Histological investigation of the tissue response to hydroxyapatite used as an implant material in periodontal treatment.

Patients with severe periodontitis and who had one or more teeth with infrabony pockets were treated by periodontal surgery with implantation of hydroxyapatite particles into the bone defects at the time of surgery. Subsequently, in three patients it was found necessary to extract a tooth for reasons not related to the previous periodontal treatment. Specimens that included the local soft tissues and crestal bone attached to the teeth were obtained at 22, 40 and 80 weeks after placement of the implant. They were decalcified and stained with haematoxylin and eosin and examined under light microscopy. The healing response was found to vary between specimens, and between sites within the same specimen. The early stage of healing showed the implant particles surrounded by collagen. Subsequently, varying degrees of resorption of the periphery of the particles was seen, and at some sites bone deposition was observed. These different healing responses were found to be progressing concurrently at sites in close proximity. Further work is needed to confirm the histological findings described in the paper.

The multinucleate cells in giant cell granulomas of the jaw are osteoclasts.

The giant cell granuloma of jaw is a well-vascularised lesion comprising a mononuclear cell infiltrate with a large number of giant cells. It has been suggested that the lesion is reparative in nature, rather than neoplastic, and that the giant cells are phagocytes accumulating in chronic reparative granulation tissue. However, the nature of the multinucleate giant cells never has been established. One possibility is that the constituent giant cells are osteoclasts. The authors assessed expression by the giant cells of several osteoclast-specific characteristics: excavation of bone; motility inhibition by calcitonin (CT); and binding of osteoclast specific monoclonal antibodies. Two tumors were disaggregated and incubated on slices of cortical bone in the presence and absence of CT. Both tumors were found to excavate bone, a function unique to osteoclasts. The giant cells also were responsive to CT, resulting in cytoplasmic quiescence and inhibition of bone resorption. Two osteoclast-specific monoclonal antibodies bound all the giant cells in one central and six peripheral tumors examined immunohistochemically. These results provide strong evidence for the osteoclastic nature of the giant cells. The presence of alkaline phosphatase-positive cells forming woven bone in giant cell granulomas suggests that osteoblasts are present in the lesion. As cells of osteoblastic lineage are known to regulate osteoclastic function, it may be that osteoblasts account for the characteristic infiltration of osteoclasts into giant cell granulomas of jaws, either as part of a reparative response by reactive osteoblasts or as an infiltrate induced by osteoblasts of aberrant function, as suggested for giant cell tumors of bone.

Central odontogenic fibroma.

An example of a central odontogenic fibroma is presented. This is a rare, benign neoplasm which affected the molar region of the left side of the mandible of a 63-year-old female Caucasian. Histologically, it consisted of fibroblast-like cells lying in a rather myxomatous delicate collagenous stroma. Few islands of odontogenic epithelium were also found. At the ultrastructural level, the tumour cells contained large numbers of fine filaments with focal densities similar to those described in smooth muscle cells. They also showed a moderately developed r ER. These features are consistent with cells referred to as myofibroblasts.

Kinetics of osteoclast formation: the significance of blood monocytes as osteoclast precursors during 1 alpha-hydroxycholecalciferol-stimulated bone resorption in the mouse.

The significance of blood monocytes as a source of osteoclast precursors was investigated during 1 alpha-hydroxycholecalciferol-stimulated bone resorption in mice. Animals were given three injections of tritiated thymidine at 8 hourly intervals in order to label blood monocytes. The proportion of labelled monocytes was then compared with the proportion of labelled nuclei in osteoclasts, the formation of which was provoked by daily injections of 1 alpha-hydroxycholecalciferol, beginning 48 hours after the first injection of isotope. Although more than 60% of blood monocytes were labelled during the period of peak osteoclast formation, labelling of osteoclast nuclei in the metaphyseal endosteum of the femur never exceeded 8%. These results suggest strongly that the majority of osteoclast nuclei were derived from a source of unlabelled precursors, and that very few osteoclasts were derived directly from blood monocytes. Although few labelled osteoclasts were found, the proportion of labelled spindle shaped cells in the metaphyseal endosteum rose gradually to 16%. It is likely, therefore, that labelled mononuclear cells, possibly blood monocytes, were attracted to the endosteum where they formed a population of tissue macrophages. At this site they may participate in bone resorption, either individually or by providing a local pool of osteoclast precursors.

Formation of osteoclasts from blood monocytes during 1 alpha-OH Vit D-stimulated bone resorption in mice.

In order to investigate a monocyte origin for osteoclasts, tritiated thymidine labelled blood monocytes, harvested from the blood of donor mice, were injected intravenously into syngeneic recipient animals in which osteoclast formation was being stimulated by concomitant intraperitoneal injections of 1 alpha-hydroxycholecalciferol. Labelled osteoclasts were found in autoradiographs prepared from the femurs of recipient mice, demonstrating for the first time that, during hormonally stimulated osteoclast formation, blood monocytes form one source of osteoclasts.

Osteoclast formation in response to intraperitoneal injection of 1 alpha-hydroxycholecalciferol in mice.

In order to assess osteoclast formation in response to 1 alpha-hydroxycholecalciferol, osteoclast counts per cm of bone surface were performed on paraffin sections of femurs of male CBA mice killed at daily intervals up to 5 days. All animals received daily intraperitoneal injections of 1 alpha-hydroxycholecalciferol up to the time of death. Peak osteoclast formation occurred during the third day, by the end of which maximum numbers of osteoclasts were achieved (11.9 +/- 0.9 osteoclast cm-1) compared to controls (3.5 +/- 0.6 osteoclast cm-1), this increase being highly significant (p less than 0.01). Although the osteoclast population was most dense at the metaphyseal plate in both experimental and control groups, osteoclast counts in this region only doubled whereas overall osteoclast counts more than tripled. The number of nuclei per osteoclast did not significantly alter following four daily injections of 1 alpha-hydroxycholecalciferol.