Jay D. Decker

Distribution of the calcium-binding protein SPARC in tissues of embryonic and adult mice.

SPARC (Secreted Protein that is Acidic and Rich in Cysteine), a Ca++-binding glycoprotein also known as osteonectin, is produced in significant amounts by injured or proliferating cells in vitro. To elucidate the possible function of SPARC in growth and remodeling, we examined its distribution in embryonic and adult murine tissues. Immunohistochemistry on adult mouse tissues revealed a preferential association of SPARC protein with epithelia exhibiting high rates of turnover (gut, skin, and glandular tissue). Fetal tissues containing high levels of SPARC included heart, thymus, lung, and gut. In the 14-18-day developing fetus, SPARC expression was particularly enhanced in areas undergoing chondrogenesis, osteogenesis, and somitogenesis, whereas 10-day embryos exhibited selective staining for this protein in Reicherts membrane, maternal sinuses, and trophoblastic giant cells. SPARC displayed a Ca++-dependent affinity for hydrophobic surfaces and was not incorporated into the extracellular matrix produced by cells in vitro. We propose that in some tissues SPARC associates with cell surfaces to facilitate proliferation during embryonic morphogenesis and normal cell turnover in the adult.

Temporomandibular joint in miniature pigs: Anatomy, cell replication, and relation to loading

The mechanical environment is a regulator of growth and adaptation of the musculoskeletal system, including joints. Although pigs (Sus scrofa) are used frequently as models for temporomandibular joint (TMJ) dysfunction, no systematic description of microanatomy exists for this species. We injected the thymidine analog 5‐bromo‐2′‐deoxyuridine (BrdU) into 10‐ to 11‐month‐old miniature pigs that were undergoing measurements of TMJ bone strain. Ten hr later, the animals were sacrificed and their heads were perfused. Histological sections were used to map the distribution of replicating cells. Additional observations were made on gross dissections of jaw joints obtained from an abattoir. The pig TMJ is better supported than that of humans laterally and medially, but more vulnerable posteriorly. The posterior attachment area of the intra‐articular disc is fibro‐fatty rather than vascular, as in humans. Cartilage lines the articular eminence as well as the condylar surface. At the posterosuperior region of the condyle, the cartilage ends abruptly and is replaced by an invaginating, actively replicating periosteum. Almost all of the BrdU‐labeled cells resided in the prechondroblastic zones. The condyle had more replicating cells than did the eminence (P < 0.02), but lateral and medial locations did not differ in either element. In sagittal sections, the condyle had more replicating cells posteriorly (P < 0.001), but no A‐P differences were seen in the eminence. Comparisons of these data with data on bone strain indicate that increased loading is negatively associated with cell replication. Anat Rec 266:152–166, 2002.

Fixation effects on the fine structure of enamel crystal—matrix relationships

The organic matrix of enamel presents two distinct forms within each prism of developing crystals. The first, which is present prior to crystal formation, is homogeneous in appearance and is confined mainly to recesses at the apical end of the ameloblast. The second, in the form of an elliptical tubule of increased electron density, surrounds each crystal. The tubule is apparently organized at the time of crystal formation, for it is not seen earlier. The absence of crystals within tubules near the cell in glutaraldehyde-fixed material is incompatible with observations made on osmium-fixed tissue, where all tubules surround crystals regardless of their distance from the ameloblast. Sequential fixation in osmium, followed by glutaraldehyde, improved the ease of tubule visualization, and all tubules contain crystals regardless of their proximity to the cell. After EDTA demineralization the relatively dense elliptical tubule persists even though the hydroxyapatite crystal is removed.

Adaptive response of the human dental alveolar process: Correction of a Class I protrusive and mutilated dentition, with 32-year follow-up

A healthy young woman with a severe Class I dental malocclusion and extreme maxillary arch protrusion was treated with conventional edgewise-arch fixed appliance therapy. Four first premolars were removed, and the mandibular second and third molars were moved into positions normally occupied by the mandibular first and second molars. Diagnostic records at ages 17 years 5 months, 22 years 11 months, and 54 years 8 months are presented. (These pretreatment and posttreatment records were presented to the American Board of Orthodontics in 1976 in partial fulfillment of its requirements for the certification process.)