Animals in space exploration studies serve both as a model for human physiology and as a means to understand the physiological effects of microgravity. To quantify the microgravity-induced changes to bone health in animals, we systematically searched Medline, Embase, Web of Science, BIOSIS, and NASA Technical reports. We selected 40 papers focusing on the bone health of 95 rats, 61 mice, and 9 rhesus monkeys from 22 space missions. The percentage difference from ground control in rodents was –24.1% [Confidence interval: −43.4, −4.9] for trabecular bone volume fraction and –5.9% [−8.0, −3.8] for the cortical area. In primates, trabecular bone volume fraction was lower by –25.2% [−35.6, −14.7] in spaceflight animals compared to GC. Bone formation indices in rodent trabecular and cortical bone were significantly lower in microgravity. In contrast, osteoclast numbers were not affected in rats and were variably affected in mice. Thus, microgravity induces bone deficits in rodents and primates likely through the suppression of bone formation.

Introduction: Estimating the risk of dental problems in long-duration space missions to the Moon and Mars is critical for avoiding dental emergencies in an environment that does not support proper treatment. Previous risk estimates were constructed based on the experience in short-duration space missions and isolated environments on Earth. However, previous estimates did not account for potential changes in dental structures due to space travel, even though bone loss is a known problem for long-duration spaceflights. The objective of this study was to systematically analyze the changes in hard tissues of the craniofacial complex during spaceflights. Methods: Comprehensive search of Medline, Embase, Scopus, the NASA Technical Report Server, and other sources identified 1,585 potentially relevant studies. After screening, 32 articles that presented quantitative data for skull in humans (6/32) and for calvariae, mandible, and lower incisors in rats (20/32) and mice (6/32) were selected. Results: Skull bone mineral density showed a significant increase in spacefaring humans. In spacefaring rodents, calvariae bone volume to tissue volume (BV/TV) demonstrated a trend toward increasing that did not reach statistical significance, while in mandibles, there was a significant decrease in BV/TV. Dentin thickness and incisor volume of rodent incisors were not significantly different between spaceflight and ground controls. Discussion: Our study demonstrates significant knowledge gaps regarding many structures of the craniofacial complex such as the maxilla, molar, premolar, and canine teeth, as well as small sample sizes for the studies of mandible and incisors. Understanding the effects of microgravity on craniofacial structures is important for estimating risks during long-duration spaceflight and for formulating proper protocols to prevent dental emergencies. Knowledge Transfer Statement: Avoiding dental emergencies in long-duration spaceflights is critical since this environment does not support proper treatment. Prior risk estimates did not account for changes in dental structures due to space travel. We reviewed and synthesized the literature for changes in craniofacial complex associated with spaceflight. The results of our study will help clinicians and scientists to better prepare to mitigate potential oral health issues in space travelers on long-duration missions.

Studying the effects of space travel on bone of experimental animals provides unique advantages, including the ability to perform post-mortem analysis and mechanical testing. To synthesize the available data to assess how much and how consistently bone strength and composition parameters are affected by spaceflight, we systematically identified studies reporting bone health in spacefaring animals from Medline, Embase, Web of Science, BIOSIS, and NASA Technical reports. Previously, we reported the effect of spaceflight on bone architecture and turnover in rodents and primates. For this study, we selected 28 articles reporting bone strength and composition in 60 rats and 60 mice from 17 space missions ranging from 7 to 33 days in duration. Whole bone mechanical indices were significantly decreased in spaceflight rodents, with the percent difference between spaceflight and ground control animals for maximum load of −15.24% [Confidence interval: −22.32, −8.17]. Bone mineral density and calcium content were significantly decreased in spaceflight rodents by −3.13% [−4.96, −1.29] and −1.75% [−2.97, −0.52] respectively. Thus, large deficits in bone architecture (6% loss in cortical area identified in a previous study) as well as changes in bone mass and tissue composition likely lead to bone strength reduction in spaceflight animals.