Bonding and Applied

Surface Phenomena

Dental applications

• Leakage around restorations.

• Retention of dentures.

• Plaque attachment to tooth structure.

• Joining of metallic components.

• Pits & Fissure sealants.

• Cementation of crowns & bridges

• Bonding of orthodontic brackets.

• Welding of gold foil.

• Enamel and dentin adhesives.

• Fluoride application.

Mechanisms of Bonding

I. Mechanical attachment

Gross Mechanical Micro-Mechanical

1.Posts & pins.

2.Clasps of RPD.

3.Undercuts.

1.Enamel & dentin

bonding.

2.Pits & fissures

sealants.

II. Chemical Bonding

Mechanisms of Bonding

II. Chemical Bonding

Cohesion Adhesion

I. Mechanical attachment

• Adhesion : attraction or bonding between dissimilar molecules

of two materials.

• Cohesion: attraction between similar atoms and molecules in two

different surfaces at room temperature when brought in close

proximity

Mechanisms of Bonding

II. Chemical Bonding

Cohesion Adhesion

Factors affecting: 1. Degree of proximity.

2. Surface contamination and adsorbed

gases.

3. Heating of metallic surfaces

(degassing).

4. Microstructure of the cohering

surfaces, crystalline solids show low

coherence capacity while cold worked

surface have high tendency to cohesion.

Types:

I. Mechanical attachment

Chemical Adhesion

True adhesion

(Chemo-sorption)

Physical Adhesion

1. Formation of surface

oxides. e.g. Au, Ag & Pt.

2. Glass Ionomer.

Capillary phenomena and

its applications. E.g

Denture base

Adhesion

Adherend (substrate)

Adherend (substrate)

Adhesive

Adhesive

junction

Definitions Adhesion:

• Adhesive: the material (usually liquid) that used to produce

adhesion.

• Adherend: the material (surface) to which the adhesive is

applied.

• Adhesive junction: the transition layer between the two

surfaces of adhesive and adherend.

Factors affecting strength of

adhesive junction

1. Type of the bond.

2. Surface roughness.

3. Surface cleanliness.

4. Thickness of adhesive

film.

5. Thermal stresses.

6. contraction stresses of the

adhesive

7. Area of contact.

8. Wettability.

Factors affecting strength of

adhesive junction

1. type of bond formed:

Chemical (true adhesion)

Primary bonds between adhesive and adherend produce

stronger adhesion than if secondary bonds are formed

(Soldered Joint –metallic bond- is stronger than glued joint -

polarization-).

Mechanical (attachment) By the flow and penetration of a liquid

adhesive into microscopic or sub-microscopic irregularities

in the surface of the adherend or substrate

2. Surface roughness.

• If roughness is irregular and deep, → air pockets →

prevent adhesive from penetrating→ no intimate contact

between adherend and adhesive→ weak adhesive bond.

• if surface roughness is regular and shallow, → no chance for

air pockets formation → intimate contact between

adherend and adhesive→ good adhesive bond.

3) Cleanliness on the adherend:

Debris or surface contaminations prevent intimate contact which is necessary to produce adhesion.

** Adhesion to clean and dry surface of enamel and dentin is better than adhesion to wet contaminated one.

4) Stresses due to setting contraction of adhesive:

Contraction of liquid adhesives during setting

→ creation of stresses at the interface

→ decreases the strength of adhesion.

5) Thermal stresses:

Different thermal coefficients of adhesive and adherend + changes in

temperature → stresses in the bond.

Close matching is required to minimize stresses and increases the strength

of adhesion.

6)Thickness of the adhesive: Thinner adhesive film → stronger adhesive junction,

** less air voids are present.

** Less thermal stresses

** Less stresses due to setting contraction

of adhesive.

7)Wettability

• Definition: the ability of the adhesive liquid

to spread over the adherend surface.

• Contact angle: measure of spread-ability or

wettability. It’s the angle formed by the

adhesive (liquid) with the adherend (solid) at

their interface.

Wettability

Factors affecting wettability: 1. Surface energy of the solid adherend

2. Surface tension of the liquid adhesive.

3. Viscosity.

4.Surface irregularities of adheren.

Wettability

• Factors affecting wettability:

1. Surface energy of the solid adeherant

– In solids, the surface energy is greater than the internal energy, because the outermost atoms are not equally attracted in all directions.

Solids tend to reduce this surface energy by adsorption of atoms or molecules.

- Surface energy wettability - contamination of surface wettability

Examples:

1. Metals usually have a higher surface

energy and are easy to wet by suitable

adhesive.

2. Waxes are not easily wetted because they

have low surface energy.

3. Teflon used in non stick cooking utensils

has low surface energy.

Wettability 2- Surface tension of the liquid

adhesive.

1. temperature surface tension

2. impurities surface tension

3. surface tension wettability

4. wettability adhesion

Wettability 3) Viscosity.

Increasing the viscosity of the adhesive, decreases the wettability.

Wettability

4)Surface irregularities of adherent.

• Importance of wettability in dentistry:

- Good wetting by saliva important for denture

retention.

- More natural appearance is achieved if

restorative material are wetted by thin film of

saliva

- To produce smooth surface of casting the wax

pattern is coated by surface acting agent (wetting

agent or debubblizer) before investing this

improve wax wettability thus, producing

smoother surface.

• Surface active agent (Surfactant)

Capillary phenomenon

When adhesive bond is tested under tension there are three

possibilities:-

• Adhesive failure (adhesive-adherend separation).

• Cohesive failure of the adhesive.

• Cohesive failure of the adherend.

Bonding to tooth structure

Factors contributing to the difficulty in bonding to

tooth structure (obstacles):

• Un-homogenous composition of enamel and dentin

• Tenacious (adherend) microscopic debris in the prepared

cavity. (Smear Layer)

• Surface irregularities of the prepared cavity.

• Inherent wettness of the surface of dentin.

Mechanical bonding bonding to Enamel

Effect of acid etching on enamel

surface: 1) Removal of surface debris.

2) Producing pores (micropores). for micro-mechanical

interlocking.

3) Increase surface energy of enamel.

4) Increase surface area exposed to the bonding resin.

:

35% phosphoric a.

60 seconds

Enamel surface wash dry bond

Micro-tags

Micro-pores

Bonding to Dentin

• Smear Layer:

Thin tenacious adherent layer develops during cutting

or grinding of tooth structure after cavity preparation.

It’s formed of:

a. Dentin chips.

b. Saliva.

c. Bacteria.

d. Collagen.

e. blood.

Smear layer Conditioned dentin

surface

Wet dentin surface primed dentin surface bonded dentin surface

Structure

of primer

Steps of bonding to dentin

Conditioning primer bonding agent

The aim of bonding to dentin is to obtain what’s called

“ HYBRID LAYER ” which is “Resin-reinforced dentin layer”.