Conditioned fear stress increases bone resorption in apical periodontitislesions in Wistar male rats

•Stress increased the size of the periapical lesion evaluated histologically.•Stress increased the total number of inflammatory cells.•Stress did not change the number of mast cells. Because the impact of conditioned fear stress on apical bone resorption is unknown, the aim of the current studywas to use a rat model to evaluate the impact of conditioned fear stress on the bone resorption of inflammatory apical periodontitis lesions. Twenty-five animals were divided into two groups. They underwent a surgical procedure in the first left lower molar tooth to expose the dental pulp and induce inflammatory apical periodontitis lesions through the retention of contamination (bacterial infection) during a 56-day period. The animals in the case group were stressed daily by using electrical stimuli (1.10 mA), whereas the animals in the control group were absent from the stressful stimuli (shocks). The open field test was performed to validate the stress methodology. The jaws were removed and collected for histological and radiographic analyses. Stressed animals presented increased levels of bone loss and inflammatory cells in the root apex in comparison with the control group (P = 0.0001). However, no radiographic differences were observed between the groups (P > 0.05). Our results demonstrated that conditioned fear stress could modify a periapical lesion by increasing the size of bone loss there. Conditioned fear stress also increased the total number of inflammatory cells compared with the control group. Studies evaluating the impact of conditioned fear stress on human periapical inflammatory lesions should be encouraged.