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DMS > General > Flashcards

General Flashcards

1
Q

3 types of forces applied to materials

A
  • compressive
  • tensile
  • shear
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2
Q

Stages of material selection effected by material characteristics

A
  1. selection (adequate)
  2. preparation required (surface on/cavity design)
  3. Placement (curing/increments)
  4. Performance (fit/longevity)
  5. Patient expectations (aesthetics/durability)
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3
Q

5 restorative materials

A
  1. Amalgam
  2. Composite
  3. Glass ionomer cements
  4. Compomers
  5. Porcelain
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4
Q

4 impression materials

A
  1. Impression compound (non-elastic)
  2. Impression paste (non elastic)
  3. Hydrocolloids (alginate)
  4. Elastomers (polysulphides, polyethers, silicones)
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5
Q

3 properties of any material

A
  • chemical
  • physical
  • mechanical
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6
Q

3 outcomes of forces applied to materials

A
  • stretch/compression
  • deform (temp/permanent)
  • fracture (failure)
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7
Q

What is stress to a material

A

Force/area where force applied = pascal (Pa) - changed to giga pascals (GPa)

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8
Q

What is strain to a material

A

Change in length / original length = strain (ratio of change in length)

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9
Q

Explain the proportionate limit (stress strain graph)

A

Where stress and strain changes become non linear (leads to fracture - fracture stress)

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10
Q

Opposites of each mechanical property of materials (I.e hard and soft)

A
  • Strong and weak
  • rigid and flexible
  • ductile and brittle
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11
Q

Explain the elastic modulus of a material

A

Lower gradient of stress strain graph means a lower elastic modulus

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12
Q

causes of failure to a material (7)

A
  1. fracturing (large force causing catastrophic destruction to structure)
  2. impact (large force causing fracturing)
  3. fatigue (repetitive small stresses causing fracture)
  4. permanent deformation (no fracturing, when releasing stress > elastic limit)
  5. abrasion (surface removed by grinding)
  6. lack of hardness (allows to be indented)
  7. de-bond (forces enough to break bond)
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13
Q

physical properties of materials

A
  • viscosity
  • thermal conductivity
  • thermal expansion
  • density
  • radiodensity
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14
Q

chemical properties of materials

A
  • setting mechanism
  • setting time
  • corrosive potential
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15
Q

explain the acid etch technique

A
  • 35% phosphoric acid acts on Ca2+ of hydroxyapatite
  • roughens surface by decalcifying causing exposure of collagen fibres for more molecular entanglement and removes smear layer increasing surface energy
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16
Q

why is it hard to bond to dentine

A
  • more organic (water puddles from tubules but material hydrophobic)
  • low surface energy
  • inconsistent structure (soft then hard)
  • smear layer
17
Q

describe technique to bond to dentine

A
  1. etching = removes smear layer exposing tubules and roughens surface
  2. wetting agent used to increase surface energy (bonding agent covers tubules)
18
Q

describe the 3 types of bonding (normally all used together)

A
  1. mechanical (physical interlocking of structures i.e. enamel and some dentine with composite)
  2. chemical adhesion (ionic bonds with mineralised part but mostly covalent bonds with organic regions
  3. van der walls adhesion (dipole interaction between bonding agent and substrate)
19
Q

describe critical surface energy (why bonding agent used on dentine?)

A

liquid must have lower surface energy than surface placed on to flow and stick
- as dentine wet has lower surface energy than composite so bonding agent fixes this

20
Q

what is a surface wetting agent

A

bonding agent (as increases surface energy allowing materials to stick)

21
Q

describe the action of a wetting agent and what its 4 property requirements

A

meshes with acid cured surface via molecular entanglement
1&2. ability to flow and low viscosity
3. ability to make good contact with dentine
4. adhesion to substrate via van der walls, chemical, mechanical or all of the above

22
Q

describe what the smear layer is and how we deal with it

A
  • layer of debris on dentine contaminated with bacteria
  • either remove by etch [total etch] or incorporate [self etch] via bonding agent penetrating it (can allow leaking thus hydrolysis)
23
Q

two types of etching

A
  1. total etch

2. self etch

24
Q

explain what total etch is

A
  • 3 components
    1. dentine conditioner
    - removes smear layer (decalcifying) while hardly demineralising HA
    2. primer (bonding agent) = double headed molecule, one phobic one phylic
    3. adhesive = resin that penetrates now hydrophobic tubules and has molecular entanglement with tubules and collagen fibres = forms hybrid layer (hydrophobic with camphorquinone)
25
Q

give an example of a primer

A

HEMA (hydroxy ethyl methacrylate)

  • Methacrylate head = hydrophobic
  • hydroxyl head polar bonds to similar regions of HA
26
Q

Photoinitiator put in materials for curing

A

camphorquinone

27
Q

issues with total etch

A
  • can over etch meaning collagen fibres collapse or too deep and etch as so primer cant reach mineralised dentine
  • too wet means is diluted and too dry means surface too smooth and only tubules as means collagen fibres collapse
28
Q

describe what self etch is

A
  • solution contains etch, primer and adhesive in one (or etch separate)
  • incorporates smear layer into hybrid later via dissolving it
  • good as less technique sensitive and less chance of post op sensitivity due to no drying stage = no breakdown of dentine architecture
  • bad as not as strong bonding and lower pH may not etch as well
  • ## uses bifunctional molecule (acidic methacrylate monomers (etch and infiltrate dentine with hydrophilic end and while usual polymerising at hydrophobic end)
29
Q

describe what self etch is

A
  • solution contains etch, primer and adhesive in one (or etch separate)
  • incorporates smear layer into bonding
  • good as less technique sensitive and less chance of post op sensitivity due to no drying stage = no breakdown of dentine architecture
  • bad as not as strong bonding
  • uses bifunctional molecule (acidic methacrylate monomers
30
Q

what primer and solvent are used in a primer and adhesive mix for self etch

A

Bis-GMA and alcohol or acetone

31
Q

draw backs to strong self etch compared to mild

A

breaks down too much HA so not as good ionic bonding and liable to allow breakdown of collagen fibres

32
Q

blacks cavity classification

A 
class i = pit and fissure caries
ii = posterior approximal caries
iii = anterior approximal caries 
iv = anterior approximal carries effecting incisal angle
v = caries effecting cervical surfaces
vi = carries effecting cusp tips

DMS (8 decks)

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