The Influence of Application Protocol of Simplified and Universal Adhesives on the Dentin Bonding Performance  
[PERSON]  
1 Department of General Dentistry, Medical University of Lodz, 251 Pomorska St., 92-213 Lodz, Poland; [EMAIL_ADDRESS] (A.Z.-D.); [EMAIL_ADDRESS] (M.L.-S.); [EMAIL_ADDRESS] (J.S.) [PERSON]  
1 Department of General Dentistry, Medical University of Lodz, 251 Pomorska St., 92-213 Lodz, Poland; [EMAIL_ADDRESS] (A.Z.-D.); [EMAIL_ADDRESS] (M.L.-S.); [EMAIL_ADDRESS] (J.S.) [PERSON]  
2 University Laboratory of Materials Research, Medical University of Lodz, 251 Pomorska St., 92-213 Lodz, Poland; [EMAIL_ADDRESS] 2 Department of Materials Technology and Chemistry, Faculty of Chemistry, University of Lodz, 163 Pomorska St., 90-236 Lodz, Poland; [EMAIL_ADDRESS] 2 Department of Materials Technology and Chemistry, Faculty of Chemistry, University of Lodz, 163 Pomorska St., 90-236 Lodz, Poland; [EMAIL_ADDRESS] 2 Correspondence: [EMAIL_ADDRESS]; Tel. : +48-42-675-7461 20 December 2019; Published: 23 December 2019 20 December 201  
enamel is etched, micro- and macro-porosities are created within hydroxyapatite crystals [4]. Due to the inorganic composition and minimal water content of enamel, hydrophobic adhesive resin uniformly covers its surface [5]. Dentin, being a more organic, water-containing tissue, requires a hydrophilic agent to be entangled within the collagen network, which becomes exposed after etching [6]. In order to eliminate the separate step of etching from bonding procedure, simplified or self-etch (SE) adhesives were introduced. Upon SE adhesive application, the dentin surface is simultaneously demineralized and infiltrated, which theoretically should ensure complete penetration of the adhesive [7]. The acidic monomers, which are responsible for dentin etching, are gradually buffered with increasing depth and finally lose the ability to further etch dentin [8]. Water and other solvents are then evaporated by air-blowing. A polymerized three-dimensional polymer/collagen network is created when the monomer-containing resin is light-cured [7]. SE adhesives require shorter application procedure, are less technique sensitive and present minimized postoperative sensitivity in comparison to etch-and-rinse (ER) adhesives [3]. Further, their performance seems to be less affected by the morphology of the tooth substrate [9]. This is particularly important during fiber post cementation in endodontically treated teeth. The endocanlar zone presents higher density of tubules compared to the crown [10]. According to the studies, the resin-dentin bond strength of ER adhesives decreases with the density of dentinal tubules. Yet, this phenomenon does not apply to SE adhesives and they are recommended to be applied in fiber post cementation [9; 11; 12]. Further, the level of cytotoxicity, presented by SE adhesives is lower than that of the ER ones [13]. Moreover, the SE strategy is valuable in direct pulp capping or endodontic procedures when applied over calcium silicate materials such as Biodentine or mineral trioxide aggregate (MTA) in order to ensure marginal seal and enable placement of composite restoration [14; 15]. However, studies show that SE adhesives do not etch enamel sufficiently to achieve a reliable, durable bond [3]. When being applied on dentin, they also present lower bond strength than ER adhesives [16]. To overcome these drawbacks, so called universal or multi-mode (MM) adhesives have been developed. There seems to be no official definition in the literature as to what qualifies as a universal adhesive. However, they can be defined as a single-bottle, no-mix adhesive systems that can be used in ER, SE, or selective-enamel-etch (SEE) mode depending on the specific clinical situation and personal preferences of the operator [17].