Cyclic Loading in Hypoplastic Facial Sutures: Can it Enhance Growth?

Abstract

University of Washington Abstract Cyclic Loading in Hypoplastic Facial Sutures: Can it Enhance Growth? Dong (David) Uk Shin Chair of the Supervisory Committee: Professor Susan W. Herring Orthodontics and Oral Health Sciences Introduction: Midfacial deficiency is one of the contributors to Class III malocclusions. Severe cases of this skeletal disharmony can be functionally debilitating, cause severe airway issues including sleep apnea, and be disfiguring in form. Many treatments have been proposed, including surgery. A less invasive alternative would be mechanical modulation of the suture, allowing for changes in growth, and overall changes in the craniofacial complex. Static forces are used in orthodontics routinely, but cyclic forces, especially in dentofacial orthopedics, have not been thoroughly studied. Previous studies using cyclic loading on normal animals have suggested positive effects, but whether the treatment would work on midface deficient animals is unknown. Cyclically loaded sutures were hypothesized to be wider, more vascular, and to have less organized collagen fibers than sham sutures. Methods: Yucatan minipigs, which are naturally midface-deficient, were treated with a protocol for cyclic loading or sham loading (n=6/group) of the right nasofrontal suture (RNFS). After euthanasia, suture samples with fluorescent bone markers were embedded in plastic and sectioned. The right and left nasofrontal suture and right coronal suture were of interest. 4x images were combined and a histomorphometric analysis of the sutural width and calcein bone apposition width was completed. Additional samples were decalcified and embedded in paraffin. Sections were stained with a lectin protocol to measure endothelial cell density and with Sirius Red to describe collagen organization. Results: The Yucatan minipigs showed no statistically significant difference in sutural width and mineral apposition between experimental and sham sutures. The targeted right nasofrontal suture tended to be narrower in the experimental minipigs, opposite to the expected result. Endothelial cell density was similar in comparing the central zones of experimental vs sham control groups, and all sutures showed a tendency for the central zone to be denser than the osteogenic zone. Sirius Red staining suggested few differences, but some experimental nasofrontal sutures had more disorganized collagen fibers throughout the suture compared to the sham controls, which had more uniform fibers, usually obliquely oriented. Conclusions: The results are not indicative that treatment will increase sutural width or increase vascularity although collagen organization may be affected. Abnormally growing sutures may be insensitive to cyclic loading or incapable of responding to it because of other constraints.