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Dental Skills Y3 > Applied Dental Materials > Flashcards

Applied Dental Materials Flashcards

1
Q

what is an alloy ?

A

a mixture of 2 or more metallic elements

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2
Q

what advantages does an alloy have over pure metals ?

A

cost, biocompatibility, mechanical properties, ease of casting

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3
Q

what are the fabrication processes of alloys?

A

forming - plastic deformation e.g. rolling, extrusion
amalgamation
casting
powder metallurgy - sintering, injection moulding, 3D printing

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4
Q

what physical properties should an alloy have for dental application ?

A

low melting point (flow)
moderately high density (castability)
low coefficient of thermal expansion

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5
Q

what chemical properties should an alloy have for dental application ?

A

corrosion resistance

electrochemical corrosion resistance

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6
Q

what mechanical properties should an alloy have for dental application ?

A 
high modulus (stiffness)
moderately high yield strength (resistance to plastic deformation ) 
hardenable by heat treatment (retention of polish )
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7
Q

what biological properties should an alloy have for dental application ?

A

biocompatible - no toxic soluble phases

non-reactive

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8
Q

what are the 2 types of casting metal alloys ?

A

noble (precious metal)

base metal

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9
Q

which alloys are noble metal alloys ?

A

gold

silver - palladium

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10
Q

which alloys are base metal alloys ?

A

cobalt-chromium and nickel - chromium

titanium

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11
Q

what are the properties of noble metals ?

A

surfaces retain lustre unclean dry air

resist oxidation, tarnish and corrosion during heating casting and soldering

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12
Q

what are the properties of gold ?

A

malleable, ductile
tarnish resistant in air and water at any temp
insoluble in nitric, sulphuric and hydrochloric acids
low strength
small amounts of impurities e.g. lead, mercury have detrimental effect on its properties

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13
Q

what is the fusion temperature of gold ?

A

106.3 deg

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14
Q

what is the density of gold ?

A

19.3g/cm^3

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15
Q

what is the coefficient of thermal expansion of gold ?

A

14.2x10^-6/degC

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16
Q

what is the MOE of gold ?

A

80 GPa

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17
Q

what are the properties of platinum ?

A

tough, malleable, ductile
high corrosion resistance
high cost
higher melting step than porcelain

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18
Q

what is the fusion temperature of platinum ?

A

1755 deg

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19
Q

what is the density of platinum ?

A

21.37 g/cm3

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20
Q

what is the coefficient of thermal expansion of platinum ?

A

8.9x10^-6/degC

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21
Q

what is the MOE of platinum ?

A

147 GPa

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22
Q

what are the properties of palladium ?

A

decreased cost
prevents corrosion of silver in oral environment
absorbs hydrogen gas when heated improperly

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23
Q

what is the fusion temperature of palladium ?

A

1555 deg

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24
Q

what is the density of palladium ?

A

11.4g/cm3

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25
Q

what is the coefficient of thermal expansion for palladium ?

A

11.1x10^-6/degC

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26
Q

what is the MOE of palladium ?

A

112 GPa

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27
Q

what are the properties of silver ?

A

malleable and ductile,
harder than gold,
best known conductor of heat and electricity,
unaltered in clean dry air,
combines with sulphur, chlorine and phosphorous resulting in tarnish in oral environment,
oxygen will evolve during solidification resulting in pits and porosities

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28
Q

what is the fusion temperature of silver ?

A

960.5 deg

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29
Q

what is the density of silver ?

A

10.4g/cm3

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30
Q

what is the coefficient of thermal expansion of silver ?

A

19.7x10^-6/degC

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31
Q

what is the MOE of silver ?

A

120 GPa

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32
Q

give 2 examples of minor alloying elements

A

iridium

ruthenium

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33
Q

what are the effects of minor alloying elements on alloys ?

A

increases tensile strength and elongation by 30 %
increases tarnish resistance
slightly increases yield strength

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34
Q

what are the uses of type 1 gold casting alloy ?

A

inlays that are well supported with no large masticatory forces
high ductility allows burnishing to improve hardness and fit

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35
Q

what are the uses of type 2 gold casting alloy ?

A

inlays - better mechanical properties that type 1 but less ductile

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36
Q

what are the uses of type 3 gold casting alloy ?

A

less support and opposing stress
class II cavities in molars
inlays, onlays, crowns, bridges

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37
Q

what are the uses of type 4 gold casting alloy ?

A

partial denture components, long span bridges

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38
Q

what is the composition of silver-palladium alloys ?

A

25% minimum palladium with small quantities of copper, zinc, indium and (gold), bulk is silver

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39
Q

what are base metal casting alloys ?

A

alloy which contain no gold, silver, platinum or palladium

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40
Q

give examples of 3 base metal casting alloys and their uses

A

nickel - chromium : crown and bridge casting
cobalt - chromium : partial denture framework casting
titanium and titanium-aluminium-vanadium alloys : implants

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41
Q

what are the properties of titanium and titanium alloys ?

A

lightweight, strong, biocompatible, corrosion resistant, low cost

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42
Q

what is the density of titanium ?

A

4.5g/cm3

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43
Q

what are the problems with casting titanium alloys ?

A

high melting point (1700deg)
chemical reactivity
need well controlled vacuum in processing
technology required makes casting expensive

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44
Q

what are the different components of dental porcelain ?

A

kaolinite, quartz, feldspar

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45
Q

what is kaolinite ?

A

china clay, hydrated aluminosilicate, Al2O3.2SiO2.2H2o

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46
Q

what is quartz?

A

silica Sio2

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47
Q

what is feldspar ?

A

mixture of potassium and sodium aluminosilicates

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48
Q

what is the composition of dental porcelain ?

A

little/no clay, mainly feldspathic glass with crystalline inclusion of feldspar

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49
Q

what are the additional components of dental porcelain and what are their functions ?

A

borax (sodium borate) - added to feldspar, reduces melting temperature
metal oxides e.g. iron - pigments
metal oxides eg zinc oxide - opalescence

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50
Q

what determines the opacity of dental porcelains ?

A

particle size
index of refraction
fabrication process

51
Q

what are the physical properties of dental porcelains ?

A

low thermal conductivity - does not conduct heat to pulp but thermal stresses can cause cracks

52
Q

what are the chemical and biological properties of dental porcelain ?

A

stable, biocompatible

53
Q

what are the mechanical properties of dental porcelain ?

A

brittle, hard, strong - tensile

54
Q

what are the common failure modes of dental porcelains ?

A

catastrophic failure

static failure

55
Q

what factors reduce the strength of dental porcelain ?

A

surface roughness
internal voids
porosity

56
Q

what is static fatigue ?

A

decrease in strength over time even in absence of applied load

57
Q

why does static fatigue happen ?

A

Si-O bonds slowly hydrolysed,
generates OH which elevates pH,
dissloves feldspathic component Na2O and K2O,
accelerated by dynamic mechanical loading

58
Q

how can the mechanical properties of dental porcelain be improved ?

A

alter processing - fabrication condition optimisation
produce stronger porcelains - composition and microstructure optimisation
reinforce - provide solid supportive core

59
Q

what are the strengths of porcelain ?

A

aesthetic, high compressive strength, inert, hardness, high elastic modulus

60
Q

what are the weaknesses of porcelain ?

A

brittle, fatigue, tooth wear

61
Q

what os the general preparation of porcelain ?

A 
powder mixed with water and binder,
moulded and carved, 
compacted and dried, 
fired and cooled, 
glazed or polished
62
Q

how is the porcelain powder/frit prepared ?

A

kaolin, silica, feldspar and other components are ground, mixed, fused, rapidly cooled and ground again

63
Q

what is the function of feldspar ?

A

melts at the lowest temperature fusing the other components together

64
Q

how is porcelain prepared for traditional crowns ?

A

porcelain frit mixed with water,
binder of sugar starch improves working properties,
aqueous plastic porcelain compacted onto platinum foil mould,
porcelain shrinks into foil,
assures good fit of crown on tooth

65
Q

how is porcelain compacted ?

A

light vibration/patting,

modern manufacturers use cold isostatic pressing to make dense green porcelain ceramics

66
Q

why is porcelain compacted ?

A

settles particles, reduces shrinkage,
gives uniform contraction over whole surface,
brings excess water to surface

67
Q

describe the process of drying and firing porcelain

A

place into warm atmosphere to dry (1000deg sometimes under vacuum

68
Q

what can happen if wet porcelain is fired at high temperatures straight away ?

A

it can bloat

69
Q

how is porcelain glazed ?

A

coated with low-fusing transparent glass

70
Q

what are the advantages of glazing porcelain ?

A

improves appearance by giving better translucency,
gives an impervious smooth coating that protects against chemical attack,
lower hardness to reduce wear

71
Q

what alloys are typically used for porcelain fused to metal crowns ?

A

high gold, low gold, silver-palladium, nickel-chromium

72
Q

what new development could allow crowns to be constructed at the chair-side ?

A

CAD/CAM

73
Q

What is the filler in a GIC?

A

Alumina and silica in a calcium fluoride flux

74
Q

What minor components are in gics ?

A

Sodium and aluminium fluoride and calcium and aluminium phosphate for flux

75
Q

What is the function of tartaric acid in gics ?

A

Chelating agent

76
Q

What poly acid is in gics ?

A

Poly acrylic or mixture of acrylic and itaconic or acrylic and Maleic acid

77
Q

What are the stages of setting of gics?

A

Dissolution, gelation, hardening

78
Q

Describe the adhesion of gics to tooth structure

A

Hydrogen bonding to collagen in dentine

Ionic bonding to hydroxyapatite in enamel

79
Q

What is the bond strength of a GIC ?

A

2-7 mpa

80
Q

Where does bond failure occur in a GIC ?

A

Cohesive failure within the material, not at bind interface

81
Q

What are diamond GIC products ?

A

Contain poly phosphoric and poly acrylic acid

Faster reaction with immediate saliva resistance

82
Q

What resin is in a compomer ?

A

UDMA

83
Q

What is the resin in resin modified gics ?

A

Water soluble HEMA

84
Q

What else is required in RMGICs ?

A

CO for free radicals

Poly acid molecules have methacryloxy groups for further polymerisation linkage

85
Q

What are the three types of retention ?

A

Macro mechanical eg amalgam
Micro mechanical eg composite
Chemical eg GIC

86
Q

What are resin tags ?

A

Resins with good surface wetting properties penetrate pores in enamel and form resin tags

87
Q

What is used for pre etch prophylaxis ?

A

Proprietary pastes containing pumice, oil, glycerine, fluoride

88
Q

What is used to etch enamel ?

A

36 % ortho phosphoric acid

89
Q

Why are etchant gels better than etchant liquids ?

A

Easier to control due to viscosity and colour

90
Q

What types of etch patterns are produced by enamel etching ?

A

Intra prismatic,
Inter prismatic,
Mixed appearance

91
Q

How long should the tooth be washed for after etching ?

A

For at least as long as the etching time

92
Q

What should happen if the tooth is contaminated with saliva after etching ?

A

Re etch for 5 seconds as glyco proteins will precipitate onto surface

93
Q

What is the strength of enamel bonding ?

A

30 mpa

94
Q

What reduces bond efficiency to enamel ?

A

Technique eg lack of bevel,
Contamination after etching,
Micro cracks developing from cavity prep,
Unsupported or fractured enamel margins

95
Q

Why is bonding to dentine not as reliable as bonding to enamel ?

A

Difference in composition

Difference in structure

96
Q

Describe the difference in composition between enamel and dentine

A

Dentine contains 12 times as much water and twice amount of organic material
Enamel is homogeneous in structure,
Dentine is heterogeneous in structure with different amounts of HA and collagen in peritubular and inter tubular dentine

97
Q

What is a smear layer ?

A

Smeared HA crystals in a matrix of partially degraded collagen, may contain bacteria
2 layers :
Thick outer layer on peri and inter tubular dentine
Thin inner layer of plugs in dentinal tubules

98
Q

What type of smear layer is created by water spray and tungsten carbide burs?

A

Thin smear layer 7um

99
Q

What type of smear layer is produced by diamond burs ?

A

Thick loose smear layer 15 um

100
Q

What are the adverse effects of smear layer removal ?

A

Tissue fluid outflow,
Bacterial invasion,
Dentine sensitivity,
Adverse pulpal response

101
Q

What are the ideal properties of adhesive resin ?

A

Non toxic to pulp,
Hydrophilic,
Good surface wetting,
Long term stability

102
Q

What is in a dentine bonding resin ?

A

Methacrylate to bond with overlying composite,
R - organic linking molecule,
X - hydrophilic molecule that interacts with the etched dentine surface

103
Q

How is bonding to dentine surface achieved?

A

Mainly entanglement or micro mechanical retention,
Bonding to appetite salts in etched dentine
Bonding to organic collagen matrix of etched dentine

104
Q

What is the bond strength of composite to etched enamel ?

A

20-25 mpa

105
Q

What does bonding by entanglement produce ?

A

Hybrid zone responsible for 80 % of bond strength

106
Q

How does bonding to appetite salts occur ?

A

Appetite salts bond ironically to ions in enamel, dentine and GIC ,
Consist mainly of phosphated esters of bis GMA eg PENTA and MDP

107
Q

Describe additional covalent bonding with the organic matrix

A

Materials contain HEMA, PMDM, aldehyde hydrophilic resins

108
Q

Describe the three step etch prime and bond technique

A

Simultaneous etching of enamel and dentine with phosphoric acid,
Smear layer removal and exposure of collagen in inter tubular dentine,
Application of hydrophilic primer to exposed collagen and tubules,
Adhesive application to copolymerise with primer

109
Q

What is primer resin dissolved in ?

A

Acetone or alcohol which displaces water from collagen due to its volatility

110
Q

Give examples of self etching primers

A

NRC,

Clear fill SE bond

111
Q

Describe the 2 step self etch primer and adhesive method

A

Simultaneous etching and priming of tooth structure using weaker acids eg maleic and itaconic acids,
Adhesive application to copolymerise with polymer,
Eliminates separate etch and wash step

112
Q

Give examples of one bottle primer and adhesive

A

Prime and bond,

Optibond solo

113
Q

Describe the 2 step etch and combined primer and adhesive method

A

Simultaneous etching or enamel and dentine using phosphoric acid,
Smear layer removal, exposure of collagen,
Application of one bottle combined primer and adhesive

114
Q

Give examples of self etching primer and adhesives

A

Prompt L pop,

Xeno

115
Q

Describe the one step etch, prime and adhesive method

A

Simultaneous etching, priming and adhesive application to enamel and dentine,
Smear layer removal, neutralisation of etch component and forms hybrid layer in one step

116
Q

Describe the mechanism of action of Xeno

A

Hydrolysis of pyro EMA,
Produces phosphoric acid groups,
Phosphoric acid groups bond to calcium ions in HA in dentine and enamel,
Phosphoric acid groups neutralised resulting in etched dentine and enamel

117
Q

How do polyakenoate cements bond to tooth structure ?

A

Don’t rely on micro mechanical retention,

Utilise ion exchange at the enamel or dentine surface to produce dynamic ionic bond

118
Q

How is the smear layer removed for polyalkenotae cement ?

A

Apply 10% poly acrylic acid for 10 seconds,
Washed for 15 seconds,
Plugs remain in tubule ends

119
Q

How are bonds formed between polyalkenotae cement and tooth structure ?

A

Free polyalkenoic acid penetrates enamel and dentine surface and the carboxyl group displaces phosphate ions,
Phosphate takes calcium with it to maintain electrical neutrality,
These combine with cement matrix and form an ion rich soup at the interface of the tooth and cement,
Firmly binds to tooth and cement

120
Q

What is the soup ?

A

Calcium/strontium/phosphate/alkenoate

121
Q

How do polyalkenoate cements bond to tooth structure ?

A

Hydrogen bonding,

Metallic ion bridges between carboxyl groups an poly acid and amino acids of collagen

122
Q

How do gic bonds fail ?

A

Weakest material is matrix holding glass particles together,

When gic is stressed it cracks cohesively between glass particles and not at ionic interface

123
Q

What is the bond strength of polyalkenoate cements to tooth structure ?

A

5-9 MPa

Dental Skills Y3 (6 decks)

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