To determine the influence of a simulated microgravity on oral cavity, 40 healthy male volunteers were studied before, during, just after and after 12 hr of the simulated microgravity condition of -6° head-down-tilt (HDT) bed rest. Facial function tests, mouth opening, jaw movements, tongue movements, facial sensation (Touch, pressure, temperature), taste, odour, perception of food, Salivary vitamins E and C, lactate dehygrogenase isoenzyme, MIP 1 á, Glucosyltransfer â, Malonaldehyde, 8- hydroxydeoxyguanosine, Thiocynate, salivary contents and salivary flow rate were measured. Flow rate, sodium, potassium, calcium, phosphate, protein, lactate dehygrogenase, MIP 1 alpha, Malonaldehyde, 8- hydroxydeoxyguanosine, thiocynate were found to increase significantly while Amylase activity, vitamin E & C and mouth opening were decreased in simulation environments in contradiction to normal and recovery stage. The threshold for MSG and capsaicin increased about 1.5 dilution step, while sodium chloride decreased about 2 dilution during microgravity as compared to normal conditions. Mild pain of teeth, facial oedema, mild pain mandibular angle regions, pain in sublingual and submandibular opening duct regions, abnormal facial expression, loss of sensation of pain and temperature, decreased the tongue and mandibular movement in simulation microgravity environments. These results suggest that reversible effect of microgravity is oedema of face, change in taste, abnormal expression of face, teeth pain and xerostomia . The non reversible effect of microgravity such as prevalence of periodontal disease, dental caries but different pattern than normal, stone formation in salivary duct, pre cancer or cancer, fracture of maxillary and mandibular bone and xerostomia more in astronaut as compared to normal persons. Further study will be required on large scale and long term effect of microgavity on oral cavity to prevent the adverse effect on oral cavity. Hence, aeronautic dentistry should be included in curriculum.

Key words Mission , Mars, Microgravity, Aeronautic Dentistry.