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Skeletal anomalies are common in patients with muscular dystrophy, despite an absence of mutations to genes that specifically direct skeletogenesis. In order to understand these anomalies further, we examined two strains of muscular dystrophy (laminin- and merosin-deficient) relative to controls, to determine how the weakened muscle forces affected skull shape in a mouse model. Shape was characterized with geometric morphometric techniques, improving upon the limited analytical power of the standard linear measurements. Through these techniques, we document the specific types of cranial skeletal deformation produced by the two strains, each with individual shape abnormalities. The mice with merosin deficiency (with an earlier age of onset) developed skulls with more deformation, probably related to the earlier ontogenetic timing of disease onset. Future examinations of these mouse models may provide insight regarding the impact of muscular forces and the production and maintenance of craniofacial integration and modularity.

Dietary protein is a limiting factor in mammalian growth, significantly affecting the non-linear trajectories of skeletal growth. Young females may be particularly vulnerable to protein malnutrition if the restriction is not lifted before they become reproductive. With such early malnutrition, limited amino acids would be partitioned between two physiological objectives, successful reproduction vs. continued growth. Thus, the consequences of protein malnutrition could affect more than one generation. However, few studies have quantified these cross-generational effects. Our objective was to test for differences in skeletal growth in a second generation of malnourished rats compared with rats malnourished only post-weaning, the first generation and with controls. In this longitudinal study we modelled the growth of 22 craniofacial measurements with the logistic Gompertz equation, and tested for differences in the equation's parameters among the diet groups. The female offspring of post-weaning malnourished dams did not catch up in size to the first generation or to controls, although certain aspects of their craniofacial skeleton were less affected than others. The second generation's growth trajectories resembled the longer and slower growth of the first malnourished generation. There was a complex interaction between developmental processes and early nutritional environment, which affected variation of adult size.

Variation between the sexes during ontogeny is frequently overlooked in discussions of the phylogenetic patterns of adult sexual dimorphism. Different growth trajectories can produce identical degrees and direction of adult dimorphism and the possibility exists that similarities in adults may be the result of differing growth patterns, suggesting independent evolutionary pathways among species to the seemingly identical adult morphology. We quantified the sexual dimorphism in craniofacial skeletal growth of Cavia porcellus, the guinea pig, using longitudinally collected radiographs. Guinea pigs have male-biased sexual dimorphism in size and in growth parameters, despite literature reports to the contrary. These results, analyzed with equivalent data for five species of rodents, and two outgroups representing similarly sized mammals, a rabbit and a marsupial, indicate that some aspects of sexual differences in growth follow phylogenetic lines, while others are a function of whether the species has male- or female-biased dimorphism., (Copyright 2003 Wiley-Liss, Inc.)

Mechanical loading of muscles on bones at their sites of attachment can regulate skeletal morphology. The present study examined the effects of muscle degeneration on craniofacial growth, using two strains of muscular dystrophic mice, Mus musculus, differing in pathological severity. We collected radiographic and weight data longitudinally and digitized radiographs to obtain distances between anatomical landmarks in different functional regions of the skull. We then quantified heterochronic and allometric differences among genotypes and between sexes. Because growth is nonlinear with respect to time, we first used the Gompertz model to obtain heterochronic growth parameters, which were then tested with ANOVA. Ontogenetic allometric analyses examined the scaling relationships between various measurements with linear regressions. For most measurements the severely dystrophic mice are significantly smaller in final size than both the control and the mildly dystrophic mice, which are statistically indistinguishable. Measures of total growth and the neurocranium exhibit more differences among groups in heterochronic parameters of early ontogeny because growth in these regions is controlled primarily by brain expansion that ceases early in development. In contrast, the face and mandible exhibit more differences in later growth parameters possibly because of the increased influence of muscles on these regions as growth progresses. The severely dystrophic mice have flatter, more elongate skulls and mandibles than those of the other two genotypes, concurrent with an absence of muscular forces to stimulate growth in a superior-inferior direction.

An experimental animal study was undertaken to evaluate the potential use of HTR polymer as a craniomaxillofacial reconstructive material. Its properties of marked hydrophilicity, a negative surface charge, and extensive porosity combined with a calcium graft coating suggested favorable osteoconductive properties. Four sites of the rabbit craniomaxillofacial skeleton were evaluated by placement of both inlay and onlay implants. Postoperative assessment at 60, 120, and 240 days consisted of histologic evaluation by tetrachrome staining of calcified sections. At 60 days, extensive osseous ingrowth into the inlay implants had occurred extending up to 2000 microns. The onlay implants, however, exhibited more limited ingrowth extending only 100 to 200 microns into the material. Over the ensuing 120- and 240-day postoperative periods, the average depth of bony ingrowth did not progress in either the inlay or onlay specimens over that observed at 60 days. Differences also were noted between the inlayed skeletal sites, with increased marrow at the recipient site resulting in increased bony ingrowth. The material appears to be biocompatible, with no evidence of infection, inflammatory reaction, or bone resorption observed around any of the implants. The implants exhibited a significant osteoconductive capability that was most manifest when implants were exposed to bleeding cortical/marrow surfaces as inlay grafts.

Landmarks digitized from lateral cephalometric radiographs of 107 Navajo Indians between 10 and 12 years of age were analyzed to determine coefficients of variation or standard deviations for 38 cephalometric measurements. These values were compared with the same measures of variation for identical measurements on North American whites derived from the Michigan and Philadelphia Growth Studies. For the majority of variables, there were no differences between groups. Variation for the genetically and environmentally isolated Navajo Indians was the same as that of the highly diverse Caucasian samples. However, measurements of upper, lower, and total anterior facial height (N-ANS, ANS-Me, and N-Me, respectively) indicate that these features are substantially less variable in Navajo Indians relative to the Michigan and Philadelphia populations.