Microbiological and toxicity analyses of the synthetic polymer polyhexamethylene guanidine hydrochloride against endodontic microorganisms

Laila Dainize Finotelli; Carlos Henrique Gomes Martins; Sara Lemes de Souza; Anna Livia Oliveira Santos; Mariana Brentini Santiago; Sérgio Ricardo Ambrósio; Rodrigo Cássio Sola Veneziani; Renato Luis Tame Parreira; Leandro Aparecido Mello; Lucas de Freitas Pereira; Fernanda Gosuen Gonçalves Dias

doi:10.1007/s42770-024-01603-8

Microbiological and toxicity analyses of the synthetic polymer polyhexamethylene guanidine hydrochloride against endodontic microorganisms

Braz J Microbiol. 2025 Jan 15. doi: 10.1007/s42770-024-01603-8. Online ahead of print.

Affiliations

¹ Department of Postgraduate Program in Animal Science, University of Franca (UNIFRAN), Av. Dr. Armando Salles Oliveira, 201, Parque Universitário, Franca, SP, CEP 14.404-600, Brazil.
² Laboratory of Antimicrobial Testing, Institute of Biomedical Sciences, University of Uberlândia (UFU), Campus Umuarama, Av. Amazonas s/n, Uberlândia, MG, CEP 38405-320, Brazil.
³ Department of Postgraduate Program in Sciences, University of Franca (UNIFRAN), Av. Dr. Armando Salles Oliveira, 201, Parque Universitário, Franca, SP, CEP 14.404-600, Brazil.
⁴ Department of Veterinary Medicine, University of Franca (UNIFRAN), Av. Dr. Armando Salles Oliveira, 201, Parque Universitário, Franca, SP, CEP 14.404-600, Brazil.
⁵ Department of Postgraduate Program in Animal Science, University of Franca (UNIFRAN), Av. Dr. Armando Salles Oliveira, 201, Parque Universitário, Franca, SP, CEP 14.404-600, Brazil. fernanda.dias@unifran.edu.br.

PMID: 39812973
DOI: 10.1007/s42770-024-01603-8

Abstract

Failures in endodontic treatments are common due to microbial resistance in the pulp canal. The study evaluated the in vitro activity of polyhexamethylene guanidine hydrochloride (PHMGH) against endodontic strains, as well as in vivo toxicity. Using minimum inhibitory concentration and minimum bactericidal concentration techniques, PHMGH was effective against all microorganisms, even at low concentrations. At 50.0 µg/mL, it inhibited Enterococcus faecalis; furthermore, when compared to chlorhexidine (CLX), it demonstrated values 19 times lower against Candida albicans. The polymer's activity was also determined by agar diffusion, evaluating products A (calcium hydroxide - Ca(OH)2, as a reference), B (Ca(OH)2 combined with physiological solution, reference with a vehicle), C (PHMGH 6.25%), D (PHMGH 3.125%), E (PHMGH 1.5625%), F (PHMGH 0.78125%), G (PHMGH 6.25% and Ca(OH)2), H (PHMGH 3.125% and Ca(OH)2), I (PHMGH 1.5625% and Ca(OH)2), J (PHMGH 0.78125% and Ca(OH)2), and K (positive control, CLX 0.12%). Products containing PHMGH were more effective than the references against all strains, and C, D, and G were more effective than CLX against Peptostreptococcus anaerobius, Actinomyces naeslundii, and Actinomyces viscosus. According to the fractional inhibitory concentration index, the combination of PHMGH and CLX showed indifference for Peptostreptococcus anaerobius, Actinomyces naeslundii, Actinomyces viscosus and Escherichia coli, antagonism for Candida albicans, and synergy for Enterococcus faecalis. The toxicity of PHMGH at different concentrations was tested in Caenorhabditis elegans and did not show lethality in nematodes, with the LC50 observed only at the highest concentration (100 µg/mL) after two days of exposure. It is suggested that PHMGH exhibited antimicrobial activity against endodontic strains and low toxicity, raising expectations for new preventive and therapeutic products in endodontics.

Keywords: Caenorhabditis elegans; Endodontic irrigant; Intracanal medication; Microbiology.