A 35-year-old woman comes to OPD complaining of fever, fatigue, and a productive cough with foul-smelling sputum for 2 weeks. She has a history of seizures, Physical examination shows dullness to percussion over the right lung fields. An X-ray of the chest shows a cavitary infiltrate with an air-fluid level in the right lower lobe of the lung. Cultures of the infiltrate grow Peptostreptococcus and Prevotella species. Which of the following is the most likely predisposing factor for this patient's condition?