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					Dentine bonding agents

      Dr Syed Sohaib Daud
• The state in which two surfaces are held together by interfacial
  forces which may consist of valence forces or interlocking or
                    (American society for testing and materials)

• An adhesive is a material that join two surfaces together and
  is able to transfer load from one surface to other.
    Mechanism of resin bonding
•   Mechanical
•   Adsorption
•   Diffusion
•   Combination of three
Dentine adhesion

• Dentine bonding relies primarily of the penetration of
  adhesive monomer into the filigree of collagen fibers left
  exposed after etching with acid.
 Mechanism of dentine bonding

                              Acid washing / rinsing
                              Removes smear layer
                              Dissolves HA

Drying shrinks remaining
Collagen polymer molecules
                             Rehydration / priming
                             Swells collagen
Mechanism of dentine bonding

                 Monomer polymerisation
                 And collagen entanglement

                    Monomer penetration
 Challenges in dentine bonding

• Dentine contains substantial amount of water and organic
  material as compared to enamel.
• It contains dens network of tubules.
• Smear layer prevents the penetration of adhesive into tubule by
  forming smear plug.
First generation
• It consisted of co monomer NPG-GMA (N-phenylglycine
  glycidyl methacrylate).
• Low in-vitro dentine bond strength.
• In-vivo results were also discouraging.
• Carbon-13 nuclear magnetic resonance analysis showed that no
  ionic bonding develops between NPG-GMA and hydroxyaptite.

 Second generation
• Clearfill bond was the first product of second generation of
  dentine adhesives.
• It was a phosphate ester(phenyl-p and
  hydroxyethylmethacrylate[HEMA] in ethanol).
• Its mechanism of action was based on the polar interaction
  between negatively charged phosphate groups in the resin and
  positively charged calcium ions in hydroxyapatite.
• They had low dentine bond strength of only 1 to 1.5 Mpa.
• Presence of loosely attached smear layer and absence of
  hydrophilic groups posed major problems.
• Resistance to water was low.
Third generation
• The concept of acid etching was first introduced in 1979 by
• Clearfill new bond was introduced in 1984 and contained
  HEMA and 10-carbon molecule known as 10-MDP(10-
  methacryloxyethyl decyl dihydrogenphosphate).
• Some materials were designed to modify smear layer and
  allow penetration of acidic monomer.
• Another treatment of smear layer with acidic primer was
  proposed using aqueous solution of 2.5% maleic acid, 55%
  HEMA, and a trace of methacrylic acid(scotchbond 2).

Smear layer       1st step
                 2ndstep: :
Residual water    -Total primer
 Primer           Leaving free minerals
 Adhesive          rd surface
                  -Rinse adhesive
                 Adding surface resin
                  -Total drying of surface
                 ,Then adding Composite
Fourth generation/Three step total etch adhesive

• Fourth generation of dentine adhesives was introduced for use
  on acid etched dentine.
• This technique is also known as total etch or etch and rinse
• Application of acid results in partial or total removal of smear
  layer and demineralization of underlying dentine up to depth of
  7.5 microns.
• Fourth generation dentine adhesive include three components
1. A phosphoric acid gel that is rinsed off.
2. A primer containing reactive hydrophilic monomers in
   ethanol, acetone, or water.
3. An unfilled or filled resin bonding agents containing
   hydrophobic monomer (Bis-GMA) combined with hydrophilic
   molecules (HEMA).
•   Acid etching also alter the free surface energy of dentine
    which is undesirable.
•   Primer in three step technique is designed to increase critical
    surface energy of dentine.
•   When primer and bonding agents are applied they results in
    formation of a hybrid layer and resin tags.
•   This generation was proved successful both in vivo and in
    vitro with dentine resin bond strength of 13-80 Mpa.

                   1st step
                  2ndstep: :
Smear layer        -Total primer
                  addingetching(removal of
Residual water     smear layer)
 Primer            Leaving free minerals on
 Adhesive resin   3surface
                    rd step:
                   -Rinse adhesive
                  Adding surface resin &
                   -Without drying
                  then composite of surface
                   (residual water left)
Fifth generation/one bottle, Total etch
• This system combine the primer and bonding agents into a
  single solution.
• Separate etching is still required.
Sixth generation/self-etching primer system
• These self etching primers, first introduced in Japan, include a
  phosphonated resin molecule that performs function of priming
  and etching simultaneously.
• They do not require rinsing off.
• The bonding mechanism is based on the simultaneous etching
  of enamel and dentine, forming a continuum in the substrate
  and incorporating smear plugs into the resin tags.
• It simplifies the bonding technique.
• Elimination of rinsing and drying reduce the possibility of over
  wetting or over drying.
• SEPs are less technique sensitive.
• Less discrepancy between the depth of demineralization and
  depth of resin infiltration.
• Less postoperative sensitivity.
• One disadvantage is that they do not etch enamel as well as
  phosphoric acid.
Self-etching primer adhesive system
Seventh generation/self etching adhesives(all in one)

• This generation include the materials that incorporates the
  classic steps of etching, priming, and bonding into one solution.
• All in one adhesive contain uncured ionic monomer that
  contact the composite material directly.
• Presence of this un reacted acidic monomer is responsible for
  their incompatibility with self cured resin.
• These adhesives act as semi permeable membrane and hence
  result in degradation of dentine resin interface.
• These resin monomer might be too hydrophilic which make
  them susceptible to water degradation.
Comparison of the Classification and Components of
Dental Adhesive Systems
STEP             4TH            5TH            6TH             6TH GEN              7TH GEN
                 GEERATION      GENERATION     GENERATION      (MIXING
                                                               SELF ETCHING         SELF ETCHING
                                                               ADHESIVE             ADHESIVE

Etching of       Etchant        Etchant        Self etching    Self-etching,        Self-etching,
enamel dentine                                 primer          self-priming         self-priming
                                                               resin/sealer         resin/sealer

Priming of       Primer         Self-priming   Self –etching   Self-etching,        Self-etching,
dentin                          resin/sealer   primer          self-priming         self-priming
                                                               resin/sealer         resin/sealer
Sealing of       Resin/sealer   Self-priming   Resin/sealer    Self etching, self   Self-etching,
enamel and                      resin/sealer                   priming              self-priming
dentine                                                        resin/sealer         resin/sealer
Comparison of the Number of System Components and Clinical Placement
Steps of Dental Adhesive Systems
Generation       steps            Description          Components

1st              2                Etch enamel, apply   2
2nd              2                Etch enamel, apply   2
3rd              3                Etch enamel, apply   2-3
4th              3                Total etch, apply    3-5
5th              2                Total etch, apply    2
6th              1                Apply self etch      2
7th              1                Apply self etch      1

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Description: dentin bonding agents ........overview