The document discusses various principles of adhesion in dentistry. It describes the different mechanisms of adhesion including mechanical adhesion, adsorption adhesion, diffusion adhesion, and electrostatic adhesion. It also outlines the requirements for good adhesion such as sufficient wetting of the adhesive, low viscosity, rough surface texture of the adherend, and high surface energy of the adherend. Additionally, it explains factors that affect adhesion to tooth structures like the smear layer and differences between adhesion to enamel versus dentin.

1. PRINCIPLES OF
ADHESION
DR. SARANG SURESH HOTCHANDANI
Dentist, Bibi Aseefa Dental College, SMBBMU.
Larkana, Sindh, Pakistan
hotchandanisarang@gmail.com

2. Mechanisms of Adhesion
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3. Mechanical Adhesion
In this type, solidified adhesive
interlock micro mechanically in
surface roughness and irregularities of
adherend by formation of resin tags
within tooth surface.
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4. Adsorption Adhesion
In this type, adhesive makes chemical bonding with
substrate or adherend (inorganic hydroxyapatite &
organic collagen fibers of tooth).
Contain all types chemical bonds like;
 Primary bonds (ionic & covalent)
 Secondary valence bonds
 Hydrogen bonds,
 Van der waals forces (dipole interaction, London dispersion)
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5. Diffusion Adhesion
In this type, adhesion or bonding occurs
between mobile molecules.
Polymers from one surface come out and react
with other surface and eventually adhesive
disappears and both parts become one.
 Precipitation of substance on tooth surface to which
resin can bound mechanically or chemically.
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6. Electrostatic Adhesion
In this two surfaces are joined by electro
static forces.
Usually one surface is resin and other is
metal.
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7. Requirements of Good Adhesion
 The materials which are being joined should be close as much as
possible.
 Adhesive should have
 Sufficient wetting of the adhesive means spread of liquid.
 Measured by contact angle of droplet placed on adherend.
 Low contact angle.
 High the contact angle less the wetting, complete wetting means 0-degree contact angle.
 Low surface tension of adhesive.
 affinity for one another that causes them to stay together rather than interact with the surface
they contact
 Adherend must be rough
 Increases the surface area & increase the potential for adhesion.
 Adhesive should not be too viscous nor too fluid.
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9. Requirements of Good Adhesion
 Adherend should have high surface energy.
 In nature, there is a desire for all objects to seek a reduced energy state, simply because
reduced energy is the most stable condition.
 Surfaces, in general, are of higher energy than the internal aspects of an object because
molecules present at the surface have unsatisfied bonds.
 In other words, molecules on surface would prefer to be covered” by other molecules to satisfy
their bond complexes and reduce their overall energy state.
 This covering can occur by;
 oxygen,
 water, or
 other molecules.
 The higher the energy of the surface, the more receptive it is to being bonded to by
another material, such as an adhesive.
 Methods of Increasing Surface Energy
 Surface cleaning by pumice or prophylactic paste
 Etching with acids
 Cleaning with solvents to remove contaminants
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10. Adhesion to Enamel is easy than Adhesion to Dentine!!
 Enamel has high surface energy due to presence of only
hydroxyapatite
 Dentine has low surface energy and is difficult because it
contains hydroxyapatite of high surface energy while collage
fibers of low surface energy.
 We need isolation of tooth for adhesion because if cavity is
contaminated by saliva it will decrease the surface energy of
surface and prevents the adequate wetting by adhesive.
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11. Adhesion to Enamel is easy than Adhesion to Dentine!!
 And also during cavity preparation smear layer is produce
which is also of low surface energy which will prevent good
adhesion as described above, that’s why we remove this
smear layer after cavity preparation.
 GIC is only dental cement to possess intrinsic adhesive
property and does not require intermediate resin to bond
restoration with tooth material, while composite requires an
intermediate bonding agent to micromechanically bond with
etched enamel or dentine.
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12. FACTORS AFFECTING ADHESION TO
TOOTH SURFACE
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13. Strength and durability of adhesive bond depends on several
factors.
 Physicochemical properties of adhesive and adherend
 External stresses which reduce the process of bonding.
 Mechanism of transmission & distribution of applied load
through bond.
 Changes in oral environment.
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14. Strength and durability of adhesive bond depends on several
factors.
Structural properties of adherend (enamel &
dentine)
 Hypo mineralized & eroded tooth structure is difficult to bond
because of weakened tooth structure.
 Hyper mineralized teeth will require longer time of etching because
they are resistant to demineralization.
 Dentine sclerosis
 Fluorosis
 Fluoride treatment
Surface contaminants during cavity preparation
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15. COMPOSITIONAL AND STRUCTURAL
ASPECTS OF ENAMEL AND DENTINE.
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16. Composition of Enamel
Inorganic content
(Hydroxyapatite)
 95% - 98% by weight (wt. %)
 86% by volume (vol. %)
Organic content
 1% - 2% by weight
 2% by volume
Water
 4% by weight
 12% by volume
 The inorganic portion is arranged in
crystallites form arranged in three
dimensional way called as prism or rods
whose ends are shaped as keyhole pattern.
 Enamel is homogenous while dentine is
heterogeneous.
 A prismatic or prism less enamel is present
on outer surface in which crystals are
parallel to each other and perpendicular to
the surface.
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17. Composition of Dentine
Inorganic
(hydroxyapatite)
 70% by weight
 50% by volume
Organic (type 1 collagen)
 18% by weight
 25% by volume
Water
 12% by weight
 25% by volume
 Dentine is permeable because it
contains dentinal tubules which radiate
from pulp to enamel-dentin junction.
 These tubules contain odontoblastic processes
and establish direct connection to pulp.
 The diameter and number of dentinal tubules
decreases from pulp to enamel-dentine
junction.
 2.5 micron (diameter) & 45,00o/mm2 (number)
near pulp
 0.8 micron (diameter) & 20,000/mm2 (number)
near Enamel-dentine junction.
 Average 30,000 tubules/mm2 in middle part of
dentine.
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18. Composition of Dentine
 Each tubule is made of peritubular dentine containing
odontoblastic process inside it and these dentinal tubules are
separated by intertubular dentine.
 Intertubular dentine is less mineralized and contain more
organic content.
 In the deepest 1/3rd of dentinal tubules it contains;
 Dentinal fluid
 Organic membrane called lamina limitans
 Intra-tubular collagen fibrils
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19. Composition of Dentine
 Dentinal tubules are arranged in fan shaped manner.
 96% superficial dentine is composed of intertubular dentine, 1% of dentinal fluid,
3% peritubular dentine because number and diameter of dentinal tubule decreases
as they move from pulp to EDJ.
 Near the pulp, 12% intertubular dentine, 66% peritubular dentine 22% dentinal
fluid.
 Dentine is intrinsically wet tissue.
 Dentinal fluid is under outward pressure from pulp.
 Intra-pulpal fluid pressure is 35-30 mmHg or 34-40 cm of water.
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20. Changes in Dentine Structure
Dentinal sclerosis
Tertiary or reparative dentine formation
Hyper mineralization & obstruction of dentinal
tubules
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21. SMEAR LAYER
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22. The Smear Layer
It is iatrogenically produced layer of
debris calcific in nature, produced by
reduction or instrumentation of
dentine, enamel or cementum that
prevent interaction with underlying
pure tooth tissue.
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23. Characteristics of Smear Layer
 Smear layer is produced by rotary or
hand instruments in cavity preparation,
root canal preparation, root planning,
so to obtain good bonding tooth
surface should be cleaned.
 The burnishing action of instrument
produces frictional heat and shear
forces which makes the smear layer to
get attached to tooth surface and
prevent it being rinsed off.
 Following conditioners are being
used for removing smear layer;
(Conditioners are chemicals which
help in removal of smear layer)
 EDTA (most effective)
 Acidic Conditioners
 Citric acid
 Polyacrylic acid
 Lactic acid
 Phosphoric acid
 Cavity cleansers (slight effect)
 Tubulicid
 Hydrogen peroxide
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24. Characteristics of Smear Layer
 Morphologic features, composition and thickness of smear layer
depends upon;
 Instrument used
 Method of irrigation/ instrumentation
 Site of tooth
 Smear layer seen in SEM to be of 0.5 to 2 micro meter in thickness,
granular in structure with irregular surface.
 The orifices of dentinal tubules are obstructed by debris tags of
smear layer called as smear plugs which may extend in dentinal
tubule up to 1 – 10 micro meter.
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25. Characteristics of Smear Layer
 The smear layer is made of;
 Crushed Hydroxyapatite
 Denatured collagen
 Bacteria
 Saliva
 The smear layer reduces dentinal permeability by 86%.
 Smear layer thickness increases with increasing the size &
roughness of bur.
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26. Characteristics of Smear Layer
 Smear layer have weak attachment to tooth and is brittle in
nature and decrease the effective bonding. To overcome
this effect two procedures are used as mentioned under;
 Etch and rinse approach
 In this procedure, smear layer is removed before application of adhesive or bonding.
 Self-etch approach
 In this procedure, bonding agent is applied without removal of smear layer which
penetrate it.
 After removal of smear layer dentinal permeability increases
by about 90%.
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27. Characteristics of Smear Layer
Adhesive techniques that require removal of smear
layers lead to post-operative sensitivity, pulp
damage, and post-operative pain due to opening of
dentinal tubules, micro gaps & micro leakages.
New etch and rinse adhesive use 30% to 40%
phosphoric acid gel for conditioning
 Alternative conditioners are; maleic acid, nitric acid, citric acid,
tannic acid.
 Polyaleknoic acid is used in GIC.
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28. Characteristics of Smear Layer
In Endo, Chelating agent
EDTA is used to remove
smear layer while sodium
hypochlorite is applied to
remove organic remnants
of bacteria..
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29. Internal & External Dentinal Wetness
Internal dentinal wetness refers to wetness of
dentine or cavity surface from fluid of dentinal
tubules, while external dentinal wetness occurs due
to environmental humidity.
Dentine is highly permeable and high permeability
results in easy penetration of bacteria and toxins to
pulp and easy exudation of dentinal fluid.
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30. Internal & External Dentinal Wetness
When removal of smear layer occur it makes
the bonding surface wet which will have
following effects;
 Fluid competes at all hard tissue sites by hydrolysis
 Interfere with polymerization of adhesives or bonding
agents.
That’s why Dentine bonding agents should be
hydrophilic for effective bonding.
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31. Dentinal Permeability & Dentinal Wetness Depends Upon;
 Diameter and length of tubules
 Deep the cavity more the wettability
because in deep cavity diameter of
dentinal tubule increase while length is
decreased.
 Occlusal dentine is more permeable
over pulp horns than at center
 Viscosity & molecular size of
dentinal fluid
 It is inversely proportional to internal
dentinal wetness
 Pressure gradient
 It is directly proportional
 Surface area available for
diffusion
 Wider the cavity more IDW
 Proximal dentine is more permeable than
occlusal dentine
 Coronal dentine is more permeable than
root dentine.
 Patency of tubules
 Sclerotic dentine or tubules blocked by
smear layer has less permeability
 Rate of removal of substance by
pulpal circulation.
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32. Wetting of Adhesive
 For good bonding the adhesive must sufficiently wet the
surface and should have low viscosity and be able to
displace air and moisture during bonding process.
 Minimum contact angel for good adhesion should be less than 15 degrees.
 Primers in current system contains; (Primers are bonding
promoters)
 Surface active agent which enhances the wettability of hydrophobic adhesive
bonding agent
 HEMA (2-hydroxyethyle methacrylate)
 Solvents for removal of air and moisture
 Ethanol or acetone
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33. Polymerization Contraction
 The linking of monomer into polymer during polymerization leads to
contraction which may de-bond the restoration.
 It creates the force which pull the adhesive from adherend.
 High filler content decreases the contraction.
 Current resins shrink up to 2.9 – 7.1 vol%.
 Polymerization contraction induces contraction/ shrinkage stress.
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34. COMPENSATION FOR
POLYMERIZATION SHRINKAGE
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35. Flow or Plastic Deformation
 Plastic deformation of set resin may relax the contraction
stresses.
 As the setting proceeds, contraction and plastic
deformation decreases due to increase in stiffness or
modulus of elasticity of material.
 Fast setting light curing resins exhibit less relaxation of
contraction stress by plastic deformation.
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36. Flow or Plastic Deformation
While self-curing or auto curing shows relaxation
with plastic deformation due to availability of time.
 That’s why marginal adaption is better with self-curing resin due to
high time for deformation to occur for relaxation and also due to
presence of air bubbles which provide space for flow.
So for better marginal adaption curing rate should
be low and formation of bond should be rapid.
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37. Flow or Plastic Deformation
 Flow or plastic deformation depends on C Factor (configuration
factor)
 It is ration of bonded surfaces to un-bonded surfaces in restoration.
 Example; in Class-1 cavity there are 5 bonded surfaces and one un-bonded surface so
the C factor will be 5.
 Increase in contraction factor lead to increase in contraction stress in restoration.
 Only the un-bonded surface is responsible for plastic deformation.
 Other methods to compensate for polymerization shrinkage.
 Placement of glass ceramic blocks into soft resin composite before light curing
 Displace the resin and provide space like air bubbles.
 Use of mega-filled resin
 Use of pre-polymerized resin
 Use of inlays24،‫مارچ‬17 SARANG SURESH HOTCHANDANI 37

38. Hygroscopic Expansion
 It is swelling of resin due to absorption of fluid.
 It my decrease polymerization shrinkage and marginal
leakage by expanding the resin.
 Micro-filled resin shows 2 & ½ times more water than
macro filled because of greater volume of resin in micro
filled.
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39. THE END
Reference: Summit’s Fundamentals of Operative Dentistry 4th Edition
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