(T1230-08-50) Development of a Novel Antimicrobial Gel for the Treatment of Endodontic Disinfection

Purpose: Endodontic success relies on effective disinfection of the complex root canal system. However, treatment failures occur when microorganisms persist in inaccessible areas like isthmuses and dentinal tubules (Pozos- Guillen et al., 2016). These failures can result in infections, discomfort, or complications such as apical periodontitis or a surgery necessity (SIQUEIRA et al., 2014; YAMAGUCHI et al., 2018). Sodium hypochlorite is the most commonly used antimicrobialagent, but it presents high cytotoxicity to periodontal tissues and is insufficient to overcome the limitations currently encountered in endodontic treatment (RUKSAKIET et al., 2020). In this context, less toxic antimicrobial drugs would be of great interest for endodontic applications, provided they are delivered through an appropriate formulation that ensures adequate contact time and penetration into the root canal system. Therefore, the development of a novel antimicrobial gel containing a less toxic agent or an association of antimicrobial agents represent a promising approach to enhance endodontic disinfection efficacy while potentially reducing toxicity concerns. 

Objective: This study aims to develop a Domifen Bromide (DB) gel and evaluate its antimicrobial potential to disinfect root canals and dentinal tubules during endodontic treatment.

Methods: Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time kill curve, and synergism tests for Chlorhexidine (CHX) and DB were performed based on CLSI standard methods. Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) of the drugs alone and in combination (1:1) were analyzed to verify interaction between the compounds. DB 0.1% gels were made with 14% of poloxamer (PLX14) and different concentrations of hydroxyethylcellulose (HEC 0.1/0.3/0.5/1.0%). The solid–gel transition temperature (Tsol/gel), was considered to be the temperature at which the two moduli were equal (G` and G` crossover),  of the gel formulations was measured using a DH-R2 rheometer (T.A. Instruments) with a stainless-steel cone (1) and plate geometry (40 mm diameter) and a gap of 25 μm between the cone and plate, with a temperature ramp (15–50 °C), increased at 10 C/min. Samples were equilibrated for at least 5 min before analysis. Following the application of a constant stress, a frequency of 1.5 Hz, and a maximum strain amplitude of 0.3 Pa, a temperature sweep analysis was performed. The analyses were performed on at least three replicates of each formulation. The antimicrobial potential of 0.1% DB gels was evaluated using an adapted inhibition halo test against E. faecalis.

Results: CHX exhibited MIC and MBC values of 5 µg/mL and 80 µg/mL, respectively and DB of 1.25 µg/mL, and 10 µg/mL, respectively. Time-kill curve tests showed that DB has a stronger antimicrobial effect than CHX (Figure 1). The synergism test demonstrated an antagonistic interaction between DB and CHX. Additionally, TG and DSC analyses confirmed that both drugs engage in molecular interactions (Figure 2); therefore, only DB (0.1%) was used to develop the antimicrobial gel. The gels are more fluid at lower temperatures, making application easier, and they remain in place upon warming to stay at the action site longer. This helped monitor complex viscosity (η) during gelation and determine Tsol/gel. Formulations containing 14% PLX and varying HEC concentrations had Tsol/gel points and viscosity ranges: PLX 14%/HEC 0.1%, up to 34.5 ± 0.70°C (η*: 0.009 to 174.2 Pa.s); PLX 14%/HEC 0.3%, up to 30.9 ± 1.29°C (η*: 0.036 to 344.5 Pa.s); PLX 14%/HEC 0.5%, up to 30.2 ± 1.16°C (η*: 0.015 to 357.9 Pa.s); PLX 14%/HEC 1.0%, at 29.4 ± 0.47°C (η*: 0.020 to 501.0 Pa.s); and the control gel with 14% PLX, at 34.4 ± 1.45°C (η*: 0.011 to 442.4 Pa.s). The gel exhibiting the largest inhibition zone against E. faecalis contained 14% PLX, 0.3% HEC, and 0.1% DB (Figure 3).

Conclusion: The novel antimicrobial gel developed exhibited significant antibacterial activity against Enterococcus faecalis, the primary microorganism involved in endodontic infections, indicating its potential as an alternative agent for root canal disinfection and for reducing the risk of treatment failure and retreatment.

References: Kalia, Y. N. et al. Iontophoretic drug delivery. Advanced Drug Delivery Reviews, v. 56, n. 5, p. 619–658, 2004.
Pozos-Guillen, A. et al. Intracanal irrigants for pulpectomy in primary teeth: a systematic review and meta-analysis. International Journal of Paediatric Dentistry, v. 26, n. 6, p. 412–425, 2016.
Ruksakiet, K. et al. Antimicrobial Efficacy of Chlorhexidine and Sodium Hypochlorite in Root Canal Disinfection: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Journal of Endodontics, v. 46, n. 8, p. 1032-1041.e7, 2020.
Siqueira, J.F., Rocas, I.N., Ricucci, D., Hulsmann, M. Causes and management of post-treatment apical periodontitis. British Dental Journal, v. 216, n. 6 p. 305–312, 2014.
Yamaguchi, M. et al. Factors that cause endodontic failures in general practices in Japan. BMC Oral Health, v. 18, n. 1, p. 1–5, 2018.

Acknowledgements:

Funding: CNPQ Universal (Proc. N. 402587/2021-9); FAPDF Learning 1930002145/2023-93.

Figure 1. Time kill curve assay of (A) CHX and (B) DB

Figure 2. TG and DSC analysis of CHX and DB isolated and in association.

Figure 3. Inhibition zone of DB gels against E. faecalis.