Applied Surface Phenomena

Question 1

Surface tension

Answer 1

The attraction force exists between the atoms or molecules of a liquid

Question 2

Factors affecting surface tension

Answer 2

1. Nature of the liquid molecules
2. Temperature & Chemical impurities
   decrease the cohesive force between surface atoms so decrease the surface tension

Question 3

Surface energy

Answer 3

The attraction force exists between the atoms or molecules of a solid

High energy surface attract the molecules of the liquid when it contact with the solid surface

Question 4

Wettability

Answer 4

The ability of liquid to spread over solid surface

Question 5

Contact angle

Answer 5

The angle between the solid surface and the line tangents to the curved surface of the liquid at the point of three planes

The smaller the contact angle more acute the better the wetting

Acute contact angle good wetting
Obtuse contact angle poor wetting
0 contact angle perfect wetting

Question 6

Clinical significance of wettability

Answer 6

The application of fluoride will reduce the accumulation of plaque as a result if reducing of the enamel surface energy

Addition if surfactants to hydrophobic addition silicone

Question 7

Factors affecting wettability

Answer 7

Surface energy of solid ⬆️ wettability ⬆️
Surface tension of liquid⬇️wettability ⬆️

Question 8

Adhesion

Answer 8

Bonding of dissimilar materials by attraction of atoms or molecules

Ex. Denture retention by thin film of saliva

Question 9

Adhesive

Answer 9

The material or film added to produce adhesion

Question 10

Adherent

Answer 10

Solid material to which the adhesive is applied

Question 11

Cohesion

Answer 11

Bonding of similar materials by attraction of atoms or molecules

Ex. Bonding two gold pieces together under pressure results from metallic bond

Question 12

Clinical significance of adhesion

Answer 12

• Denture retention by thin film of saliva
• Reduction of tooth preparation needed for retention of restorations
• Good bonding between tooth structural and restoration is important for reducing microleakage
• Reduction of post operative pain and pulp sensitivity caused by leakage
• Prevention of tooth decay by sealing of fissures and pits

Question 13

Types of bonding
Theories of adhesion

Answer 13

Chemical bond adsorption adhesion
Mechanical bond
Diffusion adhesion
Electrostatic adhesion

Question 14

Chemical bond

Answer 14

Chemical bonding between adhesive and adherent
Primary bonds true adhesion
Ex. Glass ionomer and zinc polycarboxylate with tooth

Question 15

Mechanical bond

Answer 15

Interlocking of the adhesive with irregularities in the surface of the adherent
It classified to macromechanical retention
micromechanical retention

Question 16

Macro-mechanical retention

Answer 16

Can be seen by naked eye and interlocking between two substances occur

Ex. undercuts screws

Question 17

Micro-mechanical retention

Answer 17

Can’t be seen by naked eye

acid etch technique for composite resin bonding (infiltration of adhesive resin into micropores created by acid etching). Composite + tooth structure → micromechanical.

Composite + adhesive -chemically

adhesive +tooth structure → micromechanical-

Question 18

Diffusion adhesion

Answer 18

A bond between two surfaces may be formed by inter diffusion of atoms across the interface

Ex. Adhesion between porcelain and metal in PFM restoration

Question 19

Electrostatic adhesion

Answer 19

A difference in electrostatic charge constituents at the interface may contribute to the force at attraction bonding

Question 20

Factors affecting adhesion
Factors related to adherent

Answer 20

A-Surface energy

✓ ⬆️ SE ⬆️Wetting ⬆️Adhesion

B-Surface irregularities

Rough surface provides mechanical means of retention & increase surface area for adhesion, but air pockets may be created prevent complete wetting of the entire substrate-⬇️Adhesion

C-Cleanliness on the adherent

✓Debris on the surface will prevent direct contact between adhesive and adherent ⬇️strength of adhesion

Question 21

Factors related to adhesive

Answer 21

A-Surface tension

⬆️ST⬇️ Wetting ⬇️Adhesion

B-Viscosity

✓ Low viscosity of the adhesive ⬆️flow on the surface of the adherent ⬆️strength of adhesion.

C-Thickness

Thin film thickness of the adhesive ⬆️strength of adhesion because the possibility of cohesive failure of the adhesive layer becomes too low.

D-Wetting

✔The more wetting of the adherent surface by the adhesive ⬆️strength of adhesion

Question 22

Increase adhesion

Answer 22

-Surface energy.

⬇️viscosity

-↑ Flow.

⬇️ thickness.

-↑ wetting

Question 23

Decrease adhesion

Answer 23

surface irregularities.

Cleanliss on the adherent-

-⬆️surface tension-

• Thermal stress

-Dimensional changes.

Question 24

Factors related to adhesive and adherent

Answer 24

Thermal stress
✔ Different coefficient of thermal expansion between adhesive & adherent ⬇️strength of adhesion.

B-Dimensional changes during setting

✓ Liquid adhesives undergo contraction during setting and also the adherent may show contraction during setting creation of stresses at the interface ⬇️strength of adhesion

C-Type of bond formed

✓ Primary bonds formed. stronger adhesion than if secondary bonds are formed

Question 25

Mode of failure of an adhesive function

Answer 25

Adhesive failure:

✓ This occurs at the interface between adherent and adhesive.

Cohesive failure:

✓ Fracture occurs within the adhesive or adherent materials.

Mixed failure:

✓ Where adhesive and cohesive failure occur.