## 1 Introduction  
The prevention of secondary caries around bonded restorations triggered by bacterial growth and infiltration into the bonding interface is a challenge. A method is urgently required to help preserve the bonding quality and performance over time [1, 2]. Therefore, developing antibacterial, biocompatible, and strong dental adhesives with mechanical and physical properties that match the rate of bacterial growth inhibition is a valuable pursuit [1, 2]. Researchers are exploring various additives to improve dental adhesives, focusing on strength and antimicrobial protection. Silver nanoparticles can prevent bacterial growth [3], while quaternary ammonium compounds help break down bacterial cell membranes, reducing plaque buildup [4]. To enhance mechanical properties, nano-fillers like silica are added, making polymers more resistant [5]. By reinforcing the seal against the oral environment, these enhanced adhesives could help prevent secondary caries and extend the life of dental restorations [6, 7]. Ionic liquids are organic salts formed by aliphatic chains connected to a high-molecular-weight cation associated with a low-molecular-weight anion [8]. Organic molecules, such as pyridine and imidazole, are commonly used to synthesize pyridinium and imidazolium-based ionic liquids, respectively [9, 10]. Among these, imidazole is well known for its biocompatibility and antifungal effect. Ionic liquids can present a broad-spectrum antimicrobial property, affecting gram-positive and gram-negative bacteria, mycobacteria, and fungi [10]. In the pharmaceutical industry, these salts are associated with polymers for drug delivery systems to participate in antibacterial polymer coating synthesis and other processes [9]. In dentistry, imidazolium ionic liquids have already been used to coat titanium implants, testing their adherence to the implant and antimicrobial and anti-corrosion properties [11]. In another study, an imidazolium ionic liquid was used with silver nanoparticles to disinfect root canals against _Enterococcus faecalis_. This material demonstrated greater fibroblast viability than 2.5% sodium hypochlorite and 0.2% chlorhexidine solutions [12]. More recently, the ionic liquid 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF\({}_{4}\)) was used to functionalize titanium dioxide quantum dots embedded in an experimental adhesive resin. Its incorporation associated with titanium dioxide quantum dots resulted in immediate and long-term antibacterial activity without showing cytotoxic effects on pulp cells [12]. Another ionic liquid, 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTT\({}_{2}\)) [13], shows the same cation but an anion (bis(trifluoromethanesulfonyl)imide, NTT\({}_{2}\)) with higher hydrophobicity compared to the previously used tetrafluoroborate (BF\({}_{4}\)), which could bring advantages to dental polymeric materials. The increased hydrophobicity can enhance the durability of dental polymers by reducing their susceptibility to water absorption. Materials that absorb less water are less likely to undergo hydrolytic degradation, which can weaken their structural integrity and shorten their useful life [14]--consequently, BMI.NTT\({}_{2}\) may help extend the longevity of dental restorations. The hydrophobic nature of NTT\({}_{2}\) may reduce the adhesion of bacteria and the absorption of staining agents, which are common issues in dental applications [15]. This property not only helps maintain the aesthetic appearance of dental restorations but also promotes better oral hygiene by reducing the potential for bacterial growth on the surface of the materials. To initiate studies with BMI.NTT\({}_{2}\), this ionic liquid was tested in an experimental orthodontic resin, demonstrating an antimicrobial effect against _Streptococcus mutans_ and no cytotoxicity against human keratinocytes when tested up to 5 wt.% [13]. In the present study, BMI.NTT\({}_{2}\) was incorporated into an experimental adhesive resin and tested at 1, 2.5, and 5 wt.%.