Craniofacial Bones and Teeth in Spacefarers: Systematic Review and Meta-analysis

Abstract

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.

Receptors Implicated in Microgravity-Induced Bone Loss

“…The sensing mechanisms described above could deliver signals either directly due to forces (or lack thereof) or could respond to the redistribution of fluid that occurs in low gravity. The second idea is attractive given the increase in bone density in the skull, where there is increased pressure compared with Earth's gravity [159,215].…”

Applications for oral research in microgravity – lessons learned from burning mouth syndrome and ageing studies

“…This was attributable to the altered composition and consistency of the rodent's diet. Another area of the skull that showed a trend to increase in bone volume was the calvaria, both in rodents and astronauts [ 9 ]. According to the same authors, space travel can result in unexpected changes in craniofacial bones, determining the risk of dental events in space.…”

“…Since space missions take place in an isolated environment, it is essential to avoid dental emergencies. However, dental issues have been reported during space travel [ 9 ].…”

Social Justice in Dental Research

“…Thus, understanding the impact of space travel on the craniofacial structures is essential. Based on a systematic review and meta-analysis, Moussa et al (2023) analyzed changes in craniofacial hard tissues during flights in space. They found a trend toward increased bone volume/tissue volume (BV/TV) and tissue mineral density (TMD) in rodents, as well as a significant increase in TMD in humans in the roof of the skull.…”

“…However, BV/TV significantly decreased in the mandibles of spacefaring rodents. Based on these findings, the authors suggest that space travel may engender unanticipated and varied changes in craniofacial bones; they also report that a significant research gap exists in our understanding of spaceflight-related alterations of craniofacial hard tissues ( Moussa et al 2023 ).…”