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BDS2 - dental material science > intro to dental material science > Flashcards

intro to dental material science Flashcards

1
Q

what is the dental procedure

A
  • examination
  • diagnosis
  • treatment plan (which material is suitable, how to use material, explain options to patient, select material)
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2
Q

what is the effect of dental materials

A
  • selection = adequate, best type
  • preparation = cavity design, tooth surface
  • placement = technique, increments, curing
  • performance = quality of fit, longevity
  • patient expectations = aesthetics, durability
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3
Q

what does the dental material need to have to be safe

A
  • a CE mark = an essential requirement, show material is safe
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4
Q

why just you not assume new materials are good

A

manufactures are constantly making new materials, but art doesn’t mean that they are better
- should read about material before using it

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5
Q

what are different types of restorative materials

A
  • amalgam
  • composite
  • glass ionomer cements
  • compomers
  • porcelain
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6
Q

what are different types of impression materials

A
  • impression compound
  • impression paste
  • hydrocolloids = alginate mainly
  • elastomers = polysulphides, polyethers, silicones
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7
Q

what are different types of metals/alloys

A
  • amalgam
  • cobalt chromium
  • titanium
  • gold
  • stainless steel
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8
Q

what are challenges in choosing materials

A
  • so many materials to choose form
  • constant changes to products and names
  • range of brands
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9
Q

what is porcelain used for

A

veneers

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10
Q

what is composite resin

A

used for restorations

  • can come in cartridge or nozzle
  • low to high viscosities available
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11
Q

how do impression materials work

A
  • record dentition in negative replica
  • flows into trays at low viscosity
  • undergoes setting reaction - becomes firm, stable
  • gypsum (dental stone) = gives positive replica
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12
Q

what is PMMA

A

a denture base material

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13
Q

what are the mechanical properties of the materials

A
  • force applied to material
  • stress
  • strain
  • elastic modulus
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14
Q

what are some mechanical forces materials are subjected to

A
  • biting, chewing, grinding
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15
Q

what may happen to the material from the force applied to it

A
  • stretch/compress = depends on how force is applied
  • deform/ change shape = temporarily (during application) or permanently
  • fracture = failure
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16
Q

what types of force can be applied to the material

A
  • compressive = squeeze material
  • tensile = stretch
  • shear = object bonded to another surface and apply force along parallel line of object
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17
Q

what is stress

A

force acting on an area

18
Q

what is strain

A

change in length/original length

19
Q

what is the stress-strain curve

A
  • most materials have one
  • FS = fracture stress
  • star = proportional limit (up to here stress and strain are proportional)
  • elastic modulus is in mega pascals (its the slope)
20
Q

what is the elastic modulus

A
  • also called Young/s modulus

- is the rigidity/stiffness of the material

21
Q

what are the 4 mechanical properties and their opposites

A
  • hard / soft
  • strong / weak
  • rigid / flexible
  • ductile / brittle
22
Q

what mechanical properties does enamel have

A
  • hard
  • strong
  • rigid
  • brittle
23
Q

what is the typical biting force

A
  • is a compressive force applied to upper tooth when biting

- typical biting force = 500 to 700N

24
Q

what type of forces are grinding/chewing

A
  • shear forces
  • tooth slides along surface of another
  • frictional forces are applied
  • shear forces can remove restorations (material needs to adhere to enamel or it will be removed by masticatory forces)
25
Q

what is the differences between enamel and dentine

A
  • enamel is more rigid than dentine
  • fracture stress is higher in enamel
  • enamel FS = 262MPa, dentine = 234MPa
  • enamel PL = 235 MPa, dentine = 176MPa
  • enamel EM = 33.6 GPa, dentine = 11.GPa
26
Q

how does material influence cavity design

A
  • shape for amalgam quite distinctive compared to composite = needs to be bigger, splays outwards towards base of cavity
  • composite will bond to tooth, amalgam has mechanical retention = amalgam has no bond to tooth surface, needs undercut cavity shape to stay in place
  • material must be pliable, to fit shape of interest, must set to form a hard, strong material
27
Q

how can the material fail

A
  • fracture =large forces applied cause destruction go material structure
  • hardness = not hard enough to withstand forces
  • abrasion = material surface removed from grinding
  • fatigue = repetitive small forces cause fracture
  • creep = gradual shape change from small forces
  • de-bond = forces sufficient to break material-tooth bond
  • impact = large, sudden force causes fracture
28
Q

what is abrasion resistance

A

ability to withstand surface layers being removed, so compromising surface integrity

29
Q

what is the hardness test

A
  • stainless steel with weight on top of the point (indentor)
  • leave on surface of material for certain amount of time
  • hard material will have a very small indentation, soft material will have large indentation (notch)
  • hardness is about surface, not strength
30
Q

what is abrasion

A
  • tooth grinds/slides along opposing tooth surface
  • tooth surface is abraded- loss of material surface layers/material can fall off
  • causes roughened surface
31
Q

what is fatigue

A
  • most failures are not due to the application of a single load
  • not just from one stress, but lots of little stresses over time
  • when repeated loads are applied, small forces in a material grow allowing fracture
32
Q

what is creep

A
  • repetitive small forces cause a dimensional change

- from compressive forces

33
Q

how is permanent deformation caused

A
  • applying stresses greater than elastic limit
  • once released this stress it will not recover as its past the elastic limit of the material
  • causes permanent change in shape
34
Q

how are impression materials not permanently changed on removal

A
  • they will have some elasticity
  • when removing the tray, the material will have an elastic strain as its removed and will then have elastic recovery once removed
  • with the best material, can get 99.5% elastic recovery (never 100%)
35
Q

what causes debonding

A
  • shear forces

- to remove orthodontic appliances, shear forces are applied to separate the bracket material from tooth surface

36
Q

what are some other mechanical properties

A
  • ductility
  • brittleness
  • tear strength
37
Q

what are chemical properties of materials

A
  • setting mechanism
  • setting time
  • corrosive potential
38
Q

what are physical properties of a material

A
  • viscosity
  • thermal conductivity
  • thermal expansion
  • density
  • radiodensity
39
Q

what should you do when evaluating a material

A

compare its performance to the ideal properties

40
Q

how can the oral environment affect the materials

A
  • saliva
  • temperature variations
  • ph variations
  • oral bacteria
41
Q

why is there more in vitro evidence than in vivo evidence for materials

A
  • gathering clinical evidence is time consuming, costly and limited in scope
  • means there is less robust evidence for the performance of dental materials in vivo

BDS2 - dental material science (13 decks)

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