Histopathological evaluation of periapical lesions in developing molars of young male rats

Objectives: To evaluate the histopathological features of induced periapical lesions (PL) exposed to the oral environment at different time points in developing molars of rats. Methods: Twenty-four 30-day-old Holtzman rats had the pulp chamber of the mandibular left first molar opened and root canals were exposed to the oral environment. According to the exposure time, the animals were distributed into three groups (n = 8 rats/group): PL induced for 3 days (PLG-3d), PL induced for 1week (PLG-1w) and PL induced for 9 weeks (PLG-9w). The healthy right first molars were used as control group (CG). In paraffin-embedded jaw sections, the number of inflammatory cells (ICs), IL-6-immunolabelled cells, osteoclasts and PLs area were measured. Data were subjected to two-way ANOVA analysis of variance and Tukey's post-test (p < 0.05). Results: The highest values of ICs and IL-6-immunolabelled cells were found in PLG-1w while no significant difference was observed between PLG-3d and PLG-9w specimens. PLG-1w showed a significantly greater number of osteoclasts than PLG-9w, but no significant difference was found in the PL area between these groups. Conclusions: Although the peak of the inflammatory infiltrate, bone resorption and PL size were reached after 1-week, periapical lesions were established after 3 days in developing molars of rats.