Delirium is a clinical syndrome characterized by acute attention deficits, altered consciousness, and fluctuating cognitive dysfunction, typically triggered by multifactorial causes such as physical illness, medication use, or postoperative stress . As the most common complication in hospitalized patients, delirium is highly prevalent among elderly surgical populations, with postoperative delirium (POD) occurring in 7.5%-27.5% of cases, and rates rising to 50%-70% in intensive care unit (ICU) patients . Its onset is closely associated with poor prognoses, including long-term postoperative cognitive decline , increased mortality, prolonged hospitalization, and elevated healthcare costs (annual costs in the United States ranging from 38billionto152 billion) . Early prevention and screening of POD are therefore critical to improving patient outcomes and reducing healthcare burdens.

Surgical patients' oral health issues exhibit multifactorial pathogenesis: intrinsic factors (e.g., age-related tooth loss, malnutrition-induced mucosal repair impairment, and chewing dysfunction due to reduced skeletal muscle mass) and iatrogenic factors (e.g., endotracheal intubation trauma, salivary secretion suppression from analgesics, and inadequate perioperative oral care). Poor oral health in hospitalized patients is often attributable to aging, physical dependence, cognitive decline, malnutrition, low skeletal muscle mass/strength, and comorbidities. The recently proposed concept of "Oral Frailty"-a progressive decline in oral structure and function-strongly predicts physical frailty, dysphagia, malnutrition, long-term care needs, and mortality in community-dwelling older adults

The impact of oral health on cognitive function may involve three pathways :

Mechanical pathway: Tooth loss disrupts masticatory motor function, reduces cerebral blood flow, and diminishes afferent stimulation from peripheral receptors (e.g., periodontal ligaments), leading to weakened neural connectivity and regional brain atrophy.

Neurodegenerative pathway: Tooth loss accelerates neuronal damage via apoptosis and mitophagy, increasing amyloid-beta deposition in the brain.

Inflammatory/metabolic pathway: Systemic inflammation, metabolic dysregulation, microbial-gut-brain axis interactions, and activation of microglia/astrocytes drive neuroinflammatory cascades in the central nervous system.

Given these connections, oral frailty may act as an independent risk factor distinct from general frailty and a potential contributor to POD. These findings suggest that oral frailty could serve as a unique biomarker for perioperative neurocognitive disorders, mediating their pathogenesis. Systematic investigation into the spatiotemporal relationship and mechanisms linking oral health to POD in surgical patients holds significant clinical value for developing multimodal prevention strategies.

Inclusion Criteria:

• Patients aged ≥18 years scheduled for elective cardiac or thoracic surgery requiring endotracheal intubation.

Patients without consciousness impairment, able to cooperate with the investigation.

Patients or their legal guardians informed about the study's purpose, methodology, and content, with signed informed consent forms.

Exclusion Criteria:

• Patients with pre-existing oral conditions (e.g., xerostomia, oral mucosal lesions) prior to mechanical ventilation.

Patients with a history of radiotherapy, chemotherapy, or corticosteroid use before surgery.

Patients experiencing intraoperative mortality.

Patients scheduled for elective cardiac surgery under general anesthesia requiring endotracheal intubation