[A new experimental approach to the study of mechanical force in orthodontics]

Orthodontics is based upon the cellular response to biomechanical forces. Unfortunately, however, little is known about the manner in which cells respond to such forces. We have, therefore, devised an experimental model to permit morphologic and metabolic characterization of human cells subjected to a range of cyclic or static mechanical stimuli similar to those which may prevail in orthodontic-orthopedic therapy. This system involves attachment of cells to silicon collagen coated membranes which are then subjected to continuous or cyclic stretching by a motor coupled to a movable supporting frame. Because collagenase is an enzyme likely to play an important role in the ultimate effect of orthodontic forces, we evaluated the impact of biomechanical forces on secretion of this protein in a new experimental model in vitro. We found that cyclic stretching of human fibroblasts over a four day period approximately doubles collagenase production as compared to the control. Continuous stretching, on the other hand, is only 50% as effective in enhancing the enzyme release. In contrast, secretion of the inhibitor of metalloproteinases (collagenase inhibitor) is uneffected by either form of mechanical forces. Thus, the mechanical forces applied upon fibroblasts in this system promote gene expression in favor of matrix degradation. This model, we believe, will offer major insights into the cellular basis of orthodontics.