Dentin bonding agents / rotary endodontics courses

INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
WWW.INDIANDENTALACADEMY.COM

• Introduction
• Criteria For Bonding Agent
• Terminologies
• Contents of Bonding System
• Bonding to dentin is Challenging!
• History
• Classifications
• Generations Of DBA
• Newer DBA
• Conclusion
• References

Introduction
• Today operative dentistry primarily involves “minimal
invasive or “minimum intervention” . Only the lost or
diseased tooth tissue is replaced by restorative material that
is directly bonded to remaining sound tissue.
• While effective bonding to enamel has been achieved with
relative ease, bonding to dentin has proved to be more
difficult.
• Dentin presents a less favorable substrate, for resin bonding,
with its higher organic content, tubular nature and inherent
wetness .

• Dentin adhesive systems can react with intertubular and
peritubular dentin only when the smear layer is removed or
when adhesive system is capable of difussing through this
layer of debris.
• In an attempt to improve adhesion of composite restorative
materials to dentin, research in chemical bonding has led to
the development of dentin adhesives

Criteria for Ideal Dental Adhesive System (Philips and Rage) 1961
- Provide a high bond strength to dentin that should be present
immediately after placement and that should be permanent.
- Provide a bond strength to dentin similar to that to enamel.
- Show good biocompatibility to dental tissue including pulp.
- Minimize micro leakage at the margins of restorations.
- Prevent recurrent caries and marginal staining
- Be easy to use and minimally technique sensitive
- Possess good shelf life
- Be compatible with a wide range of resins
- System should not be toxic or sensitizing to the operators
and patients.
- Should seal the tooth surface from oral fluids.

TERMINOLOGIES
• Adhesion ~ the attraction between two atoms and
molecules at the contacting surfaces of different
materials; it can be chemical (ionic), physical (van der
Waals’), and/or mechanical (micro- or macro-
interlocking)
• Adhesive ~ monomer (or related) that penetrates and
establishes intimate contact with the conditioned tissue
substrate, polymerises, and forms a strong bond
between such substrate and the restorative material
• Priming ~ cleaning, structural alteration, and
increasing adhesiveness of the substrate.

• Etching ~ dissolution of the substrate, removed by
rinsing to enhance intimate contact of adhesives
with collagen.
• Wetting ~ the ability of a liquid to come into
intimate contact with solid substrate; facilitates
bonding

Etchants, Primers & Adhesive in Bonding system:
- Etchant is an acid which selectively dissolves the tooth
structure to provide retention for the restoration.
- They are also known as conditioners.
- The most popular etchant is 37% phosphoric acid.
- Primers are hydrophilic monomers usually carried in a
solvent.
- Because of their hydrophilic nature they are able to penetrate
the moist tooth structure especially the dentin and its collagen
mesh thus improving the bond.
- Thus they serve as a bridge connecting the tooth structure to
the adhesive.
- The solvent used are acetone, ethanol or water. Some are used
without solvents.

Etchants, Primers & Adhesive in Bonding system:
• Adhesive are generally hydrophobic monomers.
• Being hydrophobic they do not wet the tooth leading to air
entrapment, air inhibition and thereby poor bonding.
• Thus they have to be used in combination with primers to
form an effective bond to tooth structure.
• The adhesive bonds the resin to the primer which in turn
penetrates and binds to the tooth structure thus completing the
bonding sequence.

CONCEPT OF A DENTIN
BONDING AGENT:
D
E
N
T
I
N
COMPOSITE
Dentin
Bonding
Agent
HYDROPHILIC
HYDROPHOBIC

Bonding to dentin is a challenge!!
Due to complexities of dentin . . .
• Complex histologic structure and variable composition of the
dentin.
• Enamel is 92% inorganic hydroxyapatite by volume, Whereas
dentine is (on average) only 45% inorganic.
• Also dentinal hydroxyapatite is randomly arranged in an
organic matrix that consists primarily of collagen, which is
permeated throughout by tubules.
• These tubules contain vital processes of the pulp odontoblasts.
Hence, vital dentine is a sensitive structure.
• The high water content provides competition with any adhesive
biomaterial for bonding to dentine.WWW.INDIANDENTALACADEMY.COM

SMEAR LAYER
• Presence of smear layer on prepared dentin surface. This smear
layer fills the orifices of dentinal tubules (forming smear plugs
and decreases dentin permeability by 80%)
• To achieve a strong bond, it is necessary to either strengthen
this smear-layer in situ or to remove it entirely.
• In the latter, it is imperative to ensure an adequately adhesive
restoration otherwise the open tubules may allow irritants or
bacteria greater access to the pulp.

• Removal of the smear layer and smear plugs with acidic
solutions may result in an increase of the fluid flow onto the
exposed dentin surface.
• This fluid may interfere with the adhesion, because the
hydrophobic resins do not adhere to the hydrophilic substrate
even if resin tags are formed in dentin tubules.

• Stresses at the Resin- Dentin interface:-
- Composites shrink as they polymerize, creating stresses of
up to 7 MPa within the composite mass depending on the
configuration of the preparation.
- Unrelieved stresses in the composite may cause internal
bond disruption as well as marginal gaps around restoration
that increases microleakage.
- Immediate bond strength of approx. 17 MPa may be
necessary to resist these contraction stresses to prevent
marginal debonding.

Development of Dentin Bonding Agents:-
• 1951 – Dr. Oscar Hagger introduced Sevitron cavity seal
(Amalgamated dental company). This was
glycerophosphoric acid dimethacrylate (GPDM) chemically
activated with sulfinic acid.
• 1956 – Buonocore et al reported that glycerophosphoric acid
dimethacrylate (GPDM) could not bond to hydrochloric acid
etched dentinal surfaces.
Limitations:-
- Low bond strength of 2-3 MPa.
- Bond was unstable in water.

• 1962 – R.L. Bowen developed bis-GMA molecule.
• 1965 – Bowen introduced N- Phenylglycine Glycidyl methacrylate
(NPG-GMA), to overcome the limitations of GPDM.
• Late 60’s to 70’s – 1st generation DBA’s.
• Late 70’s – 2nd generation DBA’s.
• 1979 – Fusayama dentin etching (total etch technique).
• 1982 – Nakabayashi “Hybrid Layer”.
• Mid 80’s – 3rd generation DBA’s.
• 1991 – 1st adhesion Symposium, Nebraska, Omaha.
- Kanca popularized total etching in U.S.
- Dentin etching gained worldwide acceptance.
• Early 1990’s - 4th generation DBA’s.

CLASSIFICATION OF DENTIN BONDING
AGENTS (DBA)
1) Based on chemistry:-
- Phosphate/ Phosphonate system
- Oxalate system
- NPG-PMDM system
- Isocyanate system
- Gluteraldehyde system
- 4- META – Tributyl borane system
2) Based on generations of dentin bonding agents:-
Generation I to VII
3) Scientific classification:- Based on treatment of smear layer and the
number of clinical steps:-
Smear layer –modifying adhesives (one/two step)
Smear layer –removing adhesives (two/three step)
Smear layer –dissolving adhesives (one/two step)
(Self-etching adhesives)

4) Based on solvents:-
- Acetone based
- Water based
- Ethanol based
5) Based on fillers:-
- Filled adhesives
6) Based on fluoride release:-
- Fluoride releasing adhesives
7) Based on type of activation:-
- Light activated
- Dual activated
8) Based on type of substrate:-
- Enamel, dentin, amalgam, porcelain, base and noble
metals.

CLASSIFICATION OF BONDING AGENTS BASED
ON THEIR SHEAR BOND STRENGTH: (EICK ET AL,
1991)
Three categories of dentinal adhesives are proposed:
• Category I includes adhesives with shear bond
strength values between 5 and 7 Mpa;
• Category II includes dentinal adhesives with shear
bond strengths between 8 and 14 Mpa; and
• Category III includes adhesives with shear bond
strength values above 20 Mpa .

CLINICAL SIGNIFICANCE OF THIS
CLASSIFICATION:
• Polymerization shrinkage
• 2.9 to 7.1% by volume
• contraction gap
• 17-20 MPa bond strength to overcome (Davidson et al)

EVOLUTION OF DENTIN BONDING
AGENTS:
• First Generation.
• Second Generation.
• Third Generation.
• Fourth Generation.
• Fifth Generation.
• Sixth Generation.
• Seventh Generation.

FACTORS INFLUENCING THE EVOLUTION
OF BONDING SYSTEMS:
• Etching/conditioning Dentin
• Smear Layer Treatment
• Handling properties
According to generations:
Evolution of
bondingagents from
No etch to
total etch
and self etch.

FIRST GENERATION DBA
• Ignored the smear layer.
• Achieved deeper penetration in D’ tubules
• These bonded to the enamel and dentin by chelation with
calcium on the tooth surface.
• They included NPG-GMA (N- Phenylglycine Glycidyl
methacrylate), the polyurethanes and the cyanoacrylates.
• NPG-GMA is a bifunctional molecule or coupling agent.
• This means that one end of this molecule bonds to dentin
while the other bonds (polymerizes) to composite resin.

• An example of an NPG-GMA bonding agent was
S.S.White’s Cervident which became available in 1965.
• Bond strengths of first generation DBA’S was 2-3 MPa.

Limitations:-
• Low bond strength of 2-3 MPa
• Loss in bond strength over time
• Lack of stability of individual components during storage
• Based on carbon-13 NMR analysis – No ionic bonding
develops between NPG-GMA and hydroxyapatite

SECOND GENERATION DBA
• These products depended upon smear layer for bonding.
• The majority of these incorporated halophosphorous esters
of unfilled resins such as bisphenol- A glycidyl
methacrylate, or bis-GMA, or hydroxyethyl methacrylate,
or HEMA.
• The mechanism by which these bonded to dentin were
postulated to be through an ionic bond to calcium by
chlorophosphate groups.
• Clearfil Bond system F (Kuraray) introduced in 1978, was
the first product.
• Bond strength range from 4.5-6 MPa.

• Limitations :-
- Primary bonding was to the smear layer which prevented intimate resin-
dentin contact, which is a pre-requisite for a chemical reaction.
- Low Bond Strength 4.5 to 6 Mpa Only

THIRD GENERATION DBA
• Three step systems.
• Dentin etching was introduced by Fusuyama.
• Followed by a primer application.
• Application of an unfilled resin.
• These systems alter or remove the smear layer prior to
bonding.
• Bond strength range between 12-15 MPa.
• Three component system consisting of –
- Conditioner
- Primer
- Adhesive

Conditioner (Cleanser, Etchant)- Is usually
• a weak organic acid (maleic acid),
• a low concentration of a stronger inorganic acid
(phosphoric or nitric acid), or
• a chelating agent (EDTA).
• Actions:-Heavily alters or removes the smear
layer.
- Demineralizes peritubular and intertubular
dentin and thereby exposes collagen fibrils
- Increases dentin permeability by 4-9
times.

DENTIN PRIMER:
• The primer contains hydrophilic resin monomers which
include hydroxyethyl trimellitate anhydride, or 4-
META, and biphenyl dimethacrylate, or BPDM.
• The primers contain a hydrophilic group that infiltrates
the smear layer, modifying it and promoting adhesion to
dentin, and
• the hydrophobic group of the primer creates adhesion
to the resin.
• Dentin primers may be 6 % phosphate penta-acrylate,
(PENTA) ; 30 % HEMA; and 64 % ethanol.

• Actions:- Links the hydrophilic dentin to the
hydrophobic adhesive resin.
- Promotes infiltration of demineralized peritubular and
intertubular dentin by its own monomers and those of the
adhesive resin.
- Increase wettability of the conditioned dentin .

• Adhesive (Bonding resin, sealing resin):- Is an unfilled
or partially filled resin, may contain some component of
the primer (e.g- HEMA) in an attempt to promote
increased bond strength.
• Actions:-
- Combines with the primer monomers to
form a resin- reinforced hybrid layer (resin-
dentin interdiffusion zone) 1-5 microns thick.
- Forms resin tags to seal the dentin
tubules.
- Provide methacrylate groups to bond with
the subsequently placed resin composite.

• Representative brands:-
- Scotch bond 2
- Universal bond
- Syntac
- Tenure

FOURTH GENERATION DBA EARLY 990’S
• 3- component system.
• Fusayama and colleagues tried bonding to enamel and
dentin by total etching the preparation with 40 percent
phosphoric acid.
• The mineralized tissues of the peritubular and
intertubular dentin are dissolved by the acidic action;
the initial surface penetration exposes the collagen
fibers.
• In this area, for a depth of 2 to 4 micrometers,
hybridization takes place, and resin tags can seal the
tubule orifices firmly.

FOURTH GENERATION DBA’S EARLY 990’S
• Ability to bond as strongly to dentin as to enamel.
• “Wet bonding” (Ability to bond strongly to moist
dentin and technique insensitivity).
• “Multi purpose bonding” (Ability to bond to many
different substrates, e.g.- enamel, dentin, porcelain,
base and noble metals, amalgam).
• Bond strength ranges between 17-24 MPa.

Etchant First step
Primer
Adhesive
Second step
Third step
All Bond 2 Pro-Bond Liner Bond 2

• The hybrid layer is defined as “the structure formed in dental hard tissues (enamel,
dentin, cementum) by demineralization of the surface and subsurface, followed by
infiltration of monomers and subsequent polymerization.”
Nakabayashi et al (1982)
Hybrid
zoneWWW.INDIANDENTALACADEMY.COM

Wet bonding
• Introduced by Kanca and Gwinnett in 1992.
• After conditioning, the enamel and dentin surfaces
should be properly treated to allow full penetration of
adhesive monomers.
• On the enamel surface – A dry condition is preferred.
• On the Dentin surface – A certain amount of moisture is
needed to avoid collapse of exposed collagen scaffold,
which impedes effective penetration of adhesive
monomers.
• Consequently it is difficult to achieve the optimal
environment for both substrates.

WET VERSES DRY BONDING
Air drying demineralized dentin reduces its volume by 65%

Keep the substrate
field dry and use
adhesive systems
with water based
primers to rehydrate
Keep the acid etched
dentin surface moist
and rely on water
chasing capacity of
acetone based primers

Etchant Primer Adhesive+ +
Etchant + Primer Adhesive
Primer
and
adhesive
3 step total etch
IV Generation
2 step
V Generation

FIFTH GENERATION DBA’S
• Unique feature is the combination of the priming and bond
resin application steps, resulting in a one component
formula.
• Also rely heavily on wet bonding.
• Most commonly used and probably the most successful
system.
• These bonding systems create a mechanical interlocking
with etched dentin by means of resin tags, adhesive lateral
branches and hybrid layer formation..

• Bond strength - > 20MPa
- Prime and bond
- Prime and bond 2.1
- One step
- Optibond solo
- Single bond
Prime & Bond- NT
Adper Single Bond Optibond Solo
Gluma Comfort Bond

INTER-COMPARISON OF V GENERATION:
Adhesive Mean Shear Bond Strength
( MPa )
Single Bond 30.0±5.5
Opti Bond Solo 23.4±3.4
One-Step 22.5±3.8
Prime & Bond 2.1 21.1±5.0

SIXTH GENERATION DBA’S
• They are self etching adhesives ( Etch & prime
simultaneously).
• They involve a somewhat different mechanism in
that, as soon as the decalcification process is
initiated, the infusion of the evacuated spaces by
dentin bonding agent is begun.
• As a result, the potential for residual vacancies
amongst the collagenous fibers is dramatically
reduced or eliminated altogether.
Etchant
Primer
Adhesive

Etchant Primer Adhesive
Etchant Primer
Adhesive
+ +
+ +
Self
etching
primer
All in one
adhesive
Sixth Generation
Type I
Sixth Generation
Type II

ADVANTAGES AND
DISADVANTAGES OF SELF-
ETCHING ADHESIVES
• Advantages :-
- Simultaneous demineralization and resin infiltration.
- No post conditioning rinsing.
- Not sensitive to diverse dentin-wetness conditions.
- Time saving application procedure.
- Consistent and stable composition.
- Hygienic application (Unidose).
- Effective dentin desensitizer.

• Disadvantages :-
- Insufficient long term clinical research.
- Adhesion potential to enamel yet to be
clinically proven.
Xeno IIIPrompt L PopClearfil SE Bond

Etchant Primer Adhesive+ +
Etchant Primer Adhesive
= All in one
adhesive
Seventh
Generation
DBA’s
Seventh Generation DBA’s

SEVENTH GENERATION DBA’S
I- Bond
Xeno IV
Dentsply
G Bond
GC

NEWEST PRODUCT
• Nanofilled :-
- Recently, bonding agents have been marketed that
contain extremely small filler particles. These are called
nanofilled DBA’s.
E.g.- Prime and bond NT (7nm fillers)
- Excite (12nm fillers)
Advantages- Make DBA stronger and tougher
- Able to cover adequately with a single coat
- Improved marginal integrity.

• Newer Antibacterial Dentin Bonding Agents:-
- Recently, bonding agents have been marketed that
contain methacryloyloxy dodecyl pyridinium bromide
(MDPB), has been developed (Imazato et al., 1994).. And
also Nano-silver!
E.g.- Clearfil Protect Bond and Prime
Bond NT
Advantages- The incorporation of MDPB is considered to be a
potential method of providing dentin adhesive systems with
antibacterial activity before and after curing.
Eradication of residual bacteria that invade the
tooth-adhesive interface by microleakage.

CELEBRATE THE BOND OF LOVE
MONOMER-POLYMERS CAREFULLY
AND UNFOLD THE ULTIMATE BEAUTY
OF ADHESION SLOWLY !

References:-
• Sturdevant’s art and science of operative dentistry, 4th
edition.
• Fundamentals of operative dentistry, James B. Summitt, 2nd
edition.
• Phillips’ science of dental materials, Kenneth J. Anusavice,
11th edition.
• Swift ED, Perdigao J, Heymann HO. Bonding to enamel and
dentin: A brief history and state of the art. Quintessence Int
1995:26:95-110.
• Walshaw PR, McComb D. Clinical considerations for
optimal dentinal bonding. Quintessence Int 1996:27:619-
625.
• Meerbeek BV et al. Adhesion to enamel and dentin: current
status and future challenges. Operative Dentistry
2003:28:215-235.

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