[Chondroid tissue]. / A propos du tissu chondroïde.

Nearly impossible to evidence with classical paraffin sections, chondroid tissue is regularly absent in the chapters of textbooks dealing with skeletal growth in which however it represents one of the major constituents. Microradiograph and methylene blue surface staining of thick undecalcified sections are the most suitable methods to reveal the presence of chondroid tissue. Moreover, all the methods used clearly indicate that this tissue is different from both calcified cartilage and woven bone or lamellar bone. The simultaneous presence, within the chondroid tissue matrix, of collagen type I, specific for bone tissue, and type II, specific for cartilage enables also to distinguish chondroid tissue from all the other calcified tissues. The presence of chondroid tissue in both fetal mandibular symphysis and in the sutural spaces of the skull strongly suggests that the same biomechanical stresses have the same consequences, i.e. the growth of the tongue separates the hemimandibles and the development of the brain has the same effect on the sutural areas. Experimental production of chondroid tissue is obtained in the space appeared between the bone fragments submitted to a continuous distraction. Finally, since the first cranial vault is also constituted by chondroid tissue islets, it has to be concluded that bone tissue is always secondary in its origin, i.e., after hyaline cartilage in endochondral ossification and after chondroid tissue in membranous ossification.

Histological observations of palatal malformations in rat embryos induced by retinoic acid treatment.

Malformations of the palate were induced in white rat embryos following maternal exposure to retinoic acid (tretinoin). Five experimental groups and the controls were treated by the following protocol: Group 1: pregnant rats received 100 mg retinoic acid (RA)/kg b.w. suspended in corn oil on gestational day (GD) 11.5; Group 2: 20 mg RA/kg b.w. from GD 8-12; Group 3: 20 mg RA/kg b.w. from GD 7.5-11.5; Group 4: 100 mg RA/kg b.w. on GD 10-11; Group 5: 100 mg RA/kg b.w. on GD 10 and 12; Group 6 received corn oil vehicle from GD 7-14.5; and Group 6: served as non-injected controls. In all retinoic acid treated groups, varying degrees of clefts with occasional attempts of fusion were noted. The severity and frequency of the malformations were dependent on dosage or gestational day of drug treatment. Our results indicate that RA, even at the lowest dose tested (20 mg/kg b.w.) severely affects the various tissues constituting the embryonic palatal shelves by altering cell interaction and possibly programmed cell death. These events would then result in lack of or inadequate differentiation with subsequent formation of aberrant craniofacial architecture.

Craniofacial abnormalities induced by retinoic acid: a preliminary histological and scanning electron microscopic (SEM) study.

Exogenous retinoic acid has been found to be teratogenic in animals and man. Craniofacial defects induced by retinoic acid have stimulated considerable research interest. The present report deals with scanning electron microscopical observations of the craniofacial region concurrent with histological examination of craniofacial dysmorphism induced in rat embryos following maternal treatment treated with varying dosages of all-trans-retinoic acid (tretinoin). Two groups of pregnant rats were treated with rat embryos exposed to retinoic acid suspended in corn oil (100 mg/kg b.w. on gestational day 11.5 and 50 mg/kg b.w. on gestational day 10, 11 and 12 respectively). A third group was treated with corn oil (vehicle) while a fourth group remained untreated. A wide spectrum of congenital abnormalities, including exophthalmos, microphthalmia and anophthalmia, maxillo-mandibular dysostosis, micrognathia of both maxilla and mandible, cleft palate, subdevelopment of ear lobe, preauricular tags and macroglossia, were observed in the offspring of retinoic acid treated animals. The abnormalities were both time and dosage dependent, and characteristic of Treacher Collins syndrome when retinoic-acid was administered on gestational day 11.5. In contrast, when retinoic acid was administered were on gestational days 10-12, the defects were similar to those seen in the first and second pharyngeal arch syndrome, as well as in the oculo-auriculo-vertebral spectrum. Whereas our data support the hypothesis that all-trans retinoic-acid disturbs growth and differentiation of several embryonic cell types essential for normal craniofacial development, its mechanism of action remains unclear.

Anterior neural tube malformations induced after all-trans retinoic acid administration in white rat embryos. I. Macroscopical observations.

For this study all-trans-retinoic acid was administered in pregnant white rats in their "prima gravida" pregnancy. Rats were divided in five groups. The first three groups were treated with 20 mg R.A./kg b.w. at several gestational days. The fourth group was treated with corn oil, while the fifth group remained untreated. All the animals were sacrificed during the first hours of the 21st gestational day. In the first group, three embryos, five absorptions and six compact embryonic masses were counted in litters. All the embryos presented exencephaly, combined with external anopthalmia. They also presented severe craniofacial malformations. In the second group, nine embryos and five compact embryonic masses were counted in litters. Three of the embryos presented exencephaly combined with external anopthalmia, while the six remaining presented complex craniofacial anomalies. In the third group, exencephaly was present in two embryos combined with anopthalmia, seven embryos had complex anomalies and four compact embryonic masses were counted in litters. Our results indicate the teratogenic involvement of all-trans-retinoic acid in anterior neural tube differentiation.

All trans retinoic acid interfering with palatal development. Scanning electron microscopical and light microscopical observations on embryonic rat palate.

Diverse studies on retinoic acid teratogenesis, during the recent years, indicate that the drug's analogues target on diverse cell population during differentiation in mammals. During an extended teratological protocol concerning retinoic acid influence in diverse embryonic tissue differentiation in experimental animals we studied all-trans-retinoic acid's influence on palatal development in the white rat embryo. For this purpose, six groups of white rat embryos were studied: Group 1 was treated with 100 mg/kilogram of body weight (k.b.w.) on gestational days (g.d.) 10th and 11th, Group 2 was treated with 100 mg all-trans-retinoic acid/k.b.w. on g.d. 11.5, Group 3 was treated with 50 mg all-trans retinoic acid/k.b.w. on g.d. 10th, 11th and 12th, Group 4 was treated with 50 mg all-trans-retinoic acid/k.b.w. on g.d. 11th and 12th, Group 5 was treated with 20 mg all-trans-retinoic acid/k.b.w. on g.d. 7.5, 8.5, 9.5, 10.5 and 11.5, Group 6 remained untreated. Embryonic heads aged 20 days were observed by light microscopy and scanning electron microscopy. In all treated groups clefts and malformations concerning the differentiation of palatal cell populations were observed. All our findings were compared with normal palatal morphology of untreated "control" embryos. Among the malformations, median clefts were observed, extended along only a part of the primary and all the secondary palate for group 2, the primary and secondary palate for groups 1, 3 and 5 while on group 4, an irregularity of the median palatal raphe and rugae were combined with a median incomplete cleft extended between the primary and secondary palate. Our results are discussed in relation with the international literature results.

Prenatal development of the human pelvis and acetabulum.

The prenatal development of the human pelvic bone and acetabulum has been studied by means of classical histology and microradiography. The embryonic phase leads to a fully developed hip within 8 weeks of gestation. The fetal period is a growth phase, including the following main features: endochondral ossification of the ilium from the ninth week, asymmetrical development of the iliac shaft from the fifteenth week, "chondroid-like" tissue formation above the acetabulum from the twenty-sixth week and haversian bone remodelling from the twenty-eighth week. The fetal development of the pelvis and acetabulum seems to be highly related to mechanical stimuli, the most important being the gluteal muscular activity and the simultaneous pressure of the femoral head.

Microradiographic aspects of the growing mandibular body during permanent premolar eruption in the dog.

In order to explore the bony changes in the mandibular body during prefunctional intraosseous eruption of premolars, 18 dogs aged from 8 to 16 wk at the beginning of experimental period, were given two intraperitoneal injections of oxytetracycline (50 mg/kg and 35 mg/kg 2 wk later) and 2 wk later a final injection of Alizarin red S (70 mg/kg). Microradiographic and fluorescent light microscopy studies showed that changes of the alveolar bony crypt walls were influenced by the growing dental germs which they surrounded. The cervical volumetric reduction, which indicates the end of crown formation, induced the apposition of lamellar and then woven bone on the adjacent alveolar walls. Furthermore, with occlusal displacement of the dental crown, the space below the tooth was immediately filled with woven bone trabeculae and chondroid tissue. The same phenomenon was observed at the level of the alveolar base, when the speed of tooth eruption was greater than that of root growth. During premolar development, the changes in the dental germ produces accommodating changes in the adjacent alveolar bone walls, and mandibular transversal growth has the same characteristics as that of a growing diaphysis.

Postmenopausal osteoporosis: microradiographic aspects.

A comparative microradiographic and histologic analysis of undecalcified bone samples was performed in men and women aged 18-98 years. These morphological methods showed that besides usual lamellar bone remodelling, all the so-called inert surfaces, namely both haversian and vascular canals as well as trabecular surfaces, were involved in weathering alterations of the superficial lamellae, resulting in eroded outlines devoid of osteoclast. These aspects, recorded in all pieces of our material, were visible from the earliest adult age and were randomly distributed. Except the grade of osteoporosis at a given age, the microradiographic and histologic aspects were similar in both aged men and women and did not allow sex distinction. These observations were consistent with the hypothesis of a particular destructive process affecting all the quiescent lamellar bone surfaces without osteoclast or cell participation. This kind of erosion, termed delitescence, could be at least partially responsible for the age-related and postmenopausal bone loss. In order to explain the increasing osteoporosis after menopause, it has been suggested that the estrogen deficiency could increase the percentage of dead osteocytes. Thereby the reduced cellular control on the bone surface could impair the remodeling process and fail to adapt the bone structure by repairing the microscopic lesions.

Oculo-auriculo-vertebral spectrum: cranial and vertebral malformations due to focal disturbed chondrogenesis.

Microradiographic and histological analyses point out a focal disturbed chondrogenesis of both the skull base and the axial skeleton in a case of oculo-auriculo-vertebral spectrum. Cartilage showed disturbed endochondral ossification with defects in calcification, deficient resorption, and abnormal crumpled areas of mineralized cartilage.

Structural changes with aging in cortical bone of the human tibia.

Structural modifications are considered to play a significant role in the age-related alterations of bone quality and strength. Senescent compact bone is characterized by an increasing heterogeneity of aspects, including high numbers of lowly mineralized osteons as well as the presence of osteons with hypermineralized lamellae or with a notched haversian canal wall, and of double-zone osteons. These latter three types of osteons are different from the structures involved in the haversian remodeling. In the present study, blocks of midshaft tibia from 7 young men (18-39 years), 14 aged men (50-92 years) and 15 aged women (57-96 years) were embedded in methyl methacrylate in order to perform microradiographic and histomorphometric analysis of undecalcified sections. The intracortical porosity was higher in the aged men than in the young ones, as were the numbers of haversian structures and, to a lesser extent, the diameters of the haversian canals. The aged women showed the same tendency, with cortical porosity still higher than in the men. The osteons with hypermineralized lamellae, those with a notched canal and the double-zone osteons appear to constitute large subgroups of the total haversian population, even in the early adult life. Among them, only the osteons with a notched canal wall increased in frequency with age. The 3 types are much more numerous than the structures involved in the typical haversian remodeling. The correlations between their frequencies as well as their significant topographic association corroborates the hypothesis that the hypermineralized lamellae may crumble down because of their excessive brittleness, giving rise to the haversian canals with notched walls. These enlarged canals could be refilled by bone apposition and result in the double-zone osteons. The 3 types of osteons could constitute different steps of one mechanism of bone desintegration and repair occurring very progressively, which might contribute to modify the bone quality and to increase the intracortical porosity.

[Additive medial osteotomy of the tibia locked with a coral callus. First results apropos of 38 operations]. / Ostéotomie tibiale d'addition interne calée par un coin corail. Premiers résultats à propos de 38 interventions.

We inserted a calibrated coral callus to lock addive medial osteotomy of the tibia in 38 patients. We followed these patients for 1 to 6 years evaluating clinical, radiological and histological outcome. Rehabilitation was very insufficient. In our later cases, the porosity of the coral insert was improved, apparently facilitating bone penetration.

Embryonic origin and fate of chondroid tissue and secondary cartilages in the avian skull.

BACKGROUND: Chondroid tissue is an intermediate calcified tissue, mainly involved in desmocranial morphogenesis. Often associated with secondary cartilages, it remained of unprecise embryonic origin. METHODS: The latter was studied by performing isotopic isochronic grafts of quail encephalon onto 30 chick embryos. The so-obtained chimeras were sacrificed at the 9th, 12th, and 14th day of incubation. The contribution of graft- and host-derived cells to the histogenesis of chondroid tissue, bone, and secondary cartilages was analyzed on both microradiographs of thick undecalcified sections and on classical histological sections after several DNA or ECM specific staining procedures. RESULTS: Chondroid tissue is deposited in the primitive anlage of all membranous bones of the avian skull. Also present on their sutural edges, it uniformly arises from the neural crest. In the face, bone and secondary cartilages share this mesectodermal origin. However, secondary cartilages located along the basal chondrocranium and bone formed on the chondroid primordium of the cranial vault, originate from the cephalic mesoderm. CONCLUSIONS: These facts provide evidence that chondroid tissue arises from a specific differentiation of neural crest derived cells and that this original skeletogenic program differs from that of secondary chondrogenesis. Moreover, they obviously indicate that in membraneous bone ontogenesis, chondroid tissue replaces functions devoted to mesodermal primary cartilages of the cranial base, and so corroborates at the tissue level, the dual embryonic and phyletic origin of the skull.

Chondroid tissue in the early facial morphogenesis of the chick embryo.

The calcified tissues involved in the early morphogenesis of the so-called intramembranous bones of the facial skeleton were studied by microradiographic and histological techniques in 22 chick embryos at the 9th, 12th and 14th days of incubation. On the 9th day, the bones of the upper face and palatal vault are made up of thin sheets of chondroid tissue, deposited in their respective mesenchymal condensations. Woven and lamellar bone formation subsequently takes place in each of them from the 12th day of incubation, mainly on the external side of their chondroid primordia. The same phenomena occur in the lower facial and mandibular bones. These facts indicate that the primitive facial desmocranium of the chick embryo, which is classically considered to be formed by intramembranous ossification, first consists of chondroid tissue. As in the cranial vault, this tissue thus represents the initial modality of the skeletogenic differentiation within the avian facial mesenchyme.

Aging effect on inductive capacity of human demineralized bone matrix.

Demineralized bone powder (DBP) prepared from human cortical bone was implanted into subcutaneous pouches of athymic Nu/Nu mice for 28 days. The osteoinductive capacity was evaluated by histomorphometry of the induced cartilage and bone, and by alkaline phosphatase activity in the implant. Very small amounts of new bone and cartilage were found at histological analysis, confirming that human DBP is much less osteoinductive than that from other species. Whereas the morphometric data of the implants from the young and aged donors were not significantly different, the alkaline phosphatase activity was significantly lower in the implants from the old donors than from the younger ones. This difference between the morphometric and biochemical results could reflect the fact that the enzymatic activity is already present in the osteoprogenitor cells. At 28 days, the osteoblastic activity in contact with DBP from the aged group is characterized by a decrease in the enzymatic amount which is not yet visible at the tissue level. This tendency to a decrease in the osteoinductive capacity of bone matrix is an additional aspect of the age-related alterations which occur in bone tissue and could be attributed to modifications of different proteins of the bone matrix, including bone morphogenetic protein.

Microradiography and fluorescence microscopy of bone remodeling on the basal crypt of permanent mandibular premolars in dogs during eruption.

Alveolar bone of erupting teeth was studied in order to define the types of calcified tissues deposited as well as the rate of tooth growth. The third (P3) and fourth (P4) mandibular premolars of 30 dogs aged 12-24 weeks were analyzed by microradiography and microscopy in fluorescent and ordinary light. The bone plate separating P3 and P4 from the mandibular canal presented a complex arrangement of lamellar and woven bone, and even of chondroid tissue. During the pre-eruptive phase, this plate shifted towards the base of the mandible by means of selective resorption and apposition activities. As soon as the furcation was formed, bone apposition appeared on the alveolar side and became the main activity under P3 at the outset of eruption. Under the roots of P4 it occurred 4 weeks later. Dynamic morphometry in fluorescence microscopy showed that eruption progressed faster than the radicular growth. The formation of interradicular bone underwent the same acceleration as the eruption. However, though the tissues were formed at a high rate, it cannot be inferred therefrom that they are responsible for tooth shifting. They might just fill the space left by the erupting tooth.

Cancellous bone in human acetabulum: microradiographic and histomorphometric aspects.

The acetabular cancellous bone of 18 subjects aged 57-88 years was characterized by low mass and a poorly ramified pattern according to microradiographic analysis. There was no correlation between the histomorphometric data of this region and those of the iliac crest. Microcalluses were visible in 13 acetabular samples, whereas they were absent from the iliac crest. As the acetabular trabeculae appeared decidedly longitudinal, age-related bone rarefaction is suggested to occur in two different ways: uniform thinning of the trabeculae and selective disappearance of transverse elements. The remaining longitudinal trabeculae are considered to be most useful for the weight-bearing function of the hip joint.

Hypermineralized lamellae below the bone surface: a quantitative microradiographic study.

Hypermineralized lamellae similar to interstitial resting lines were identified by microradiography beneath haversian, endocortical, and trabecular resting surfaces in 42 subjects aged 18-96 years. In cross-sectioned osteons, this hypermineralized lamella appeared as a circle showing the same high microdensity as the inner margin of the haversian canal. Bone tissue separating this circle and the margin was more mineralized than the peripheral lamellae of the osteon. In the tibia, 13.7 +/- 0.9% (Mean +/- SE) of Haversian canals exhibited a hypermineralized circle, localized at a distance of 20 +/- 0.4 microns from the canal wall. The scalloped haversian canals, different from osteoclastic resorption cavities, represented 9.9 +/- 0.7% of the haversian canals. There was a significant correlation between both types of haversian canals. Therefore, hypermineralized lamellae can appear at the end of bone apposition, whatever the bone surface. Their high mineral content may secondarily lead to an increased brittleness of the most superficial lamellae and even to their disaggregation.

[Contribution to the study of pelvic stress during weight-bearing. Role of the pubic branch and trabecular bone]. / Contribution à l'étude des contraintes du bassin en charge. Rôle de la branche pubienne et de l'os spongieux.

INTRODUCTION: Several authors have reported evidence of loosening of the acetabular component in 14 per cent of cases at 10 years follow-up. To understand this phenomena, parametric studies of the acetabulum have involved finite element analysis, photo elastic models or strain gauges. The differing and sometimes contradictory results were due to the way the model was solicited. If the classic "Resultant" is accurate for the study of the forces on the hip, Pauwels described other forces on the pelvis during the gait. The effect of the application of these other forces on the acetabulum are the object of this study. MATERIALS AND METHOD: Four pelvises were loaded with different forces. Nine strain gauges were pasted around the acetabulum. The pelvis was loaded up to 140 Kg and a compressive force was applied to the pubis by 10 Kg increments up to 40 Kg. The stress data with and without the second force were recorded. A cortical window was bored on the anterior inferior iliac spine. Through this patch, the trabecular bone of the acetabular roof was cut up to disturb its mechanical properties. The load was once again applied to the pelvis and the stress data recorded. RESULTS: The compressive force applied to the symphyseal surface decreases the deformation of the posterior acetabular rim and increases deformation in the proximity of the ischio-iliac and iliopubic junctions. The disruption of trabecular bone generates an increase in deformation mainly perpendicularly to the acetabular rim. DISCUSSION: The decrease of the stress on the posterior acetabular rim is interpreted as a reduction of the solicitations on a fragile zone and its increase on the iliopubic and ischio iliac junctions expresses the application of the acetabular horn on the femoral head permitting better settling of the hip during the gait. The constatation of a stress increase around the acetabulum after disruption of the traecbular bone is interesting. The bone behavior with different acetabular cup models on different pelvis may be studied by strain gauges pasted on the cortical bone. The variable quality of the trabecular bone may introduce an error factor in the measurement. CONCLUSION: The deformation of the acetabulum during gait has to be studied following the different forces described by Pauwels. The compressive force on the pubic symphysis during one leg stance permits a decrease of the stress on the acetabular rim and an increase in the setting of the femoral head. Different qualities of trabecular bone change the deformation of the cortical bone for an equivalent load. This incites us, in comparative studies, to be careful in the deduction of the acetabular roof stresses from the recorded cortical bone deformations.

Comparative SEM and TEM examination of the ultrastructure of the resin-dentin interdiffusion zone.

The resin-dentin interdiffusion zone produced by a dentin-adhesive system that removes the smear layer and concurrently decalcifies superficial dentin was morphologically examined by both scanning and transmission electron microscopy. Cross-sectioned resin-bonded dentin discs were etched with an argon-ion beam to make the resin-dentin interface observable by SEM. For the TEM examination, the sections were partly decalcified by an aqueous EDTA solution to facilitate ultramicrotomy and to disclose the ultrastructure of the interdiffusion zone. Both SEM and TEM confirmed the presence of the resin-dentin interdiffusion zone as the junction between the deep unaltered dentin structure and the restorative resin. Within the interdiffusion zone, three sublayers with characteristic ultrastructure and staining were identified by TEM. An upper diffuse black layer contained few structural features. Underneath, partially-altered collagen fibrils were closely packed, mostly running parallel with the interface and perpendicular to the dentinal tubules. Their outline was electron-dense, forming tunnel-like structures. At the base of the upper layer, several stained projections were found to bulge out into the underlying collagen network and appeared to be confined by obstructive, parallel-running collagen fibrils. Finally, the third dense layer, containing hydroxyapatite crystals, demarcated the superficially demineralized dentin layer from the deeper unaltered dentin. Resin diffusion into the decalcified dentin surface layer was evident, but diminished with depth, presumably reducing deeper resin impregnation into the interfibrillar spaces. The citric acid dentin-pretreatment probably caused denaturation of the superficial collagen fibrils. Its decalcifying effect gradually weakened with depth, leaving behind hydroxyapatite crystals at the base of the interdiffusion zone.(ABSTRACT TRUNCATED AT 250 WORDS)