Acid etching: what does this dental procedure consist of?

When it comes to recovering the functions and aesthetics of damaged teeth, adhesive restorations are an excellent option. We tell you about acid etching, a fundamental step in this type of treatment.

Last update: September 16, 2022

acid etching it is a necessary dental procedure when placing adhesive restorations on teeth. This is a fundamental step when it comes to joining any dental material with tooth surfaces.

A crown, a veneer, a bridge, an inlay or a filling require the use of adhesive systems that allow the bonding of the materials to the dental tissues. For this connection to be made effectively, it is necessary to prepare the tooth structure and acid etching is part of this process.

What is acid etching?

Acid etching is a procedure used in dentistry when making adhesive restorations. Is about a step prior to the placement of the systems that join dental materials to the tooth.

When it comes to repairing a damaged tooth, one of the biggest challenges is getting the filling material to firmly bond to the tooth structure. The humidity of the mouth, the chewing forces and the changes in pH and temperature are obstacles that must be overcome so that the restoration remains in the tooth, restoring its functionality.

In this retention process of dental materials to dental tissues, acid etching plays a fundamental role. Submitting the dental structures to the action of these products allows obtaining more porous surfaces that facilitate adhesion.

Depending on the tooth surface to be etched, two types of etching acids can be used:

  • phosphoric acid: It is the most popular material in the acid etching technique, as it can be used on both enamel and dentin. It is capable of providing an optimal surface for adhesion to both tissues.
  • Hydrofluoric acid: It is used for etching glass and ceramics, improving their adhesion and mechanical resistance.

There are also other types of acids used for dentin conditioning, such as polyacrylic acid and no-wash etchants. In general, these products consist of a colored gel to make it visible. They are marketed in pre-filled syringes that facilitate their handling in the clinic.



What does acid etching do to the tooth?

In the same way that before painting a piece of furniture, we sand its surface to remove the remains of varnish and obtain a more neat result; Acid etching prepares the dental tissues so that the adhesion system works better. By applying acidic substances on the structures of the teeth, these become more porous, thus increasing the retention of the materials to be placed.

At a microscopic level, acid etching generates a controlled erosion of tooth surfaces. The product is capable of dissolving some of the minerals in enamel and dentin, generating microporosities.

These small irregularities on the tooth surface allow better reception of adhesive systems and filling materials. As the products enter these small pores, the union surface increases and, in this way, the restoration is able to remain fixed and stable on the tooth.

To place veneers or crowns, an acid etching must first be performed on the teeth to be treated.

Acid etching techniques

Depending on the type of restoration to be made, the material and the extent of the lesion, the dentist chooses the type of acid. In addition, when performing the procedure, you can choose between the following three basic engraving techniques.

1. Total acid etching

The total acid etching technique is the intervention that It is performed on both enamel and dentin. The same product is used on both tissues, covering a large part of the cavity to be filled.

This technique is used in cavities that require a lot of filling and where adhesion could be a problem. When the tooth preparation is neither deep nor close to the pulp, total acid etching is the most efficient procedure.

By placing the acid on the enamel an etching pattern is generated that creates micro-mechanical retentions. In dentin, because it has a tubular structure and a mostly organic composition, the effect is to expose its collagen matrix so that the hydrophilic monomers of the adhesive material are able to penetrate inside.

When performing this technique, it is important to remember that dentin etching time is less than enamel: only 15 seconds. In addition, it is important not to dry out its surface and to retain some of its moisture, which is why drying with compressed air takes only 5 seconds.

For this technique a 30% or 40% orthophosphoric acid gel is used that prepares both enamel and dentin for adhesive procedures. It has the advantage of achieving high bond strength and not interfering with the polymerization of dual-cure resins, making it fairly universal in use.

2. Selective engraving

This type of dental etching consists of the application of phosphoric acid only on the surface of the enamel. In this case, care is taken that the product does not reach the dentin area.

It is useful for patients who have a tendency to experience sensitivity in the deep areas of the tooth. With this type of procedure these subsequent discomforts can be prevented.

3. Self-engraving

There are adhesive systems that include the etching agent in their composition. In this way, With a single product and the same application, the tooth is engraved and bonded.

The liquid is applied to the enamel and dentin without having previously etched them. It is important to follow the manufacturer’s recommendations.

This technique is very effective for preparations that are already retentive and the new restoration is not at risk of falling out. In addition, these types of products have the great advantage of preventing postoperative sensitivity.

On the other hand, given the ease and speed of its installation, It is a system that is becoming more and more popular. in the dental environment.

Characteristics of etching acids

The dentist has different products, brands, presentations and concentrations. It will always be the dentist who chooses the one that best suits each particular clinical case.

But when choosing between one or the other, the professional takes into account multiple characteristics that clarify and define their choice. We tell you:

  • Acid Types: phosphoric acid will be the choice if enamel or dentin is to be etched. Hydrofluoric is used to prepare materials such as porcelain.
  • Concentration: the percentage of product varies if it is phosphoric or hydrofluoric acid. In the first case, the concentrations available on the market vary between 30% and 40%, its use being 37% more common. Hydrofluoric acid is used in concentrations of 5% or 10%.
  • Presentation: The most common presentation of etching acids are pre-filled syringes that come in various sizes, from 1.2 ml to 50 ml. They can also be found in 5 ml or 15 ml bottles. It is usual that they come accompanied by application tips that facilitate their handling.
  • Solution viscosity: The consistency of the product must facilitate its application, allow great precision and be able to stay in the place where it has been deposited. Thus, in general, they are in the form of a thixotropic gel, that is, capable of flowing when applied, but viscous and without slipping off the tooth surfaces.
  • Liquid/Gel: Etching acids can be presented in a liquid state or as a gel, the latter being the most common. In both cases they can come in syringes or in bottles.
  • Color: in order to be able to distinguish the product from the tooth and to know where it is and what surfaces it has reached, the acids are colored. They are green, purple, yellow or blue.
  • Application time, washing and drying: the application, washing and drying times vary depending on whether the product is applied to enamel or dentin. In addition, each manufacturer indicates the specific number of seconds for their own product, so it is essential to follow the recommendations of each brand.

Acids with exceptional characteristics

Advances in the field of dentistry allow finding increasingly practical and successful materials. Thus, today it is possible to find new products with novel properties.

One of the new capabilities that some cutting-edge adhesive systems have achieved is the ability to be self-limiting. This means that the product decalcifies the dentin to a certain depth and then stops acting. With this, the risk of wearing out excess tissue and causing complications such as sensitivity is avoided.

Compatibility with all filling materials is another novel feature that various engraving systems are seeking to achieve. In this way, the professional can count on a single product for all the types of restorations he performs.

When doing an acid etching, the professional chooses the product that best suits the patient, according to its characteristics.

How is acid etching done?

The method for acid etching a tooth depends on the technique to be used and the product manufacturer’s recommendations. Thus, the times of each step vary from one brand to another.

The procedure is very simple and fast; It usually doesn’t take more than 1 minute. Although there are variations depending on the technique and the brand, in general, these are the steps:

  1. Prepare the tooth: the tooth in the mouth should already be free of cavities and ready to receive the restoration. If it has not been done yet, it is time to isolate it and dry it very well.
  2. Bring the product to the tooth: the acid is applied with the dispenser that brings the product, covering the areas to be engraved. It is left to act for the time stipulated by the manufacturer and according to the type of fabric. They should not be more than 60 seconds.
  3. Rinse: The material is removed, applying a jet of water on the tooth surface until there are no remains.
  4. Drying: The area is slightly dried, allowing some moisture to remain in the dentin.

Thus, the dental surfaces are already engraved and ready to receive the chosen adhesive system. Then, we proceed with the dental restoration.

Risks of acid etching

Although it is true that this procedure increases the fixation of the restorations to the tooth, it can also cause some complications, such as postoperative sensitivity. Some treated pieces may present discomfort with cold or heat for a few days or even weeks.depending on the depth of the restoration.

In any case, with adequate isolation, respecting the etching times and placing a desensitizing agent in the preparation, the risk of sensitivity decreases.



A procedure to recover the smile

Acid etching generates microporosities and opens the dentin tubules on tooth surfaces. This, in combination with the adhesive systems, improves the union and retention of filling materials to the teeth. Having this procedure allows you to repair damaged dental pieces and achieve functional and beautiful finishes.

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