Biological response to endodontic treatment in one versus two-visit: a systematic review and meta-analysis of animal studies

To perform a systematic review of animal studies that compared the histopathological characteristics between teeth with apical periodontitis after endodontic treatment in one or two visits. This systematic review was registered on the International Prospective Register of Systematic Reviews (PROSPERO) – CRD42022340849. Studies were collected from PubMed/MEDLINE, LILACS, EMBASE, Livivo, SciELO, Web of Science, Scopus, and Cochrane Library and manual and gray literature searches. Animal studies that evaluated histological characteristics after endodontic treatment of teeth with apical periodontitis in one or two visits were included. Risk of bias analysis of the included studies was performed using the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) tool. Data synthesis of the included studies with quantitative data was performed, and meta-analysis was conducted with the Comprehensive Meta-Analysis software, using the random effects model and odds ratio (OR). Eighteen studies met the inclusion criteria (Kappa = 0.891). Meta-analyses indicated values in inflammatory infiltrate intensity with effect size of 5.5% (95% CI: 0.020–0.148; p < 0.001), periodontal ligament thickness: 25.6% (95% CI: 0.134–0.487; p < 0.001), dentin resorption: 13% (95% CI: 0.015–1.141; p = 0.066), cementum resorption: 7.1% (95% CI: 0.015–0.325; p = 0.001), bone resorption: 1.4% (95% CI: 0.002–0.130; p < 0.001), mineralized tissue resorption: 42.8% (95% CI: 0.110–1.671; p = 0.222), biological apical sealing: 13.1% (95% CI: 0.055–0.314; p < 0.001), and presence of microorganisms: 10.3% (95% CI: 0.014–0.747; p = 0.025). When considering animal studies, the two-visit endodontic treatment, using calcium hydroxide-based intracanal medication, resulted in better biological repair characteristics. A two-visit endodontic treatment with calcium hydroxide-based intracanal medication yields superior histopathological outcomes.