The document provides a historical perspective and current status of dental bonding agents. It discusses how bonding agents have evolved over generations from early calcium ion-based first generation agents with low bond strengths to today's multi-step etch-and-rinse and single-step self-etch adhesives. Current adhesives can achieve bond strengths of 20-50 MPa to enamel and 13-80 MPa to dentin. While newer single-step adhesives offer simplicity, their long-term performance is still being evaluated compared to multi-step systems. Proper technique remains important for clinical success with any bonding agent.

1. HISTORICAL PERSPECTIVE AND
CURRENT STATUS OF
BONDING AGENTS
NIRAJ KUMAR
JR-PROSTHODONTICS
AIIMS-NEW DELHI 1

2. contents
• HISTORY
• DEFINITIONS
• IDEAL REQUIREMENTS
• COMPONENTS
• BONDING TO ENAMEL & DENTIN
• GENERATIONS OF DBA
• CURRENT STATUS
• ROLE OF SMEAR LAYER
• EXPANDED CLINICAL INDICATIONS
• SUMMARY
• REFERENCES
2

3. HISTORY
3
Major turning points and events in dental bonding technologies
Historical evolution of bonding agents is an ongoing process
which dates back to late 50s in a continuous effort to improve the
bonding of the restoration to the tooth snd simplify the clinical steps.

4. DEFINITIONS
• Dentin conditioner
- An acidic agent that dissolves the
inorganic structure in dentin, resulting in a collagen mesh that
allows infiltration of an adhesive resin.
• Hybrid layer
- An intermediate layer of resin, collagen, and
dentin that is produced by acid etching of dentin and
infiltration of resin into the conditioned dentin.
• Primer
- A hydrophilic, low-viscosity resin that promotes
bonding to an adherend substrate, such as dentin.
4

5. • Resin tag
- Extension of resin that has penetrated into etched
enamel or dentin.
• Smear layer
- Poorly adherent layer of ground dentin
produced by cutting a dentin surface; also, a tenacious
deposit of microscopic debris that covers enamel and dentin
surfaces that have been prepared for a restoration.
5

6. - Requirements for a successful dentin bonding
system :
a) Adequate removal or dissolution of the smear layer from
enamel and dentin.
b) Maintenance or reconstitution of the dentin collagen
matrix.
c) Good wetting.
d) Efficient monomer diffusion and penetration.
e) Polymerization within tooth structure.
f) Copolymerization with the resin composite matrix.
6

7. COMPONENTS
Irrespective of the number of bottles or components, a typical
dentin bonding system includes :
- etchant - relatively strong acids (pH:1-2)
-removes smear layer
- gel (colloidal silica) – precise placement
-adhesive bisGMA, UDMA
- primer - maintains expanded collagen network
-hydrophillic monomers (phosphate, carboxylic
acid, esters) in solvents. [HEMA , 4-META]
- solvents used for primers (water, ethanol & acetone)
- initiators (photo ,chemical or dual cure)
- fillers silica(40nm)- reinforce
- other ingredients - glutaraldehyde - desensitizer
- MDPB & parabene – AMA
- F and CHX (prevents collagen degradation)
7

8. 8
BONDING TO ENAMEL & DENTIN

9. Bonding to enamel
- Acid etching transforms the smooth enamel into an irregular
surface and increases its free surface energy.
Bonding agents (resins) penetrate into the
surface (capillary action).
Monomers polymerize and become interlocked
-Formation of resin microtags – is the fundamental of resin-
enamel adhesion.
9

10. - Enamel etching results in 3 different micro-morphologic
patterns:
a) Type I
- dissolution of prism cores without involving the
prism peripheries.
b) Type II
- dissolution of peripheral enamel with the rods intact.
c) Type III
- less distinct than the other two patterns
(a combination of the two types)
10

11. 11
(Type I) (Type II) (Type III)

12. - In either of the cases the resin tags are
approximately
- 6µm (diameter)
- 10-20 µm (length)
12

13. concentration & time
( two important parameters )
• Buonocore – 85%
• Gwinnet – suggested the use of lower concentrations to
prevent the formation of precipitates.
- a number of acidic agents have been used to produce the
required microporosity.
However , phosphoric acid at a concentration between 30% and
50% , (typically 37%) is the preffered etchant.
13

14. >50%
Deposition of an adherent layer
monocalcium phosphate
monohydate
Prevents further dissolution
<27%
Creates a dicalcium phosphate
monohydrate precipitate
Cannot be removed easily
Interferes with adhesion.
14

15. - An etching time of 60 seconds was originally recommended for
concentrations between 30% to 40%.
- studies using scanning electron microscopy showed
that a 15 sec etch resulted in a similar surface roughness as
that provided by a 60 sec etch.
- other in vitro studies have shown similar bond
strengths and microleakage for both 15 and 60 sec.
15

16. Bonding to dentin
- Adhesion to dentin is relatively difficult.
- Dentin adhesion relies primarily on
- the penetration of adhesive monomers into
the filigree of collagen fibers left exposed by
acid etching.
16

17. Challenges in dentin bonding
- consists of a substantial proportion of water and organic
material (type I collagen)
- dense network of tubules connecting the pulp with the DEJ.
- cuff of hypermineralized dentin (peritubular) lining the
dentinal tubules.
- Presence of smear layer .
17

18. Moist versus dry dentin surfaces
If the dentin suface is:
a) air dried
-the collagen undergoes immediate collapse
(spatial alteration)
prevents resin monomers from penetrating
the nanochannels formed by dissolution
of hydroxyapatite crystals between collagen fibers.
18

19. 19

20. b) Pooled moisture on dentin surface:
- excess water dilutes the primer
and renders it less effective.
c) Glistening hydrated surface:
- ideal condition for bonding.
20

21. 21
EVOLUTION OF
DENTIN BONDING AGENTS

22. FIRST GENERATION
- surface active comonomer NPG-GMA
(N- phenylglycine glycidyl methacrylate)
-chelates with calcium of tooth structure and generates water
resistant chemical bonds.
-aimed only to bond with calcium ion and not the organic matrix
(collagen).
22

23. -- Since they could bond with calcium ions in tooth
structure, they form stronger bonds with enamel than dentin.
- role of smear layer was ignored.
• example - Cervident
23
Amino-carboxylate
based bonding agent
Calcium ion in the
tooth structure

24. LIMITATIONS :
- Low bond strength: 2-3Mpa.
- Loss of bond strength over time.
- magnetic resonance analysis showed no ionic bond
formation
24

25. SECOND GENERATION
• Clearfil Bond F
- first product
- introduced in Japan (1978)
- phosphate ester material.
- phenyl-P and HEMA in ethanol solution.
25

26. - polar interaction between the :
- negatively charged phosphate group in resin
and
- positively charged calcium in smear layer..
Example: scotchbond, bondlite and prisma universal.
LIMITATIONS:
-loosely attached smear layer - weakest link
-low Bond Strength : 1-5MPa
26

27. THIRD GENERATION
- Introduced in 1979.
-- designed not to remove the entire
smear layer, but rather to modify it and to allow penetration
of acidic monomers.
- treatment of smear layer with acidic primer using an
aq.solution of
- 2.5%maleic acid
- 55% HEMA
- trace- methacrylic acid
27

28. Scotchbond-2
- first DBA to receive “provisional” and
“full acceptance” from ADA.
- overall aim of 3rd gen DBA was
- preservation of a modified smear layer, with
- slight demineralization of the underlying
intertubular dentin.
28

29. • LIMITATIONS:
- because of the hydrophobic nature of bonding
agents , acid etching did not produce the significant
improvement in dentin bond strength inspite of flow of resin
into open dentinal tubules.
- Pulpal inflammatory responses were thought to be
triggered due to application of acid.
29

30. 30
- Early DBA were based on the successful model of
silane coupling agents. (used in composites to bond the inorganic
-- filler to the matrix resin)
M R X
UNSATURATED
METHACRYLATE GROUP
-capable of copolymerizing
with the composite resin.
GROUP
-that is capable of
chemically reacting
with the siliceous
substrate.
R
-is a spacer group
that ensures mobility
of the M group after
the X group has been
immobilized by reaction.
Composite Tooth

31. 31
( γ-methacryloxypropyl trimethoxysilane)
organosilane

32. Changing concepts
- organization into generations is somewhat artificial to mark
key advances in materials and techniques along a more-or-
less continuous developmental pathway.
- a more logical and straightforward classification for
contemporary adhesive systems based rather on their
- mechanism of adhesion and the
- number of clinical steps involved.
32

33. - developed by Van Meerbeek et al. (2003).
-is based on approaches to etching , priming, and application of
bonding resin to dentin and enamel
& further subdivided into the number of steps in the
process.
Thus, the major categories of bonding systems are
known as:
- “etch-and-rinse” and
- “self-etch” systems,
- with two subcategories, each according to the number of
clinical steps involved.
33

34. Etch & rinse
adhesives
Self etch
adhesives
Three step
(4th gen)
Two step
(5th gen)
Two step
(6th gen)
One step
(7th gen)
34

35. Three-step (fourth generation)
- the most established, most reliable adhesion method
- consists of three steps:
(1) an acid etchant application,
(2) application of the primer, and
(3) application of the actual bonding agent .
-The primer contains hydrophilic functional
monomers dissolved in an organic solvent such as acetone,
ethanol, or water.
35
E P A

36. Two-step (fifth generation)
- simplified method
- this category combines the primer and adhesive resin into one
application.
This etch-and-rinse strategy is the most effective to achieve
efficient and stable bonding to enamel.
36
E P A

37. Two-step (sixth generation):
- does not involve a separate etching step.
- an acidic monomer which is not rinsed, is used to condition
and prime the tooth at the same time.
37
EP A

38. - There are two types of self-etch adhesives :
- mild and
- strong
- Strong self-etch adhesives -- have been documented with a
bonding mechanism that resembles the etch-and-rinse
adhesives.
- Mild self-etch adhesives -- only partially dissolve the dentin
surface, so a substantial amount of hydroxyapatite remains
available within the hybrid layer.
38

39. One-step (seventh generation)
- this category combines conditioner, primer, and bonding resin
into a single step.
-Most one-step or “all-in-one” systems are delivered by a bottle,
vial, or single-unit dose applicator, which are formulated as a
single component.
39

40. One-step, self-etch adhesives are an attractive approach for
clinicians because of the :
- reduced and less complex number of clinical
steps required .
- there is no need for rinsing or drying of the
tooth structure.
40
E P A

41. Current status
- At this time,
products in the one-step
self-etch category
have undergone limited clinical experience and
consequently not enough is known concerning their
performance and bond durability under long-term clinical
conditions compared with the two-step self-etch and etch
and- rinse products.
41

42. - Recently, however,
- van Landuyt et al.(2011)
showed in a randomized clinical trial that a
one step, self-etch adhesive had similar clinical
performance after 3 years compared with that of an
etch-and-rinse adhesive in class V restorations.
However, the one-step
group exhibited more incisal marginal defects and
discoloration compared with the etch-and-rinse group.
42

43. 43

44. Adhesive system Enamel (Mpa) Dentin (Mpa)
Older systems
Second generation 10-20 2-4
Third generation 10-30 3-13
Current options
Total-etch three steps 20-50 13-80
Total etch one bottle 20-45 3-75
Self-etch primer systems 5-35 10-75
All-in-one self etch
adhesives
0-35 0-60
44
Bond strengths of several generations of adhesives

45. SMEAR LAYER
--- when enamel and dentin tissues are mechanically
cut, especially with a rotary instrument, a layer of adherent
debris and organic film known as a smear layer is left on their
surfaces and prevents strong bonding.
-Different quantities and qualities of smear layer are produced
by the various cutting and instrumentation techniques,
for example,
- during cavity or
- root canal preparation.
45

46. In dentin,
-- the smear layer becomes burnished into the
underlying dentinal tubules and
-- lowers dentin permeability, which is a protective
effect.
However, it is also a very weak cohesive material and interferes
with strong bonding.
- various cleaning or treatment agents and procedures
are employed to either remove the smear layer or enhance
its cohesive strength and other properties.
46

47. - application of acid is used to remove the smear
layer from both enamel and dentin.
Alternatively, in dentin the smear layer can be left partially in
place and modified such that adhesive resins penetrate
through it and bond to the intact dentin structures below.
47

48. 48

49. 49

50. Expanded clinical indications
• Desensitization
- GLUMA desensitizer
(aq. Sol of 5% glutaraldehyde and - 35% HEMA)
• Adhesive amalgam restorations (amalgabond)
- marginal discoloration
-secondary caries &
-pstoperative sensitivity
• Indirect adhesive restorations
50

51. SUMMARY
- Reliable bonding of resins to enamel and dentin has
revolutionized the practice of dentistry.
- Improvements in dentin bonding materials and techniques
are likely to continue.
- Even as the materials themselves become better and easier to
use , however, proper attention to technique and a good
understanding of the bonding process remain essential for
clinical success.
51

52. REFERENCES
• PHILLIPS’ Science of dental material; 12th ed.
• Strudevant’s Art & science of operative dentistry; 4th ed.
• Craig’s – restorative dental materials ;13th edition.
52

53. 53
Thank you