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Dentistry Module 6 > Dental Materials > Flashcards

Dental Materials Flashcards

1
Q

What is fibre reinforced composite?

A

Synthetic material composed of reinforced fibres which are embedded in a resin matrix (polymer).

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2
Q

Why are carbon graphite fibres no longer used in composition of FRC?

A

Due to aesthetic reasons, they are black in colour.

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3
Q

What are the 3 most common glass fibres used in the dental industry?

A
  1. E-glasses
  2. R-glasses
  3. S-glasses
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4
Q

How can E-glass fibres be modified to make them more resistant to acid attacks?

A

By adding boron oxide (B2O3) and reducing CaO

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5
Q

Can FRC be seen on radiograph?

A

Yes, it is radiopaque.

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6
Q

What are the two types of polymer matrix for FRC?

A
  1. Linear (thermoplastic)
  2. Cross-linked (thermoset)
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7
Q

Give two examples of linear polymers that create a matrix?

A

MMA and PMMA

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8
Q

Give three examples of cross-linked polymers used to create a matrix?

A
  1. EGDMA
  2. Bis-GMA
  3. Epoxi resins
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9
Q

In dentistry, what three resin systems (polymers) are used as the matrix for FRC?

A
  1. Bis-GMA
  2. TEGDMA
  3. UDMA
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10
Q

What is a semi inter-penetrating polymer network (Semi-IPN)?

A

A combination of a linear polymer with a cross-linked polymer

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11
Q

What are the three advantages of a semi-IPN matrix for FRC?

A
  1. Better clinical handling properties
  2. Better bonding to indirect restorations, post and veneers
  3. Higher toughness
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12
Q

What is resin impregnation?

A

“Relates to surface wetting properties of fibres by resin, distance of individual fibres from each other in the fibre product and viscosity of the resin material.”

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13
Q

What is the common preimpregnation method for FRC?

A

PMMA is dissolved in a high evaporate solvent. The solvent evaporates and the fibres stay impregnated with PMMA.

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14
Q

Why are dental glass fibres always pretreated with coupling agents, silanes?

A
  1. They help with adhesion, enabling the chemical adhesion between the fibres and polymer matrix.
  2. Improve the wetting surface of fibres.
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15
Q

The direction of the fibres will affect the mechanical properties of the FRC.
True or false?

A

True

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16
Q

What are the four different directions that fibres can adopt within a matrix?

A
  1. Continuous unidirectional
  2. Continuous bidirectional
  3. Continuous random orientated (long fibres)
  4. Discontinuous random orientated (short fibres)
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17
Q

What direction of fibres is described?

  • All fibres in one single direction embedded in resin.
  • improved strength in the direction of the fibres
  • reduced strength in all other directions
A

Unidirectional fibres

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18
Q

What uses do unidirectional fibres have in FRC application?

A

For posts, fixed prosthodontics

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19
Q

What direction of fibres is described?

  • fibres aligned in two directions
  • improved strength and stiffness in both directions
  • used when both flexural and tensile strength required
  • increases the load bearing capacity and the resistance to fracture
A

Bidirectional fibres

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20
Q

What uses do bidirectional fibres have in FRC application?

A

Dental bridge frameworks, splints, removable dentures

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21
Q

What direction of fibres is described?

  • fibres randomly dispersed
  • anisotropic properties (different properties in different directions)
  • cost effective for short term solutions
A

random orientated fibres

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22
Q

What is the use of random orientated fibres in FRC application?

A

As a provisional/temporary restoration

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23
Q

What are the three key properties of FRC?

A
  1. Biocompatible
  2. Radiopaque
  3. High modulus of elasticity (reduces stress, helps load distribution and minimises fracture)
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24
Q

What is the benefit of a longer fibre length of FRC?

A

Longer fibres transfer stress more efficiently

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25
Q

What is the benefit of a shorter fibre length of FRC?

A

Help with material handling, less risk of fibre agglomeration

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26
Q

What are the two main limitations of FRC?

A
  1. The humidity of the oral cavity may degrade and weaken the interface between the matrix and fibres, causing failure
  2. Easy to fracture and delaminate (although easy to repair)
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27
Q

What are the 5 clinical uses of FRC?

A
  1. Removable dentures
  2. Fixed dental prosthesis
  3. Root canal posts
  4. Splints
  5. Direct restorations
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28
Q

What is the limitation of FRC as a splint?

A

Wear/debonding

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29
Q

What type of FRC are recommend for use as direct restorations?

A

Short FRC

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30
Q

Name two types of bulk fill composites. What is their purpose?

A
  1. SDR flow
  2. Filtek

Reinforces structure of restoration

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31
Q

How many types of traditional casting gold alloys are there?

A

4

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32
Q

What type of casting gold alloy would be used for an inlay, where the casting is subject to slight stress?

A

Type 1 Low strength

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33
Q

What type of casting gold alloy would be used for an inlay/onlay, where the casting is subject to moderate stress?

A

Type 2 medium strength

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34
Q

What type of casting gold alloy would be used for an onlay/pontic/full crown, where the casting is subject to high stress?

A

Type 3 high strength

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35
Q

What type of casting gold alloy would be used for partial denture framework, crowns and bridges, where the casting is thin in cross section?

A

Type 4 extra high strength

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36
Q

As we move from low (type 1) to high (type 4) strength casting gold alloy, what happens to the:

  1. hardness
  2. Proportional limit
  3. Strength

Of the material?

A

They all increase

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37
Q

As we move from low (type 1) to high (type 4) strength casting gold alloy, what happens to the:

  1. ductility
  2. Corrosion resistance

Of the material?

A

Decreases

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38
Q

Why, as gold content decreases, does hardness increase?

A

Due to solution hardening (formation of solid solutions with gold)

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39
Q

Why are heat treatments only possible for casting gold alloys type 3 and 4, and not types 1 and 2?

A

For types 3 and 4 - results in further hardening by precipitation hardening of Ag/Cu and Au/Cu systems.
For types 1 and 2 - due to lack of silver and copper that are required.

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40
Q

How is premature hardening of casting gold alloys avoided?

A

By cooling casting rapidly from excess of 600 degrees Celsius

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41
Q

What important property is enhanced in leucite containing dental porcelain compared to normal dental porcelain? What is the advantage of this?

A

Leucite containing porcelain has higher coefficient of thermal expansion. Aim is to prevent crack propagation within ceramic.

42
Q

Name a hydrated aluminosilicate, better known as clay?

A

Kaolin

43
Q

What are the three main constituents of dental porcelain?

A
  1. Kaolin
  2. Quartz
  3. Feldspar
44
Q

Why does cooling of porcelain after firing need to be controlled?

A

To avoid cracking of material

45
Q

What is one way to reduce stress concentrations of porcelain and limit crack propogation?

A

Porcelain fused metal crowns where metal crowns have a layer of porcelain fused onto the metal.

46
Q

Name 4 available PFM alloys.

A
  1. High gold alloys
  2. Low gold alloys
  3. Silver palladium alloys
  4. Nickel-chromium alloys
47
Q

What is the disadvantages of nickel chromium alloys?

A
  • Prone to high casting shrinkage with voids
  • poorer bond strength to porcelain than other alloys
  • poor biocompatibility
48
Q

What are the three classes of dental ceramic?

A
  1. Glassy ceramics
  2. Particle filled glasses
  3. Polycrystalline ceramics
49
Q

What is the key advantageous property of dental ceramics that are glassy?

A

Highly aesthetic

50
Q

What is the key advantageous property of dental ceramics that are crystalline?

A

High strength

51
Q

What stops crack propogation in porcelain?

A

Compressive forces

52
Q

Generally, conventional acid base cements must not be used except with what type of ceramic?

A

Zirconium oxide based ceramics

53
Q

What is die relief, and why is it important?

A

It is a paint-on die spacing material, achieves sufficient space to accommodate luting cement thickness between metal castings and tooth surface.

54
Q

What is the function of a luting cement?

A

Used from retention of indirect restorations and to seal the space between the restoration and the tooth.

55
Q

Describe an “active” luting material?

A

One that:
1. Bonds to tooth and restoration
2. Plays a role in retention
3. Creates a marginal seal

56
Q

Describe a “passive” luting material?

A

One that:
1. Fills the gap between tooth and restoration
2. Where there is no bond between the tooth and restoration
3. Does not provide direct retention

57
Q

Give 4 examples of passive luting cements (all water based as aqueous acid).

A
  1. Zinc phosphate
  2. Zinc polycarboxylate
  3. GI luting materials
  4. RMGI luting cements
58
Q

What is meant by luting cement being “pseudo plastic”?

A

Coats the fit surface of restoration without slumping, but flows readily under pressure on fitting.

59
Q

What are the key properties of glass ionomer as a luting cement?

A
  1. Fluoride release
  2. Bond to enamel and dentine
  3. Initial acidity (may cause pulpal inflammation)
60
Q

What are the advantages (5) of using RMGI over GI as a luting cement?

A
  1. Low solubility
  2. Improved biocompatibility
  3. Improved fluoride release
  4. Improved physical properties (tensile strength)
  5. Improved adhesion to tooth tissue
61
Q

Why should RMGI cement be avoided under all ceramic crowns?

A

Because it can undergo hygroscopic expansion, because there is exposed porcelain near margins in all ceramic crown, crack propagation could occur under expansion.

62
Q

Give an example of a commonly used RMGI luting cement?

A

Rely X luting cement

63
Q

What type of resin luting cement could be used with all ceramic restorations, indirect composite or quartz fibre posts (e.g. veneers, dentine bonded crowns)?

A

Conventional resin luting cements

64
Q

What type of resin luting cement could be used for adhesively bonding to metals (e.g. resin retained bridges, metal veneers, poorly retained indirect restorations)?

A

Chemically adhesive resin luting cements

65
Q

State the steps to micromechanically and chemically bond tooth to fit surface of ceramic using luting cement.

A
  1. Acid etch with hydrofluoric acid
  2. rinse, dry
  3. dentine bonding agent (silane coupling agent)
  4. Place cement
66
Q

What components of modified Bis-GMA adhesive resin luting cement have a high affinity for metal oxide on base metal alloys (bring about a chemical bond)?

A

4 META and MDP

67
Q

What were porcelain jacket crowns composed of?

A

Feldspathic porcelain with added alumina

68
Q

What are the disadvantages of porcelain jacket crown and why it is no longer used?

A

Needs at least 1-2mm tooth reduction, prone to fracture, more preferable alternatives.

69
Q

What is a coping?

A

A thin metal, resin or ceramic cap covering a prepared tooth.

70
Q

What does CAD-CAM stand for?

A

Computer aided design- computer aided manufacture

71
Q

What is the main advantage of using high alumina porcelain?

A

Can be etched

72
Q

Name an aesthetic, high-strength and etchable glass ceramic which is made using CAD-CAM technology and used for veneers, inlays/onlays, crowns and covering zirconia frameworks.

A

Lithium di-silicate glass ceramic (E-max)

73
Q

Name a porcelain-filled composite material used for provisional crowns?

A

Cermoeric restorations (shofu ceramage)

74
Q

Name 6 tooth coloured crown materials.

A
  1. Feldspathic porcelain
  2. Lithium disilicate ceramics
  3. All polycrystalline ceramics crowns
  4. Glass (leucite re-enforced)
  5. Ceromeric crowns
  6. Composite crowns
75
Q

What are the three ways to manufacture tooth coloured crowns?

A
  1. Addition of porcelain slurry
  2. Injection moulded/pressed/cast
  3. CAD-CAM
76
Q

What is the main advantage of adding aluminium to feldspathic porcelain and give an example of this material by trade name?

A

Increases its strength, procera.

77
Q

What is zirconia?

A

A polycrystalline ceramic which achieves its strength by sintering

78
Q

What does the incorporation of lithium disilicate into ceramic crown material result in?

A

Significantly increased strength with excellent aesthetics

79
Q

What does CAD/CAM stand for?

A

Computer aided design/ computer aided manufacture

80
Q

What are the three ways of recording a digital impression?

A
  1. Intra-oral scanner
  2. Digitise in lab conventional impressions
  3. Digitise in lab model cast from impression
81
Q

Give 4 examples of non contacting scanner systems

A
  1. Time of flight (emits radiation)
  2. Triangulation
  3. Parallel confocal imaging technique (utilises red light laser beams)
  4. Active wavefront sampling (rotation image capture)
82
Q

What are the patient factors affecting the accuracy of hand held scanners?

A
  1. Limited patient mouth opening
  2. Patient movement
  3. Saliva flow
  4. Intraoral humidity
83
Q

What are the anatomical factors affecting the accuracy of hand held scanners?

A
  1. Tooth form
  2. Tooth position
84
Q

STL file format is used in processing of standard digital data. What does STL stand for?

A

“Standrad triangle language” or “standard tessellation language”

85
Q

What is XML and why is it used?

A

Extensible Markup Language.
This is a software and hardware independent tool for storing and transporting data.

86
Q

What are the 4 main component parts of digital workflow?

A
  1. Data acquisition
  2. Design stage (CAD)
  3. Manufacturing stage (CAM)
  4. Final processing and treatment delivery
87
Q

What are the two main methods of data acquisition as part of digital workflow?

A
  1. Intra-oral scanning (IOS)
  2. Laboratory bench-top scanning
88
Q

What does DICOM stand for? And what is DICOM?

A

DICOM = digital imaging and communications in medicine.

DICOM is the international standard for medical images and related information.

89
Q

What technology do most conventional scanners use?

A

Structured light technology

90
Q

What is the material is the benchmark of digital fixed restorative output materials, holding the most benefit in terms of fit, function and aesthetics?

A

E.MAX CAD

91
Q

Name three RPD output materials?

A
  1. Laser Sintered chrome cobalt
  2. Flexible denture (milled)
  3. Acetal (milled)
92
Q

For each digitally designed denture, how many files are produced?

A

Two. One for the denture base and the other for the arch of teeth.

93
Q

What is used to accurately locate implants within an arch during implant data acquisition?

A

Scan body

94
Q

What is scan body?

A

A scannable object used to accurately translate the position of an implant in the oral cavity into a digital file that can be utilised within the implant design software.

95
Q

What is the leading material used in digital implant manufacture and why?

A

Titanium, due to its biocompatibility and strength-to-weight ratio.

96
Q

Name two examples of 3D surface imaging technologies that utilise parallel confocal microscopy and white light.

A
  1. ITero
  2. Trios
97
Q

Name an example of a 3D surface imaging technologies that utilise stereoscopic vision.

A

Direct scan

98
Q

Name an example of a 3D surface imaging technologies that utilises active wavefront sampling and blue light.

A

Lava COS system

99
Q

What type of cement would you use if you have a retentive tooth prep for crown and bridge?

A

Luting cements

100
Q

What type of cement would you use if you have a non-retentive tooth prep for crown and bridge?

A

Adhesive resin cement (bonding)

Dentistry Module 6 (15 decks)

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