This document discusses the fundamental concepts and mechanisms of adhesion in dentistry, focusing on enamel and dentin bonding techniques. It outlines the various generations of dentin bonding agents, highlighting their advancements in terms of bonding strength and application methods. The conclusion emphasizes the growing capabilities of adhesive technology to effectively bond restorative materials to tooth structures.

1. Adhesive system
in dentistry
86618 4/5DDS Shao-Wei Chao

2. CONTENTS
1. Basic concepts of adhesion
2. Enamel adhesion
3. Mechanism of etching and etch patterns
4. Dentin adhesion
5. Generations of dentin bonding agents
6. Conclusion
7. Bibliography

3. BASIC CONCEPTS OF ADHESION
The state in which two surfaces are held together by
interfacial forces which may consist of valance forces or
interlocking forces or both.
 ADHESION :
(The American Society for Testing and Materials Sp. D 907)
• An adhesive is a material, frequently a viscous fluid, that joins two
substrates together and solidifies and is able to transfer load from
one surface to the other. (Sturdevant)

4.  ADHESIVE : this refers to the bonding agent that when
applied to the surfaces or substances, can join them
together, resist separation and transmit loads across the
bond.
 ADHEREND : this refers to the surface or substrate that
is adhered to.
MECHANISMS OF ADHESIONS :
1. Mechanical adhesion : interlocking of the adhesive with
irregularities in the surface of the substrate, or adherent.
2. Adsorption adhesion : chemical bonding between the adhesive
and adherent
3. Diffusion adhesion : interlocking between mobile molecules, such
as the adhesion of two polymers through diffusion of polymer
chain ends across an interface,

5. In dentistry bonding of resins to the tooth structure is a result of four
possible mechanisms, as follows :
4. Electrostatic adhesion : an electrical double layer at the interface of
a metal with a polymer that is part of the total bonding mechanism
1. Mechanical : penetration of resin and formation of resin tags within
the tooth surface.
2. Adsorption : chemical bonding to the inorganic component
(hydroxyapatite) or organic components (mainly type I collagen) of
tooth structure
3. Diffusion : precipitation of substances on the tooth surfaces to
which resin monomers can bond mechanically or chemically.
4. A combination of the previous three mechanisms

6. ENAMEL ADHESION
• Buonocore in 1955 introduced the acid-etch technique for the
adhesion of resin to the tooth.
• He envisioned the use of acids to etch enamel for sealing pits and
fissures.
• Acid etching transforms the smooth enamel into an irregular
surface and increases its surface free energy.

7. • When a fluid resin-based material is applied to the irregular etched
surface, the resin penetrates into the surface, aided by capillary action.
• Monomers undergo polymerization and the material becomes
interlocked with the enamel surface.
• The formation of resin microtags within the enamel surface is the
fundamental mechanism of resin-enamel adhesion
• Presently a 37% concentration of phosphoric acid is preferred.

8. MECHANISM OF ETCHING AND ETCH PATTERNS
• Acid etching converts smooth enamel into a very irregular
surface with high surface energy.
• It removes 10µm of surface enamel and creates a microporous
layer which is 5 to 50µm deep.
• Optimum concentrations of acid produces monocalcium
phosphate monohydrate precipitate which can be easily rinsed
off.

9. • After etching, the enamel surface should be thoroughly rinsed
with a continuous stream of water spray for 5-10 seconds so
that the acid is completely washed off.
• This should be followed by proper drying which will produce a
frosty, white appearance.

10. ENAMEL BONDING AGENTS
• Originally enamel bonding agent consisted of Bis-GMA or UDMA
resins with a diluent like TEGDMA to lower their viscosity.
• These agents flow easily into the microporosities of the enamel
surface and when polymerized by light activation form ‘resin tags’
which lock them into the enamel surface.
• Bond strength of composite resins to etched enamel is in the range
from 15 to 25 MPa.

11. DENTIN ADHESION
• The classic concepts of operative dentistry were challenged in the
1980-90s by the introduction of new adhesive techniques to dentin
as well as to the enamel.
• Dentin adhesion primarily relies on the penetration of adhesive
monomers into the filigree of collagen fibers left exposed by acid
etching.

12. • Dentin is an intrinsically hydrated tissue, penetrated by a maze of 1-
2.5µm-diameter- fluid filled dentinal tubules.
• Cut dentinal surface form an unique structure called as the ‘smear
layer’. It is composed of debris of hydroxyappatite crystals and
denatured collagen.
• The smear layer fills the orifices of dentin tubules, forming ‘smear
plugs’ and decreases dentin permeability by 85%.
• The removal of smear layer and smear plugs with acidic solutions
will result in an increase of fluid flow onto the exposed dentin.
• This fluid can interfere with adhesion because of the hydrophobic
nature of resins even if the resin tags are created.

13. FIRST GENERATION
• NPG-GMA(N-phenyl glycine glycidyl methacrylate), a surface active
comonomer is considered as the first generation dentin bonding
system.
• Both Invitro and invivo clinical study results were discouraging.
• Theoretically, the comonomer could chelate with calcium on the
tooth surface to generate water-resistant chemical bonds of resin
to dentin.
• Based on C-13 nuclear magnetic resonance analysis, It seems that
no ionic bonding develops between NPG-GMA and hydroxyapatite.
• Example : Cervident
DENTIN BONDING AGENTS

14. SECOND GENERATION
• They are phosphate ester material (phenyl-P and hydroxyethyl
methacrylate in ethanol)
• Mechanism of action is based on polar interaction between
phosphate group and calcium in the smear layer.
• The smear layer was the weakest link in the system because of its
loose attachment with dentin.
• Bond strength was also poor (<10MPa). In addition to this, the resins
were relatively devoid of hydrophilic groups.
• They show less wettability and penetration into the dentin crossing
the smear layer.
• Example :Clearfil Bond, Scotchbond, Bondlite

15. THIRD GENERATION
• The third generation dentinal adhesives attempted to deal smear
layer in two ways.
• Either by modification of the smear layer to improve its properties
or by the removal of the smear layer by keeping the smear plugs
intact.
• Fusayama et al in 1979 introduced the concept of phosphoric acid
etching of dentin prior to the use of phosphate-ester type bonding
agent.
• Materials like phenyl-P or PENTA was used to achieve smear layer
modification by penetration of acidic monomers.
• Treatment of smear layer using acid primers were also attempted.
2.5% maleic acid, 55% HEMA, and traces of methacrylic acid were
used for this.

16. • The removal of smear layer using chelating agents such as EDTA
was also tried (GLUMA system).
• Example : Clearfil New Bond, Scotchbond 2, GLUMA system

17. FOURTH GENERATION
• They are; three step, total etch adhesive systems.
• Although smear layer acts as a ‘diffusion barrier’ that reduces the
permeability of dentin, it also can be considered as an obstacle to
the bonding.
• Based on this this consideration a fourth generation dentin
adhesives was introduced for use on acid etched dentin.
• This method is commonly known as the total-etch technique or the
etch and rinse technique.
• The acid will result in complete or partial removal of smear layer
with demineralization of underlying dentin. They also exposes the
collagen.

18. • The fourth generation dentin bonding system consist of three
essential components.
1. Phosphoric acid etching gel that is rinsed off
2. A primer containing reactive hydrophilic monomers in
ethanol, acetone, or water
3. An unfilled or filled resin bonding agent
• Acid treatment not only alters the mineral content of the dentin
substrate but also alters the surface free energy.
• When primer and bonding resins are applied to etched dentin, they
penetrate the intertubular dentin, forming a resin-dentin
interdiffusion zone, or ‘hybrid layer’.
• Examples : Scotch Bond Multi Purpose(3M), All Bond 2, Panavia 21

20. FIFTH GENERATION
• These adhesives are a simplified version of the fourth generation
adhesives. Also known as ‘one bottle’ system.
• The primer and adhesive is combined in one bottle. A separate
etching step is still required.
• Though they require fewer steps to achieve dentin bonding, these
agents are inferior to the fourth generation bonding agents in
terms of bond strength.
• Example : Single Bond(3M), One-Step, Gluma Comfort Bond.

21. SIXTH GENERATION
• Sixth generation dentin boding systems try to further simplify the
process of dentin adhesion by minimizing the clinical steps.
• Acids of lower concentration are generally used :10% Phosphoric,
2.5%nitric, 10% citric, 10% maleic acids.
• They are also known as SEP – Self Etching Primers.
• Commercially they are available in two forms :
1. Self etching primers : etchant and primer
is in one bottle while adhesive is in a
separate bottle. First the etchant and
primer are applied on the tooth surface
which is then followed by application of
adhesive agent.
example : Clearfil SE bond, Xeno

22. 2. Self etching adhesives : in these, the etchant, primer and
adhesive are all in one package but require mixing before
application on the tooth surface
example : Prompt-L-Pop(3M)

24. SEVENTH GENERATION
• Also known as All-in-one adhesive system.
• They combine etchant, primer, and adhesive in one bottle. They do
not require any mixing prior to application.
• Primarily these agents are intricate mixes of hydrophilic and
hydrophobic components in one bottle.
• Their bond strength is less than fourth and fifth generation
adhesives.
• Example : Cleaefil S3 Bond, G-Bond, Xeno IV

25. EIGHTH GENERATION
• They combine etchant, primer, and adhesive in one bottle.
• Use of nanosize fillers in this bond 12 nm fillers.
• The use of nanosize fillers increases the penetration of resin
monomers and the hybrid layer thickness, which in turn improves
the mechanical properties of the bonding systems.
• Filled bonding agents produced higher bond strength than any
other generations.

26. CONCLUSION
The mechanism of bonding is primarily micromechanical by
formation of a hybrid layer.
The various advances in adhesive technology have expanded the
applications of dentin bonding agents to include bonding of
composite, ceramic as well as metallic restorations successfully
to tooth structure.

27. BIBLIOGRAPHY
 Sturdevant’s Art and Science of Operative Dentistry
 Grover, Vishakha & Kumar, Ashish & Jain, Ashish & Chatterjee,
Anirban & Grover, Harpreet & Pandit, Nymphea. (2022). ISP Good
Clinical Practice Recommendations for the management of Dentin
Hypersensitivity. Journal of Indian Society of Periodontology. 26.
307-33. 10.4103/jisp.jisp_233_22.
 SH, Ku & Tan, Yee Shin & Yahya, Noor. (2014). The Effect of Different
Dental Adhesive Systems on Hybrid Layer Qualities. Annals of
Dentistry. 21. 29-37. 10.22452/adum.vol21no1.5.