Synergistic effect of secondhand smoke and apical periodontitis on lung tissue damage in rats

Apical periodontitis (AP) is a prevalent immunoinflammatory disease affecting adults worldwide, this disease is also often co-occurring with high exposure to cigarette smoke. While the harmful effects of secondhand smoke (ShS) are well-documented, its interaction with AP and systemic health implications remain underexplored. This study investigated the combined effects of ShS and AP on disease progression and lung health in a rat model. Twenty-eight female Wistar rats were assigned to four groups: control (no ShS, no AP), control-AP (AP without ShS), ShS (ShS without AP), and ShS-AP (ShS with AP). ShS exposure involved daily inhalation of smoke from up to four cigarettes for 10 weeks, with AP induced via pulp exposure in the lower first molar. Post-euthanasia, jaws and lung tissues were analyzed. Micro-computed tomography confirmed ShS exposure significantly increased the volume and area of apical lesions. Oxidative stress levels in the lung tissue were highest in the ShS-AP group, along with increased total oxidant activity and reduced antioxidant enzyme activity. AP and ShS together were associated with pronounced alveolar destruction and chronic airway remodeling in the lungs. These findings suggest a synergistic interaction between AP and ShS, exacerbating both local and systemic effects. This underscores the critical need to address the interplay between oral and systemic health, particularly in the context of environmental exposures like ShS.