Analysis of titanium dental implants after failure of osseointegration: combined histological, electron microscopy, and X-ray photoelectron spectroscopy approach.

A multitechnique approach has been used to characterize the surface of nonosseointegrated titanium implants and the surrounding biological tissues. Five pure titanium dental implants were used as reference, and 25 removed implants were studied. Surface and in-depth chemical compositions of the implants (from a total of 16 patients) were investigated by X-ray photoelectron spectroscopy (XPS). Histological slides of the surrounding tissues were examined by light microscopy, XPS, and electron microprobe analysis. None of the failed implants presented the regular surface composition and depth profile of the TiO2 overlayer; foreign elements (Ca, Na, P, Si, Cl, Zn, Pb, and Al) were observed on some implants. Fibrosis, lymphocytic and plasmocytic infiltrates, and granulomatous lesions were detected in the surrounding tissues. XPS and electron microprobe analysis indicated the presence of Zn, Fe, Sn, and Ti in the tissues. As a possible scenario for implant failure, we propose and discuss a oxidoreduction mechanism, leading to a partial dissolution or the complete dissociation of the protective titanium dioxide overlayer and to ion diffusion through the surrounding tissues.

Experimental odontomas in osteopetrotic op/op rats.

Osteopetrosis is an autosomal recessive disease in several mammalian species. Osteopetrotic op/op rats suffer from complete failure of tooth eruption related to reduced bone resorption. In our earlier studies, op/op rats grafted with bone marrow cells 3 days after birth were cured of the disease and their molar eruption was restored. However, the incisors failed to erupt and their proliferating ends were distorted, forming odontomas. The purpose of the present investigation was to study the odontogenic tissues in the odontomas, using the correlated techniques of radiography and microradiography of undecalcified material, together with histology of decalcified material and scanning electron microscopy.

Monocytic origin of fibrosis. In vitro transformation of HLA-DR monocytes into neo-fibroblasts: inhibitory effect of all-trans retinoic acid on this process.

We report here the spontaneous in vitro transformation of blood monocytes into fibroblasts in a patient who developed pulmonary fibrosis following ciclosporin-mediated immunosuppression, necessitated by heart transplantation. The blood monocytes with this capacity expressed HLA-DR specificity. Monocytes/macrophages were identified by immunofluorescence using monoclonal antibodies against a specific monocyte/macrophage antigen, while the neo-fibroblasts were identified by electron microscopy and immunofluorescence using monoclonal antibodies against a cytoplasmic enzyme specifically involved in the synthesis of collagen. The secretion of collagen was demonstrated using antibodies against collagen. Both the monocytes/macrophages and the neo-fibroblasts express macrophage and fibroblast markers and are able to synthesize collagen. The all-trans retinoic acid derivative (all-trans RA) inhibits this in vitro transformation of HLA-DR monocytes/macrophages into neo-fibroblasts. Therefore, the possible therapeutic role of all-trans RA in controlling the development of fibrosis remains open to investigation. Until now, no efficient therapy is known for fibrotic diseases which are often lethal when affecting the lungs.

Immune cell defects affect bone remodelling in osteopetrotic op/op mice.

The aim of the present work was to further characterize immunological defects in osteopetrosis. The op/op mutant mouse is of particular interest since a marrow cavity develops spontaneously in older animals. The interleukin production (IL-1, IL-2, IL-3, IL-4, IL-6), the presence of macrophage differentiation antigens and the evolution of the bone lesions were studied in osteopetrotic and normal mice. Low levels of IL-1, IL-3 and IL-4 were observed at the age of 6 weeks in the op/op mice. However, at 22 weeks of age, the level of IL-1 and IL-4 returned to normal value in these op/op mice whereas the level of IL-3 remained partially decreased at the same age. Furthermore, macrophage expression of MAC-2 antigen, reduced at 12 weeks of age was found to be normal 10 weeks later. These immunological defects and their recovery seems to be concomitant with the healing of the bone lesions.

Microradiography and light microscopy of mineralization in the pulp of undemineralized human primary molars.

This study was undertaken to investigate the prevalence, location and histologic features of the different types of mineralization observed in the pulp of human primary molars. Microradiography and light microscopy of undemineralized material disclosed that 95% of primary molars contain pulp calcifications. Histologically, their structure may be classified into four different types: (1) pulp stones, (2) diffuse calcifications, (3) eburnoid tissue and (4) spherulitic calcifications.

Brushite in the pulp of primary molars.

This study was undertaken to investigate the mineral phase of spherulitic calcifications discovered in the pulpous mesenchyme of human primary molars by microradiography. Analytical scanning electron microscopy and x-ray diffraction disclosed that well-crystallized brushite is the major compound of the spherulites. The mechanism leading to the crystallization of brushite is far from well understood. Histologically, on decalcified sections, inflammatory cells and capillaries can be seen trapped in the spherulites. In the light of these findings, it could be suggested that metabolic conditions may promote the crystallization of brushite in the pulp of primary molars.

Effects of bone marrow transplantation on impacted dental germs in osteopetrotic op/op rats.

The osteopetrotic op/op rats suffered from a complete failure of tooth eruption in association with a reduced bone resorption. An unresorbed occlusal bone overlaid the germs which remained embedded in bone. The process of prefunctional eruption in limited growing teeth depends on the resorption of the alveolar bone covering the germs. The aim of this study was to investigate the effects of hematopoïetic grafts in newborn op/op rats on the process of prefunctional eruption. Fifteen op/op treated rats were used for radiographic, microradiographic and histologic examinations. After transfusion of bone marrow cells, we observed the restoration of bone resorption and a delayed eruption of the molars. The incisors never erupted. They developed odontome-like tumors near their apices. These results confirm the dependence of tooth eruption on bone resorption.

Histopathology of the interactions between alveolar bone and impacted dental germs in osteopetrotic op/op rats.

Osteopetrosis, a general increase in bone density, is well-known as an autosomal recessive disease in several mammalian species. Compared with normal littermates, the osteopetrotic rats suffered from a complete failure of tooth eruption. Histologic and microradiographic studies show that the molars and the incisors developed a progressive ankylosis, the bone invades the germs and finally dissociates them. As early as the first days after birth, the incisors and the first molars are affected by the osteopetrotic process while the second and the third molars remain untouched. The periodontal membrane of the incisors is rapidly invaded by the osteopetrotic bone trabeculae. After the eleventh day, the process reached all molars. The germs were overlaid by an occlusal unresorbed bone. The formation of the gebernacular canal appeared to be independent of the prefunctional eruption.

[Ultrastructure of microcalcifications of the pulp mesenchyme of human deciduous teeth]. / Ultrastructure des microcalcifications du mésenchyme pulpaire des dents temporaires humaines.

Scanning electron microscopic observations of pulp calcifications in deciduous molars were correlated with microradiographic findings. Numerous spherical calcifications were found in appearance similar to those in the permanent dentition. In a second type, mineralization took the form of diffuse deposits of calcium. The discrete diffuse foci coalesced into large islands of mineralized connective tissue. A third type of calcification was observed in which rhombic crystals were associated in a spherulitic pattern. The exact cause of the crystal formation is unknown. Moreover, as we are aware, the spherulitic calcifications have never been previously reported in this location. The preliminary results indicated that mineralization in the pulp of deciduous molars, takes a variety of forms, suggesting that calcium deposition can occur by different processes.

[Enamel pearls in the deciduous teeth]. / Les perles d'émail des dents de lait.

A microradiographic study of 40 human deciduous teeth showed an unexpected high frequency (33%) of enamel pearls at the junctional interradicular line of the molars. An electron probe analysis showed that the composition of the pearls is similar to that of the coronal enamel. The pearls are located on normal dentine and are in contact with a hypermineralised layer separating cementum from dentine. It is hypothesised that the origin of this hyaline layer and the observed high frequency of pearls is not due to a possible differentiation of Hertwig sheath cells but results from variations of an usual biological process.