**Abstract**

The oral cavity functions in taste, mastication, solubilization and digestion of nutrients, as well as in respiration and speech, and participates in innate and adaptive immunity. Saliva creates and regulates the environment of the oral cavity, and changes in its composition and rate of secretion have significant effects on oral tissues as well as on systemic health. The effects of microgravity on the salivary glands, mandible and teeth were studied in mice flown on US space shuttle STS-131 and STS-135 missions, and the Russian Bion-M1 biosatellite. Significant changes in morphology and secretory protein expression occurred in parotid glands; submandibular glands were affected only on the 30-day Bion-M1 mission, indicating tissue specificity of the effects due to changes in gravity which may be similar to those taking place in humans. Changes also occurred in mandibular bone and incisor teeth. Collection of saliva is a non-invasive procedure for assessing physiological status and diagnosis of several disorders and provides a simple method for monitoring astronaut health during extended spaceflight.

**Keywords:** salivary glands, mandible, teeth, morphology, protein expression
