Reversible and irreversible effects of temperature on amelogenesis of hamster tooth germs in vitro.

Hamster first hamster molar tooth germs in early secretory stage of amelogenesis were cultured for one day in vitro at 6 degrees C, 22 degrees C, 37 degrees C or 45 degrees C in the presence of 3H-proline, 45Ca and 32P-orthophosphate. Other explants were cultured without these labels and after culture examined by histology. The highest temperature tested was lethal to the explants, decreased total dry weight and rapidly increased total uptake of the radiolabelled mineral ions, probably merely due to physicochemical modification of the existing preculture minerals. Optimal synthesis and secretion of amelogenins were measured at physiological temperature (37 degrees C). Effects of exposure to both temperatures below the physiological value were virtually reversible when explants were grown at physiological temperature (37 degrees C) for another day. However, amelogenin secretion during this recovery period did not reach values as high as those found for the first day in explants initially grown at physiological temperature during the first day. We concluded from the four temperatures examined that the optimal temperature for enamel matrix deposition in vitro was 37 degrees C. At this temperature enamel biosynthesis and its secretion are high. Lowering the temperature slows down the metabolism without any apparent harmful effect. Normal development of the tooth explants in vitro resumes when the culture temperature is restored to physiological levels (37 degrees C). For temporary storage of tooth germ explants prior to any reimplantation, we therefore recommend a temperature of 6 degrees C.