[Peri-tumor mandibular demineralization]. / Déminéralisation mandibulaire paratumorale.

This study describes hitherto unpublished observations suggesting mechanism by which a tumor can cause massive resorption of the mandible. Microradiographic analysis of the cancerous areas has shown a mobilization of minerals from compact and spongious bone tissue accompanied by incomplete degradation of collagen fibres. The minerals are deposited in the lumen of the Haversian canals, the medullar cavity and the perimandibular soft tissue, areas which are not normally mineralized. Electronic microprobe and X-ray diffraction analysis revealed that in the mineralized zones undergoing demineralization, and in the heterotropic regions, a transformation of the crystal structure of the calcium phosphate salts had occurred. These zones, composed of hydroxylapatite in normal bone and dental tissue, had changed instead to brushite (known to be stable in acidic conditions). Our observations add a new dimension to the bone marrow demineralization process.

[The pathogenesis of osteoradionecrosis]. / La pathogénie de l'ostéoradionécrose.

The microradiographic analysis of thick sections of fragments removed from irradiated patients suffering from osteoradionecrosis has made it possible to bring to the fore two types of bone resorption caused by cells: an osteoclastic one not followed by a relevant osteogenesis, and another, pathognomonic of postradic complications, linked with an altered activity of the osteocytes. Those cells, which have been affected, because of a progressive infection, are responsible for an irreversible widening of the osteoplasts, set in the properly vascularized bone regions, in particular in the wall of haversian canals. The coalescence of widened osteoplats causes polycylic cavities which is a typical feature of osteoradionecrosis. A third type of bone postradic damage consists in a massive demineralization, related to the presence of saliva or pus.

[The dental system and facial growth]. / Le système dentaire et la croissance faciale.

1. As they grow, the dental germs build their chamber, exerting tensions on a fibrillar structure facing their occlusal side or incisive edge. This structure now stretches the circular margin of the alveolus, made of chondroïd tissue. 2. The maxillary bases, of negligible volume during foetal formation and prime infancy, have to be considered as adaptive structures among genetically determined growth factors: brain, basicranium and a number of dental germs. Those factors are the real agents forming the face. 3. In case of malformation due to a lack of space, the wording "cranio-dental dysharmony" seems to be more adequate than "dento-maxillary dysharmony".

Long-term sequelae of pelvis irradiation: histological and microradiographical study of a femoral head.

Despite the lack of radiological signs, a femoral head showed histological and microradiographical features of osteonecrosis, 54 years after massive irradiation of the right hip. Intertrabecular spaces were invaded by connectivo-vascular tissue with focal accumulation of mast cells, and several resorption foci were filled with mononucleated cells. Moreover, all the microradiographs showed peculiar hypercalcified lines, sometimes containing empty osteocytic lacunae, the origin of which is difficult to precise. This study suggests that massive irradiation of weight-bearing epiphyses may be responsible for particularly long-term hypovascularity, osteonecrosis and disturbed bone remodeling.

Radiation osteitis of the clavicle following radiotherapy and radical neck dissection of head and neck cancer.

The bone alterations in the region of the clavicle (3 cases) are similar to those we have observed and described elsewhere in the skeleton i.e., the mandible, maxillary and ethmoid bones. Rarefaction is the result of three different types of bone destruction: osteoclasia, a kind of osteocytic osteolysis only observed after irradiation and obviously related with infection, and a pure demineralization of the osseous tissue by contact with pus. Reconstruction processes, although unable to prevent spontaneous fracture, are also present and correspond to islets of chondroid tissue surrounded by lamellar bone. However, these recently deposited calcified tissues are already necrotic since most of their lacunae are empty.

Skeletal growth and chondroid tissue.

Membranous and endochondral ossification processes are insufficient to describe all the aspects observed in the growing skeleton. The presence of chondroid tissue that we have identified by means of all modern histological techniques, including those able to detect the different types of collagen, has also to be explained. Present in the mandibular symphysis of either the human or cat fetuses, chondroid tissue has also been observed in the other parts of the mandible, in the sutural areas of the skull and in all the bones of both axial and appendicular skeleton. The differentiation of the mesenchyme into chondroid tissue could probably be related with mechanical forces exerted simultaneously in opposite directions or with a transient ischemia.

Bone vitality in the cat's irradiated jaw. Histological study.

The vitality of the mandible in cats was studied from two to 15 months after irradiation. Dose of 80 Gy in three days was delivered using three hairpin shape iridium-192 wires surrounding the mandibula. The osseous vitality was assessed from the percentages of lacunae inhabited by osteocytes (IL). The results are compared with those obtained by microradiography. At two months, a small reduction of vitality is already observed, it becomes progressively more important. At one year, vitality is recovered nearly fully in the ventral part of the mandibula, mainly at the level of the alveolar crest. Vitality remains reduced in the dorsal part. Microradiographic lesions appear more slowly; they are apparent at six months.

Considerations about the cloverleaf skull.

The study of four cloverleaf skulls (two fetuses, one infant, and a young adult) concerns two Pfeiffer syndromes, a thanatophoric dysplasia and an isolated case. Clinical and radiologic examinations showed malformations at the level of the calvarium, the base, orbital cavities, and, sometimes, limb abnormalities. Correlations between these findings and the microradiographic analysis of nondemineralized sections elucidate this trilobular appearance of the skull. Premature temporoparietal suture closure terminates at a constricted surface of the lateral sides of the skull during the fetal life. Extension of the synostosis to coronal and frontal sutures and thickening of the occipital bone squama block lengthening of the skull. The consecutive reduction in skull volume is compensated by the maintenance of the permeability during the neonatal period of the sagittal and lambdoid sutures. Microradiographic examination shows that this anomaly may be of vascular origin and associated with abnormal osteoclastic resorption.

Bone vitality in induced radionecrosis of the mandible estimated by osteocytic population counting.

To understand the changes of the irradiated mandibular bone, we tried to define, in space, how the lesions of the osseous tissue appear and involve. We estimated the vitality of the removed jaw fragments by counting the number of inhabited lacunae (I.L.) and empty lacunae (E.L.) in the sections, without previous decalcification, after surface staining with methylene blue. The results, expressed as percentages of the total amount of osteocytes lacunae, have been compared with the microradiographic aspect of the sections. The most paradoxical finding is that the highest percentages of osteocytes appear in the most destroyed areas. As a conclusion, one may wonder how to proceed to avoid the radiotherapy being followed by attempts for repair: attempts which, indeed, are the source of the complications.

Histological and microradiographical study of Crouzon's disease.

A histological and microradiographical study of thin undecalcified sections from the cranial vault of three different cases of Crouzon's disease has been performed. The fundamentally abnormal aspects of the bone tissues observed in this disease consist of a premature closing of the sutures, an external membranous bone apposition and an internal selective bone resorption leading to the production of the crests already visible in the clinical radiographs. A thickening of these crests by secondary bone apposition has been observed. The bone fragment removed in a fourth case during a second surgical treatment, when studied by the same technique, showed apparently normal bone.

Contribution to the histological and microradiographic study of the craniostenosis.

The authors describe the microradiographical and histological aspects of ill sutures in cases of trigonocephalies, brachycephalies and oxycephalies. This is based on the study of fragments coming from 30 cases of craniostenosis. They question the responsibility of the dura mater and invoke an encephalic cause producing by error forces at the level of the sutural areas. They also stress the absence of chondroid tissue at this particular level.