Etch & Rinse

7/31/2019 Etch & Rinse

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Etch & Rinse

Multistep



“Multistep total-etch adhesives”

Generally, in commercial products, the acid componentis between 30% to 40%; the application time on the enamel

suggested by several should not be less than 15 seconds,while on the dentin, it should not be more than 15 seconds.Acid removes the smear layer, exposing both the intertubularand peritubular collagen, and opens the tubules in a funnelconfigurations. It also reduces the superficial free energy.

The primer contains bifunctional molecules (bothhydrophilic and hydrophobic). It wraps round the exterior of the collagen fibrils and brings the superficial free energy up tolevels compatible with a hydrophobic restorative material.

The resin fluid contains monomers that are mainly

hydrophobic, such as Bis-GMA; in any case, it can contain asmall percentage of hydrophobic monomers, such as HEMA.The resin fluid copolymerizes with the primer molecules. Itpenetrates and polymerizes the interfibrillar spaces, acting asa sustaining structure to the hybrid layer, and it alsopenetrates into the dentinal tubules, forming a resin plug.



Etch & Rinse

“Single-step total-etch adhesives”

The acid removes the smear layer, exposingboth the intertubular and peritubular collagen andopens the tubules in a funnel configuration. It alsoreduces the superficial free energy. The first layerapplied on the etched dentin acts as a primer;therefore, it increases the superficial free energy of the dentin. The second layer acts in the same way

as the fluid resin used in the multistep applicationmaterials; it fills the spaces situated in the densenetwork of collagen fibrils.



Self EtchingMultistep

“multistep with primer”

The self-etching primer does not remove the smearlayer of the preparation, but it modifies it and exposesroughly 0.5 to 1 m of intertubular collagen due to its

acidity (pH 1.25 to 1.40). Although the smear plug thatoccludes the tubules becomes impregnated with acidmonomers, it is not removed. By saturating the plug, theself-etching primer prepares the way for the penetrationof the fluid resin, which will then be applied in the

microcanals that crisscross the plug.The primer uses the same type of fluid resin

belonging to the multistep total-etch adhesives. The plugsof resin are formed as the material penetrates into themicrocanals of the smear plug saturated with primer.



Self EtchingOnestep

“Single-step”

As the enamel is etched, the smear layer isintegrated into the interface. The phosphonate

monomer solution demineralises and penetratesthe dentin at the same time, leaving a precipitateon the hybrid layer. This forms a very thin adhesivelayer with a low resistance to the bonding;

therefore, application of more than one layer isadvised. These adhesives are more compatible withcompomers than composites.

Etch & Rinse

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