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Dentistry Module 5 > Dental materials > Flashcards

Dental materials Flashcards

1
Q

Within the EU what body regulates the materials that come to market?

A

Medical devices directive

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2
Q

If the medical devices directive decides assessment of a material is favourable, what will indicate this?

A

A CE mark will be awarded

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3
Q

Give three examples of notified bodies and the number alongside the CE mark, that identifies them.

A
  1. TuV SuD Product Service (CE 0123)
  2. British Standards (CE 0086)
  3. Sgs prodcert (CE 0120)
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4
Q

Define each step of the three phases involve in a standardised transparent approach to material product selection.

A

Phase 1- regulatory and quality evidence
Phase 2- clinical trails
Phase 3- blinded assessment by restorative consultants

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5
Q

What specification does endodontic instruments fall under?

A

ISO 3630-1

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6
Q

In terms of physical properties of endodontic materials, define:

resistance force per unit of area of the material against deformation when an external force is applied, it is measured in newtons by square metres.

A

Stress

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7
Q

In terms of physical properties of endodontic materials, define:

the capacity of a material to withstand loads that are trying to elongate the material

A

Tensile strength

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8
Q

In terms of physical properties of endodontic materials, define:

stress the material can withstand without being deformed permanently.

A

Yield strength

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9
Q

In terms of physical properties of endodontic materials, define:

the change of the original dimension under stress of a material

A

Strain

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10
Q

In terms of physical properties of endodontic materials, define:

the greatest stress that an elastic solid can withstand without being deformed permanently

A

Elastic limit

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11
Q

In terms of physical properties of endodontic materials, define:

“The ability of a solid to undergo permanent deformation, a non-reversible change of shape in response to applied forces”

A

Plastic deformation

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12
Q

In terms of physical properties of endodontic materials, define:

breaking point of a material

A

Plastic limit

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13
Q

What are the two key properties of nickel titanium?

A

Super-elasticity and shape memory

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14
Q

What is the composition of stainless steel?

A

18% chromium
8-10% nickel
0.12% carbon

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15
Q

By what manufacturing process are hedstrom stainless steel files created?

A

Micro grinding of stainless steel block into shape of Endo-file

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16
Q

What are the advantages of manual stainless steel ?

A
  • hard
  • tortional effect
  • cutting efficiency
  • fracture resistant
  • Low cost
  • high corrosion resistance
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17
Q

What are the disadvantages of manual stainless steel used in Endo-files?

A
  • rigid, so greater risk of procedural error
  • less predictable canal shape after preparation
  • incomplete debridement of canal
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18
Q

What is the composition of NiTi?

A

45% titanium
55% nickel

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19
Q

What are the three different crystal phases of NiTi? State which phase is an intermediate phase.

A
  • Austenitic
  • R-phase (intermediate)
  • martensite
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20
Q

When using a NiTi rotary file for RCT, what crystal phase is the file mostly in before beginning treatment?

A

Austenitic phase

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21
Q

When using a NiTi rotary file for RCT, what crystal phase is the file mostly in when used in root canal treatment and subjected to stress which will produce a change in shape, volume and density of the file?

A

Martensitic phase

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22
Q

What are the two properties of NiTi alloys that allow for the change between Austenite to martensite and vice versa?

A
  • thermoplasticity
  • superelasticity
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23
Q

What crystal phase of NiTi is described:

Stable at high temperature and no stress

A

Austenitic phase

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24
Q

What crystal phase of NiTi is described:

Stable at low temperature and high stress

A

Martensitic phase

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25
Q

What will happen to a NiTi file if we increase the heat, or reduce stress on the file?

A

It will be in Austenitic phase where the file returns to its original shape (straight)

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26
Q

What will happen to a NiTi file if we lower the temperature, or increase stress on the file?

A

It will be in Martensitic phase, which will be more soft and flexible and this will be able to flex the file to fit into curved canals int he root.

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27
Q

Why are NiTi files unable to precurve?

A

Due to shape memory effect

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28
Q

What treatment would remove manufacturing errors in NiTi wires (e.g. grooves and chips)?

A

Electropolishing

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29
Q

Define, thermoplastic material that is formed around a crystalline structure.

A

Wax

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30
Q

What are the dental applications of wax?

A
  • indirect modelling wax
  • direct inlay wax
  • joining components to facilitate union
  • to make record blocks
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31
Q

What use does wax have as a modelling material in dentistry?

A

Used to form dental restoration or prosthesis

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32
Q

What are the three main advantages of using modelling wax in the construction of acrylic dentures?

A
  1. Withstands intra-oral temperature at try in stage
  2. Amendable to chairside/laboratory adjustment
  3. No residue in investment mould upon boiling out
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33
Q

What type of wax is used to make crowns/inlays/bridges?

A

Inlay wax

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34
Q

What are investment materials used for?

A

To encase the wax designed for the lost wax casting technique

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35
Q

What is another term for “the lost wax technique”?

A

Investment casting

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36
Q

What are the 5 main steps involved in the lost wax technqiue?

A
  1. Create wax pattern
  2. Sprue wax pattern
  3. Invest wax pattern
  4. Use furnace to burn wax pattern, creating a mould.
  5. Force molten alloy into mould
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37
Q

What is a refractory die?

A

“ any die material that is capable of enduring the high temperatures that occur during the firing or casting procedures.”

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38
Q

What is the purpose of refractory dies?

A

To support materials during processing (e.g. porcelain or ceramic veneers or cobalt chromium frameworks) that would deform/disintegrate otherwise.

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39
Q

Name 4 types of investment materials?

A
  1. Dental plaster or stone
  2. Gypsum bonded
  3. Silica bonded
  4. Phosphate bonded
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40
Q

Why would dental plaster or stone not be used for any alloy casting? And only used in the construction of acrylic dentures.

A

Because dental plaster and stone is not heat resistant

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41
Q

What investment material is most likely used in the construction of acrylic dentures?

A

Dental plaster

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42
Q

What investment material is most likely used in the construction of gold casting alloys?

A

Gypsum bonded

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43
Q

What investment material is most likely used in the construction of base metal casting alloys?

A

Phosphate bonded

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44
Q

What investment material is most likely used in the construction of gold casting alloys, base metal alloys, cast ceramics and glasses?

A

Phosphate bonded

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45
Q

What are the ideal properties of investment materials?

A
  • accurate shape, size and surface detail
  • high compressive strength
  • compensate for casting shrinkage
  • alloy compatible
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46
Q

What are the principal components for alloy, porcelain and glass casting?

A
  • binder
  • refractory material (usually silica)
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47
Q

What property of investment mould means that it will expand in the presence of water?

A

Hygroscopic

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48
Q

Which type of investment material lacks porosity?

A

Silica bonded

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49
Q

what is the temperature required for wax burn out in the “lost wax technique” of base metal alloys (includes co/cr)?

A

815-900 degrees

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50
Q

What are the 4 casting faults that can occur in metal casting?

A
  1. Finning and bubbling
  2. Incomplete casting
  3. Porosity in casting
  4. Over/under sized casting
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51
Q

What is meant by finning/bubbling of cast?

A

Extra appendages on casting due to investment mould cracking under forces

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52
Q

Why might incomplete metal casting occur?

A
  • poor space design or failure
  • alloy not sufficiently heated
  • lack of force
53
Q

Why does porosity (fault) occur in metal casting?

A

due to alloy entrapment of oxygen taken up by Cu, Au, Ag,Pt and Pd in alloys when molten

54
Q

What base metal casting alloy is most often used for partial denture frameworks and complete denture bases?

A

Co/Cr

55
Q

What base metal casting alloy is most often used for applications in crown and bridge?

A

Ni/Cr

56
Q

What is the main action of Co and Ni?

A

Hardness and strength

57
Q

What is the action of Cr?

A

Confers both hardness and corrosion resistance through passivating effect

58
Q

What is the passivating effect?

A

Chromium when exposed to atmosphere becomes oxidised, this forms chromium oxide which protects against corrosion

59
Q

What is the fusion temperature for both co/cr and ni/cr?

A

1200-1500 degrees Celsius

60
Q

What are the most widely used wrought alloys for making instruments, burs and wires?

A

Steel and stainless steel

61
Q

What two phases of steel exist below 723 degrees Celsius?

A
  • ferrite
  • cementite
62
Q

What is a mixture of ferrite and cementite termed as?

A

Pearlite

63
Q

On a phase diagram, what is the term for any alloy to the left of the eutectic alloy (X)?

A

Hypo eutectiod

64
Q

On a phase diagram, what is the term for any alloy to the right of the eutectic alloy (X)?

A

Hyper eutectoid

65
Q

Give an example of a hyper-eutectoid alloy that could be used in clinical applications?

A

Cementite

66
Q

Give an example of a hypo-eutectoid alloy that could be used in non-cutting instruments such as forceps?

A

Ferrite

67
Q

How does stainless steel differ from just steel?

A

Steel with the addition of chromium

68
Q

What is the benefit of stainless steel?

A

Improved corrosion resistance by passivating effect

69
Q

Additions of what metals to steel reduce the critical temperature of alloys?

A

Chromium and nickel

70
Q

What form of stainless steel is not amendable to heat treatment as the critical temperature is below where atomic movements are possible?

A

18/8 stainless steel

71
Q

What are the three grades of stainless steel where there is less than 0.15% carbon content?

A
  • soft
  • half hard
  • hard
72
Q

What two processes can join stainless steel alloys?

A
  • soldering
  • welding
73
Q

When welding, what is temperature change proportional to?

A

I^2Rt

74
Q

What do the letters stand for in I^2Rt?

A

I= current
R= electrical resistance
T= time current passes

75
Q

Martensitic stainless steel contains Ni and Cr, true or false?

A

False. It does not contain Ni, only 12% Cr

76
Q

What is Martensitic stainless steel used for?

A

Construction of probes and cutting instruments

77
Q

What is impression compound?

A

“A mucocompressive thermoplastic (so it softens when heated and hardens when cooled) and rigid impression material”

78
Q

What are the two presentations of impression compound?

A
  1. Impressions compound in a 5mm thick sheet
  2. Green stick
79
Q

When might an impression compound in a 5mm thick sheet be indicated for use?

A

In a stock tray for impressions of:
- edentulous ridges
- free end saddles for partial dentures prior to alginate wash impression

80
Q

When is green stick indicated?

A

Used for border extensions of impression trays

81
Q

What are the components of impression compounds? And their functions?

A
  1. Thermoplastic material: characterises softening temperature
  2. Filler: gives body & decreases thermal contraction
  3. Lubricant: improves flow
82
Q

How can impression compound be conditioned?

A

Place block of composition into 55-65 degree Celsius napkin/cloth lined water bath

83
Q

Why should you avoid placing impression compound in lined water bath for a prolonged time?

A

Because stearin acid will leach out causing damage

84
Q

Why is green stick used?

A

To extend peripheral border of extension trays

85
Q

What are the 3 steps to conditioning green stick?

A
  1. Heat in flame
  2. Apply to tray
  3. Temper in water before use
86
Q

What form of prosthetics impression material can be used for complete dentures?

A

Zinc oxide euganol impression material

87
Q

How many paste presentations of zinc oxide euganol impression materials are there?

A

2

88
Q

Describe the two paste presentations of zinc oxide euganol impression materials.

A

Paste 1:
- ZnO
- olive oil
- zinc acetate + water

Paste 2:
- euganol
- kaolin/Talc

89
Q

Describe the setting reaction of zinc oxide euganol impression materials?

A

-OH group of euganol acts as a weak acid which undergoes acid base reaction with ZnO, this forms a salt of zinc euganolate +water

90
Q

What type of special tray must be used for zinc oxide euganol impressions? And what spacer is required?

A

Close-fitted special tray with 1mm spacer

91
Q

What does “Tg” stand for?

A

Glass transition temperature

92
Q

What are the ideal physical properties of a denture base?

A
  • appearance
  • high Tg
  • dimensional stability
  • low specific gravity so that denture does not drop out of mouth
  • high thermal conductivity
  • radiopaque
93
Q

What are the ideal mechanical properties of denture bases?

A
  • rigid
  • high flexural strength
  • high fatigue limit
  • high impact strength
  • high abrasion resistance
94
Q

What are the ideal chemical properties of denture bases?

A
  • insoluble in oral fluids
  • no uptake of saliva/water
95
Q

What are the ideal biological properties of denture bases?

A
  • safe to use
  • non toxic
  • non irritant
  • none sustenance of bacterial or fungi growth
96
Q

What are the ideal miscellaneous properties of denture bases?

A
  • cheap
  • long shelf life
  • easily manipulated and processed
97
Q

What materials constitute the powder component of denture base materials?

A

Polymer- PMMA beads
Initiator - benzoyl peroxide
Pigments- salts of Cd/Fe or organic dyes

98
Q

What materials constitute the liquid component of denture base materials?

A

Monomer- MMA
Cross linking agent- ethyleneglycoldimetharcylate
Inhibitor- hydroquinone
Activator

99
Q

Why is it very important to get the correct powder to liquid ratio when mixing and processing for acrylic denture base materials?

A

This is because the monomer shrinks, by achieving the correct ratio this reduces shrinkage

100
Q

Describe the elemental composition of cobalt chromium alloy denture bases and the proportions each of these elements take up.

A

Cobalt: 35-65%
Chromium: 25-35%
Molybdenum: 4% or more
Nickel: 0-30%

101
Q

What is the major alloy component of Co/Cr alloy denture bases?

A

Cobalt

102
Q

What component of Co/Cr alloy denture bases hardens by solution hardening and undergoes the passivating effect?

A

Chromium

103
Q

What components of Co/Cr alloy denture bases improves casting, handling and mechanical properties?

A
  • molybdenum
  • nickel
104
Q

What is the Co/Cr alloy fusion temperature?

A

1200-1500 degrees Celsius

105
Q

What is the purpose of a tissue conditioner?

A

It is temporarily applied to fit surface of denture to permit a more equal distribution of load and assumption of a more normal mucosal position.

106
Q

Give an example of when a tissue conditioner would be used?

A

In an immediate denture a few weeks after extraction, following infection of denture bearing area to adapt fit to healing tissues.

107
Q

What is the purpose of a functional impression material?

A

Applied to fit surface of denture to allow a more definitive impression to be taken under functional conditions

108
Q

What are the three purposes of a permanent resilient lining (soft lining)?

A
  • It is applied as a “shock absorber” to avoid pain from movement of the denture upon nerves (e.g. mental nerve)
  • avoids pain from movement of obturator/facial prosthesis against bearing structures
  • useful to utilise undercuts by flexing in and out
109
Q

Describe the properties of a tissue conditioner once set?

A

Soft but not capable of undergoing substantial deformation (elastic)

110
Q

Describe the properties of functional impression material once set?

A

Soft but deforms plastic ally to record impression of denture bearing area or neutral zone

111
Q

What property do most tissue conditioners and functional impression materials share that means they flow under pressure but are resilient under dynamic forces such as chewing?

A

They are visco-elastic

112
Q

What are the two different presentations of tissue conditioners and functional impressions materials?

A
  • powder/liquid
  • preformed sheets of acrylic gel
113
Q

What are the 4 types of resilient lining materials?

A
  1. Heat cured acrylics
  2. Self cured acrylics
  3. Heat cured silicones
  4. Self cured silicones
114
Q

What are the disadvantages of using silicone as lining material?

A
  1. Silicones are susceptible to Candida albicans growth
  2. Difficult to achieve bond between silicone and PMMA denture base (peels away)
115
Q

What is the correct thickness required for a resilient lining material?

A

2-3mm

116
Q

What two materials can be used to make artificial teeth?

A
  • acrylic
  • porcelain
117
Q

Why is porcelain produced in moulds that are 30% larger than required?

A

Because Porcelain shrinks when its fired

118
Q

How are acrylic teeth retained to denture base?

A

By chemical interaction

119
Q

How are porcelain teeth retained to denture base?

A

Via holes or pins

120
Q

Which material used to make artificial teeth has a more realistic appearance?

A

Porcelain

121
Q

What are the disadvantages of porcelain artificial teeth?

A
  • click on chewing
  • transmit greater load to denture bearing area
  • more likely to chip and fracture
122
Q

What compound control the setting rate of alginate?

A

Trisodium phosphate

123
Q

What is the melting point of paraffin wax?

A

48-70 degrees Celsius

124
Q

If microcrystalline is added to paraffin wax, how does this change the melting and softening point?

A

It increases the melting point (65-90 degrees Celsius) and lowers the softening point

125
Q

What are the two major causes of porosity?

A
  1. Polymerisation shrinkage associated contraction porosity
  2. Gaseous porosity (volatilisation of monomer)
126
Q

Why does contraction porosity occur in PMMA dentures?

A

Because the monomer contracts by some 20% of its volume during processing

127
Q

How does gaseous porosity occur?

A

If the temperature of the resin exceeds 100 degrees Celsius before the polymerisation process is completed then a gaseous monomer will be formed - which is the cause of gaseous porosity.

128
Q

Why must polymerisation of acrylic dentures be carried out slowly and under pressure?

A

To prevent gaseous porosity and to avoid contraction porosity

Dentistry Module 5 (9 decks)

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