Understanding Oral Hygiene and Periodontal Health in Space Using a Bedrest Analog Model for Weightlessness (NASA Sensorimotor Countermeasures Study)

AIMS: To investigate longitudinal alterations in oral hygiene, gingival inflammation, and salivary secretion during a 60-day head-down tilt bed rest (HDTBR) protocol as a validated ground-based analog of microgravity. MATERIALS AND METHODS: Twenty-four healthy volunteers participated in a 60-day, 6° HDTBR study conducted under strictly controlled conditions. Oral health assessment safety measures were performed at baseline, mid-head-down tilt (HDT), end-HDT, and post-recovery. RESULTS: Plaque accumulation and gingival inflammation increased, with increases from baseline to end-HDT in the Quigley-Hein Plaque Index (1.8 ± 0.4 to 2.3 ± 0.4; p < 0.01), Gingival Index (0.8 ± 0.4 to 1.2 ± 0.2; p < 0.001), and bleeding on probing (BoP) (18.4 ± 11.6% to 35.1 ± 16.6%; p < 0.001). BoP partially recovered post-HDT, while QHI and GI remained elevated compared with baseline. Periodontal Screening Index scores shifted toward higher grades during HDT without evidence of destructive periodontal breakdown. The unstimulated salivary flow rate remained unchanged throughout. CONCLUSIONS: Prolonged gravitational unloading induces a plaque-driven deterioration of gingival health in systemically healthy individuals, likely related to impaired mechanical plaque control and microcirculatory changes rather than salivary dysfunction. Gingival tissues appear to be sensitive biomarkers of adaptation to unloading conditions, supporting the need for optimized oral hygiene and adjunctive preventive strategies during future long-duration space missions. TRIAL REGISTRATION: German Clinical Trial Registry (DRKS00033882, registration date 03-15-2024, https://www.drks.de/search/de/trial/DRKS00033882/details).