OBJECTIVEThe study was to investigate the circadian rhythm of the proliferation index (PI) of the mandibular osteoblast after distraction osteogenesis (DO) by a comparative study to explain the different rhythm characteristics.

METHODSForty-eight healthy goats were employed and divided randomly into DO group and control. Four weeks after the right side mandible of DO group was distracted, animals of the both groups were killed at 0:00, 4:00, 8:00, 12:00, 16:00, 20:00 time point subsequently. Samples of 2 cm x 2 cm x 0.5 cm bone tissue were excised from distracted zone of DO group and the right mental foramen zone of the control. Primary cell culture method was employed to isolate the osteoblast from bone tissue and a flow cytometric analysis was used to detect the PI of osteoblast. The data was analyzed with cosinor rhythmometry method and the different rhythm between the two groups were investigated.

RESULTSThe PI in the two groups demonstrated cosinor waves. The mesor and amplitude in DO group were significant higher compared with the control(P < 0.05), but there was no significant difference for the acrophase between the two groups (P > 0.05).

CONCLUSIONThe PI of osteoblast after DO showed significant circadian rhythm. It is suggested that DO is helpful to promote osteoblast proliferation and bone regeneration.