OBJECTIVETo calculate the bone mineral density (BMD) of buccal and lingual mandibular cortical bone in psychological stressed rats.

METHODSOne hundred adult male SD rats were randomly divided into psychological stress group(PS group, 40 rats), control group (C group, 40 rats) and foot shock group (FS group, 20 rats). In addition, the PS group and C group were equally divided into week 1, week 2, week 3, week 4 and week 5 subgroup at random. The animals placed intervally in the communication box to receive the psychological stimuli were considered as the PS group animals. The stressors were from their neighboring FS group rats which were receiving foot shock. After observing the behavioral changes of the PS group rats and C group rats with elevated plus maze test, the mandibles were removed carefully and BMD of regions of interest (ROI) in the mandible were calculated by Micro-CT. The ROI were located at the equidistant five points, i.e. A, B, C, D and E, along the anteroposterior border and approximately halfway between the superior and inferior border of the mandible.

RESULTSSignificant decrease of time spent in the open arms, ratio of open arms time and ratio of open arms entries were observed in PS group [time spent in the open arms: (16.6 ± 2.3), (17.1 ± 2.4), (15.8 ± 1.6), (15.8 ± 2.2), (17.9 ± 2.6) s]; ratio of open arms time: [(30.5 ± 3.7)%, (30.3 ± 2.5)%, (26.8 ± 3.8)%, (26.5 ± 2.0)%, (27.4 ± 2.6)%]; ratio of open arms entries: [(34.1 ± 4.4)%, (34.6 ± 4.1)%, (32.6 ± 3.9)%, (34.5 ± 4.8)%, (31.8 ± 3.3)%] compared with control group at each time point (P < 0.05), no differences were observed among PS groups (P > 0.05). On the buccal side of mandibular body, BMD in point D of week 5 PS group [(1 085.4 ± 88.5) mg/cm³] was higher than that of matched control group [(782.3 ± 53.7) mg/cm³) ]and week 1 PS group [(825.2 ± 88.5) mg/cm³] (P < 0.05). Similar results of BMD were obtained in point E between week 5 PS group [(657.2 ± 101.7) mg/cm³] and control group [(415.9 ± 99.7)mg/cm³], week 1 and 2 PS group [(348.1 ± 111.3), (339.3 ± 74.0) mg/cm³] (P < 0.05). On the lingual side of mandibular body, the alterations of BMD were observed in point B and C between week 5 PS group [(1 755.6 ± 156.6), (1 367.8 ± 115.8) mg/cm³]and matched control group [(1 364.6 ± 120.2), (922.6 ± 102.6) mg/cm³] and week 1 PS group [(1 299.7 ± 172.9), (1 052.3 ± 107.9) mg/cm³] (P < 0.05). No differences of BMD were observed in the other points between PS group and control group at each time point(P > 0.05).

CONCLUSIONSPsychological stress induced by communication box could result in the anxious behavior of SD rats and increase the BMD of cortical bone in certain regions of the mandibular body.