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Dental materials > Adhesion > Flashcards

Adhesion Flashcards

1
Q

Is tooth structure hydrophobic or hydrophilic?

A

Hydrophilic

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2
Q

Are most dental restorative materials hydrophobic or hydrophilic?

A

Hydrophobic

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3
Q

Define adhesion

A

Force that binds two dissimilar materials together by the attraction of atoms and molecules

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4
Q

Define Cohesion

A

Attraction between similar atoms/molecules within one substance

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5
Q

Name 3 stresses that weaken adhesive bonds

A
  • Thermal expansion coefficient (hot drink)
  • Dimensional changes
  • Moisture from tooth structure hydrating active groups in the material
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6
Q

Was is an adherent?

A

Surface of a material

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7
Q

What binds two solid adherents together?

A

An adhesive interface

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8
Q

How does water cling to a glass surface?

A

Via van der waal forces

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9
Q

What are the 5 factors governing adhesion?

A
  • Surface Energy/Tension
  • Viscosity of the adhesive
  • Wettability of substrate by adhesive
  • Contact angle
  • Surface roughness
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10
Q

Explain the atomic forces in the bulk of a solid/liquid

A
  • Atoms have attractive forces in all directions and are in dynamic equilibrium
  • The molecules inside are attracted to all
    molecules around them.
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11
Q

Explain the atomic forces at the surface of a solid/liquid

A
  • There is a net inward attraction to the bulk atoms

- These forces result in a Surface Energy/Tension

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12
Q

What is the difference between Surface energy and Surface tension?

A
  • Surface energy (solids)

- Surface tension (liquids)

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13
Q

How do you measure surface tension?

A

Wilhelmy Plate method

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14
Q

Why is PTFE (polytetrafluoroethylene) difficult too wet?

A

Has a low surface energy

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15
Q

Typically do metals have high or low surface energies?

A

High surface energies

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16
Q

What can reduce surface energy/tension?

A
  • Increasing temperature
  • Presence of impurities
  • Surface active agents (surfactants in soaps)
17
Q

Comment on the viscosity of a good adhesive

A
  • Should be able to spread easily but not too easily

- If too viscous then flow is too slow and cannot penetration surface crevices

18
Q

Give an example of good wettability

A
  • Wetting of metal with water

- Water flows across and spreads

19
Q

Give an example of poor wettability

A
  • Wetting of PTFE with water

- Water forms globules (does not spread)

20
Q

What is wettability?

A

NO LECTURE DEFINITION
BUT GENERALLY….

How easy water can spread across a surface, ie droplet of not.

21
Q

Name 3 factors that affect wettability

A
  • Surface cleanliness
  • Surface irregularities
  • Viscosity of adhesive
22
Q

What is the contact angle?

A

Angle between liquid and solid interface

23
Q

What is the contact angle for perfect wetting adhesion? What does this mean?

A
  • Contact angle = 0
  • surface completely covered with adhesive
  • Therefore maximum bond strength is achieved
24
Q

How does increasing surface roughness affect adhesion?

A
  • Improved bond strength

- More difficulty for adhesive penetration due to trapped air

25
Q

How do surface irregularities affect bond strength?

A
  • Increase bond strength

- More bonds created

26
Q

Name 4 types of adhesive bonds

A
  • Mechanical
  • Physical
  • Chemical
  • Molecular entanglement
27
Q

How do mechanical adhesive bonds work? (2)

A
  • Have interlocking components between substrate and adhesive
  • Adhesive penetrates pits and undercuts
28
Q

How do physical adhesive bonds work? (2)

A
  • Dipole-Dipole interactions between polar molecules

- Small VDW forces

29
Q

How do chemical adhesive bonds work? (2)

A
  • Bonding at the molecular/atomic level

- Chemisorption (chemical reaction with adsorption)

30
Q

What is molecular entanglement?

A

Usually a combination of mechanical, physical and chemical bonding

Dental materials (8 decks)

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