Principle of Adhesion in dentistry

1. Review of Principles of Adhesion
Presenter: Ndakama, Elisha K. (MDS I 2020)
Moderator; Dr O. Osiro

2. PRESENTATION OUTLINE
• Introduction
• Mechanism of Adhesion
• Requirement of adhesion
• Factors affecting adhesion
• Adhesive materials
• Bonding system
• Success and failure adhesive
• Reference

3. Introduction
• Bonding and adhesion comprise a complex set of physical,
chemical and mechanical mechanisms that allow the attachment
and binding of one substance to another.
• A dental bonding system performs three essential functions:
• Provides resistance to separation of an adherend substrate (enamel, dentin, metal,
composite, ceramic) from a restorative or cementing material;
• Distributes stress along bonded interfaces; and
• Seals the interface via adhesive bonding between dentin and/or enamel and the
bonded material,
• Hence increase resistance to microleakage and decrease the risk
for postoperative sensitivity, marginal staining, and secondary
caries.

4. Introduction
• The word adhesion comes from the Latin adhaerere - “to
stick to”
• An adhesive is a material, frequently a viscous fluid, that joins
two substrates together by solidifying and transferring a load
from one surface to the other.
• Adhesion is defined as “the state in which two surfaces are
held together by interfacial forces which may consist of
valence forces or interlocking forces or both.
• Adherend—A material substrate that is bonded to another
material by means of an adhesive

5. Introduction
• Interfacial force-Is the resistance to separation of two parallel
surfaces that imparted by a film of liquid between them
• Cohesion forces. This is the electromagnetic force of
attraction between the molecules of the same material

6. Event in dental bonding technologies

7. Clinical significance of Adhesion
• Inhibition of marginal leakage
• Reinforcement of the tooth structure
• Solving the problem of retention
• Adjusting esthetic defects
• Fulfilling the requisite of the modern esthetic practice

8. Mechanism of Adhesion
1. 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.
2. Adsorption adhesion—Chemical bonding between the
adhesive and the adherend; (inorganic hydroxyapatite &
organic collagen fibers of tooth), the forces involved may be
primary (ionic and covalent) or secondary (hydrogen bonds,
dipole interaction, or van der Waals) valence forces

9. Mechanism of Adhesion
3. Diffusion adhesion—Interlocking between mobile molecules,
such as the adhesion of two polymers through diffusion of
polymer chain ends across an interface
• 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
4. Electrostatic adhesion—An electrical double layer at the
interface of a metal with a polymer that is part of the total
bonding mechanism
• In this, two surfaces are joined by electro static forces.

10. Requirements of good Adhesion
Bond strength values of 17-20 Mpa are required to counteract the
shrinkage stresses of composites during polymerization.
• 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

11. Requirements of good Adhesion
• Adherend should have high surface energy.
• 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

12. FACTORS AFFECTING ADHESION
Strength and durability of adhesive bond depends on.
• 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
• Moisture and oil contamination from the hand piece
• Fluoride content of the enamel
• Location and size of the dentinal tubule
• Presence of plaque, calculus, stains and debris impact bonding
• Presence of bases/liner on prepared tooth
• Residual temporary cements

13. 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 (smear layer)

14. STRUCTURAL COMPONENT OF ENAMEL AND DENTINE
• 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.

15. 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) & 45,000/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

16. Composition of dentine cont.….
• 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 1/3 of dentinal tubules it contains;
• Dentinal fluid
• Organic membrane called lamina limitans
• Intra-tubular collagen fibrils

17. Composition of dentine cont.….
• 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

18. Smear layer
• Any debris, calcific in nature, produced by reduction or
instrumentation of dentin, enamel or cementum or as a
‘contaminant’ that precludes the interaction with the underlying pure
tooth tissue.
• Produced layer of debris has a great influence on any adhesive bond
formed between the cut tooth and the restorative material
• The composition and thickness of the smear layer are determined to
a large extent by the type of instrument used, the method of
irrigation employed and by the site of dentin at which it is formed.

19. Smear layer cont…
• Its composition reflects the structure of the underlying dentin mainly
containing crushed Ha and altered collagen, mixed with saliva,
bacteria and other grinding surface debris.
• The thickness of the smear layer has been reported to vary from 0.5–
5 µm.
• Although smear layer occludes the dentinal tubules with the formation
of smear plugs, the smear layer is porous and penetrated by
submicron channels, which allows a small amount of dentinal fluid to
pass through.
• Smear layer is reported to reduce dentinal permeability by 90%.

20. Adhesive materials
• Bis-GMA Bisphenol-glycidyl methacrylate
• EDTA Ethylenediamine tetra-acetic acid
• GPDM Glycerophosphoric acid dimethacrylate
• HEMA 2-Hydroxyethyl methacrylate
• 10-MDP 10-Methacryloyloxy decyl dihydrogen phosphate
• 4-META 4-Methacryloxyethyl trimellitate anhydride
• MMEP Mono (2-methacryloxy) ethyl phthalate
• NPG-GMA N-phenylglycine glycidyl methacrylate
• PENTA Dipentaerythritol penta-acrylate monophosphate
• Phenyl-P 2-(Methacryloxy) ethyl phenyl hydrogen phosphate

21. First generation
• Buonocore et al in 1956 reported that glycerophosphoric acid
dimethacrylate (GPDM) could bonding to HCl acid etched dentinal
surfaces
• Another, surface active comonomer NPG-GMA was manufactured
by the Cervident company (S.S. White, Inc., Lakewood, NJ),
• Theoretically, this comonomer could chelate with calcium on the tooth
surface to generate water-resistant chemical bonds of resin to dentinal
calcium.
• In vitro dentin bond strengths of these material were, in the range of
only 2 to 3 Mpa
• NPG-GMA from Cervident had poor clinical results when used to
restore non-carious cervical lesions without mechanical retention

22. Second generation
• In 1978, the Clearfil Bond System Fc was introduced in Japan (Kuraray Co.,
Ltd., Osaka, Japan)
• It was a phosphate-ester material derivative such as HEMA or Bis -GMA
• Action was based on the polar interaction between negatively charged
phosphate groups in the resin and positively charged calcium ions in the smear
layer
• The smear layer was the weakest link in the system because of its relatively
loose attachment to the dentin surface, failed bond side revealed smear layer
debris
• Lack of adequate bond strength that could overcome contraction stresses
• Hydrophobic nature–close adaptation to the hydrophilic dentin was not
achieved .

23. 2nd generation
• Other phosphate-ester dentin bonding systems were introduced in the early 1980s,
Scotchbond (3M EPSE Dental Products, St. Paul, MN), Bondlite (Kerr Corporation,
Orange, CA),Prisma Universal Bond (DENTSPLY Caulk, Milford, DE).
• These bonding systems had in vitro bond strengths of only 1 to 5 MPa, which was
considerably below the 10 MPa value estimated as the threshold value for acceptable
in vivo retention
• Were relatively devoid of hydrophilic groups and had large contact angles on
intrinsically moist surfaces
• They did not wet dentin well, did not penetrate the entire depth of the smear layer,
and, therefore, could not reach the superficial dentin to establish ionic bonding or
resin extensions into the dentinal tubules.
• In vivo performance of these materials was found to be clinically unacceptable 2
years after placement in cervical tooth preparations without additional retention, such
as beveling and acid-etching.

24. Third Generation
• Fusayama et al in 1979, introduced concept of phosphoric acid-etching
of dentin before application of a phosphate ester-type bonding agent
• Japanese philosophy of etching dentin to modify or remove the smear
layer to allow resin penetration into underlying dentin before the
application of the actual adhesive
• Acid-etching did not produce a significant improvement in dentin bond
strengths, despite the flow of the resin into the open dentinal tubules
• Pulpal inflammatory responses were thought to be triggered by the
application of acid on dentin surfaces, providing another reason to avoid
etching

25. Third generation
• Kuraray introduced Clearfil New Bond in 1984
• This phosphate-based material contained HEMA and a 10-carbon
molecule known as 10-MDP, which includes long hydrophobic and short
hydrophilic components
• Laboratory results, some of the bonding mechanisms never resulted in
satisfactory clinical results
• Treatment of the smear layer with acidic primers was proposed using an
aqueous solution of 2.5% maleic acid, 55% HEMA, and a trace of
methacrylic acid (Scotchbond 2, 3M ESPE Dental Products)
• With this type of smear layer treatment, manufacturers effectively
combined the dentin etching philosophy advocated in Japan with caution,
not to completely remove smear and slightly demineralization of
intertubular dentinal surface

26. Third generation
• Clinical results were mixed, with some reports of good performance and
some reports of poor performance
• The removal of the smear layer using chelating agents such as EDTA
was recommended in the original Gluma system (Bayer Dental,
Leverkusen, Germany) before the application of a primer solution of 5%
glutaraldehyde and 35% HEMA in water.

27. Other generations

28. Eighth Generation
• Self etch which contains nanosized fillers by the addition of
nano-fillers with an average particle size of 12 nm that increases the
penetration of resin monomers and the hybrid layer thickness,
which in turn improves the mechanical properties of the bonding
systems.
• Nano-bonding agents are solutions of nano-fillers, which produce
better enamel and dentin bond strength, stress absorption, and
longer shelf life

29. Classification of Dental Bonding Systems and Examples of Commercial Products Currently Available for
Clinical Use

30. Fourth-
generation
For bonding composite cores,
three-step, etch-and-rinse systems are
usually recommended.
Fifth-
generation
For bonding anterior and posterior composites and
cementation of veneers with resin cements, two-step
etch-and-rinse systems provide the best performance
Sixth-
generation
For bonding posterior composites, self etch, two-step
systems are the better choice.
Seventh-
generation
Dual-cure one-step, self-etch systems are advised for esthetic
posts and ceramic restorations bonded with resin cement,
Light-cured one-step, self-etch systems are recommended for
bonding posterior composite restorations.

31. Enamel adhesion
• Acid-etching with 35% phosphoric acid in 15s open spaces
between enamel prisms allowing the permeation of resin
monomers between the crystallites.
• This transforms the smooth enamel into an irregular surface
and increases its surface free energy
• Fluid resin-based material is applied to the irregular etched
surface, the resin penetrates into the surface, aided by capillary
action
• Monomers in the material polymerize, and the material
becomes interlocked with the enamel surface
• The formation of resin micro tags within the enamel surface is
the fundamental mechanism of resin-enamel adhesion

32. Morphologic pattern of
Enamel
• Type I pattern involves the
dissolution of prism cores without
dissolution of prism peripheries
• Type II etching pattern is the
opposite of type I: the peripheral
enamel is dissolved, but the cores
are left intact
• Type III etching. No prism
structure is evident

33. Dentin adhesion
• Dentin adhesion relies primarily on the penetration of adhesive
monomers into the network of collagen fibers left exposed by
acid etching
• However, bonding to dentin, presents a much greater challenge.
• Factors account for this difference between enamel and dentin
bonding.
• Dentin contains substantial proportion of water and organic
material primarily type I collagen.
• When tooth structure is prepared with a bur/other instrument
residual organic and inorganic components form a ‘smear plugs’
which decreases dentinal permeability by up to 86%.

34. Conti……….
• Primer with hydrophilic component e.g. HEMA that wet dentin and
penetrate its structure.
• Primer contain solvent that displace water and carry the monomer into
micro porosities in the collagen network
• 37% phosphoric acid removes the mineral content, creating micro
porosities within the collagen network.
• Acid is rinsed, caution on drying will dehydrate the outer surface and cause
the remaining collagen scaffold to collapse onto itself
• Excess moisture tends to dilute the primer and interfere with resin
interpenetration
• The infiltration of resin within the collagen scaffold is termed
hybridization
• Diffusion process called, resin-interpenetration zone or resin-inter
diffusion zone or hybrid layer.

35. Hybrid layer
• Zone in which resin of the adhesive system micro mechanically
interlocks with dentinal collagen.
• Three hybrid layer
• First Layer; Amorphous electron – dense phase – which can be
attributed to denatured collagen
• More loosely arranged collagen fibrils which are directed towards adhesive resin
and the interfibrillar spaces filled with resins
• Middle Layer. longitudinally sectioned collagen fibrils separated by
electronucleant spaces.
• These interfibrillar channels which have typical dimensions of 10-20 nm, represent
the reason wherein HA crystals had been deposited and have been replaced by
resin as a result of the hybridization process.
• Base Layer: has gradual transition to the unaltered dentin, with a
partially demineralized zone of dentin containing HA crystals enveloped
by the resin or by a more abrupt transition.

37. Adhesion to dentin.

38. Conditioner of dentin
• Alteration of dentin surface including the smear layer with the objective
of producing a substrate capable of micromechanical and possibly
chemical bonding to a dentin adhesive.
• Physical effect; decreases the thickness and morphology of smear layer
and dentinal tubules
• Chemical effect; modify the fraction of organic matter, decalcification
of inorganic portion of dentin

39. Chelator
• A chelate refers to a compound with a central rectal ion surrounded
by covalently bonded atoms, ions or molecules called ligands which
possess additional bonds for chemical reaction.
• The best known chelator conditioner is EDTA adjusted to a pH of
7.4.
• It was developed for use in Gluma system when used for 30
seconds, the smear plugs are fully removed with this conditioner

40. Thermal conditioning
• The recent trend to use lasers in conditioning of dentin.
• These may serve as a potential alternative to acids for conditioning of
dentin.
• It is speculated that the lasers cause recrystallization of dentin resulting
in fungi form appearance that contributes to increased microporosite
and possible chemical adhesion of a restorative material to the tooth
structure.
• Further, they remove the organic elements, leaving behind an apatite
substance in a new alpha form.

41. ADHESIVE PROMOTER
Coupling agent
• An intermediary substance can be used
that is able to bond to both of the
materials in question
• Displace the adsorbed water and
provide a strong chemical link between
the oxide groups on the glass surface
and the polymer molecules of the
resin.e.g Silane
• Silanes are very effective in promoting
adhesion for silica-based materials such
as porcelain,
Primer
• Promoting agents that contain
monomers with hydrophilic
properties.
• Affinity to the exposed collagen
fibrils and hydrophobic properties
for copolymerization with
adhesive resin e.g. HEMA and 4-
META
• Modify and enhance adhesive
complete penetration

42. BONDING IN OTHER CLINICAL SITUATIONS
Bonding of GIC to hard tissue:
• Can adhere to enamel and dentin
Also can bond to reactive polar
substrate- base metals
• Primary mechanism of bonding
chemical mainly micro mechanical
Bonding of Composite to GIC
• Sandwich technique; 37% H3PO4
used to etch enamel and GIC, open
the glass particle to stand out matrix,
resin penetrate the micro pore to
form mechanical interlock
Bonding of Composite to
Porcelain. Partly – Mechanical
interlocking partly – Chemical union
Mechanical Retention
Etching the surface of porcelain with
HF acid/ grit blasted with aluminia
increase surface roughness
Bonding of Amalgam to Resin
 Resin and amalgam –
micromechanical as amalgam
interlocks with fluid resin during
condensation. E.g. All bond,
Amalgam Bond and Panavia

43. Cast Alloys:
• Sandblasting with aluminum oxide to
prepare substrate,
• Electrolytic etching can be used with
base metal alloys,
• Silane solution is applied to the
treated metal
• a surface capable of bonding to
dimethacrylate based resins.
• Monomers such as 10-MDP and 4-
META are used in resin cements to
improve retention of cast alloys
restorations
Fiber Posts;
• Silanization,sandblasting, or the
association of both treatments
often have effective to improve
the bonding between the resin
cement and the fiber post.
Metal ceramic restoration
repair;
• Sandblasting with alumina
followed by the application of
silane and adhesive resin, then
composite
• Fractured porcelain can be
sandblasted, etch with HF
10%,silane-adhesive-composite

44. SUCCESS AND FAILURES OF ADHESIVES
• Material factors-Like hydrophobic bonding agents-Incomplete resin
penetration-No significant hybrid layer
• Substrate/adherends
• Maxillary vs. mandibular arch because of less chances of
contamination and lower tooth flexural effects than in upper jaws.
• Patients age, Increased age dentin sclerosed, decreased coronal
adhesiveness, increased tooth flexure
• Dentinal wetness: bonding agents with effective wetting capacity
ensure successful bonding.

45. SUCCESS AND FAILURES OF ADHESIVES
• Tooth flexure: Influencing factor on retention. Adhesives especially at
cervical restoration. Heavy centric occlusal and eccentric forces
respectively for general compressive and tensile forces- cervical area–
gradually dislodge and debond the resin restoration. So compressive
with adequate elastic capacity like micro filled are preferred in rich
lesion.
• Elastic bonding concept: due to shrinkage during polymerization
debonding can occur.-So intervening adhesive resin–sufficiently
elastic to absorb the poly stress.-Can be achieved by using–relation
thick layer of separately polymerized unfilled/semi filled resins.

46. Reference
• Dental Adhesion: Mechanism, Techniques and Durability. The Journal of clinical
pediatric dentistry April 2012: 36(3): 223–234, 2012
• Applied dental materials.– 9th ed./ J.F.McCabe,A.W.G.Walls.p pg. 225-241.2008
• Phillips’ science of dental materials. Kenneth J. Anusavice, Chiayi Shen, H. Ralph
Rawls.—12th ed.pg 257-273,17-29
• Pocket Dentistry; Fundamental Concepts of Enamel and Dentin Adhesion. Jorge
Perdigão, Edward J. Swift, Jr. and Ricardo Walter; Jan 9, 2015 Chapter 4
• Adhesion Concepts in Dentistry: Tooth and Material Aspects; Özcan, Mutlu ;
Dündar, Mine ; Erhan Çömlekoğlu, M. University of Zurich Main Library: 2012
• Craig’s Restorative Dental Materials. Thirteenth Edition. pg. 327-337