DENTIN BONDING AGENTS
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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 macrointerlocking) 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.
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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
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% by volume 3%
12%
water organic mineral 85%
Inorganic component is homogenous, regular rods and prisms
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Acid etching removes approx 10 microns of enamel Creates microporous layer 5-50 microns
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Human dentin is a heterogenous material composed of a solid (circumpulpal) phase surrounding a network of tubules. These tubules, measuring about 1 to 3 micrometer in diameter, contain elongated cell bodies that radiate from the the dental pulp organ throughout the entire dentin. Their average density is about 30 000 tubules/square mm..
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Structurally dentin is composed of mineral crystals deposited between a network of protein fibrils. Approximately 90% of this network is type I collagen, the balance consisting of a sheath of phosphoproteins surrounding the collagen, and other proteins in small amounts.
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% by volume
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45% water organic mineral 33%
22%
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Inorganic component is heterogeneous, peritubular and intertubular dentin Low surface free energy - wets less easily
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Dentinal tubules Diameter (microns) • Number • Tubular surface area •
Pulp
DEJ
2.5 0.8 45,000 20,000 25% 3%
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Complex histologic structure and variable composition of the dentin. Whereas enamel is 92% inorganic hydroxyapatite by volume, 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 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.
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Tooth surface instrumented with a rotary or manual instrument Composed of:
Pulverized hydroxyapatite Altered collagen Bacteria Saliva
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To achieve a strong bond, it is necessary to either strengthen this smear-layer in situ or to remove it entirely.
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In the latter, it is imperative to ensure an adequately adhesive restorative otherwise the open tubules may allow irritants or bacteria greater access to the pulp.
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Removes smear layer.
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Exposes a microporous scaffold of collagen fibrils increasing the microporosity of intertubular dentin.
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Various acids used Phosphoric Citric Maleic Nitric
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D E N T I HYDROPHILIC N
Dentin Bonding Agent
COMPOSITE HYDROPHOBIC
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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 .
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Polymerization shrinkage
2.9 to 7.1% by volume contraction gap 17-20 MPa bond strength to overcome (Davidson et al)
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According to generations:
Evolution of
bonding
agents from
No etch to
total etch and
self etch. www.indiandentalacademy.com
First Generation. Second Generation. Third Generation. Fourth Generation. Fifth Generation. Sixth Generation. Seventh Generation.
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Etching enamel Etching/conditioning Dentin Smear Layer Treatment Handling properties
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These contained N-phenylglycine and glycidyl methacrylate or NPG-GMA. 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. The bond strengths of these early systems were only 1 to 3 MPa.
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In the late1970s, the second-generation systems were introduced. 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. These were weak bonds with a range of 2-7 MPa. www.indiandentalacademy.com
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Since dentin was not etched in these early bonding systems bonding was with the smear layer. Water immersion.
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Three step systems. Dentin etching was introduced by Fusuyama. Followed by a primer application. Application of an unfilled resin.
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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 pentaacrylate, (PENTA) ; 30 % HEMA; and 64 % ethanol. www.indiandentalacademy.com
Denthesive
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The fourth generation bonding system contains two or more bottles. One consists of the primer and the other the adhesive.
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Etchant
Etchant
+
Primer
+
3 step totalPrimer etch IV Generation Primer and adhesive
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Adhesive
Adhesive
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Fusayama and colleagues tried to simplify bonding to enamel and dentin by total etching the preparation with 40 percent phosphoric acid.
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The mineralized tissues of the peritubular and intertubular dentin are dissolved by the acidic action; the initial surface penetration exposes the collagen fibers.
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In this area, for a depth of 2 to 4 micrometers, hybridization takes place, and resin tags can seal the tubule orifices firmly .
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Results from the polymerized methacrylate and dentin.
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) www.indiandentalacademy.com
Hybrid zone
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The formation of resin tags and adhesive lateral branches complete the bonding mechanism between the adhesive material and etched dentin substrate.
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All Bond 2
Pro-Bond
Liner Bond 2
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Scotch Bond
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.
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These bonding systems create a mechanical interlocking with etched dentin by means of resin tags, adhesive lateral branches and hybrid layer formation..
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3 step total etch Etchant
Etchant
IV Generation +
+
Primer
Primer
+
Primer and adhesive
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Adhesive
Adhesive
2 step V Generation
Gluma Comfort Bond Adper Single Bond
Prime & Bond- NT
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Optibond Solo
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
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. The bonding agent is either applied after the self etching primer or mixed together before single application. www.indiandentalacademy.com
Sixth Generation Type I Etchant
Self + etching primer
+
Primer
Adhesive
Sixth Generation Type II
Etchant
+
All in one adhesive Primer
+
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Adhesive
Clearfil SE Bond
Prompt L Pop
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Xeno III
Etchant
Etchant
+
Primer
+
Adhesive
Primer
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Adhesive
=
All in one adhesive
I- Bond
G Bond
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Xeno IV
1.
Modify the smear layer & incorporate it into the bond. One step – Prime & Bond 2.1 Two step – Pro Bond
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2. Completely removes the smear layer: Two step – Clearfil Liner Bond 2. Three step – Clearfil Liner Bond.
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3. Dissolves the smear layer than removing it.  Prime & Bond 2.0.
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Difference in the degree of mineralisation.
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Concentrations of both calcium and phosphorus in both peritubular and intertubular dentin are lower in primary teeth.
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The tubular diameter and density in dentin of primary teeth is lesser than that in permanent teeth.
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Dentin of primary teeth is more sensitive to the acid etch/ conditioning procedure.
This leads to an increased thickness of the hybrid layer and the subsequent lack of complete penetration of the adhesive resin into the demineralised dentin.
Ideally the concentration and duration of etch/ conditioning has to be re-calculated for primary teeth. www.indiandentalacademy.com
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Carious dentin is a combination of porous and nonporous zones.
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The resultant deposition of Whitlockite may warrant additional etching/ conditioning times compared to sound dentin.
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Simple to use. Minimally irritating to the tissue. Less technique sensitive. Clinically satisfactory bond.
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Chemically bonding the resin molecule to the collagenous structure of dentin rather than by means of micromechanical retention (as is done now). Incidentally, another approach to dentinal adhesion could center on the chemical bonding of the resin to the hydroxyapatite .
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Conclusion
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Thank You!............
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Prime & Bond 2.0 – Total etch Prime & Bond 2.1 – No etch Prime & Bond NT – Nano-Technology
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Drying the dentin will produce a relatively impermeable amorphous layer:
Denatured collagen Collapse of collagen layer
Must remain moist to resist this impermeable layer. Pooled moisture should be removed by blotting and not with a blast of air. Dry dentin should be remoistened with a wet cotton pledget.
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The total-etch technique permits the etching of enamel and dentin simultaneously using phosphoric acid for 15 to 20 seconds. The surface must be left moist (“wet bonding”), however, in order to avoid collagen collapse . The application of a hydrophilic primer solution infiltrates the exposed collagen network forming the hybrid layer .
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Bonding Agent Smear Layer
Smear layer not removed in second generation adhesives
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