Apical periodontitis as an aggravating factor for the severity of rheumatoid arthritis: An animal study

Abstract Aim The present study investigated the influence of apical periodontitis (AP) on the severity of rheumatoid arthritis (RA) using a Wistar rat model. Methodology Forty male Wistar rats were distributed across four groups ( n = 10) based on the induction of RA and AP: Control, RA, AP, and RA + AP. RA was induced through two immunisations with type II collagen emulsified in incomplete Freund's adjuvant, followed by one immunisation with complete Freund's adjuvant. After 21 days of RA induction, AP was induced by exposing the pulp of four molars. Animals were euthanized after 28 days of pulp exposure. Through the experiment, visual and behavioural assessments tracked RA development and the knees and hind paw joints were measured. Micro‐computed tomography scans of knees and hind paws, as well as mandibles and maxillae, were conducted to evaluate RA severity and the presence of AP, respectively. Serum samples were collected to analyse proinflammatory cytokines (IL‐1β, IL‐2, IL‐17, and TNF‐α). Non‐parametric data were analysed using the Kruskal‐Wallis test followed by Student–Newman–Keuls test, while one‐way anova followed by Tukey's test was performed for parametric data. A significance level of 5% was employed. Results All molars submitted to access cavity developed AP. All joints subjected to arthritis induction developed the disease, with AP + RA demonstrating a higher arthritis severity when compared to the RA group ( p < .05). RA + AP group displayed a significantly larger hind paw and knee circumference compared to the RA group ( p < .05). Micro‐CT images of RA and RA + AP groups revealed joints with erosions and bone deformities, with a significantly lower bone surface density, lower trabecular number and higher trabecular separation in the hind paw and a significantly lower percent bone volume and higher trabecular separation in the knees of RA + AP group compared to RA group ( p < .05). RA + AP group exhibited a significantly higher level of TNF‐α and a lower level of IL‐2 compared to all other groups ( p < .05). Both RA and RA + AP groups had significantly higher IL‐17 levels ( p < .05), while there was no significant difference in IL‐1β levels among the groups ( p > .05). Conclusion The findings from this study underscore a possible relationship between apical periodontitis and the exacerbation of rheumatoid arthritis.