Polymeric Sustained-Release Chlorhexidine Coating on Gutta-Percha Points for Prolonged Intracanal Antimicrobial Delivery: An In Vitro Study

Background: Persistent endodontic infections involving Enterococcus faecalis and Candida albicans are a major cause of root canal treatment failure. Although conventional irrigants, such as sodium hypochlorite and chlorhexidine (CHX), exhibit strong immediate antimicrobial activity, microbes may survive and recover from the initial antimicrobial effect, hence limiting their effectiveness, especially in complex root canal anatomies and in the apical terminus of the tooth. Antibacterial dressing techniques were not proven satisfactory due to depletion of the antibacterial component or difficulty in spreading it evenly along the entire root canal. This study aimed to develop and evaluate the antimicrobial efficacy and release characteristics of a novel sustained-release device (SRD), delivering CHX via gutta-percha points coated with a sustained-release formulation used as a temporary intracanal medicament. Methods: Gutta-percha points were coated with two sustained-release CHX varnishes (CHX1 and CHX2) or a placebo and assessed in vitro. Antimicrobial activity against E. faecalis and C. albicans was evaluated using agar diffusion assays over time. Release kinetics were analyzed using Rhodamine-labeled SRD in a 3D-printed acrylic molar tooth model via fluorescence microscopy. Additionally, biofilm-infected acrylic molar teeth were treated with a placebo, a single 2% CHX irrigation, or SRD-coated gutta-percha points placed as an intracanal dressing prior to obturation. Microbial viability was quantified by colony-forming unit (CFU/mL) analysis from root canals and gutta-percha points. Statistical analysis was performed using one-way ANOVA followed by Tukey’s post hoc multiple comparison test (p < 0.05). Results: SRD-coated gutta-percha points demonstrated sustained antimicrobial activity for up to 21 days against E. faecalis and 19 days against C. albicans. Fluorescence analysis, in an acrylic tooth model, confirmed continuous release for up to 15 days, with pronounced diffusion in the isthmus and palatal canals. In biofilm-infected acrylic teeth models, SRD treatment resulted in a significant reduction of 2–3 log10 CFU/mL compared to placebo groups (p < 0.001) and prevented microbial rebound over the 14-day observation period. In contrast, a single application of 2% CHX solution showed only transient reduction followed by regrowth. Conclusions: Sustained-release CHX delivery via polymer-coated gutta-percha points provided prolonged antimicrobial activity against bacterial and fungal biofilms compared to conventional single-dose CHX application in this in vitro model. These findings support the potential use of coated gutta-percha points as a removable intracanal drug delivery platform prior to final obturation, although further studies incorporating direct-release quantification and in vivo validation are required before clinical translation.