Characterization of Histopathology and Microbiota in Contemporary Regenerative Endodontic Procedures: Still Coming up Short

Abstract

Introduction: This study aimed to investigate microbiota and the histopathology of infected immature teeth microenvironments after disinfection with calcium hydroxide, triple antibiotic paste, and a synthetic antimicrobial peptide (synthetic human beta-defensin-3-C15) for regenerative endodontic procedures (REPs). The null hypothesis was that there is no difference among intracanal medications on disinfection in REPs. Methods: Pulp necrosis and periapical lesions were induced in immature beagle dog premolars. Block randomized teeth were uninfected (negative control, n = 6), left infected (positive control, n = 6), or medicated with a disinfectant (n = 6/ group). After disinfection (2 weeks), teeth were reaccessed, irrigated with 17% EDTA, blood clot induced, sealed with ProRoot MTA (Dentsply Tulsa Dental, Tulsa, OK), and restored with resin modified glass ionomer. Animals were monitored radiographically and euthanized (12 weeks) for histopathologic and metagenomic analyses. Results: REP-treated roots showed radiographic repair of periapical radiolucency (67.65%, 23/34), continued root development (73.53%, 25/34), and apical closure (70.59%, 24/34) regardless of the disinfectant used (P . .05). Canal microenvironments histologically devoid of bacteria contained new mineralized and pulp-like tissues in characteristic patterns that varied by disinfectant. Next-generation sequencing (16S ribosomal RNA) identified Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes as dominant phyla of microbiota in immature teeth. Infection-induced teeth showed changes in diversity and richness of microbiota from negative controls. Compared with positive controls, all treated teeth exhibited depleted operational taxonomic units, with lower phylogenic diversity from synthetic human beta-defensin-3-C15-treated teeth. Conclusions: There were no differences among the medicaments investigated in radiologic treatment outcomes, but disinfectants in REPs showed altered microbiota from normal and diseased immature teeth with different histologic patterns of regeneration. (J Endod 2021;47:1285-1293.)