| Objectives. Maxillary protraction is an alternative to surgical maxillary advancement, but little is known about its molecular and cellular mechanisms. This study was to detect bone strains transmitted from maxillary protraction and examine cell differentiation and proliferation in bone remodeling of craniofacial sutures and the cranial base. Methods. Twenty-two, six-week-old, male NZW rabbits were allocated into strain measurement, protraction and control groups. A computer-programmed 2-Newton tensile force was delivered to rabbit's premaxilla. Bone strain was recorded across the premaxillomaxillary suture (PMS) and the nasofrontal sutures (NFS) in strain measurement group. Rabbits in protraction group were loaded for 20 min/d over 12 days following a comprehensive evaluation by using histologic, histomorphometric, immuno-histologic, vital staining, and polarizing microscopic techniques. Results. Bone strain at the PMS was much greater than that of the NFS. Protracted rabbits demonstrated: (1) significant osteogenesis at the PMS showed by Brdu labeling osteoblasts and calcein marked new bone; (2) regional bone resorption occurred at the NFS as evidenced by multinucleated osteoclasts; (3) increased chondrogenesis including chondrocyte proliferation and hypertrophy indicated by high BrdU labeling indices and morphometric measurements at the sphenooccipital synchondrosis (SOS); (4) remarkable trabecular bone formation at SOS subchondral bones; (5) widened and sagittally oriented collagen bands viewed under polarized light at the SOS. Conclusion. The specific strain patterns transmitted from maxillary protraction enhanced both intramembranous bone growth at the PMS and endochondral bone growth at the SOS. Regional osteoclastogenic change at the NFS was likely due to a forward maxillary rotation. Supported by NIH DE13964. |
