Redevelopment of the calvaria after partial craniectomy in growing rabbits: the effect of altering dural continuity

A circular calvariectomy procedure was performed on 24 New Zealand white rabbits at 6 weeks of age. In 12 animals, the continuity of the dura mater was interrupted. The remaining animals served as controls. The animals were sacrificed at intervals to document the regenerative potential of the altered dural tissues. The results of this experiment show that bone deposition leading to calvarial redevelopment is directly dependent upon the presence of the dura mater. In addition, the rate of deposition is apparently affected by dural continuity, animal age, and localized differences in the thickness of the dural layers. The redevelopment and patency of the cranial sutures are strongly influenced by alterations in the continuity of the dura mater.

The effects of mechanical immobilization on sutural development in the growing rabbit

Methyl-2-cyanoacrylate was used to mechanically immobilize the coronal suture unilaterally in a series of New Zealand white rabbits at varying ages. The animals were separated into groups; some were sacrificed at 30 day and some at 60 days postoperatively. Amalgam markers were placed in the parietal and frontal bones across the coronal suture, and were measured immediately after surgery and at the time of sacrifice to confirm mechanical immobility. The animals were studied radiographically and histologically in order to document the presence or absence of sutural bone union. Based on the results of this study, it appears that immobilization of the coronal suture results in the formation of an ectocranial periosteal bone bridge in rabbits less than 8 weeks of age. Bone union was not found in animals older than 8 weeks of age. This age-related difference in response is believed to be due to decreased periosteal depository activity on the ectocranial surface of the calvaria once the brain ceases to expand actively. Furthermore, bone union or synostosis was never seen within or across the internal portion of the sutural ligament. It is suggested, therefore, that sutural immobilization at young ages in the rabbit does not result in sutural synostosis and that the term "periosteal bone bridge" should be used when referring to this biological response.

Partitioning the components of maxillary tooth displacement by the comparison of data from three cephalometric superimpositions

Using roentgenographic cephalograms from a sample of subjects with metallic implants, appropriately superimposed tracings were used to distinguish developmental and treatment-associated displacements of the maxillary central incisor and first molar associated "local" changes within the periodontium from "secondary" changes which reflect sutural and appositional growth at more distant osseous loci. Tracings were superimposed on anterior cranial base (ACB), on the maxillary implants only (IMP_MAX), and according to the best fit of maxillary anatomic structures without reference to the implants (A_MAX). Using the IMP_MAX superimposition, one could measure total local displacement at any landmark taking into consideration the effects of all appositional and resorptive changes on the superior and anterior surfaces of the palate, whereas using the A_MAX superimposition one could measure local displacement without consideration of surface appositional and resorptive changes. If the second of these measurements were subtracted from the first, the result would be a direct measurement of the effects of surface appositional and resorptive changes as they are expressed at that particular landmark. This strategy has enabled us to quantify and report the amount of accommodation which occurs at the location of each dental landmark in association with the resorptive and appositional changes which occur through time on the superior and anterior surfaces of the hard palate.