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
what is the differences between enamel and dentine
- 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
how does material influence cavity design
- 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
how can the material fail
- 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
what is abrasion resistance
ability to withstand surface layers being removed, so compromising surface integrity
29
what is the hardness test
- 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
what is abrasion
- tooth grinds/slides along opposing tooth surface - tooth surface is abraded- loss of material surface layers/material can fall off - causes roughened surface
31
what is fatigue
- 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
what is creep
- repetitive small forces cause a dimensional change | - from compressive forces
33
how is permanent deformation caused
- 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
how are impression materials not permanently changed on removal
- 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
what causes debonding
- shear forces | - to remove orthodontic appliances, shear forces are applied to separate the bracket material from tooth surface
36
what are some other mechanical properties
- ductility - brittleness - tear strength
37
what are chemical properties of materials
- setting mechanism - setting time - corrosive potential
38
what are physical properties of a material
- viscosity - thermal conductivity - thermal expansion - density - radiodensity
39
what should you do when evaluating a material
compare its performance to the ideal properties
40
how can the oral environment affect the materials
- saliva - temperature variations - ph variations - oral bacteria
41
why is there more in vitro evidence than in vivo evidence for materials
- 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