Association between regional heterogeneity in the mid-facial bone micro-architecture and increased fragility along Le Fort lines.

BACKGROUND/AIM: Le Fort lines have traditionally been considered as zones of weakness in the mid-facial skeleton although the structural basis of increased bone fragility at these sites has not yet been investigated. Considering recent findings of occlusal loading-related regional heterogeneity in the mid-facial bone micro-architecture, the aim of this study was to explore whether such heterogeneity in cortical and cancellous bone micro-architecture may contribute to increased fragility at Le Fort fracture sites. MATERIALS AND METHODS: Twenty-five cortical and thirteen cancellous bone specimens were harvested from a dry skull and analyzed by micro-CT. Specimens were classified into Le Fort or Non-Le Fort groups based on their location in the mid-facial skeleton. RESULTS: Cortical bone along Le Fort lines showed tendencies toward lower thickness (1.5±0.63 vs 1.75±0.79; P=.39) and greater porosity (11.48±5.67 vs 10.28±5.28; P=.59). A significant difference was detected in the trabecular degree of anisotropy which was higher in cancellous bone from Le Fort fracture sites (2.14±0.69 vs 1.58±0.34; P=.02). CONCLUSIONS: Regional heterogeneity in cortical bone micro-architecture could not fully explain increased fragility of the mid-facial skeleton at the Le Fort lines. However, regional differences in trabecular bone anisotropy may contribute to increased bone fragility.

Properties and architecture of the sperm whale skull amphitheatre.

The sperm whale skull amphitheatre cradles an enormous two-tonne spermaceti organ. The amphitheatre separates this organ from the cranium and the cervical vertebrae that lie in close proximity to the base of the skull. Here, we elucidate that this skull amphitheatre is an elastic, flexible, triple-layered structure with mechanical properties that are conjointly guided by bone histology and the characteristics of pore space. We contend that the amphitheatre will flex elastically to equilibrate forces transmitted via the spermaceti organ that arise through diving. We find that collisions from sperm whale aggression do not cause the amphitheatre to bend, but rather localise stress to the base of the amphitheatre on its anterior face. We consider, therefore, that the uniquely thin and extended construction of the amphitheatre, has relevance as an energy absorptive structure in diving.

Ectodermal Wnt/ß-catenin signaling shapes the mouse face.

The canonical Wnt/ß-catenin pathway is an essential component of multiple developmental processes. To investigate the role of this pathway in the ectoderm during facial morphogenesis, we generated conditional ß-catenin mouse mutants using a novel ectoderm-specific Cre recombinase transgenic line. Our results demonstrate that ablating or stabilizing ß-catenin in the embryonic ectoderm causes dramatic changes in facial morphology. There are accompanying alterations in the expression of Fgf8 and Shh, key molecules that establish a signaling center critical for facial patterning, the frontonasal ectodermal zone (FEZ). These data indicate that Wnt/ß-catenin signaling within the ectoderm is critical for facial development and further suggest that this pathway is an important mechanism for generating the diverse facial shapes of vertebrates during evolution.

High resolution image in bone biology I. Review of the literature

La valoración de la microestructura ósea se ha realizado habitualmente mediante la obtención invasiva de muestras y el procesado y evaluación de las mismas con métodos convencionales histomorfometricos. La mejora de los sistemas de obtención de imágenes con alta resolución permite la valoración no invasiva de la morfología ósea con evaluaciones tridimensionales más precisas, con las denominadas “biopsias virtuales” que permiten realizar la valoración del hueso en procesos de regeneración o remodelación. Este trabajo de revisión describe las características y limitaciones de la evaluación ósea de diferentes sistemas de imagen de alta resolución (Tomografia computerizada mediante radiación sincrotrón; Micro tomografía computerizada; Microscopio de escaneado acústico; Micro imagen por resonancia). También se describen diversas variables morfométricas que pueden ser obtenidas a partir de las imágenes obtenidas y que pueden ser comparadas con las variables histomorfométricas convencionales

Bone microstructure has usually been assessed by obtaining samples invasively and analyzing them with conventional histomorphometric methods. Improvements in high-resolution image acquisition systems have enabled non-invasive assessment of bone morphology and a more precise 3-D evaluation by means of “virtual biopsies”, permitting bone assessment in regeneration or remodeling processes. This review describes the characteristics and limitations of bone assessment using different high-resolution image systems (synchrotron-radiation computed tomography, micro-computed tomography, acoustic scanning microscope; micro-magnetic resonance imaging). Morphometric variables that can be obtained from these images are reported and compared with conventional histomorphometric variables

Advances in imaging: impact on studying craniofacial bone structure.

Methods for measuring the structure of craniofacial bones are discussed in this paper. In addition to the three-dimensional macro-structure of the craniofacial skeleton, there is considerable interest in imaging the bone at a microscopic resolution in order to depict the micro-architecture of the trabecular bone itself. In addition to the density of the bone, the microarchitecture reflects bone quality. An understanding of bone quality and density changes has implications for a number of craniofacial pathologies, as well as for implant design and understanding the biomechanical function and loading of the jaw. Trabecular bone micro-architecture has been recently imaged using imaging methods such as micro-computed tomography, magnetic resonance imaging, and the images have been used in finite element models to assess bone mechanical properties. In this paper, some of the recent advances in micro-computed tomography and magnetic resonance imaging are reviewed, and their potential for imaging the trabecular bone in mandibular bones is presented. Examples of in vitro and in vivo images are presented.

Element release from titanium devices used in oral and maxillofacial surgery.

Optical microscopy, scanning electron microscopy and X-ray microanalysis (EDS system) were used on c.p. titanium devices (21 grids and 10 plates) removed from 28 patients without signs of inflammation 6-24 months after surgery. Plates, grids and surrounding tissue were investigated to evaluate the titanium release and accumulation. Titanium was only present in the interfacial bone, probably due to fretting, and in all fibrous tissue surrounding the devices. Titanium content followed a decreasing gradient extending from the device surface and was not detected at a distance greater than 1mm. High titanium levels were found in blood cells in the connective tissue. In conclusion, titanium release from the devices stops only after bone is laid down on the titanium surfaces. Titanium release does not seem to interfere with the osteogenic process but perhaps may interact with it.

[The role of matrix vesicles during development of the mineralizing tissues of tooth germ and craniofacial bone].

OBJECTIVE: To evaluate the role of matrix vesicles (MVs) during the development of mineralizing tissues. METHODS: The ultrastructure of MVs of tooth germ, calvarial bone and mandibular bone were observed by transmission electron microscopy in fetal Wistar rat. RESULTS: (1) The MVs were formed by osteoblast of the secret type, dentinoblast and process; (2) There was a mature process of the MVs in the extracellular matrix. The appearance of the hydroxyapatite (HAP) was a major mature feature; (3) HAP formed initially in the MVs entered into collage matrix and eventually mineralized; (4) The shifting sign of HAP from MVs to the surface of collage fibril was observed. CONCLUSIONS: The MVs played an important role in the biomineralization, but the special arrange pattern of mature collage fiber provided a suitable environment and a model to the growth of HAP for further mineralization.

A comparative analysis of the microarchitecture of cortical membranous and cortical endochondral onlay bone grafts in the craniofacial skeleton.

Previous work in this laboratory established that an onlay bone graft's survival is determined primarily by its relative cortical and cancellous composition rather than its embryologic origin. A volumetric analysis of external bone graft resorption, however, does not explain the internal microarchitectural changes that may be occurring as these grafts become incorporated. To expand the knowledge of bone graft dynamics beyond volumetric parameters, a better understanding of the internal processes of bone graft remodeling is needed. In this comparative study of cortical onlay bone graft microarchitecture, the authors propose to show that cortical onlay bone grafts undergo measurable internal microarchitectural changes as they become incorporated into the surrounding craniofacial skeleton. In addition, the authors propose to further demonstrate similarities between the internal microarchitecture of cortical onlay bone grafts of different embryologic origin over time. Twenty-five adult New Zealand White rabbits were used for this study. They were divided into two groups of eight animals and one group of nine. The groups were killed at 3, 8, and 16 weeks. Cortical membranous and endochondral bone grafts were placed subperiosteally onto each rabbit's cranium. In addition, five ungrafted cortical endochondral and membranous bone specimens were used as controls. Microcomputed tomography (MCT) scanning and histomorphometric analysis were performed on all of the specimens to obtain detailed information regarding the microarchitecture of the cortical bone grafts. The parameters of bone volume fraction, bone surface area to volume, mean trabecular number, and anisotropy were used to give quantitative information about a bone's micro-organization. The results showed that there is no statistically significant difference between the cortical endochondral and the cortical membranous bone grafts for bone volume fraction, bone surface to volume, mean trabecular number, and anisotropy measurements for all time points. There were, however, statistically significant differences when comparing the control and 3-week groups to the 16-week group for all parameters. The advanced MCT technology and histomorphometric techniques proved to be effective in providing a qualitative and quantitative ultrastructural comparison of cortical endochondral and membranous onlay bone grafts over time. In this study, a statistically significant change in the internal microarchitecture of cortical onlay bone grafts of different embryologic origins was seen as they were remodeled and resorbed at all time points. Specifically, the onlay cortical bone grafts developed a less dense, more trabecular, and less organized internal ultrastructure. In addition, no difference in the three-dimensional ultrastructure of cortical endochondral and membranous bone was found. These results challenge some of the currently accepted theories of bone-graft dynamics and may eventually lead to a change in the way clinicians approach bone-graft selection for craniofacial surgery.

The behaviour of titanium as a biomaterial: microscopy study of plates and surrounding tissues in facial osteosynthesis.

Titanium has become the biomaterial of choice for facial osteosynthesis. Titanium is considered a highly biocompatible and corrosion resistant material, although the ultrastructural behaviour of titanium in human tissues after bone fixation is not well documented. A prospective scanning electron microscopy study was carried out on 37 commercially pure titanium miniplates which were removed from 23 patients who had undergone surgery for maxillofacial trauma or deformity. Twenty two cases were used as a control group. Implant-bone specimens were excised using tungsten burs and studied with a scanning electron microscope (Jeol JSM-T-300). Findings at the bone-titanium interface were analyzed, as well as the presence of contaminating bodies on the specimen surface. Biopsies were also obtained from the soft tissues adjacent to 20 miniplates, then sectioned and stained with Haematoxilin-Eosin for histological evaluation by light microscopy. The results showed good ultrastructural osseointegration of the osteosynthesis material in most cases (81.8%). Mobility was found upon removal in 80% of plates which showed clinical complications. A significant correlation was found between the degree of microscopical osseointegration and macroscopic fixation of the plate. Microscopical contamination was found in 100% of the nine plates with intraoral exposure, while only 36% of the 22 miniplates of the control group had contaminating elements (P < 0.001). Thirty-five point one percent of the plates showed hole-like substance loss images, whose size ranged from 10-25 mu. Light microscopy showed granular deposits in soft tissues surrounding the plates in 80% of the 20 specimens investigated. Our findings suggest a higher development of corrosion in titanium than previously reported. These findings are not correlated, however with the clinical complications.

Rieger syndrome.

PURPOSE: To discuss the clinic features of Rieger syndrome, the reasons of making wrong diagnosis, the way of treatment, and the research progress of its molecular characterization and gene mapping of this syndrome. METHODS: Two cases of Rieger syndrome which affected a patient and his daughter were studied. Multiple clinical examinations including photography of anterior segment, gonioscopy and fundus, Humphrey perimetry, A-scan ultrasonography, multiple tonometry in a day and chromosome examination were performed. Most importantly, ultrasonic biomicroscope (UBM) was first used to show the abnormalities of anterior segment in this syndrome. RESULTS: Gonioscopic examination revealed many mesoderm tissues remained and some parts of the iris adhered to cornea. In addition to cornea, iris and chamber angle, UBM showed that there was also hypoplasia of ciliary body. The result of the chromosome examination indicated normal. CONCLUSIONS: Rieger syndrome is an autosomal-dominated disorder with mesoderm dysgenesis. Recent researches have confirmed that a locus for this syndrome maps to 4q25. Besides hypoplasia of cornea, iris and chamber angle, its ocular phenotype maybe include dysgenesis of ciliary body which is probably one of the reasons of secondary glaucoma.

Alterations in Msx 1 and Msx 2 expression correlate with inhibition of outgrowth of chick facial primordia induced by retinoic acid.

Spatially-restricted expression domains of Msx 1 and Msx 2 in the developing chick face suggest that they may play a role in epithelial-mesenchymal interactions governing outgrowth of facial primordia. Retinoid application to developing chick faces reproducibly inhibits upper beak outgrowth but the lower beak is unaffected. In the normal face, high levels of Msx gene transcripts in upper and lower beak primordia correlate with regions of outgrowth. Following retinoid treatment, Msx 1 and Msx 2 transcripts are rapidly down-regulated in upper beak primordia where outgrowth is inhibited, but remain largely unchanged in lower beak primordia, where outgrowth is unaffected. Decreases in gene expression precede retinoid-induced morphological changes in the upper beak, suggesting that Msx gene products are involved in mediating the effect of retinoids on facial development.

Effects of retinoic acid on embryonic development of mice in culture.

The effects of all-trans-retinoic acid (RA) (tretinoin) on the craniofacial development of mouse embryos were examined using whole embryo culture. In day 8 embryos cultured for 48 h, embryonic growth was inhibited concentration-dependently by all-trans-RA treatment. Most of the treated embryos exhibited hypoplasia of the primary palatal processes and a reduction in the development of the first visceral arches. In day 10 embryos cultured for 48 h, although embryonic growth was not inhibited at any concentrations of all-trans-RA, median cleft lip (93%), hypoplasia of the primary palatal processes (37%) and limb reduction deformities (48%) occurred commonly. Furthermore, RA treatment greatly reduced the size of the secondary palatal processes. The incorporation of 3H-thymidine in the treated maxillary processes was decreased to 65% of the control value at 1.0 x 10(-7) M all-trans-RA. These findings indicate that all-trans-RA is teratogenic in mouse whole embryo culture.

A study of facial growth in the sooty mangabey Cercocebus atys.

This study examines the pattern of facial bone growth remodelling in the sooty mangabey (Cercocebus atys) by scanning electron microscopy (SEM) of high-accuracy replicas. The efficacy of the technique is appraised by SEM interpretations of facial remodelling in the crab-eating macaque (Macaca fascicularis) and correlative histological examination. The results indicate that the distribution of depository and resorptive areas in Cercocebus closely parallels that which has been observed in Macaca. It is suggested that the different adult facial morphologies in the sooty mangabey and crab-eating macaque are the result of changes in the rates of remodelling events that may be coupled with different patterns of sutural growth (which could not be studied by SEM).

[Fibrous dysplasia and ossifying fibroma. Morphologic criteria]. / Dysplasie fibreuse et fibrome ossifiant. Critères morphologiques.

Among a series of 42 ossifying fibromas and 32 fibrous dysplasias, 5 cases were studied by histoenzymological and electron microscopic methods. The histological study in 2/3 of cases is sufficient for the diagnosis between the two diseases: trabecular bone in a connective tissue with regular collagen fibres in the ossifying fibroma; nodular indented bony areas with irregular collagen frame in fibrous dysplasia. By histoenzymology, the diagnosis between the two affections is not easy: same activity of ATPases and alkaline phosphatases in fibroblasts and osteoblasts. By electron microscopy, the morphology of the two lesions is different: in ossifying fibroma, numerous well-differentiated osteoblasts and large areas of ossification are seen; in fibrous dysplasia, undifferentiated cells are numerous and the collagen frame is irregularly mineralized. This method is also useful for the histogenetic understanding of these two osteopathies.

[Experimental teratological studies on facial anomalies induced in mice by bis(dichloroacetyl)diamine. II. Pathogenesis of bis(dichloroacetyl)diamine-induced median cleft face syndrome in mice].

The present study was performed to clarify the pathogenesis of bis(dichloroacetyl)diamine (abbreviated as bisdiamine hereafter)-induced median cleft face syndrome in mice. Bisdiamine was administered by oral intubation to pregnant Jcl: ICR mice at a dosage of 3,200 mg/kg/day at days 7.5 and 8.5 of gestation (VP = day 0). Embryos were recovered at 4, 12, 24, 48, 72 and 96 hr after bisdiamine treatment at day 8.5 of gestation and morphological differences between the bisdiamine-treated and control embryos at the specific time intervals were quantitatively examined by the light and scanning electron microscopy. First, bisdiamine caused extensive death of cranial, mainly prosencephalic and mesencephalic, neural crest cells and neuroepithelial cells. Second, the former damage resulted in reduced numbers of mesenchymal cells in the frontonasal prominences and the latter resulted in dorsolateral deviation of the nasal placodes. Consequently, the medial nasal prominences were abnormally widely spaced and then, the median cleft face syndrome was induced. In addition, the findings suggesting that bisdiamine might cause aberrant movement of neural crest cells and/or mesenchymal cells were observed.

Isotretinoin-induced craniofacial malformations in humans and hamsters.

Oral administration of 40-80 mg/d of isotretinoin (13-cis-retinoic acid, Ro 4-3780, Accutane) during the first month of human pregnancy can induce severe congenital malformation. The human Accutane dysmorphic syndrome includes rudimentary external ears, absent or imperforate auditory canals, a triangular microcephalic skull, cleft palate, depressed midface, and anomalies of the brain, jaw, and heart. Children who suffer from this syndrome have large occiputs with narrowing of the frontal bone. Microphthalmia is reported in two cases; notations are made about the orbits in three cases; and the fact that infants could not follow with their eyes is noted in three cases. A decrease in muscle tone is noted in six, cleft palate is present in four, and limb reduction defects are described in two. The cardiac malformations usually include overriding aorta, interrupted or hypoplastic aortic arch, and septation defects of atria and ventricles. There are at least two cases of abnormal origin of the subclavian arteries. Oral isotretinoin in the pregnant hamster also induces similar congenital malformations. A human case of isotretinoin-induced dysmorphia is presented and compared with other affected infants and affected hamsters. The metabolic fate and pharmacokinetic parameters of isotretinoin in humans and rodents are discussed in relation to the teratogenic response. The results suggest that humans are approximately 16 times more sensitive to the teratogenic effects of oral isotretinoin than are hamsters.

Highlights of craniofacial morphogenesis in mammalian embryos, as revealed by scanning electron microscopy.

The craniofacial region has a complex developmental history. Some of the major morphogenetic events of this region are described for the mouse embryo, as revealed by the use of scanning electron microscopy. The three germ layers, the primitive building blocks of the embryo, are delineated during gastrulation. During neurulation, the outer ectodermal layer gives rise to the nervous system. Several other events occur concomitantly with neurulation. These include regional subdivision of the mesoderm, body folding, turning, and formation of the heart and gut. The craniofacial region, as well as a number of other regions or organ systems, undergoes major developmental events during the phase of embryogenesis called organogenesis. The visceral (branchial) apparatus develops around the primitive oral cavity and pharyngeal region of the foregut, and gives rise to many of the structures of the head and neck. The face develops from the first visceral arches and derivatives of the frontonasal prominence. The tongue also originates from tissue prominences derived from the visceral arches. The oral and nasal cavities are initially continuous broadly with one another. As a result of partitioning, paired nasal cavities develop and become largely separated from the underlying oral cavity. Scanning electron microscopy reveals much about the morphological events occurring during formation of the craniofacial region. However, emphasis in future studies should be placed on determining the underlying cellular and molecular mechanisms causing these events.