DMS Flashcards

1
Q

What are the constituents of stainless steel and their proportions

A
  • Iron – 72%
  • Chromium – 18%
  • Nickel – 8%
  • Titanium – 1.7%
  • Carbon – 0.3%
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2
Q

What is work hardening

A
  • Work done at temperatures below recrystallisation temperature (such as bending, swaging or rolling)
  • This causes slip so any dislocations in the lattice collect at grain boundaries
  • This results in a stronger, and harder material
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3
Q

what is sintering (in regards to fabrication of a ceramic crown)

A

when the particles melt and fuse together as one mass

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4
Q

define springiness

A

the ability to undergo large deflections without permanent deformation

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5
Q

what are some disadvantages of self-cure PMMA

A
  • water absorption can cause expansion
  • poorer mechanical properties
  • unreacted monomer can act as irritant
  • poorer colour stability
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6
Q

what are some ideal properties of acrylic denture base

A

-high softening temp
- unaffected by oral fluids
- radiopaque
- non toxic, non irritant
- low density
- high strength, stiffness, hardness, toughness

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7
Q

why is mould liner used in fabrication of an acrylic denture

A

to prevent the penetration and adhesion of resin into the surface of the plaster mould
- it is usually a solution of sodium alginate

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8
Q

what is gaseous porosity and why does it happen?

A

when the temp exceeds boiling temp of PMMA before the polymerisation process is complete
–> should be carried out slowly to avoid

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9
Q

how is porcelain prepared in the lab to improve bonding

A

etched to hydrofluoric acid

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10
Q

what bonds porcelain to composite resin luting cement?

A

silane coupling agent

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11
Q

how does silane coupling agent act chemically

A
  • one end forms strong bonds b/w the oxide groups on the porcelain
  • the other end has C=C that bonds to the composite resin luting agent
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12
Q

when would youse use dual cured composite as a luting agent

A

when bonding to a metal, as light will not penetrate
i.e. when cementing most crowns, bridges, posts…

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13
Q

why would you do to a metal in a lab to prepare?

A

sandblast the metal surface

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14
Q

what chemical agent is used to bond metal?

A

MDP and 4-META

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15
Q

what metal can be use for an acid-etch retained bridge

A

non precious metal alloys e.g. CoCr, NiCr

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16
Q

What are the two main differences in composition between decorative and dental ceramic

A

Decorative ceramics contain Kaolin - makes it opaque in appearance
Dental ceramics need to be translucent so Kaolin is removed and feldspar and silica replace it
dental ceramics are glasses

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17
Q

Explain what the following terms mean with regard to optical properties of the materials
a. Translucency
b. Opalescence

A

Translucency is the relative amount of light transmission or diffuse reflection from a substrate surface through a turbid medium

The opalescence of dental materials is defined as the difference in chroma between the reflected and transmitted colours.

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18
Q

how does an alumina reinforced feldspathic core increase the strength of a ceramic crown

A

the alumina particles act as crack stoppers preventing cracks propagating through the material and causing fracture

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19
Q

what is a problem with alumina cored crowns

A

lacks flexural strength

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20
Q

what are the strongest crown types

A

monolithic block crowns - they are milled from a single block of material

21
Q

key comparison between crowns with layered and monolithic block crowns

A

layered =better aesthetics BUT more likely to chip due to stresses between core and crown

22
Q

For the same material a milled crown will be stronger than a built up or pressed crown. WHY?

A

the block will have been subjected to the ideal heat treatments to maximise tits properties and all blocks will be consistent

23
Q

what are some problems with zirconia cored crowns

A

expensive equipment required
Potential for veneering porcelain to debond from core

24
Q

what types of crowns are typically used in posterior teeth

A

Monolithic Zirconia

25
Q

what types of crowns are typically used in anterior teeth (single crown)

A

LiDiSi (up to premolar)

26
Q

what types of crowns are typically used for longer span or heavier occlusion

A

Zirconia cored with zirconia where occlusal contacts will meet

27
Q

what are the characteristics of PORCELAIN

A

Rigid - large stress to cause strain
Hard - withstands abrasion
Strong - high compressive strength
BUT
Tendency to form surface defects –> leads to fractures at low stress
Brittle

28
Q

what helps eliminate defects/cracks on porcelain surface

A

bonding to metal oxide - it acts as a support and limits the strain that porcelain experiences

29
Q

what are the required properties when choosing alloy for porcelain to fuse with

A
  • Good wetting
  • similar thermal expansion coefficient
    -discolouration
  • Mechanical = bond strength, hardness, elastic modulus
  • melting/recrystallisation temp of allow MUST be HIGHER than fusion temp otherwise CREEP
30
Q

define wetting

A

the ability of a liquid to form an interface with a solid surface

31
Q

define CREEP

A

gradual increase in STRAIN (permanent) experienced under prolonged application of STRESS

32
Q

what are WROUGHT ALLOYS

A

an alloy which can be manipulated by cold working

33
Q

what is an ALLOY

A

TWO metals that form a COMMON LATTICE structure are soluble in one another = Form a SOLID SOLUTION

34
Q

what are the 2 types of substitutional solid solutions

A

RANDOM - where both types of atoms in the lattice structure are arranged in random fashion.

ORDERED - can predict the type of atom based on its location.

35
Q

what is an interstitial solid solution

A

where the two atoms are markedly different in size

36
Q

define welding

A

a fabrication process whereby two or more parts are fused together by means of heat, pressure or both forming a join as the parts cool

37
Q

what are ways to mitigate the risks during the process of welding stainless steel

A

use of:
- low carbon steel - expensive
- stabilised SS (with small amounts of Ti and niobium)

38
Q

how are elastomers formed?

A

by polymerisation with cross-linking of polymer chains.

39
Q

what properties affect the ACCURACY by which the SURFACE features are recorded in elastomers

A

surface detail
flow/viscosity
contact angle/wettability

40
Q

what properties affect the ACCURACY by which the DIMENSIONS and SHAPE of final impression

A

elastic recovery
stiffness
tear strength

41
Q

define wettability and contact angles

A

determines how well the material envelops hard/soft tissue surface.

The contact angle indicates how readily the IM “wets” the tooth surface.
ie how closely the IM envelops the tooth surface.

42
Q

what does viscosity determine

A

a material’s potential for making close contact with hard/soft tissue surfaces

43
Q

what happens if an IM exhibits LARGE contact angles

A

it means the IM is more likely to have gaps between each globule of material. This means the IM won’t replicate the whole tooth surface.

44
Q

what is the term to describe an IM that has been stretched/compressed and it fails to return to its original dimensions/shape

A

permanent deformation

45
Q

what types of materials are temporary materials

46
Q

what are some problems with ZINC PHOSPHATE cement as a luting agent

A
  • low initial pH = can cause pulpal irritation
  • exothermic setting reaction
  • not adhesive to tooth/restoration (just fills spaces)
  • not cariostatic
  • brittle
  • final set takes 24nrs
47
Q

advantages with using ZINC POLYCARBOXYLATE cement

A
  • bonds to tooth surface
  • less heat during reaction
  • pH low to begin but returns to neutral more quickly
  • cheap
48
Q

disadvantages of using ZINC POLYCARBOXYLATE cement

A
  • difficult to mix and manipulate
  • soluble in oral environment at lower pH
  • lower modulus and compressive strength than zinc phospahte
49
Q

problems with RMGI (as a luting agent)

A

HEMA is cytotoxic
HEMA expands in wet environment
no bond to indirect restoration