## 1 Introduction  
Eugenol, in combination with zinc oxide (ZOE), is one of the most common materials used as a root canal sealer in endodontics [1; 2; 3; 4; 5], as well as a pulp sedative in cases of pulpotomies [6; 7; 8; 9] and an impression material for dedutulous patients [10; 11; 12; 13]. In restorative dentistry, ZOE cements are frequently applied as temporary materials during indirect restorations [14]. It is also known that ZOE cements can perform as anodynes for pulpal pain [15], especially in those patients presenting dentin hypersensitivity after tooth preparation and temporary restorations [16].  
ZOE cements used in temporary luting procedures are usually characterized by reasonable retention and compression strength and they can be removed quite easily [17]. Several techniques to eliminate residual provisional cements from dental preparations have been advocated. These include grating the tooth with a hand instrument (usually scalers or spoon excavators), cleaning the tooth preparation with a prophylaxis cup in combination with a water-pumice paste slurry, and/or using an intraoral air abrasion system commonly in combination with alumina or sodium bicarbonate. Although such temporary cements may be considered user-friendly materials in the clinic, there is evidence that the residual eugenol remaining on the dentin surface after setting can jeopardize the bonding performance of resin-based materials due to polymerization inhibition [1, 18, 19, 20]. The current literature shows conflicting results and a distinct lack of robust evidence about this issue.  
The remaining presence of eugenol-containing cements on dentin can act as a physical barrier [21, 22], impairing the degree of monomer conversion of resin-based materials [23] due to the existence of radical-scavenging molecules in such phenolic compound [24]. Indeed, the reactivity of monomers is reduced due to the hydroxyl groups within the eugenol molecule, which can protonate free radicals during the polymerization reaction [25]. Hence, an optimal removal of provisional eugenol-containing cements must be achieved in order to accomplish a suitable adhesion of permanent resin-based restorations to dentin [1, 26].  
Dentin hybridization through the use of adhesive systems is an essential mechanism for tooth/material adhesion [27]. Adhesive systems are made of photocurable resin monomers, which are responsible for micromechanical interlocking with the dental tissues. Such adhesive systems can be classified according to their mode of interaction with the bonding substrate as (i) etch-and-rinse (ER) or (ii) self-etch (SE) systems [28]. Studies confirmed that eugenol can jeopardize their bonding performance, although it is still unclear which type of adhesive (ER or SE) is more at risk of debonding in case of contact with eugenol. A recent meta-analysis has shown that sealers with eugenol may be able to reduce the push-out strength of fiber posts applied in the root canal in combination with resin-based cements [29]. Although many studies tried to elucidate the effect of eugenol on the bond strength of resin adhesives to coronal dentin, there is still no consensus about this issue [18, 19, 20, 30, 31, 32, 33, 34, 35].  
Therefore, this study aimed to analyze whether the residual presence of eugenol in the coronal dentin may compromise the bond strength of resin-based restorative materials. The hypothesis tested in this study was that the presence of residual eugenol on dentin surface would potentially interfere with SE and/or ER adhesive systems.