## 1 Introduction  
In the last 20 years, universal adhesive systems have been introduced into dentistry. This type of bonding system, also known as \"multi-modal\", since they can be used in etch-and-rinse, self-etch (single-step), selective enamel etching and on virtually any kind of dental or prosthetic substrate, simplifies operative procedures significantly by reducing steps and the need for different adhesives for different substrates [1; 2; 3]. Exclusively in relation to the intended use, these kinds of adhesives are similar to older and now-surpassed single-step adhesives [4]. The universal adhesives contain hydrophilic and hydrophobic monomers, polymerization promoters, solvents, stabilizers and fillers. The composition is similar to the self-etch all-in-one adhesives, except for the presence of carboxylate or phosphate monomers, as 10-MDP (10-methacrylolydexped) dihydrogen phosphate) are capable of forming ionic bonds with the calcium of the hydroxyapatite and forming insoluble calcium salts [5]. The 10-MDP is a hydrophilic monomer with mild-etching properties and allows universal adhesive to be used with any type of etching technique [4; 6]. Universal adhesives also contain biphenyl dimethacrylate (BPDM), dipentaerythnitol pentaacrylate phosphate acid ester (PENTA) and polyalkenoic acids, which improve adhesion in terms of durability, reducing water absorption and the hydrolytic degradation of the adhesive interface. Hydrolytic degradation represents one of the main causes for delayed adhesive bonding failure [7; 8]. Universal adhesives also contain hydrophilic monomers (HEMA-hydroxyethyl methacrylate), hydrophobic (D3 MA--decanediol dimethacrylate) and intermediates, such as bis-GMA (bisphenol A-glycidyl methacrylate) meant for the creation of bonding bridges between the hydrophilic surface of the tooth and the hydrophobic surface of the resin. Finally, most universal adhesives contain silane, whose function is to facilitate adhesion to glass-ceramic substrates. The universality of these products made them a viable option in many different applications for direct and indirect restorations. Despite the improvements shown in simplified techniques, universal adhesives continued to demonstrate a typical pattern of hydrolytic degradation. This is derived from the water content, an indispensable component for the ionization of acid monomers. In this regard, it is particularly important to respect and, if possible, prolong the evaporation time of the solvent prior to the curing of the adhesive [9; 10]. This new class of adhesive was recently described as the \"eight-generation\" of enamel-dentinal adhesives, both for their characteristics of use and for the composition (e.g., their content of nanoparticles). In the composition of universal adhesives there can also be nanofillers (10-20 nm), which reinforce the resinous monomers bond to the collagen fibers of the dental tubules, increasing the quality of the hybrid layer with the consequent general improvement of the mechanical strength of the adhesive system. All these chemical features are meant to achieve greater bond strength and clinical durability of the adhesion [4; 11; 12; 13; 14]. The nanoparticles present inside universal adhesives are involved in the cross-linking during the polymerization phase, reducing polymerization shrinkage. The type of nanometric particles and the method of incorporation within the adhesive affect its viscosity, wettability and penetration ability within the collagen fibers [13]. The versatility of one adhesive technique for multiple substrates is a key feature of universal adhesives. Given their composition and their multipurpose use, and given their use on sclerotic dentin, dentin contaminated by metal oxides and on NCCL (Non-Carious Cervical Lesions) [15; 16], it is hypothesized that these adhesives could also operate on pathological substrates, such as on teeth affected by dentinogenesis imperfeta type II (DI-II).