Applied Surface Phenomena Flashcards
Surface tension
The attraction force exists between the atoms or molecules of a liquid
Factors affecting surface tension
- Nature of the liquid molecules
- Temperature & Chemical impurities
decrease the cohesive force between surface atoms so decrease the surface tension
Surface energy
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
Wettability
The ability of liquid to spread over solid surface
Contact angle
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
Clinical significance of wettability
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
Factors affecting wettability
Surface energy of solid ⬆️ wettability ⬆️
Surface tension of liquid⬇️wettability ⬆️
Adhesion
Bonding of dissimilar materials by attraction of atoms or molecules
Ex. Denture retention by thin film of saliva
Adhesive
The material or film added to produce adhesion
Adherent
Solid material to which the adhesive is applied
Cohesion
Bonding of similar materials by attraction of atoms or molecules
Ex. Bonding two gold pieces together under pressure results from metallic bond
Clinical significance of adhesion
- 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
Types of bonding
Theories of adhesion
Chemical bond adsorption adhesion
Mechanical bond
Diffusion adhesion
Electrostatic adhesion
Chemical bond
Chemical bonding between adhesive and adherent
Primary bonds true adhesion
Ex. Glass ionomer and zinc polycarboxylate with tooth
Mechanical bond
Interlocking of the adhesive with irregularities in the surface of the adherent
It classified to macromechanical retention
micromechanical retention
Macro-mechanical retention
Can be seen by naked eye and interlocking between two substances occur
Ex. undercuts screws
Micro-mechanical retention
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-
Diffusion adhesion
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
Electrostatic adhesion
A difference in electrostatic charge constituents at the interface may contribute to the force at attraction bonding
Factors affecting adhesion
Factors related to adherent
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
Factors related to adhesive
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
Increase adhesion
-Surface energy.
⬇️viscosity
-↑ Flow.
⬇️ thickness.
-↑ wetting
Decrease adhesion
surface irregularities.
Cleanliss on the adherent-
-⬆️surface tension-
- Thermal stress
-Dimensional changes.
Factors related to adhesive and adherent
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
Mode of failure of an adhesive function
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.
