Adhesion simplified

1. Adhesion and Surface
Phenomenon
Dr Ambreen Azam
MSc Dental Materials, UK

2. Analyze the surface properties and its
effects on adhesion.
Describe the components of an adhesive
junction and their role.
What is adhesion & How it takes place.
What factors affect adhesion
Enlist the Criteria for successful bonding
Application of adhesion on tooth
structure
INTENDED LEARNING OUTCOMES

3. Surface is the outermost layer of an object
or a material
When two surfaces face each other they
form an interface. Related Important
concepts:
Adhesion
Surface energy and surface tension
Contact Angle
Wettability.
What is Surface?

4. Different techniques to analyze surface
PHOTO EMISSION SPECTROSCOPY
Shows presence of contamination on the surface.
ELECTRON SPECTROSCOPY
Study structure and dynamics of surface atoms
AUGER ELECTRON SPECTROSCOPY
Provides depth profiles of elements
METHODS TO ANALYZE SURFACE

5. Surface attachment process between two dissimilar substances is
called adhesion.
Formation of bond at interface
Cohesion same kind of molecules involved
Bonding of similar materials at their interface
Like joining two metal pieces together by welding
Adhesive & cohesive forces
Adhesion and cohesion co-exist
ADHESION

6. COMPONENTS OF ADHESIVE JUNCTION & TYPES OF
ADHESION
Adherend & adhesive together form an adhesive joint.
Adhesive is a material used to produce adhesion. e.g.
bonding agent.
Adherend is the surface where adhesive is applied
Mechanism of surface attachments:
Mechanical bonding / Adhesion
Chemical bonding/ Adhesion
Physical Adhesion
Results in Wetting of the surface
Adherend 1
Adherend 2
Adhesive System
or Luting Cement
Interface 2
Interface 1
Tooth Restoration
Adhesive Joint

7. MECHANICAL ADHESION
May involve penetration of adhesive
into microscopic irregularities present
in the surface of the substrate.
Micro mechanical adhesion
On hardening these adhesive
projections provide anchorage for
mechanical attachment.
Substrate 2
Surface
Irregularities
Adhesive

8. Adhesive possess chemical affinity for the adherend surface
Covalent and ionic links result in stronger attraction
Waander waal,s or secondary bonding results in weaker
adhesion
GIC bonds chemically with the tooth structure
CHEMICAL ADHESION

9. PHYSICAL ADHESION
Retention of a denture with the oral mucosa having a
thin film of saliva between the denture and the tissue
surface is called physical retention or physical
adhesion.

10. SURFACE ENERGY & SURFACE TENSION
 Energy at the surface of the solid is greater than that of its
interior.
 Important consideration for an adherend.
 Surface energy can be regarded as measure of the excess
energy/ reactivity at the surface of material.
 When another material attaches to the surface the
surface free energy is reduced. For example; Impurity.
 Metals have high surface energy and adsorb molecules
more readily onto the surface. For example Tarnish &
Corrosion.
 Waxes have low surface energies. Interior atom
Surface Atoms .

11. Due to the intermolecular bonds or cohesive
forces between the molecules of a liquid.
It gives them a spherical shape as a sphere has
the smallest possible surface area to volume ratio.
Surface tension is the increase in energy per unit
area of the surface.
Chemistry of surface layer more important than
the bulk properties
SURFACE ENERGY & SURFACE TENSION

12. Surface active agent (Surfactant)
effect the surface tension at the
liquid-air interface.
Occupy surface positions displace
surface molecules
Reduce cohesive forces over the
surface area.
SURFACTANT

13. Wetting or wettability is the relative affinity of a liquid for the surface of
the solid.(Important for the adhesive)
The ease with which the liquid will flow onto the surface the more will be
the wettability
Defined as the interfacial tension b/w liquid and the solid substrate
having a contact angle of 0 degrees.
Wettability of a liquid is the function of surface tension at interfaces.
WETTING

14. Wetting can be measured by measuring the angle
of contact between the liquid and the solid
surface.
It is due to a balance b/w surface and interfacial
energies.
Lower the contact angle greater the ability to wet
the surface . Complete wetting occurs at 0
degrees. No wetting will occur at 180 degrees.
CONTACT ANGLE

15. DIFFERENT CONTACT ANGLES
Surface energy will

16. If surface tension of adhesive is high there is
decreased wetting or vice versa.
If viscosity of adhesive is high there is decreased
wetting.
Film thickness of adhesives low better flow, better
wetting.
Wetting important in adhesive materials
FACTORS EFFECTING WETTING
1- ADHESIVE RELATED FACTORS

17. Surface cleanliness increases surface energy promotes adhesion.
Surface irregularities if shallow will promote mechanical interlocking
increasing adhesion but if too deep will prevent adhesive from flowing in
to them thus decreasing adhesion.
 Surface energy of the adherend should be greater than the surface
tension of the adhesive.
Type of bond if it is a primary bond stronger adhesion as compared to
secondary bonds
Thermal stresses can generate between adhesive and adherend due to
large difference in coefficient of thermal expansion and contraction.
FACTORS EFFECTING WETTING
1- ADHEREND RELATED FACTORS

18. Criteria for successful adhesion
 Low surface tension of the adhesive.
 Low viscosity of the adhesive.
 Low setting contraction of the adhesive.
 Thin adhesive film.
 High surface energy of the adherend.
 Proper surface irregularities of the adherend.
 Clean surface of the adherend.
 Closely matching in coefficient of thermal expansion of the adhesive
and the adherend.
 Primary bond formed between the adhesive and the adherend.

19. Failure of the adhesive junction
Adhesive Failure between the adhesive and the
adherend
Cohesive Failure within the adhesive or within
the adherend
Adhesive failure Cohesive failure

20. Importance of adhesion in Dentistry
 Decrease marginal leakage between restoration and cavity walls.
 Used in retention of restorations e.g Ceramometallic restoration
 The prevention of tooth decay by sealing pits and fissures.
 Aesthetic coating for treating enamel defects.
 Complete denture retention through thin film of saliva.
 Required for bonding agents.
 Used in Soldering operation.
 Acrylic teeth in acrylic non metallic denture base

21. Application Of Adhesion on Tooth Structure
Challenges in bonding to tooth structure
 Bonding to tooth structure ↔ Exchange process
Replacement of minerals from Tooth by Resin
Primarily micromechanical interlocking

22. The Challenges of Adhesion in Dentistry
1. Simultaneously bond to enamel & dentin [different substrates.]
2. Work in the presence of
3. Stresses of the restorative materials on the tooth structure
4. Technique sensitive
5. Biocompatible.
1. Moisture.
2. Surface irregularities
3. Surface contaminants

23. enam
 More homogenous in composition
Organic 2%
Water 12%
• Bonding in enamel • Bonding in dentin
More heterogeneous in
composition
Comparison By Volume
Enamel Dentine
Organic
25%

24. Bonding to Enamel by Acid Etching
 The most commonly used acid etch is 30-50 % phosphoric or citric
acid.
 Etch the surface of enamel by applying the acid for 15-30 seconds.
 The acid dissolves the smear layer( Debris layer)
 The acid removes about 5 microns of the surface of enamel and
produce microtags.
 Adhesive resin flown in to these microtags and forms an adhesive
bond.
 Surface area & surface energy is increased.

25. Bonding to Dentine
 Difficult than enamel more heterogeneous composition
 Hydrophilic nature due to presence of water within the dentinal tubules
 Smear layer also a problem.
 done in three steps
 1. Etching (conditioning)using acid low surface energy.
 2 .Priming. Primer has two ends hydrophilic and hydrophobic.
Elevates surface energy of dentine ,Makes dentine hydrophobic
 3. Bonding. Applying a bonding agent or an adhesive on top of which
the composite resin is applied and cured.

26. HYBRID LAYER
 Etch /dentine conditioning, Priming , Bond or adhesive application
 Two approches to acheive this
 Total Etch Adhesives (Either 3 or two steps)
 Self Etch Adhesives (Either 2 or 1 step)
 Formtion of a hybrid layer a resin infiltrated/ re-inforced layer at
the bulk dentine and resin interface

27. 27
Hybrid Layer Formation in Dentine
ETCHANTPRIMER
ADHESIVE RESIN
Intertubular
Dentine
Peritubular
Dentine
Dentinal Tubules
Hybrid
Zone
Collagen

28.  McCabe Applied Dental Materials 9th Edition.
 Phillips Science of dental materials 12th edition
 Craig’s Restorative Materials 13th Edition.
 Watch : http://www.youtube.com/watch?v=cbTwMoNOwag
 Watch : http://www.youtube.com/watch?v=Pe12NedfYC0
REFERENCES