Chronic Stress Predictability Modulates the Severity of Apical Periodontitis Induced in Wistar Rats

To evaluate the effects of predictable and unpredictable chronic stress on the development and severity of periapical lesions in rats.

Thirty-two male Wistar rats were randomly allocated into four groups (n = 8 each): control, apical periodontitis without stress, apical periodontitis with predictable stress, and apical periodontitis with unpredictable stress. Emotional stress protocols were applied for 42 days, and apical periodontitis was induced on day 21 by pulp exposure. Stress induction was confirmed through behavioural evaluation using the open field and Y-maze tests. The severity of periapical lesions was assessed by microcomputed tomography and histological analysis. Data were analysed using Student's t-test, Mann-Whitney, one-way ANOVA, or Kruskal-Wallis tests (p < 0.05).

Behavioural tests confirmed successful stress induction, with both stressed groups demonstrating reduced exploratory activity compared to non-stressed animals. Animals exposed to unpredictable stress developed significantly larger periapical lesions and exhibited higher inflammatory infiltrate scores than those subjected to predictable stress or no stress (p < 0.05). Microcomputed tomography findings corroborated the histological results, confirming the greater severity of apical periodontitis in the unpredictable stress group (p < 0.05).

Unpredictable chronic stress significantly exacerbated the development and severity of periapical lesions, suggesting that stress predictability may act as a modulatory factor in apical periodontitis progression.