Adhesion principles 1

Question 1

Adhesion definition

Answer 1

= an attraction phenomenon between 2 different materials brought together in an intimate contact.
It occurs due to the attraction F which is exerted between the particles of the 2 materials brought at very small distances (like a molecule).

Question 2

Cohesion

Answer 2

=an attraction phenomenon between the atoms or similar molecules of the same material.
It explains the opposite resistance of the material at the attempt of physical disintegration.

Question 3

Applications of the adhesive techniques

Answer 3

sealing the pits and fissures
• bonding of the brackets on the teeth’s surfaces
• desensitization of the zones which have a hypersensitive dentin
• composite restorations
• fixedoradhesiveamalgamfillings
• direct veneers
• bonding of the composite or ceramic prosthetic restorations (veneers, inlays, onlays, adhesive bridges)
• repairs of the ceramic veneers of a FPD
• bondingofthefractureddentalfragments
• adhesive repairs over prepared dental abutments
• dental splints

Question 4

The adhesion between solid materials

Answer 4

microscopic rough surfaces the intimate contact at the microscopic level is difficult to be obtained, because the maximum distance between the molecules of the 2 materials = 0.7nm
It is necessary an intermediate medium in a fluid state = ADHESIVE

Question 5

The adhesion between a solid and a fluid material

Answer 5

s based on the capacity of the liquid to get into close contact with a larger surface of the solid, in order to form physical, micromechanical, chemical or intermolecular bonds
• E.g.:theadhesive(A)overtheharddentaltissue(B)(enamelor dentine)

Question 6

Necessary conditions to obtain the adhesion between a solid and a fluid material

Answer 6

1.
2. 3.
a good wettability of the adherent by the adhesive
a low viscosity of the adhesive
a low surface roughness of the adherent

Question 7

WETTABILITY

Answer 7

= the ability of the adhesive to realize an intimate contact with the whole surface of the adherent

• The wettability is a specific property of the adhesive for a certain adherent
• The interaction between the solid and the liquid is influenced by the surface Forces

Question 8

wettability

Answer 8

the intensity of the surface F depends on :
- superficial energy (on the surface) of the adhesive
- superficial energy of the adherent
-the surface energy of the liquids =surface tension
-intermolecular forces F which determine the drops formation (minimal surface, so a minimal surface energy for a given volume)

Question 9

gettability and contact angle

Answer 9

The wettability of an adhesive onto an adherent can be measured with the help of the contact angle between a liquid drop and the surface of the adherent

smaller—>better larger—>worse

Question 10

hydrophilicity and hydrophobicity

Answer 10

• Hydrophilic material = solids with surface energy&raquo_space; water

* Hydrophobic material = solids with surface energy

Question 11

how to increase the surface energy of the adherent

Answer 11

Appliance of the surface-active substances (detergents, emulsifiers, dispersion agents)
Solids with low surface energy
Increasing the surface energy of the adherent
E.g.:
- Washing the wax-pattern with detergents before investment materials
- Acid etching of the dental enamel

Question 12

Necessary conditions to obtain the adhesion

Answer 12

1.
2.
3.
Necessary conditions to obtain the adhesion
a good wettability of the adherent by the adhesive
a low viscosity of the adhesive
a low surface roughness of the adherent

Question 13

The viscosity of the adhesive

Answer 13

A high viscosity restrain the flow of the adhesive through the micro crevices of the adherent
!!! the values of the contact angle are directly proportional with the viscosity of the adhesive
Penetration coefficient (PC) =the capacity of a liquid to infiltrate the capillary spaces
γ = surface tension of the adhesive
θ = the angle between the adhesive and the adherent η = viscosity of the adhesive

Question 14

The surface roughness of the adhesive

Answer 14

The adherent roughness can affect:
- – increase of the surface for the contact with the adhesive
- – due to contamination with air or other substances Micro crevices= capillaries
•If the adhesive has a high surface tension => high capillary F = the adhesive will infiltrate into micro crevices and it will driven out the air
•Surface tension of the adhesive

Question 15

Necessary conditions to obtain the adhesion -conclusion-

Answer 15

1. 2. 3.
      Necessary conditions to obtain the adhesion -conclusion-
      the surface of the adherent has to be perfectly cleaned, without any contamination
      air/water removal from the micro crevices before the appliance of the adhesive
      the surface tension of the adhesive has to be slightly ↓ than the surface energy of the adherent
      Micro crevices of the adherent = advantage for an efficient adhesionthrough :
      - the increase of the available surface to chemically react with the adhesive
      -Mechanical retentions, if there is a retentive morphology of the micro crevices