Abstract: PURPOSE: To demonstrate the histological changes of the maxilla-facial sutures caused by retractive forces of a zygomatic implant anchorage to the maxilla of rhesus monkeys. METHODS: Four young male rhesuses were employed, 3 in the experimental group (1 was been distracted for 1.5 months and 2 for 3 months), and 1 as control. HE staining and vital fluorescent were used to observe histological changes in the circum-maxillary sutures (i.e. zygomaticomaxillary suture, transverse palatine suture, frontomaxillary suture and pterygopalatine suture) and the posterior sutures (i.e. zygomaticotemporal suture and sphenozygomatic suture, sphenozygomatic suture) of zygoma bone caused by retractive forces of zygomatic implant to the maxilla of rhesus monkeys. RESULTS: Obvious reactions of compressive stress and bone resorption were observed around the 4 circum-maxillary sutures. There were 3 patterns of sutural reactions, indicating the direction of sutural stress influenced by sutural position and morphology. Reactions of interdigitate wedging were observed in the transverse palatine suture and frontomaxillary suture, showing a bony collision that the tip of bony process and the hollow were resorbed markedly. Phasic reactions were found in the pterygopalatine suture reaction, representing a bony sliding that one side of a bony surface was deposited while the opposite side was resorptive. Both reactions were observed in the zygomaticomaxillary suture. Tensile stresses were observed in the 3 sutures around anchoraged zygoma bone (i.e. zygomaticotemporal suture, sphenozygomatic suture and sphenozygomatic suture) with similar three-pattern reactions. CONCLUSIONS: Histologically, significant changes differing from physiological remodeling are observed in the circum-maxillary sutures and posterior sutures of zygoma bone, but no destructive changes are found. These findings demonstrate that bone resorptions are major reactions caused in the 4 circum-maxillary sutures. Different sutures respond slight histological differences. The maxillary complex is retracted distally with some rotation. Tensile stress occured in the posterior sutures around zygoma bone with a zygomatic implant anchorage, which is different from the effect with a headgear.

Key words: Zygomatic implant anchorage, Retractive force to maxilla, Rhesus monkey, Maxillofacial sutures, Histological changes