Histologic Reaction of the Interosseous Suture Following Mechanical Separation of the Pre-Maxillary Bones of the Albino Rat

Abstract

It is the purpose of this study to examine, by histologic methods, the sutural changes and reactions produced by a controlled mechanical stress, namely tension, and more particularly, the changes produced by expansive and compressive forces upon the premaxillary suture of the albino rat. As a further corollary, this study is also concerned with the changes in the expanded suture after the tension has been removed. This second part of the study, namely what happens to the expanded suture following removal of spreading tension is also considered from two points of view as follows: first, the histologic changes occurring when the suture is allowed to rest; and second, the changes resulting from subsequent pressure upon the expanded suture. Eighty young male rats of the Sprague-Dawley strain of albino rats were used in this experiment. Before the experiment, six rats were sacrificed and classified as the normal untreated controls. All the remaining seventy-four animals had their premaxillary sutures expanded for seven days by means of rubber wedges of increasing thicknesses placed between their maxillary central incisors which were expanded and were the means of expanding the closely approximating premaxillary sutures. These animals were then divided into two main groups: one, the rest group, had the wedges removed and nothing else done; and the other, the compressed suture group, had the wedges removed and a continuous compressive force applied to the now expanded central incisors and premaxillary sutures. Animals in each of these groups were sacrificed at zero, one, three and seven day intervals. Decalcified, histologic, microscopic sections through the affected suture areas were prepared. These sections were studied microscopically and the histologic description of each sub-group was presented. Following the description of each group, comparisons of the histologic changes associated with tension, nontension and pressure upon the premaxillary suture were made and the differences were discussed. It was the purpose of this study to discover what happens when controlled mechanical stresses were applied to the premaxillary sutures of albino rats. These sutures were expanded. Some of the expanded sutures were then subjected to the period of rest and some were subjected to a period of continuous compressive stress. The material was then subjected to a microscopic, histologic examination from which the following conclusions were drawn:

The fundamental change resulting from mechanical stress is one of marked activation of the uncalcified connective tissue of the suture and closely approximating medullary connective tissue of the bone. A period of rest on an expanded suture allows the suture to return to normal shape and cellular density. Pressure on an expanded suture tends to hasten only slightly the return of the suture and adjacent tissue to normal proportions. A the fusion point of the osteophytic matrix, particularly where their tips come together under pressure, new matrix shows reduced cellularity and old matrix shows empty lacunae. This is apparently a pressure phenomenon at the pressure points. Remodeling and bone resorption take place simultaneously. Although osteoblastic and osteoclastic activity only occur simultaneously, osteoblastic activity seems to predominate. The osteogenic layers lining the borders of the suture are the elements involved in bone matrix formation. The marginal osteoid tissue, under the influence of mechanical stress, is no more resistant to resorption than is the underlying bone matrix.