What are universal adhesives?
From time to time the dental market is "invaded" by some potential innovation in products that generates a trend. This trend may be related to the formulation of new materials or, in some cases, simply a marketing strategy. It is possible to identify a "trend" of the market when, for example, several manufacturers offer trade in similar products. This has happened in the past with simplified adhesives, nanohybrid composites (before that all of the same class were called microhybrid), some time ago with the self-adhesive resin cements and more recently with the “bulk-fill" resin type.
One of the most recent market trends of dental materials is the universal adhesives, also called “multimode adhesives".
The objective of this paper is to present these materials and discuss potential advantages and limitations in comparison to other materials on the market.
Universal Adhesives - why call them this way?
To be considered universal or multimode, adhesives must be able to be used in various restorative techniques, they should expand the use of adhesives currently available on the market. Of course, the title "universal" is given by the manufacturer, which may be a marketing ploy, and it must be considered that there is a great variation between brands. The "universality" of use may include conventional etching preceded by phosphoric acid, using it with the self-etching technique (link to our other post here), using it to replace the silane in vitreous ceramic (ex.: porcelain, lithium disilicate) or glass fiber posts, or even replacing the ceramic’s primer (ex.: alumina and zirconia). In other words, universal adhesives are not only simplified adhesive, theoretically, they can be used safely and are effective in multiple adhesive procedures not restricted to enamel and dentin. Still, many manufacturers report that universal adhesives are more compatible with materials of dual and chemical cure that the other simplified adhesives, which often cannot be used with materials of dual or chemical cure (Tay et al. , 2013). When the first universal adhesives were launched, it was even considered the use in dry dentin even in the conventional technique, after the application of phosphoric acid. This would dry the demineralized dentin, not taking into consideration the collapse promoted by drying of the collagen mesh. However, today no manufacturer indicates the application in dry dentin after acid etching. Table 1 indicates the adhesives called universal present in the international dental market and their indications informed by the manufacturers. Note the large amount of brands already available, suggesting the "market trend" mentioned previously.
What changes in the composition of these materials?
The main advantage of universal adhesives compared to the other ones is the greater breadth of use, allowing the use in a wide range of adhesive techniques (see Table 1). The applicability of universal adhesive strongly depends on its composition, which is summarized in Table 2. It can be noted that the overall composition of universal adhesive is not so different from the one step self-etching adhesives (link to our other post here). By the way, almost all the universal adhesives are used in a single step, but OptiBond XTR (Kerr).
Some components that are not usually found in the conventional adhesives, as the silane, for example, are added to the universal ones to allow better union to inorganic surfaces containing silica, which also allows the intraoral repair of direct and indirect restorations. Perhaps the major challenge when formulating of universal adhesives is the polymerization system, which should allow polymerization of different molecular species without separation between hydrophobic and hydrophilic phases and without the formation of a superficial layer of low pH, poorly polymerized because of the contact with oxygen, to avoid incompatibility with dual or chemical cure materials. For this reason, many manufacturers resort to the use of more than one initiator, not only the camphorquinone.
Is there evidence of the performance of these materials?
There is little laboratory and clinical evidence of the available materials, which is a problem exacerbated by the wide variety of materials and by intrinsic variations between brands. One of the first in vitro studies of universal adhesives (Hanabusa et al. , 2012) indicated that the performance of the material seemed satisfactory. However, the authors found that the adhesive interface seemed more vulnerable to degradation when the adhesive was applied on the dentin that had been conditioned by phosphoric acid, which is corroborated by the results found in another study (Marchesi et al. , 2014). A study performed by a international group, including Brazilians (Munoz et al. , 2013), reported that the performance of universal adhesives is dependent on the material tested and that many multimode adhesives showed properties such as union resistance to the dentin or degree of conversion of C=C (which measures how much of the material actually cures) lower than the not universal ones. Clinically speaking, there is very little evidence published. A clinical study of 18 months (Perdigao et al. , 2014) showed that the retention of a universal adhesive in non-carious cervical lesions was not influenced by the type of application technique (conventional or self-etching). But the adhesive tested was not compared to other material, which is a limitation of this study. Thus, in spite of the potential benefits of universal adhesives, clinical studies with longer time of follow-up are still needed to confirm the effectiveness of these materials.
Do I have to change the system that I am using?
The simple answer to this question is "no", if the adhesive system that you currently use is working well. There is no evidence of gain in performance and, in fact, there are hardly evidence of this kind. The gain with universal adhesive is the simplification of the quantity of materials used for adherence to different substrates, however, the materials used in isolation (non universal adhesives, silanes, primers for ceramics crystalline) work at least in the same way that universal adhesives, and are often superior. Though they look safe, there is a need for more evidence (especially clinical) of the effectiveness of universal adhesives in different clinical situations. There is a well known phrase in dental materials that seems to fit at the moment: "we must not be the last to use new materials or techniques in dentistry, but we must also ensure that we are not the first". Still, care should be taken, once not all universal adhesives have the same indications (some may not be used in the conventional technique, for example) and the same steps of application (some are of two bottles, some require the application of an activator). Although all manufacturers indicate that its use is possible to almost "all" the restorative techniques, the clinician should be familiar with the material before purchasing it and even better before using it in the clinical environment. I hope this will help you understanding what are the universal adhesives, which are their indications and what are the main differences between the adhesives already on the market.
Rafael R. Moraes
Contato: [email protected]
Hanabusa et al. (2012) - http://www.sciencedirect.com/science/article/pii/S0300571212000589
Marchesi et al. (2014) - http://www.sciencedirect.com/science/article/pii/S0300571213003436
Munõz et al. (2013) - http://www.sciencedirect.com/science/article/pii/S0300571213000730
Perdigão et al. (2014) - http://www.jopdentonline.org/doi/abs/10.2341/13-045-C
Tay et al. (2003) - http://www.ncbi.nlm.nih.gov/pubmed/12729081
My purpose is to help you gain autonomy through knowledge, facilitating the dentistry and communication. AND how do I do this?
I put myself in your shoed, I identify what is preventing you from being happy with your results and untie the knots by means of a simple and accessible language! I graduated from UNESP | Araçatuba; did my Master and PhD in Operative Dentistry at UNESP Araraquara | I am a Professor of Operative Dentistry at the Federal University of Pelotas | RS.
Jul, 27th 2015