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Remodeling the Dentofacial Skeleton: The Biological Basis of Orthodontics and Dentofacial Orthopedics

Department of Oral Sciences, Faculty of Dentistry, University of Otago, PO Box 647, Dunedin, New Zealand; murray.meikle{at}z

View larger version (28K): [in this window] [in a new window]   Figure 1. Dorsal view of a miniature pig skull (Sus scrofa) showing average peak strains during mastication. Solid arrows directed toward sutures indicate compressive strains; open arrows indicate tensile strains. The sutures of the braincase are predominantly tensed, while those of the snout are compressed. 500 µ = 500 microstrains. (Redrawn from Rafferty and Herring, 1999)

View larger version (106K): [in this window] [in a new window]   Figure 2. Structure of facial sutures. (A) Photomicrograph of the zygomatico-frontal suture of an adult Macaca mulatta monkey. Hematoxylin and eosin stain, original magnification 75x. Numerous reversal lines (arrowheads) are indicative of past remodeling activity. The absence of cellular activity within the sutural ligament is indicative of a quiescent suture. (B) Section through the frontomaxillary suture of an adolescent Macaca mulatta monkey after application of a posteriorly directed force to the maxillary teeth. Mallory stain. Original magnification, 120x. This active suture shows a complex pattern of remodelling activity, with highly cellular new bone (blue) deposited on old bone (red). Sutures consist of type I collagen and non-collagenous glycoproteins uniting adjacent bone surfaces; also visible (arrowheads) is a central zone of fibroblastic cells. Scale bars not available.

View larger version (103K): [in this window] [in a new window]   Figure 3. Undue emphasis on the midpalatal suture (11) rather obscures the fact that, for rapid maxillary expansion to be successful, several facial sutures, particularly the zygomatico-maxillary (9) and the zygomatico-frontal (4,5), will need to be extensively remodeled and then retained to eliminate any residual strain. (From McMinn et al. (1981), A Colour Atlas of Head and Neck Anatomy, Wolfe Medical Publishers Ltd. Reproduced with the kind permission of Mr. Ralph Hutchings.)

View larger version (98K): [in this window] [in a new window]   Figure 4. Autoradiograph of a coronal section through the squamo-mandibular joint of a rat, 24 hrs after an intraperitional injection of 3H-thymidine to label cells synthesizing DNA. Most of the labeled cells are located within the proliferative zone. It is the mesenchymal stem cells of the PZ that differentiate into the chondroblasts of the cartilage layer under the influence of function. Counting both labeled and unlabeled cells in a ’representative’ field to obtain a labeling index is a laborious procedure, and, in young animals, it is also sometimes difficult to distinguish the boundaries between different cellular layers. SJS, superior joint space; D, interarticular disc; AZ, articular zone; PZ, proliferative zone; CC condylar cartilage. Hematoxylin stain. Original magnification, 350x. Scale bar not available.

View larger version (34K): [in this window] [in a new window]   Figure 5. Summary of remodeling changes in the surface contours of the TMJ in the rhesus monkey following experimental anterior mandibular displacement. Condylar growth appears to be directed more posteriorly, and the shape of the condyle becomes less rounded; bone is also deposited along the anterior surface of the post-glenoid tubercle. Compensatory resorption occurs along the posterior surface of the post-glenoid tubercle, and the insertion of the lateral pterygoid muscle into the neck of the condyle.

View larger version (116K): [in this window] [in a new window]   Figure 6. Photomicrograph of a sagittal section through the head of the mandibular condyle ( human, aged 10–12 yrs, the age when functional appliance treatment is usually started). There is some evidence of endochondral ossification, but chondrogenesis itself does not appear to be particularly active. IJS, inferior joint space; AZ, articular zone; PZ, proliferative zone; CC, condylar cartilage. Hematoxylin and eosin stain. Original magnification, 20x. Scale bar not available.

View larger version (42K): [in this window] [in a new window]   Figure 7. Growth velocity curves for the mandibular condyle based on the movement of the condylion on serial mandibular tracings superimposed on natural reference structures (Björk’s structures). Percentiles were used to describe individual variation and growth curves drawn by growth rates plotted at each age, with the lines between smoothed. (Redrawn from Buschang et al., 1999)