Space flight inevitably involves human interaction with microgravity which is 1-millionth that experienced on earth. The effects of floating and weightlessness are well known, as are the impact that microgravity has on fluid balance, cardiovascular output, calcium balance, muscular atrophy and importantly space osteoporosis (SO), a condition characterized by significant loss of bone density particularly in the weight bearing bones such as pelvis and femurs. For prolonged space flight of 4 to 6 months up to 14% loss in bone density has been recorded in the femoral necks of astronauts. These effects are similar to those seen in immobilized patients where in the absence of loading stimuli there is a net bone resorption with increased calcium excretion, according to the principles of Wolff’s law.
Bone height measurements around a dental implant after a 6-month space flight: a case report.
A case report
For astronauts on long flights, a regime of exercise, high calcium intake and the use of vibration plates to stimulate bones helps mitigate the onset of SO to some extent but calcium absorption is significantly reduced in space even in the presence of high calcium diets, and as such a net calcium loss is inevitable. This is further accentuated by a decrease in osteoblast activity and an increase in osteoclast activity, even though there is no notable change in hormone balance. Perhaps of most interest is that full body scans have revealed a net loss of bone density in the lower extremities of the weight bearing skeleton with a redistribution to the head where some slight increase in bone density has been seen. This may have ramifications for bone supporting dental implants. In this case report the peri-implant bone of a French astronaut was monitored after a 189-day space flight.
Material and Methods A 46-year old male astronaut had received a 13 x 4.7mm titanium alloy dental implant (Screw-Vent, Zimmer Dental) to replace his missing right mandibular first molar. The implant had been successfully in function for 15 months when he was scheduled for a 6-month mission to the Mir Space Station.
One month prior to departure baseline bone heights were measured at the implant and the contralateral first molar, which was restored with a ceramometal crown. Radiographs were taken in a paralleling device for standardization and bone height was measured at 13.5x magnification using a photomicroscope. For the implant the bone height was determined by measuring the distance from the implant-abutment junction to the first bone contact on the mesial and distal surfaces. For the control, bone height was measured from the metal chamfer-root junction to the peak of interproximal bone adjacent to the root mesially and distally. Follow-up radiographs were taken one month after his return to earth and again 8 months later after his recovery phase.
Results A notable difference existed on mesial and distal surfaces with a net gain of bone height mesially of +0.41mm from baseline to 1-month post flight follow-up compared to a net loss of bone height distally of -0.20mm during the same period. This trend continued over the 8-month recovery period with a net gain of +0.02mm mesially and a net loss of -0.11mm distally to give a total bone height change of +0.43mm mesially and -0.31mm distally. In contrast there was a total net bone loss on both mesial (-0.18mm) and distal (-0.11mm) surfaces at the contralateral control tooth.
Discussion and Conclusions Previous studies on bone density changes in astronauts subject to long space flights have shown that there is a net loss in the weight bearing bones, with the greatest loss in the tibia. This supports Wolff’s law that mechanical stress determines the form and function of bone. In contrast to these findings some studies have indicated an absence of bone loss in the regions of the head. The current study would support this view since there was only minor changes in marginal bone levels, consistent with those seen for implants subject to normal gravitational forces experienced on earth. Indeed there was a small bone height gain mesially. Whilst one implant represents the smallest sample size, it can be concluded that exposure to microgravity for 6 months does not appear to affect marginal bone levels around dental implants.
Crédits : Haigneré C, Jonas P, Khayat P, Girot G.
Dernière mise à jour le: 17/05/2020