • more w/p ratio = less expansion, less strength
  • more spatulation more expansion
  • smaller particle size, more hygroscopic expansion
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67
Q

where should sprue be attached

A

part where there is greatest bulk and least anatomy

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68
Q

what is purposed of wax reservoir in casting

A

wax reservoir = small amt of additional wax attached to sprue near the junction of wax pattern to prevent localised shrinkage porosity

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69
Q

reasons for these casting failure:

a) poor margins
b) investment crack

A

a) poor margins - too little casting pressure

b) investment crack - too much casting pressure

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70
Q

purpose of flux for casting

A

flux = a material added to molten alloy before alloy is spun into the mould
o Prevents O2 from causing hot metal to oxidise
o Flux will dissolve oxides that may form when metal is heated
o increase fluidity of metal
o decrease porosity

71
Q

define strain

A

strain = deformation from tensile force, elongation is in the same axis that force is applied in

72
Q

define modulus of elasticity

A

MOE = stress / strain, the amount of stress required for the corresponding strain
high MOE = large amount of force applied but relatively low amount of deformation (material is very rigid)

73
Q

define plastic deformation

A

deformation until material cannot go back to its original shape

74
Q

define toughness

A

toughness = ttl energy required to fracture a material

aka AUC of a stress/strain

75
Q

define hardness

A

hardness = resistance of a material to penetration

76
Q

define COTE

A

COTE = change in length per increase in 1 degree

77
Q

define creep

A

creep = permanent deformation after being exposed to stress constantly even if stress is within elastic limit

78
Q

what is the composition of amalgam

A

dental amalgam = AgHg matrix containing filler particles of AgSn
[matrix] = gamma 1 (AgHg) and gamma 2 (SnHg)
[filler] = gamma (AgSn)

79
Q

amalgam LCP vs SP

A

LCP better corrosion resistance
SP harder to pack tightly, tend to overhang
SP smaller SA:Vol ratio, req less Hg, better properties and surface finish

80
Q

functions of diff components of amalgam

A

Ag - increase strength, expansion, reactivity, decrease flow, creep
Sn - decrease strength, hardness, expansion, increase flow, setting time, corrosion, contraction
Cu - increase strength hardness, expansion, flow, decrease creep, corrosion
Zn - oxide scavenger, cause delayed expansion, better clinical performance

81
Q

3 principles of adhesion

A
  1. adherents need to be close together
  2. surface of adherent needs to be clean
  3. adhesive must have good wetting with adherent, contact angle less than 90degree
82
Q

what does etchant do to enamel

A

etchant = 37% phosphoric acid

  • removes smear layer
  • produce pores on surface for mechanical interlocking of adhesives, improved retention of resto
  • increased SA and roughness of enamel for resto to bond to
83
Q

what does conditioner do to dentin

A

!cannot etch dentin!
conditioner = 10-25% polyacrylic acid
- alter surface characteristic of dentin
- removes smear layer wo demineralising tooth surface
- produce pores in dentin surface
- opens dentinal tubules and collagen network for primer and adhesive to flow in

84
Q

function of primer

A

primer = coupling agent for dentin and resin
primer consist of bifunctional monomer dissolved in suitable solvent to bond hydrophobic resin to hydrophillic dentin
polar component of primer binds to col fibres + apolar component of adhesive bind to resto = binding a hydrophobic surface to a hydrophillic surface

85
Q

consequence of insufficient polymerisation

A 
#1 poor colour stability
inferior physical and mechanical properties 
higher solubility
86
Q

why cr discolour over time

A

water hydrolyses silane filler bonds, forces polymer chains apart, weaken CR structure, allows contaminants to enter and cause discolouration

87
Q

how to activate polymerisation in CR

A
  1. chemical (free radicals)
  2. UV light / visible light (diketone)
  3. blue light activated (cpq)
88
Q

purpose of fillers in CR

A
  • improve physical and mechanical properties
  • decrease polymerisation shrinkage
  • more viscous, less liquidy
89
Q

COTE of CR

A

relatively close to enamel and dentin (compared to amalgam)

90
Q

COTE of amalgam

A

much higher than CR/enamel/dentin

91
Q

how does CR bond to enamel

A

Relies on micromechanical interlocking with unfilled resin and the acid-etched enamel

92
Q

how does CR shrink upon polymerisation

A

CR shrinks away from less retentive surface (NOT towards light source)
*place CR in increments reduce shrinkage stress but not volumetric shrinkage constant

93
Q

light curing for CR

A

cure in increments of <2mm depth to decrease shrinkage stress

  • light tip must place <6mm from resin
  • LED blue light only works for CPQ initiated polymerisation
94
Q

what rxn is GIC

A

acid base rxn btwn polyalkenoic acid and calcium fluoro alumino silicate glass base

95
Q

function of tartaric acid in GIC

A

increase working time decrease setting time

96
Q

how does GIC bond to tooth

A

chemical adhesion
- ion exchange w HAP to form intermediate layer of polyacrylate, phosphate, ca2+ or bond directly to ca2+
- hydrogen bonding w dentin col network, ionic bond to HAP
bc enamel has more HAP, bonding to enamel > dentin

97
Q

factors that allow GIC to set faster

A
  • higher temp
  • tartaric acid
  • smaller particle size (larger SA)
  • more alumina / silica ratio
  • higher powder : liquid ratio
98
Q

advantages of GIC

A
  • v close COTE to enamel
  • cariostatic fx that is rechargeable
  • weak acid + big chonky molecule = gentle to pulp
  • self adhesive = conservative prep
  • lower acid erosion values than other cement
99
Q

GIC & CR

A
  • no need to etch GIC before putting on CR on top of GIC

- GIC only mechanically bond to CR

100
Q

what is RMGIC

A

water in GIC replaced to water-HEMA, PAA replaced to PAA w side chains that polymerises upon light curing
amt of resin = 4-6%

101
Q

RMGIC & CR

A

chemical bond bc of HEMA

102
Q

synersis

A

loss of water hence causing shrinkage

103
Q

imbition

A

gain of water hence causing expansion

104
Q

how to minimise deformation when using alginates

A

snap removal
pour within 15mins
keep in humid environment

105
Q

polysulfide polymerisation reaction

A

condensation polymerisation

by pdt = water

106
Q

polyethers polymerisation reaction

A

additional polymerisation

107
Q

compare setting time of elastomers

A

PS
CPS
APS
PE (shortest)

108
Q

compare hardness of elastomers

A

PE (hard af)
APS
CPS
PS (softest)

109
Q

compare dimensional stability (opposite of shrinkage) of elastomers

A

APS
PE
PS
CPS

110
Q

compare deformation (opposite of elastic recovery) of elastomers

A

PS
PE
CPS
APS

111
Q

compare tear resistance of elastomers

A

PS (v tear resistant)
APS, CPS
PE

112
Q

disadvantage of PE

A

taste like shit

imbition weakness

113
Q

disadvantage of APS

A

latex cannot touch
expensive
hydrophobic

114
Q

properties of compound

A
  • thermoplastic
  • soften when heated, hard and brittle when cooled
  • poor conductors of heat (inside often not softened enough)
  • no undercuts
  • not dimensionally stable, deforms upon storage, pour impression within 1h
115
Q

plaster vs stone

A

plaster: large irregular porous particles that dont pack well -> need lots water
stone: smaller regular no porous particles that pack well -> req less water

116
Q

factors that decreases setting time of stone

A
  • smaller particle size
  • more impurities
  • less water
  • more mixing
  • accelerators / retarders
117
Q

factors to increase strength of stone

A
  • less water
  • less porosity
  • less spatulation time
  • less acc/ret
118
Q

stages of heat cure acrylic resin

A 
[74deg]
sandy stage 
stringy stage 
doughy stage 
rubber stage - can't be moulded, cannot make any more adjustments 
stiff stage
119
Q

how is cold cure acrylic resin activated

A

tertiary amine

120
Q

cement reaction

A

mixing basic ceramic powder w acidic liquid

121
Q

ZnOE advantages and disadvantages

A

+ bacteriostatic + soothing fx

- high solutbility, doesnt adhere to dentin and enamel

122
Q

ZnPO

A
  • mechanical interlocking
  • brittle af
    working time = 3-6mins
    setting time = 5-12 mins
  • not anticariogenic
  • v acid
123
Q

Zn polycarboxylate

A
  • chemical bonding
  • gd mechanical properties
  • not as brittle as ZnPO
  • antibacterial
124
Q

consequence of over trituration of amalgam

A

increase Hg consumption

net contraction

125
Q

consequence of overdrying etched dentine

A

col fibres may collapse

126
Q

can ZnOE be used for undercut

A

NO!!!!!!

127
Q

in visible lc resto material, what light absorber is used

A

CPQ

128
Q

in elastomers, what conveys stiffness

a) chain lengthening
b) cross linking

A

chain lengthening

129
Q

in elastomers, what conveys elasticity

a) chain lengthening
b) cross linking

A

cross linking

130
Q

martensite -> austenite transformation by what means

A

heating

131
Q

austenite -> martensite transformation by what means

A

stress / forces

132
Q

how does sodium hypochlorite work as an endo chemical disinfectant

A
  • saponification to form organic products
  • interfere cell metab and inhib bacterial enzymes
  • inactivate enzymatic sites by hydroxyl ions and chloramination rxn
133
Q

mechanism of CaOH as a medicament

A

high pH level help to hydrolyse proteins, fats, bacterial enzymes

134
Q

dental wax melting temp exists as a _______

A

range (not as a point)

135
Q

properties of wax

A

low MOA
low proportional limit (deforms easily)
brittle and fragile at low temp

136
Q

dental wax have better flow when

A
  • higher temp
  • more force
  • long time that force is applied
137
Q

dental wax ductility increases w _________

A

temp

138
Q

how to clean dentures

A

use chemical cleansers, brush gently w soap and water

don’t leave denture out to dry

139
Q

which type denture cleanser least discolouration

A

acid type denture cleanser

140
Q

which type denture cleanser most discolouration

A

alkaline peroxide

141
Q

amalgam reaction

A

AgSn + Hg -> AgSn (gamma) + AgHg (gamma 1) + SnHg (gamma2)

142
Q

high Cu amalgam

A

AgCu + SnHg (gamma 2) -> AgHg (gamma 1) + CuSn

less gamma 2, more creep and corrosion resistant, stronger, harder

143
Q

undertrituration

A

grainy crumply amalgam, too much Hg

144
Q

spherical amalgam

A

less Hg
less expansion
tendency for overhang but better properties

145
Q

consequences of poor amalgam condensation

A
  • porosity, inferior properties
  • poor marginal seal
  • poor mechanical retention
  • excess gamma 2, excess Hg not removed
  • harder to carve and polish
146
Q

what is smear layer

A

inorganic + organic components of tooth structure, pieces of burr, proteins, pulp tissue, saliva, blood, bacteria
amorphous irregular granular appearance that interferes w adhesion

147
Q

purpose of adhesive

A

adhesive contains hydrophillic resins that polym w primer to form mechanical interlocking w dentin + form chemical bond w CR

148
Q

what is hybrid layer

A

hybrid layer = interpenetrating layer of dentin and resin, consists of dentin primer and adhesive

149
Q

can bis GMA be activated by blue light

A

Not activated by blue light
bisgma uses TPO (a diff light absorber)
if blue light = cpq as light absorber, bis gma = TPO, which will not be blue light!

150
Q

what are coupling agents

A

coupling agents = intermediary substance that help to bond one material to another. in the absence of a coupling agent these 2 materials would not be able to bond to each other effectively
e.g. bonding hydrophillic to hydrophobic

151
Q

what is the purpose of silanes in CR

A

silanes = coupling agent = a molecule w central Si and 4 bonds

  • bonds resin matrix and fillers tgt
  • efficient stress tf from resin to glass, better properties
  • promotes wettability and dispersion
  • decrease viscosity
152
Q

light cure depth problem

A

light activated CR conversion from paste to solid relies on ability of light to access and initiate curing in all parts of resto
when light hits composite, photons are reflected, scattered, absorbed. this limits the penetration that light can achieve and limits the depth of material that can be cured
inverse square law: light cure efficiency drops significantly further away from tip

153
Q

cr failure

A
  • contamination of water, bacteria, plaque
  • discolouration
  • fracture from wear and heavy ocl contact
  • poor marginal seal
  • weak foundation
  • residual monomer causing post op sensi
154
Q

GIC setting rxn

A
  1. dissolution: acid attack glass, release Ca Al F and leave behind silica gel. H+ diffuse into glass and replace lost ions
  2. gelation: cross linking of carboxyl and Ca/Al forms polysalt and physical properties
  3. hardening: glass particles sheathed by siliceous hydrogel bonded by a matrix of hydrated fluoridate Ca Al polysalt
155
Q

GIC components

A

PAA + Ca F Al silicate glass base

156
Q

most impt factor for gd detail capturing for impressions

A

low viscosity

157
Q

dihydrate vs hemihydrate

A

dihydrate: CaSO4.2H2O
hemihydrate: (CaSO4)2.H2O
plaster vs stone:
plaster greater degree of hemi -> di

158
Q

benefit of cold cure acrylic resin

A

less shrinkage

159
Q

ZnOE

A
  • rigid once set, no undercuts
  • sets in 4-10 mins to form Zn eugenolate crystals
  • bacteriostatic
  • gd surface reproduction, low viscosity
  • high solubility
  • gd for temp resto
  • acid base rxn
160
Q

why ZnPO need to mix in increments

A

exothermic rxn, heat increases setting rate
mix in increments to delay rxn, prolong working time
spread over large area to dissipate heat decrease setting rate
able to mix in more powder, high powder/liquid ration stronger material
can mix into ideal consistency

161
Q

define eutectic composition

A

eutectic composition = the lowest point in which any alloy composition of 2 metals can be entirely liquid. at this point allow solidifies at a constant temp

162
Q

CoCr composition

A

varies but majority Co, followed by Cr

carbon content <0.4%

163
Q

CoCr vs gold in terms of shrinkage

A

CoCr has higher shrinkage lvl

164
Q

reasons for back pressure porosity

A
  • low w/p ratio, insufficient porosity
  • short sprue
  • insufficient casting pressure
165
Q

heat treatment for softening alloys

A

heat alloy to 700deg for 10mins then quench in water

166
Q

heat treatment for hardening alloys

A

heat alloy for 424deg for 2 mins, 250deg for 30 mins, quench

167
Q

composition of 18/8 ss

A

Fe 60-65%
Cr 17-19%
Ni 12-14%

168
Q

which has greatest amt of expansion: quartz/cristobalite/tridymite

A

cristobalite

169
Q

purpose of boric acid/NaCl in gypsum investment

A

regulate setting expansion and setting time, prevents most of gypsum shrinkage

170
Q

phosphate bonded investment for what

A

for metal ceramic alloys

171
Q

austenite -> twinned martensite

A

cooling

172
Q

gutta percha is susceptible to degradation, how should it be stored?

A

5 to -10deg

173
Q

e.g. of ceramic fillers

A

leucite

lithium disilicate

dm (1 decks)

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