Response of zygomaticomaxillary suture to experimental malocclusion in rats

The purpose of this study was to examine the response of the zygomaticomaxillary suture (ZMS) to experimental malocclusion in rats. Thirty-two male Wistar rats were divided into two groups. Malocclusion was produced in the experimental group (n = 20) by gluing a wire, 1 mm in diameter, on the upper left first molar. Duration of the procedure was 20 min. In the control group (n = 12), rats were forced to open their mouths for the same time as in the experimental group. Histomorphological changes of the ZMS were examined at intervals of 1, 2, 4 and 8 weeks. The specimens were stained with hematoxylin-eosin and Mallory's azan. The suture in the control group showed a regular functional arrangement of component fibers, and osteoblasts lined the periphery of new bone at the inner half of the suture. On the untreated side in the experimental group, osteoclasts were most abundant after 2 weeks. Histomorphometric quantification of the sutural width revealed that, at the inner half of the suture, the width of the sutural space on the treated side in the experimental group was greater than that in the control group after 4 weeks (p < 0.05). The argyrophilic nucleolar organizer region (AgNOR) technique was used to investigate the transcriptional activity of fibroblasts in the suture. At the inner half of the suture, the number of AgNORs on the untreated side in the experimental group was greater than that on the treated side and that in the control group after 2 weeks (p < 0.05). Around the tip of the suture and at the outer half of the suture, there was no appreciable difference in the AgNOR number between the experimental and control groups. It was concluded that unilateral changes in occlusion had different effects on the treated and untreated sides of the ZMS. Moreover, the inner and outer halves of the suture showed different histological changes in response to experimental malocclusion.