Dental adhesive systems are one of the most widely used materials in the dental clinic and their large number of different types, varieties and characteristics make it often difficult to make the decision on the most appropriate system to use. In addition, as you know, dental adhesion is a complex process, especially in dentin due to its sensitivity to the technique, and often unpredictability, which occurs due to its heterogeneous composition and consequently can cause problems such as bacterial microleakage, secondary caries and alterations. irreversible pulps. But don't worry, in this article, although it seems very ambitious, we will try to develop some approaches related to adhesives in enamel and dentin. And by the way, we will recommend some products that have some differential that proposes to make your adhesion procedures easier and more successful. Let's get started!
Introduction to dental adhesives
The evolution of dental adhesive systems over the years has been based on mainly in the modification of its composition to improve its qualities in clinical conditions, what is confusing about all this is that from these modifications different classifications have been created that have made it difficult to choose the appropriate adhesive for each case. In 2013, an interesting classification was proposed that was based on the interaction of adhesives with dental substrates and their number of steps (one, two or three).
Dental adhesives today
Today, in addition to knowing more about dental adhesives, we know more about dental substrates and better understand their role in the bonding process. This has been of great relevance to improve the technology and efficiency of current dental adhesives.
Today, universal adhesives that chemically bond to tissues and simplify all procedures are of great interest. necessary compounds in one bottle, so enamel and dentin are etched, conditioned and primed in one step. The virtues of this type of dental adhesive are multiple, among them, of course, its biocompatibility, its optimal adhesion and its marginal sealing. Another advantage of doing these three steps simultaneously is that the smear layer is not removed, but rather modified, reducing the depth of the demineralized layer, making it more homogeneous, regular and thin. to facilitate the complete penetration of the adhesive.
But is adherence so important for the clinical success of treatment? We couldn't say no. The adhesive layer joins the tooth substrate with the restorative material and its main objective is to form a hybrid layer, through the penetration of the adhesive into the tooth tissue.
Even today, some dentists prefer to use adhesives on which phosphoric acid etching is done separately, it is common and correct practice. Although the use of self-etch adhesives is increasingly widespread, which can be used to etch dentin, enamel and, if required, perform a selective enamel etching. Another considerable advantage of this type of dental adhesive is that by having all three steps in the same bottle, it reduces the chances of errors and therefore the technique becomes less sensitive.
Enamel adhesion
Talking about adhesion to enamel is talking about the beginnings of adhesive dentistry, when Michael G. Buonocore presented his work describing how acrylic resin could bond to enamel etched with 85% orthophosphoric acid. Since then, everything has advanced a lot and today we know that such a concentration of acid is not necessary and that prophylaxis and isolation are required beforehand to improve the conditions of the adhesive procedure.
Selective etching of tooth enamel: adhesive to use
When selective enamel etching is required, it should be noted that some authors consider that self-etching adhesives are not optimal, since they have low micromechanical retention and enamel hydroxyapatite has low chemical reactivity, for which reason it would be more convenient, in this case, to record the margins with phosphoric acid.
The best conditions for adhesion to dental enamel
Enamel etching with phosphoric acid increases its surface energy and creates microporosities that increase the surface area to enhance adhesion.
The best bases for adhesion in dental enamel must consider the increase in surface energy, acid and resin with wettability. Of course, we do not stop recommending thorough cleaning of the tooth and absolute isolation to obtain even better results.
Actually adhesion to enamel is much easier than dentin, as the low-viscosity flowable resin in the adhesive system simply wets the high-energy surface it has created acid etching and light curing will polymerize within the microporosities of the enamel.
Dentin adhesion
The adhesion in dentin is a more elaborate process given its complex structure and the fact that it requires the formation of a hybrid layer that was discovered by Nakabayashi in 1982 and is the result of the diffusion and impregnation of the monomers of the dental adhesive within the subsurface of the dentin pretreated as a substrate and its polymerization. Other names for this layer are: interdiffusion zone, interpenetration zone, dentin-resin interdiffusion zone, primer-resin infiltrated dentin, or resin-impregnated dentin layer.
Difficulty in dentin adhesion
There are many determinants of the successful dentin adhession, among which are: humidity, the depth of the substrate, the ability of the adhesive to penetrate the dentinal tubules and the bonding of the adhesive with the collagen fibers of the demineralized intertubular dentin.
In Europe and the United States, unlike countries like Japan, dentin etching only began when there was better knowledge about its effects, the incorporation of primers to facilitate wetting and Consequently, the adhesion and emergence of hydrophilic resins established that dentin acid etching was acceptable.
The fact that there is a hybrid layer that is durable, insoluble and resistant is of vital importance in the adhesion to the tooth that definitively seals the tooth-restoration interface and eliminates leakage, to avoid future problems such as pulpal irritation and secondary caries.
Composites, no matter how advanced they are, still cannot eliminate 100% polymerization shrinkage and this is a challenge for the adhesion capacity of the hybrid layer, which has to be able to to resist the forces that are generated during the contraction of the composite.
How is the hybrid layer formed?
We should ensure that the hybrid layer is effectively formed, which is essential for proper dentin adhesion. For this, it is essential to remove the dentin debris with the use of etching acid or dentin conditioners and subsequently prepare the fibers collagen from dentin with a primer, which is a product that contains hydrophilic monomers. For this reason, dentin etching is a very technique-sensitive procedure and care must be taken with the timing of the acid application to avoid weakening the dentin by creating excessive demineralization. Another important point is the choice of acid, there are some on the market that are capable of not exceeding the required depth of etching, these are the self-limiting etching acids and a clear example is Ultradent Ultra Etch IndiSpense acid etching.
In summary, regarding the formation of the hybrid layer that favors adhesion in dentin, we will say the following:
- The application of phosphoric acid decalcifies the dentin which removes the layer of dentin debris.
- When the dentinal tubules are decalcified, the collagen fibers that are normally immersed in an inorganic matrix are exposed.
- The primers, thanks to their hydrophilic monomers, alter the collagen fibers, in addition to their elasticity and wettability to favor the penetration of the adhesive.
- By applying monomers, the spaces between the collagen fibers are widened, which maintains and maintains their original level.
- The hydrophilic monomers have the task of being receptors in the copolymerization of the adhesive resin that will be applied later. This copolymerization allows a union between the collagenous mesh present in the dentin and the materials of the adhesive and restorative resin, which gives rise to the formation of the hybrid layer and as we have said, this layer is a interdiffusion zone between resin and dentin.
Composition of dental adhesive systems
Newer adhesive systems that come in a single bottle are easier to use and reduce errors associated with the technique. In addition, they have a better bonding capacity to different tissues, including enamel and dentin. This type of dental adhesive is classified as one-component because it contains a vehicle that transports the different chemicals in its composition. These adhesive systems use various solvents such as water, ethanol or acetone or bifunctional molecules used in primers. In the case of adhesive systems that come in multi-bottles, these bifunctional molecules have one end Highly hydrophilic, capable of moistening dentin, especially its collagenous mesh, preparing for proper bonding with other restorative materials. The other end is hydrophobic and is prepared to bond with whatever adhesive or restorative material is used.
These bifunctional molecules, also known as adhesion promoters, are chemically based on three main groups: HEMA (hydroxyethylmethacrylate), BPDM (biphenyl-dimethacrylate) and 4META (methacryl-oxy-ethyl-trimellitate-anhydride).
Radiopacity: a highly relevant characteristic in a dental adhesive
Have you ever wondered why if all composites and cements are radiopaque, most dental adhesives are not? It is curious that the radiolucency of dental adhesives is almost a constant, especially in products launched on the market before the year 2020. Did the manufacturers realize in 2020 that it was necessary to make them radiopaque? The reality is that, by applying a dental adhesive neatly and correctly, it should form such a thin film that it would be imperceptible in any radiographic image, but in the clinical environment, in reality, with the hurry, limitations or perhaps due to simple carelessness or ignorance, sometimes the layers of adhesive are much thicker than they really should be and it is also possible that the adhesive accumulates at some angle or discontinuity in the base or walls of the cavity. These layers of accumulated dental adhesive, if they are greater than 40 microns thick, can be seen on an x-ray as a radiolucent area under the restoration. And what do you think when you see this? Secondary caries! Probably? Perhaps to be safe you decide to replace the restoration and it is the wrong decision.
The addition of radiopaque fillers to dental adhesive is not recommended
When we add non-organic radiopaque fillers to composites and cements, it is a practical solution, but it is not in the case of adhesives for a very simple reason: adding radiopaque fillers would increase their viscosity and impairs its wetting and penetration properties in the dental structure. Also the addition of these fillers would require that the bottle be shaken each time the adhesive is used, thus creating a factor for error if this is not done or done inconsistently.
The 3M brand has developed the evolution of the Universal Adhesive Scotchbond, the Universal Scotchbond Plus Adhesive with a radiopacity similar to dentin without affecting its viscosity by adding radiopaque fillers, but rather what it has done has been to develop a radiopaque monomer, not derived from bisphenol A, distributed throughout the material homogeneously. This greatly facilitates the correct interpretation of dental radiographs in cases where adhesive accumulates for some reason, so as not to unnecessarily portray teeth due to suspected secondary caries.
Scotchbond Universal Plus: 3M Radiopaque Universal Adhesive
3M Scotchbond Universal Plus universal adhesive is an improved version of its predecessor as it has very high radiopacity compared to other adhesives, to prevent over-treatment and make a correct radiographic diagnosis.
- Perfect adhesion to all tooth tissues.
- Indicated for all direct and indirect restorations and all etching techniques.
- One bottle, no need for primers, silanes or activators.
- BPA and BisGMA free.
- No or very reduced post-operative sensitivity.
- Added Radiopacity So you can never go wrong!.
Buy Scotchbond Universal Plus 3M
Final thoughts on dental bonding
In conclusion, despite the fact that there are multiple generations of adhesives and their properties have improved over time, many professionals choose to continue using previous generations of these materials out of habit, comfort or simply for personal preference, however, It seems that since dentin is a heterogeneous tissue, unlike enamel, which is homogeneous and almost exclusively mineral, it presents some complications related to its aqueous and organic content, which becomes a challenge when using a dental adhesive material. The fundamental difference from the dental adhesives used today, that is, those that require prior etching or are self-etching, lies in the fact that separate acid etching causes exposure of the collagen fibers dentin to form the hybrid layer, but this process may not be entirely efficient, given the risk of dehydration deterioration of these exposed collagen fibers. On the other hand, the advantage of self-etching adhesives is that they have the acid incorporated into their formula, in such a way that it demineralizes and infiltrates simultaneously, leaving no uninfiltrated areas.
Whatever adhesive system you use, you can surely find it at Dentaltix, since we have a wide variety of them so that you can always successfully solve even your most difficult clinical cases. Take a look!
We end our article today, leaving you invited to follow us on our social networks and to be attentive to our new publications that will always keep you up to date on the most current topics in dentistry. See you soon!
