## 1 Introduction  
Composite resins have been used clinically for approximately half a century, and the evolution of this type of material was largely motivated by the gaps they presented in clinical practice. The first two decades were dedicated to the development of composite resins with better mechanical and polishing properties [1]. Then the focus became the production of resins with less polymerization shrinkage as a way to reduce post-operative sensitivity, cusp deflection and the formation of gaps and increase the durability of these materials [1, 2]. Composite resins reached a degree of development that allowed them to have excellent aesthetic characteristics [2, 3], optics, wear resistance, radiopacity, biocompatibility, adhesion to dental tissue, handling and polishing [3]. New trends in dentistry are focused on non-invasive and minimally invasive procedures [4], and thus adhesive restorations continue to dominate and evolve in the market. These restorations allow for a more conservative approach to caries removal and cavity preparation [1, 3, 4, 5]. In References [2, 5], microleakage is defined as the undetectable clinical passage of bacteria, fluids, molecules and ions between the cavity wall and the restorative material [3, 6]. It can be measured with help of nuclear medicine, through the decay rate (half-life) of radioactive isotopes [3]. It is considered one of the most important factors in the longevity of restorations, so that marginal sealing should be one of the main goals of the clinician [3, 5]. The performance of composite resins depends mainly on the adhesive technique and humidity control, using absolute isolation [4, 7]. Some studies have revealed limitations in its use, especially in posterior teeth [8, 9]. Glass ionomer cements (GIC) are the most used self-adhesive material in direct restorations, with two components, an acid (aqueous solution of polyacrylic acid) and a base (fluoroluminosilicate powder) that mix in an acid-base reaction [10, 11, 12]. Its chemical adhesion to the tooth structure is achieved through the carboxylic groups (\(-COOH\)) present in its acid component, which establish chemical bonds with the calcium of hydroxyapatite [1, 13]. This adhesion is responsible for promoting a good marginal seal and reduced microleakage, but it is not considered strong enough to retain the material in the cavity [1, 10, 14]. They can reject isolation protocol, as they are less sensitive to moisture and acid conditioning is also redundant [3, 10, 14]. Studies report few cases of postoperative sensitivity and low cytotoxicity to the pulp-dentin complex [15, 16, 17]. In addition to their self-adhesiveness, GICs also show bioactivity with the release of fluorine, aluminum and calcium ions from the fluoro-alumino-silicates (FAS) contained in their composition, inducing dental tissue remineralization and a cariostatic effect [10, 13]. Their acid-base mixing reaction allows these materials to have a \"bulk-fill\" application, that is, in a single layer [13]. However, they present worse mechanical, aesthetic and polishing properties and adhesion strength when compared to resins [3, 4, 7, 10]. In literature [10, 11, 13], conventional GICs are not indicated for definitive restorations due to their strong tendency to abrasion, fracture and detachment [18]. RM-GICs have better adhesion and flexural characteristics [19] but still show low abrasion resistance and should be applied according to the manufacturer's instructions on the temporary restorations of permanent teeth or the definitive restorations of primary teeth [20]. The ideal would be to combine the characteristics of both dental materials described above, thus obtaining a single material with good aesthetics, good mechanical properties, moisture tolerance, self-adhesive, durable, simple technical application and handling and with low microfiltration.