[en] Objective: To study the developmental characters of the normal mandible in growing children. Methods: Twenty growing children undergoing skeletal scintigraphic study for isolated bone disease other than bones of the head and neck at hospital and turned out with normal results finally were studied. The ⁹⁹Tc^m-MDP uptakes in the mandibular condyle, ramus, body and the fourth lumbar vertebra in these cases were quantitated and a ratio of the uptake in the three mandibular regions to that in the fourth lumbar vertebra was obtained. Results: The analysis results showed that the ⁹⁹Tc^m-MDP uptake ratios of the three mandibular regions decreased in linear fashion with age increasing and leveled off after age of 20. The regression equations are: the mandibular condyle, Y-circumflex = -0.052 2X + 1.792 8; the mandibular ramus, Y-circumflex = -0.015 1X + 0.766 7; the mandibular body, Y-circumflex = -0.014 2X + 0.741 0. There was no significant difference of the ⁹⁹Tc^m-MDP uptake ratio between the two sides of the mandible and between the male and female. Conclusion: The results suggest that the ideal time to undergo orthognathic surgery should be at the age of 20 or so if the circumstance of the deformity is not quite clear