Background <p>The elimination of pulpal infection is critical for the success of vital pulp therapy (VPT) in mature permanent teeth with carious pulp exposure. However, commonly used pulp capping materials often possess inadequate antibacterial properties, which limits treatment success. This study aimed to develop a zinc-containing ionic liquid (IL-Zn)/carboxymethyl chitosan (CMCS) composite and evaluate its potential as an adjunctive pulp capping material for VPT.</p> Methods <p>IL-Zn was characterized by energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), and electrospray ionization mass spectrometry (ESI-MS). Its antibacterial activity against <i>Streptococcus mutans</i> (<i>S. mutans</i>) and <i>Lactobacillus casei</i> (<i>L. casei</i>) was assessed using minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time-killing curves, and scanning electron microscopy (SEM). The effect on dual-species biofilms was evaluated by crystal violet staining and live/dead staining. The potential for bacterial resistance to IL-Zn was examined through serial passage experiments. IL-Zn was then combined with CMCS to form the IL-Zn/CMCS composite. The antimicrobial efficacy of the composite against <i>S. mutans</i> and <i>L. casei</i> was tested by measuring the optical density of bacterial suspensions. The biocompatibility of the IL-Zn/CMCS composite was assessed via cell adhesion and SEM imaging. An animal model of pulpitis was used to evaluate the IL-Zn/CMCS composite as an adjunct to iRoot BP Plus for pulp capping.</p> Results <p>EDS, FTIR, ¹H NMR, ESI-MS collectively confirmed the successful synthesis of IL-Zn. In vitro antibacterial experiments demonstrated that IL-Zn, which exhibited a low propensity for inducing resistance, significantly inhibited both planktonic bacteria and dual-species biofilms. The IL-Zn/CMCS composite showed good antibacterial activity and biocompatibility with L929 cells. In animal tests, the composite improved pulp healing and dentin formation compared with iRoot BP Plus alone.</p> Conclusions <p>This study developed an IL-Zn with strong antibacterial properties and a low risk of resistance. When combined with CMCS, the composite exhibited favorable antibacterial activity and biocompatibility. Used together with iRoot BP Plus for the treatment of carious pulp exposure in mature permanent teeth, it significantly enhanced pulp healing and dentin repair, offering a promising strategy to improve the success rate of vital pulp therapy.</p>