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Module 6 Exam > Dental Materials > Flashcards

Dental Materials Flashcards

1
Q

FRC: Why are carbon graphite and aramid fibres not used anymore?

A

Aesthetic issues

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2
Q

FRC: What types of fibres are used in dentistry?

A

Glass

(E- glasses, R-glasses and S-glasses)

eat red strawberries !

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3
Q

Describe the structure of FRC

A

A polymer matrix with fibres.

Semi interpenetrating polymer network (semi-IPN) combination of linear polymer with a cross linked polymer.

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4
Q

What polymers are in dental resin systems?

A

bis-GMA, TEGDMA, UDMA

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5
Q

What three factors will effect the resin impregnation of the fibres?

A
  1. Surface wetting properties of the fibres by the resin
  2. The distance of individual fibres from each other in the fibre product
  3. The viscosity of the resin material
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6
Q

How is the resin impregnated into the fibres?

A

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

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7
Q

FRC: silanation

A

Fibres are pretreated with silanes “coupling agents” which are antistatic compounds (help bonding of fibres to matrix) - they also improve the surface wetting of the fibres

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8
Q

FRC: Unidirectional fibres

A

Uses: posts, fixed prosthodontics

Good tensile strength

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9
Q

FRC: Bidirectional fibres

A

Uses: dental bridge frameworks, splints, removable dentures

Good flexural and tensile strength

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10
Q

FRC: random orientation

A

Uses: provisional restorations

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11
Q

FRC: woven fabric

A

Uses: orthodontic applicances, indirect restorations

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12
Q

FRC: What is volume fibre fraction?

A

More fibres = better strength etc

Too many fibres = affects flow ability of the composite (handling issues upon placement)

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13
Q

FRC: fibre length

A

Long = transfer stress more efficiently, decreased mechanical properties

Short = better material handling, less risk of fibre agglomeration

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14
Q

Traditional casting gold alloys: type 1 (name and uses)

A

Low strength - inlays

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15
Q

Traditional casting gold alloys: type 2 (name and uses)

A

Medium strength - inlays/onlays

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16
Q

Traditional casting gold alloys: type 3 (name and uses)

A

high strength - onlays, thin cast backings, pontics, full crowns

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17
Q

Traditional casting gold alloys: type 4 (name and uses)

A

extra high strength - saddles, bars, clasps, crowns, bridges, and partial denture frameworks.

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18
Q

Gold content: carat

A

Parts by weight of gold in 24 parts alloy

75% gold is 18 carat

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19
Q

Gold type 1: Percentage composition

A

gold (Au) ——-—-> 85
silver (Ag) ———–> 11
copper (Cu) ——–> 3
pallidium (Pt/Pd) -> —
zinc (Zn) ————-> 1

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20
Q

Gold type 2: percentage composition

A

gold (Au) ——-—-> 75
silver (Ag) ———–> 12
copper (Cu) ——–> 10
pallidium (Pt/Pd) -> 2
zinc (Zn) ————-> 1

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21
Q

Gold type 3: composition percentage

A

gold (Au) ——-—-> 70
silver (Ag) ———–> 14
copper (Cu) ——–> 10
pallidium (Pt/Pd) -> 5
zinc (Zn) ————-> 1

22
Q

Gold type 4: composition percentage

A

gold (Au) ——-—-> 65
silver (Ag) ———–> 9
copper (Cu) ——–> 15
pallidium (Pt/Pd) -> 10
zinc (Zn) ————-> 1

23
Q

What can be said for alloy strength as gold content decreases?

A

As gold % decreases (type 1–> 4) strength increases.

Ductility and corrosion resistance decreases though.

24
Q

“Low gold alloys”

A

Gold content ~45-50%
high palladium (“white in colour”)

Classified as type 4 —> cheap with good clinical performance.

25
Q

Which types of gold alloys can be further hardened and why?

A

Type 3 and 4 —> by used of heat treatments

Cannot do this for type 1 and 2 as there is insufficient quantities of copper and silver to achieve this.

26
Q

What is the difference between ceramic and porcelain?

A

Ceramic is the raw material which when combines with other minerals such as silica and feldspar become porcelain.

27
Q

What is added to the porcelain to control pigments for tooth aesthetics?

A

metal oxides

28
Q

The porcelain powder has been mixed with water and now is in an aqueous plastic mass, what does this undergo next?

A

Compaction
- brings out excess water, this reduces the porosity and thus reduces the firing shrinkage.
- also ensures uniform shrinkage (so the shape of the crown is not compromised)

29
Q

Following compaction of the porcelain, what is the next stage?

A

Firing in the furnace (occasionally under vacuum)
- vacuum can also aid porosity reduction
- MUST be dry (otherwise steam forms and there will be crumbling or even explosion of the material)

30
Q

How could firing of the porcelain cause blackening and how could this be avoided?

A

The binders included in the material (sugar/starch) ignite, it’s important the door is left ajar to allow the contents of combustion to escape and avoid blackening of the surface of the material

31
Q

Why is glazing advantageous for porcelain after firing?

A

Aesthetics improved and improves the surface of the material through “filling in the gaps” etc

32
Q

What is a way in which crack propagation is avoided in ceramics?

A

Compressive strength (to counteract the tension stress which causes the cracks)

33
Q

Ceramics: glassy vs crystalline

A
34
Q

Feldspathic porcelain crowns

A
35
Q

Lithium disilicate glass ceramic crowns

A
36
Q

Zirconia crowns

A
37
Q

Examples of passive luting cements

A

Zinc phosphate
Zinc polycarboxylate
GI luting materials

38
Q

Why might Zinc phosphate or zinc polycarboxylate cause issues post-op?

A

Low pH —> irritating too the pulp (Zinc phosphate’s pH is lower)

39
Q

What must you have to be able to use a passive luting cement?

A

Retention resistance form (based off your prep)

40
Q

What is Rely X luting (3M ESPE)?

A

Resin modified glass ionomer cement (active luting cements)

41
Q

Why are GI luting cements still considered passive despite forming intermediate bonds on to the dentine?

A

Although glass ionomers form intermediate layers on dentin they do not bond to materials etched by hydrofluoric acid or treated with silane and are considered passive.

42
Q

What are uses of conventional RLCs and chemically adhesive RLCs?

A

Conventional = all ceramic restorations, indirect composite (i.e. veneers, dentine bonded crowns)

Chemically adhesive = adhesively bonding to metals (i.e. RRBs, metal veneers etc)

43
Q

What must you do to prep the ceramic before it can be bonded to tooth structure?

A

IN THE LAB —> hydrofluoric acid etching
THEN ON CLINIC—> silane coupling agent applied and air dried.

44
Q

High alumina porcelain

A

Can be etched
Opaque —> good for hiding metal?

45
Q

Zirconia bonding process

A

 CANNOT ETCH, CANNOT BOND – MUST have a luting cement!
• Sandblasting with silica, then silanate
• Possible to fire feldspathic glaze onto the fit surface and etch that…

46
Q

Why might ceramics be made/milled larger than intended before firing?

A

to account for the ~20% shrinkage that occurs during firing

47
Q

When can calcium hydroxide be used as a luting cement, and why is it advantageous?

A

Used as a provisional luting cement, high pH means it’s not at risk of irritating the pulp (direct pulp capping)

48
Q

What is TempBond, and when is it used?

A

zinc-oxide eugenol-based temporary cements - for provisional cementation (i.e. temporary crown)

49
Q

How does eugenol interrupt the polymerisation of resin and why is this important in dentistry?

A

Eugenol may be in the temporary cement used for the provisional crown, it is VITAL this is properly removed before permanent cementation with a resin-based cement as any residual eugenol can act as a scavenger and prevent the polymerisation of the resin and thus the bond strength!

50
Q

Parallel confocal imaging technique

A

Uses red light laser beams, pass through focussing optics, leaves scanner hits object surface —> intensity of reflected light is measured.

51
Q

Active Wavefront sampling

A

Camera that rotates rapidly, taking lots of images as it spins —> these are collated and depth can be determined using photogrammetric principles.

52
Q

Time-of-flight imaging systems

A

Emit some kind of radiation, detects the reflection of that radiation back to scanner —> times how long this takes —> allows for depth perception.

Module 6 Exam (10 decks)

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