Molecular analysis of intracanal microbial reduction to compare the effectiveness of glycyrrhizin and calcium hydroxide as intracanal medications: a randomised controlled trial

Endodontic treatment aims to thoroughly clean and disinfect the root canal system; however, current techniques, instruments, and irrigants limit complete root canal sterilisation. This study aimed to assess and compare the antibacterial effectiveness of glycyrrhizin (Gly) and calcium hydroxide (Ca(OH)2) as intracanal medicaments using molecular analysis. This double-blind (participant- and assessor-blind) study included 28 patients with single-rooted teeth diagnosed with pulp necrosis and asymptomatic apical periodontitis. Following field disinfection, bacterial samples were collected before and after chemomechanical preparation (S1 and S2, respectively) and 7 days after intracanal medicament placement (S3). Participants were randomly assigned to Group 1 (Ca(OH)2) or Group 2 (Gly) (n = 14 each). All samples were promptly transferred for molecular analysis, and bacterial DNA and RNA levels were assessed using real-time polymerase chain reaction. Data were log-transformed and evaluated using mixed‑effects two‑way repeated‑measures models (time × treatment). The change in log‑transformed DNA and RNA between S2 and S3 (Δlog S3–S2) was compared between groups using the Mann–Whitney U test, with a significance level of 0.05. Twenty-eight participants (14 per group) were included in the statistical analysis at S1, S2. At S3, data were available for 10 and 11 participants for DNA and 11 and 10 participants for RNA in groups 1 and 2, respectively. Mixed‑effects two‑way repeated‑measures analysis showed significant effects of group and time on log‑transformed bacterial DNA and RNA levels, with a significant group×time interaction (p < 0.0001). The reduction in log‑transformed RNA (primary end-point) and DNA from S2 to S3 (Δlog S3–S2) was significantly greater in Group 2 than in Group 1 (RNA: p < 0.0001; DNA: p = 0.0004). Compared with Ca(OH)2, Gly demonstrated greater antibacterial activity through greater reductions in bacterial DNA and RNA levels. This may support the potential of Gly as an alternative intracanal medicament during root canal therapy. This study was retrospectively registered on clinicaltrials.gov under the identifier NCT06291623 on March 4, 2024.