The distribution of Ca, S, Mg, and P was mapped within the incisors using an electron microprobe. Medial sections of incisors from Spacelab-3 rats and ground-based controls were analyzed with the electron microscope. Traverses were Fourier analyzed and frequency smoothed by recombining 50% of the harmonics. Calcium ratios were determined. Results were compared with ground-based controls and incisor studies conducted on other space-flown rodents.

Results:

Newly-formed incisor dentin from SL-3 flight rats contained higher than normal concentrations of calcium, and lower than normal magnesium concentrations. Though mean tissue Ca/P ratios in flight rats were normal, detailed analysis indicates that the Ca/P ratios tend to be lower than normal in the most recently formed dentin of the flight rats. Ca/Mg ratios were statistically different in the flight rats. Ca/S ratios were highest in flight rats by virtue of higher tissue Ca. Though not as pronounced, these results are consistent with Cosmos 1129, where large sulfur-"spikes" were observed in the rat dentin, apparently a result of the longer duration (18.5 days) of that flight. Results further suggest that continuously growing rat incisors provide useful records of the effects of weightlessness on Ca metabolism. The failure of flight rat dentin to exhibit the normal decrease in Ca++ within about 100 micrometers of the pulp cavity could indicate that dentinogenesis was slowed during the mission, allowing time for the secondary mineralization/apatite crystal growth to increase the local Ca/P and Ca/Mg ratio.