RESUMEN
Few studies of distraction osteogenesis in the craniofacial region have examined the dynamic nature of the bone healing process. This study investigated bone formation in distraction sites at various times following slow, moderate, and rapid rates of mandibular distraction in adult rats. After a 3-day latency period, 16 groups of 8-9 rats underwent unilateral mandibular distraction for 5 days at four different rates (0, 0.2, 0.4, and 0.6 mm/day) and were sacrificed at four different time points (6, 10, 24, and 38 days). Vital bone labels were injected prior to sacrifice and histological sections were examined under epifluorescence to measure mineral apposition rate (MAR) and the number of red and green pixels that corresponded to the wavelengths of the two bone labels. These pixel counts were designed to quantify the amount of fluorescent bone formation. For MAR and the pixel counts, no significant differences were found between the distraction rate groups. Over time, MAR was significantly higher (p < 0.001) at 24 days (4.50 microm/day) compared to 38 days (3.78 microm/day). Thus, MAR appears to be elevated at mid-consolidation compared to late consolidation. The pixel counts showed that the 6-day (mid-distraction) and 10-day (early consolidation) time points had significantly lower total fluorescent activity compared to the 24-day (mid-consolidation) and 38-day (late consolidation) time points (p < 0.001). The red, green, and red + green pixel counts were found to correlate significantly but weakly with microdensity (r = 0.318, 0.307, and 0.334, respectively). The pixel counts and microdensity both showed similar patterns over time.
Asunto(s)
Regeneración Ósea , Mandíbula/cirugía , Osteogénesis por Distracción , Animales , Masculino , Mandíbula/fisiología , Osteogénesis por Distracción/métodos , Periodo Posoperatorio , Ratas , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
In this study we use molar microwear analyses to examine the trophic distinctions among various taxa of Malagasy subfossil lemurs. High resolution casts of the teeth of Megaladapis, Archaeolemur, Palaeopropithecus, Babakotia, and Hadropithecus were examined under a scanning electron microscope. Megaladapis was undoubtedly a browsing folivore, but there are significant differences between species of this genus. However, dietary specialists appear to be the exception; for example, Palaeopropithecus and Babakotia probably supplemented their leaf-eating with substantial amounts of seed-predation, much like modern indrids. Hadropithecus was decidedly not like the modern gelada baboon, but probably did feed on hard objects. Evidence from microwear and coprolites suggests that Archaeolemur probably had an eclectic diet that differed regionally and perhaps seasonally. Substantial trophic diversity within Madgascar's primate community was diminished by the late Quaternary extinctions of the large-bodied species (>9 kg).
Asunto(s)
Dieta , Lemur/anatomía & histología , Diente Molar/anatomía & histología , Adaptación Fisiológica , Animales , Evolución Biológica , Esmalte Dental/anatomía & histología , Esmalte Dental/patología , Fósiles , Lemur/fisiología , Diente Molar/patologíaRESUMEN
Among non-mammalian vertebrates, rigid skulls with tight sutural junctions are associated with high levels of cranial loading. The rigid skulls of mammals presumably act to resist the stresses of mastication. The pig, Sus scrofa, is a generalized ungulate with a diet rich in resistant foods. This report synthesizes previous work using strain gages bonded to the bones and sutures of the braincase, zygomatic arch, jaw joint, and mandible with new studies on the maxilla. Strains were recorded during unrestrained mastication and/or in anesthetized pigs during muscle stimulation. Bone strains were 100-1000 micro epsilon, except in the braincase, but sutural strains were higher, regardless of region. Strain regimes were specific to different regions, indicating that theoretical treatment of the skull as a unitary structure is probably incorrect. Muscle contraction, especially the masseter, caused strain patterns by four mechanisms: (1) direct loading of muscle attachment areas; (2) a compressive reaction force at the jaw joint; (3) bite force loading on the snout and mandible; and (4) movement causing new points of contact between mandible and cranium. Some expected patterns of loading were not seen. Most notably, strains did not differ for right and left chewing, perhaps because pigs have bilateral occlusion and masseter activity.
Asunto(s)
Maxilares/fisiología , Mamíferos/fisiología , Masticación , Músculos/fisiología , Animales , Fenómenos BiomecánicosRESUMEN
Osteoprotegerin (OPG) is a CD40-regulated gene in B cells and dendritic cells (DCs). We investigated the role of OPG in the immune system by generating opg(-/-) mice. Like its role as a regulator of bone metabolism, OPG also influences processes in the immune system, notably in B cell development. Ex vivo, opg(-/-) pro-B cells have enhanced proliferation to IL-7, and in opg(-/-) spleen, there is an accumulation of type 1 transitional B cells. Furthermore, opg(-/-) bone marrow-derived DCs are more effective in stimulating allogeneic T cells than control DCs. When challenged with a T-dependent Ag, opg(-/-) mice had a compromised ability to sustain an IgG3 Ag-specific response. Thus, in the immune system, OPG regulates B cell maturation and development of efficient Ab responses.
Asunto(s)
Linfocitos B/inmunología , Huesos/metabolismo , Glicoproteínas/fisiología , Receptores Citoplasmáticos y Nucleares/fisiología , Animales , Subgrupos de Linfocitos B/patología , Linfocitos B/patología , Huesos/patología , Diferenciación Celular/genética , Diferenciación Celular/inmunología , Células Dendríticas/inmunología , Marcación de Gen , Glicoproteínas/biosíntesis , Glicoproteínas/deficiencia , Glicoproteínas/genética , Hematopoyesis/genética , Hematopoyesis/inmunología , Cambio de Clase de Inmunoglobulina/genética , Inmunoglobulina D/biosíntesis , Isotipos de Inmunoglobulinas/biosíntesis , Inmunoglobulina M/biosíntesis , Activación de Linfocitos/genética , Activación de Linfocitos/inmunología , Recuento de Linfocitos , Linfocitosis/genética , Linfocitosis/inmunología , Linfocitosis/patología , Ratones , Ratones Endogámicos , Ratones Noqueados , Osteoporosis/genética , Osteoporosis/inmunología , Osteoporosis/metabolismo , Osteoprotegerina , Receptores Citoplasmáticos y Nucleares/biosíntesis , Receptores Citoplasmáticos y Nucleares/deficiencia , Receptores Citoplasmáticos y Nucleares/genética , Receptores del Factor de Necrosis Tumoral , Linfocitos T/inmunologíaRESUMEN
Despite a number of previous biomechanical studies on the zygomatic arch, unanswered questions remain about its three-dimensional loading and growth. Using young miniature swine, we have for the first time recorded strains from both the medial and lateral aspects of the squamosal bone during mastication and masseter muscle stimulation. Strains from the zygomatic bone flange and zygomatic arch growth data were also obtained from the same animals. A second study on a younger group of animals examined the growth of the zygomatic flange following partial removal of the masseter. Strain data indicated that the squamosal bone is bent out-of-plane and that this pattern of loading is quite different from that of the adjacent zygomatic bone, which experiences much lower strains with little evidence of out-of-plane bending. Surprisingly, strains were higher in the zygomatic flange during contralateral chews and contralateral masseter stimulations than during ipsilateral chews/stimulations. These strains proved to arise from movement of the condyle, explaining why partial removal of the masseter had little effect on the growth of the flange. Other growth results indicated an approximately threefold greater rate of subperiosteal deposition on the lateral surface of the squamosal bone than on the zygomatic bone. This difference in growth rate is attributed to the presence of sutures that contribute to the lateral displacement of the zygomatic bone but not the squamosal bone. This explanation does not exclude the possibility that the rapid apposition on the lateral squamosal surface is regulated by the high surface strains that result from out-of-plane bending.
Asunto(s)
Masticación/fisiología , Cigoma/fisiología , Animales , Estimulación Eléctrica , Electromiografía , Femenino , Colorantes Fluorescentes , Masculino , Músculo Masetero/crecimiento & desarrollo , Músculo Masetero/fisiología , Desarrollo de Músculos , Estrés Mecánico , Porcinos , Porcinos Enanos , Soporte de Peso , Cigoma/anatomía & histología , Cigoma/crecimiento & desarrolloRESUMEN
The growth and morphology of craniofacial sutures are thought to reflect their functional environment. However, little is known about in vivo sutural mechanics. The present study investigates the strains experienced by the internasal, nasofrontal, and anterior interfrontal sutures during masticatory activity in 4-6-month-old miniature swine (Sus scrofa). Measurements of the bony/fibrous arrangements and growth rates of these sutures were then examined in the context of their mechanical environment. Large tensile strains were measured in the interfrontal suture (1,036 microepsilon +/- 400 SD), whereas the posterior internasal suture was under moderate compression (-440 microepsilon +/- 238) and the nasofrontal suture experienced large compression (-1,583 microepsilon +/- 506). Sutural interdigitation was associated with compressive strain. The collagen fibers of the internasal and interfrontal sutures were clearly arranged to resist compression and tension, respectively, whereas those of the nasofrontal suture could not be readily characterized as either compression or tension resisting. The average linear rate of growth over a 1-week period at the nasofrontal suture (133.8 micrometer, +/- 50.9 S.D) was significantly greater than that of both the internasal and interfrontal sutures (39.2 micrometer +/- 11.4 and 65. 5 micrometer +/- 14.0, respectively). Histological observations suggest that the nasofrontal suture contains chondroid tissue, which may explain the unexpected combination of high compressive loading and rapid growth in this suture.
Asunto(s)
Suturas Craneales/crecimiento & desarrollo , Disostosis Craneofacial , Masticación/fisiología , Animales , Suturas Craneales/ultraestructura , Femenino , Modelos Lineales , Masculino , Estrés Mecánico , Porcinos , Porcinos EnanosRESUMEN
This study investigates the structural design of the femoral neck with respect to phylogeny, locomotor behavior, and body size in a large comparative sample of primates. Since a bone's strength is determined by the amount and arrangement of its constituent material, the amount and distribution of bone in the femoral neck are the focus of the present study. Two types of data were collected. First, the total distribution of bone across the femoral neck (perpendicular to the femoral neck axis) was examined using image analysis techniques. The distribution of both cortical and trabecular bone are included in this analysis. Secondly, the external dimensions of the femoral neck and the thickness of the superior and inferior cortices, measured from radiographs, were used to calculate femoral neck cross-sectional properties (cortical area and second moment of area). These data were input into a simplified cantilevered beam model that incorporates femoral neck-shaft angle and femoral neck length and is used to predict stress under one unit body mass of loading on the femoral head. The patterns of bone distribution in the femoral neck between taxa are broadly similar for the analysis that includes both trabecular and cortical bone and that which includes only cortical bone. In all cases, there tends to be more bone on the inferior aspect of the femoral neck compared to the superior aspect. However, the non-human hominoids and New World monkeys (e.g., Ateles and Alouatta) have a more even distribution of bone across the femoral neck and have thicker superior cortices relative to inferior cortices compared to the rest of the comparative sample, including humans. It is proposed that the more equal distributional pattern in the non-human hominoids and atelines reflects less stereotypical, more generalized loading orientations. Differences between species in overall strength of the femoral neck are a function of both body size and locomotor mode.
Asunto(s)
Cuello Femoral/anatomía & histología , Primates/anatomía & histología , Adulto , Animales , Estudios Transversales , Femenino , Humanos , MasculinoRESUMEN
A distal tibia of Proconsul major from Napak, Uganda, is described. It is morphologically similar to other Proconsul tibiae, only much larger in size. This specimen and others are used to estimate the body weight of P. major from postcrania for the first time. Body weight is predicted from articular and diaphyseal dimensions using regression equations derived from a modern comparative sample of catarrhine primates. The estimated body weight of P. major based on the Napak tibia is 86.7 kg, whereas two other P. major specimens are smaller, giving a total range of 63.4-86.7 kg and an average of 75.1 kg. The regression equations are also used to predict the body weight of specimens from Rusinga/Mfangano belonging to P. nyanzae and P. heseloni. As the body weight estimates generated here are consistent with previous postcranial-based estimates for Proconsul species, the two sets of estimates are pooled to give means of 10.9 kg for P. heseloni (n = 6) and 35.6 kg for P. nyanzae (n = 12). These findings support the traditional assignment of two species at Rusinga/Mfangano. The postcranial body weight estimates for the three species of Proconsul are compared to body weights estimated from M1 area in order to investigate possible differences in scaling between the teeth and limbs in these species. Despite being based on a smaller sample size, the postcranial estimates clearly differentiate the three taxa, whereas the dental estimates form a more continuous distribution. Molar area overestimates body weight in P. heseloni, indicating that it is megadont compared to a large sample of modern anthropoid primates. In contrast, molar area underestimates body weight in P. Nyanzae and especially P. major, suggesting relative microdonty in these taxa.
Asunto(s)
Antropometría/métodos , Peso Corporal , Hominidae/anatomía & histología , Tibia/anatomía & histología , Animales , Huesos/anatomía & histología , Humanos , Diente/anatomía & histología , UgandaRESUMEN
It has been demonstrated in clinical and experimental studies that subarticular trabecular bone responds to mechanical loads transmitted across joints through changes in mass and structural organization. We investigated differences in mass, volume, and density of subarticular trabecular bone of the humeral and femoral head in Hylobates syndactylus, Colobus guereza, and Papio cynocephalus. Our hypothesis was that variations in trabecular properties between taxa may reflect differences in mechanical loading associated with different locomotor repertoires. A nondestructive method for measuring trabecular properties using optical luminance data measured from radiographs was developed. We also examined the relationship between internal trabecular properties and the external size and surface area of the humeral and femoral heads in these taxa. Our results suggest that internal and external articular structure are relatively independent of each other and may be adapted to different aspects of the mechanical environment. Differences in trabecular mass between taxa appear to correspond to differences in the magnitudes of mechanical loads borne by the joint, whereas articular volume and surface area are related primarily to differences in joint mobility. Because of the apparent physiological "de-coupling" of articular mass and volume, variations in articular density (mass/volume) are difficult to interpret in isolation. Comparisons of internal and external articular structure may provide new ways to reconstruct the locomotor/positional behavior of extinct taxa.