Features and stages of the alcohol protocol in dentistry, types of adhesive systems

Composite materials have been used in dentistry for eliminating aesthetic defects and restoring teeth damaged by caries for 40 years. During this period, adhesives have been improved more than once, and their use has become easier. To improve adhesion as a result of dentin hybridization, an alcohol protocol is used.

What is an alcohol protocol?

A protocol in medicine is recommendations for treatment developed by scientific and medical communities. These recommendations are scientifically based, within the framework of evidence-based medicine, practice-oriented guidelines for action.

The alcohol protocol is a recommendation for the use of an alcohol solution, which is necessary for dentin hybridization. Alcohol is used to inhibit metalloproteinase enzymes, which are formed in dentin under the influence of phosphoric acid.

What are adhesives used for in dental treatment?

An adhesive is an intermediate substance to provide a bond between surfaces. An example is the connection of etched tooth enamel and a composite material, between which an enamel bonding adhesive is placed.

For what purposes do doctors use adhesives? They are necessary for installing composites when restoring anterior teeth that have been damaged mechanically or by caries, and when correcting visual defects of dental units.

Adhesive systems

Dental composite materials do not have independent adhesion (a connection of a physical and chemical nature between dissimilar surfaces) to dental tissues. Therefore, filling teeth with composites requires the mandatory use of special adhesive systems (bonds). In other words, to create a strong connection between the composite and tooth tissues, it is necessary to use additional materials that have chemical or micromechanical adhesion to tooth tissues. Failure to comply with this condition leads to disruption of the adhesion of the composite to the dental tissues (due to shrinkage of the composite during polymerization) and the appearance of a marginal gap, the occurrence of secondary caries and sometimes damage to the pulp. The main components of the organic matrix of composites have fairly high adhesion to enamel, but in relation to wet dentin they behave as hydrophobic substances that do not adhere well to its surface.

Tooth enamel consists mainly of an inorganic substance (biological apatite, about 95% by weight), an organic component (collagen fibers, 1-1.5%) and water (4%). Thanks to this composition, the enamel can be dried, which ensures good adhesion of the hydrophobic organic component of the composite. To increase the effectiveness of adhesion of enamel and composite, the filling (restoration) technique involves preliminary acid etching of the enamel with a liquid or gel based on phosphoric (10-37%) or maleic (10%) acid. As a result of acid etching, organic plaque is removed from the enamel surface, proteins are denatured and, most importantly, enamel microporosity is formed due to the dissolution of areas of enamel prisms and substances in the interprismatic space to a depth of about 40 microns. After removing the etching agent with water and thoroughly drying, the surface is treated with enamel adhesives, which are a mixture of low-viscosity monomers (usually without filler), chemical composition close to the organic matrix of the composite and capable of penetrating into the spaces between the prisms of the etched enamel. Therefore, after polymerization, the enamel adhesive forms a mechanical bond with the enamel (due to polymerization in the micropores of the enamel) and a chemical bond (due to copolymerization) with the organic matrix of the filling composite.

Tooth dentin consists of inorganic substances (biological apatite, 70-72%), an organic component (collagen and other proteins, carbohydrates) and water (10%). Unlike enamel, dentin is penetrated by a large number of dentinal tubules filled with dentinal fluid, pulp substance, and cellular processes. The dentin surface is always moist, as fluid constantly flows through the dentinal tubules. Therefore, dentinal adhesion is a more complex problem, the modern solution of which takes into account a number of specific factors.

Since the dentin surface is always wet, dentin adhesive systems must contain hydrophilic components that can wet the dentin surface and penetrate the dentin tubules.

After removing tissues affected by caries, a “dentinal wound” is formed (exposure of dentinal tubules, damage to odontoblast processes, etc.), through which toxins and chemical reagents can penetrate into the dental pulp. Therefore, measures aimed at sealing the dentin surface are necessary.

As a result of instrumental processing of dentin, so-called dentin is formed on its surface. smear layer (an amorphous layer approximately 5 µm thick) consisting of inorganic particles, denatured collagen fibers, and destroyed remains of odontoblasts. This layer makes it difficult for adhesive systems to diffuse into the surface layers of dentin. Preliminary acid etching of the dentin surface improves adhesion to the dentin adhesive due to the opening of the dentin tubules, demineralization of the surface layer and (for example, when using 35-37% phosphoric acid) removal of the smear layer. Etching does not have a harmful effect on the dental pulp.

Methods for using dentin adhesive systems include the following main steps.

• Cleaning (conditioning, etching) of prepared dentin with acid solutions (phosphoric, citric, etc.), chelating reagents, and ethylenediaminetetraacetic acid (EDTA) solution.
• The use of a primer (primer), which is a solution of acidic and hydrophilic polymerizable monomers. The need to use primers is mainly due to the presence of dentinal tubules.
• The use of dentin adhesive (a chemical compound that ensures the formation of a bond between the filling composite and the primer layer on the dentin surface).

Despite differences in application techniques and compositions, modern dentin adhesive systems are united by the fact that they are all based on solutions of hydrophilic methacrylates. Along with their high activity towards the collagen structure of dentin, they easily polymerize in the hydrophilic environment of dental tissue. The first 2 stages are preparatory and facilitate the penetration of dentinal adhesives (due to the hydrophilic parts) into the dentinal tubules and spaces previously occupied by biological apatite, followed by encapsulation of collagen fibers. After polymerization of the adhesive, a thin layer of substance is formed, consisting of adhesive components and collagen fibers of dentin (the so-called hybrid layer). The hybrid layer ensures reliable fixation of the composite to the dentin (during subsequent filling of the cavity) and is a protective barrier against the penetration of microorganisms and chemicals into the dentinal tubules and tooth cavity, blocks the movement of fluid in the dentinal tubules and prevents postoperative sensitivity. The adhesion strength of the hybrid layer to the dentin surface is very high and exceeds the adhesion strength of natural dentin and enamel. Typically, modern dentin adhesive systems contain components that combine Stages 1 and 2 (self-conditioning, self-etching primers), Stages 2 and 3 (single-pack formulations), or Stages 1, 2 and 3 (single-stage, single-stage preparations, self-etching adhesives)

Currently, there is a wide variety of dentin adhesive systems, each of which has a unique chemical composition and application characteristics. But the mechanisms of their adhesion to dentin can be classified in relation to their effect on the smear layer (i.e., according to the different way in which the hybrid layer is formed).

1. The adhesive system preserves and modifies (strengthens) the smear layer due to its impregnation with hydrophilic low-viscosity monomers followed by polymerization. Adhesion in this case occurs due to the connection of the modified smear layer with the structural elements of dentin and, on the other hand, due to the chemical connection with the filling composite. The disadvantage of these systems is shallow penetration into the smear layer and insufficient adhesion.
2. The adhesive system transforms the smear layer through the action of a self-conditioning primer, which includes hydrophilic monomers and organic acids (for example, maleic). When exposed to such a primer, the smear layer is partially dissolved, the dentin surface is demineralized and the dentinal tubules partially open (into which hydrophilic components of the adhesive can enter to form polymer processes). In addition, reactive groups of adhesive molecules (amine, carboxyl, etc.) can interact with functional groups of molecules of organic components of dentin. In this case, the hybrid layer has a more complex structure.
3. Dissolution and removal of the smear layer as a result of acid etching of the dentin surface followed by rinsing. At the same time, the dentinal tubules open, the dentin surface is demineralized, and collagen fibers are exposed. The components of the adhesive system penetrate the dentinal tubules and the demineralized surface layer of dentin and bind collagen fibers. This hybrid layer provides a strong bond with dental tissues.

In modern dentistry, adhesive systems of several generations are used.

4th generation adhesive systems contain 3 components: an etchant or conditioner (for etching enamel and dentin), a primer (a mixture of hydrophilic monomers) and an adhesive. A three-stage technique is provided - etching (enamel takes a longer time than dentin) followed by washing and drying, application of a primer with drying (primer contact with the enamel does not affect the adhesion strength; when etching only enamel, the use of a primer is not necessary), application and polymerization of the adhesive. They provide an adhesion force to enamel and dentin of about 30 MPa.

5th generation adhesive systems are preparations in which the primer and adhesive are combined (one-component system). They provide a two-stage technique - etching (conditioning) and application of a one-component adhesive. These adhesive systems are easier to use, but the adhesion strength is slightly less (10-30% in laboratory conditions) than that of the 4th generation adhesive systems.

6th and 7th generation adhesive systems are one-step preparations that combine the properties of a cleaner (conditioner, etching agent), primer and adhesive. Not yet widely used.

Adhesive systems also differ in the technique of etching dental tissue. The selective etching technique involves separately etching dentin and enamel (usually with different etching agents). Complete (total) etching is carried out with the same etching agent applied to both enamel and dentin. Conditioners (contain low concentration acids) have appeared as part of modern adhesive systems. The mechanism of action of conditioners is identical to the mechanism of action of etching agents (containing acids in higher concentrations). Conditioners are less aggressive and penetrate to a lesser depth into the enamel and dentin; they are used when the resistance of dental tissues to caries is low.

Adhesive systems are cured in three ways:

• under the influence of light (light-curing) (used in the frontal group of teeth, where light access can be easily obtained);
• chemical and light (double curing) (consist of a base and a catalyst, after mixing which light curing is carried out followed by final chemical curing; used for chewing teeth);
• chemically (self-curing) (used in cases where light exposure is difficult).

When using adhesive systems, lining materials are used only in deep carious cavities (pointwise, within the peripulpal dentin). The treatment pad (based on calcium hydroxide) must be covered with an insulating pad, since the components of the treatment pad disrupt the polymerization process.

The fundamental issue with regard to adhesive systems is the purpose of using dentin adhesives, namely, strong fixation of a filling (restoration) or sealing the border of a filling with tooth tissue. Recent studies show that the fixation of the filling is ensured mainly by micromechanical adhesion to dentin, as well as adhesion of the composite to the enamel. This point of view assigns a secondary role to dentinal adhesion (the significance of dentinal adhesion is questioned), and the main thing is to ensure the tightness of the filling-dentin interface, prevent microleakage, and protect dentin and pulp.

Typical representatives of adhesive systems and their components are the following.

Etch-Rite>, Pulpdent. Etching gel for dentin and enamel. Contains phosphoric acid (38%), amorphous silica gel.

Gel Etchant. Etching agent, contains phosphoric acid (37.5%).

Prime Bond NT. Universal (for enamel and dentin), one-component (primer and adhesive together in one bottle) light-curing adhesive system. Contains nanofiller for increased strength and improved edge adaptation. When additionally mixed with a chemical polymerization activator (Self-Cure Activator), a dual-cure adhesive system is obtained (used for areas not easily accessible to light). The advantage of this system is the presence in its composition of a combination of 3 elastomers (polymers capable of large reversible deformations). This allows the adhesive layer to stretch when the filling (restoration) deforms under repeated chewing load and prevents depressurization of the connection between the composite and dental tissues.

Optibond Solo. A universal one-component light-curing system, barium glass is used as a filler component (25%).

These adhesive systems provide high adhesion strength of composites and compomers not only to dental tissues, but also to metals and ceramics.

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Stages of the procedure

Procedure:

1. First, the enamel is etched with phosphoric acid for 5 s, then the dentin is etched for 5 s. After which the acid is washed off with a water jet without further drying.
2. The cavity is washed with 95% alcohol for 30 s. It is applied using a syringe, spreading it over the cavity with a brush or using a moistened cotton ball, rubbing it into the surface. For 4th generation adhesives, alcohol is required; if preparations of 5th generation and higher are used, then a solution containing 95% alcohol and 2% chlorhexidine is used.
3. After the alcohol is applied, the surface is not dried, but the adhesive is immediately rubbed in. It is rubbed in 3 times and then dried. At the end, a fluid-flowing composite is used and the surface is polymerized.

Opinion of Alexey Olegovich Sazonov

In the video, Sazonov’s technique:

Alexey Olegovich Sazonov graduated from MGMSU - Moscow State Medical and Dental University named after. A.I. Evdokimov, majoring in Dentistry. Doctor - dentist-therapist, orthopedist, chief physician of the Art-pro clinic. Work experience - 19 years.

He does not use Chlorhexidine, because he considers its action useless: “MMPs are needed for the transition of altered dentin to sclerotic types.” This is necessary in the presence of deep caries, to strengthen the affected but healthy tissues. Chlorhexidine, according to the doctor, can prevent this. Sazonov uses 95% alcohol. For different generations of adhesives, the operating algorithms are different. More often, Alexey Olegovich adheres to the following sequence (4th generation: acid, primer, adhesive):

1. Selective dynamic etching of enamel 15 sec with phosphoric acid, dentin 3-5 sec.
2. Rinse with water, DO NOT dry, add 95% alcohol (water from a syringe for 30 seconds), do not dry.
3. Rub in the primer 3 times, dry well (1 time).
4. Rub in the adhesive and inflate.
5. Apply the fluid-flowing composite in a thin layer.
6. Polymerization - 10 sec.

There are many articles and studies on this topic, they often contradict each other. First of all, you need to understand the causes of the problems, and not blindly accept recommendations on faith. The relevance of the alcohol adhesive protocol in dentistry will only be confirmed by the long-term durability of restorations.