Line of Sight in Hominoids.

OBJECTIVES: It remains unclear how the realignments of the face and basicranium that characterize humans were acquired, both phylogenetically and ontogenetically. The developmentally constrained nature of the skull has been previously demonstrated in other primates using Donald H. Enlow's mammalian craniofacial architectural relationships. Here, we compare crania of our closest relatives to gain greater understanding of how and why the relationship of the face and cranial base is developmentally constrained in order to inform instances of abnormal growth and clinical intervention. STUDY DESIGN: A method for evaluating these fundamental architectural relationships using 3D landmark data was developed, thereby taking overall size and the geometric relationships among points into account. A sample of cone-beam computed tomography scans derived from humans and extant apes were analyzed (n=10 and n=6, respectively), as well as fossil hominid crania (n=7). Landmarks for 23 craniofacial architectural points were identified and recorded. RESULTS AND CONCLUSIONS: Principal components analyses reveal that despite the similarities in craniofacial architecture between humans, extant apes and fossil hominids, appreciable trends in variation between the extant species suggest that the repositioning of the foramen magnum was only one of a constellation of traits that realigned the basicranium and face during the transition to bipedalism.

Craniofacial growth variations in nasal-breathing, oral-breathing, and tracheotomized children.

INTRODUCTION: Childhood oral breathing can alter muscular balance and lead to facial deformities. No articles in the literature have reported on the alteration of facial growth patterns in patients who have received tracheotomies. The purpose of this study was to evaluate craniofacial developmental consequences originating from variations in breathing mechanisms in children who are nasal breathers or oral breathers, and those who have been tracheotomized. METHODS: The sample was divided into 3 groups of 10 each. The nasal group had a mean age of 13.9 years, the oral group had a mean age of 12.7 years, and the tracheotomy group had a mean age of 12.8 years. The masseter and suprahyoid muscles were evaluated with electromyography. The following measurements were made: facial, maxillary, and mandibular widths; nasion-sella-gnathion angle; and facial index. RESULTS: The tracheotomized group was similar to the nasal group for greater activity of the masseter muscles than of the suprahyoid muscles during mastication, as well as in the measurements of facial, maxillary, and mandibular widths. The oral group showed reductions in each category. The tracheotomized group was similar to the oral group during maximum dental occlusion for significantly higher activity of the suprahyoid muscles compared with the masseter muscles, with reductions in vertical values. CONCLUSIONS: A childhood tracheotomy might affect facial development in a way comparable with that of oral breathers, including abnormal facial growth variations.

Lamellar bone is an incremental tissue reconciling enamel rhythms, body size, and organismal life history.

Mammalian enamel formation is periodic, including fluctuations attributable to the daily biological clock as well as longer-period oscillations that enigmatically correlate with body mass. Because the scaling of bone mass to body mass is an axiom of vertebrate hard tissue biology, we consider that long-period enamel formation rhythms may reflect corresponding and heretofore unrecognized rhythms in bone growth. The principal aim of this study is to seek a rhythm in bone growth demonstrably related to enamel oscillatory development. Our analytical approach is based in morphology, using a variety of hard tissue microscopy techniques. We first ascertain the relationship among long-period enamel rhythms, the striae of Retzius, and body mass using a large sample of mammalian taxa. In addition, we test whether osteocyte lacuna density (a surrogate for rates of cell proliferation) in bone is correlated with mammalian body mass. Finally, using fluorescently labeled developing bone tissues, we investigate whether the bone lamella, a fundamental microanatomical unit of bone, relates to rhythmic enamel growth increments. Our results confirm a positive correlation between long-period enamel rhythms and body mass and a negative correlation between osteocyte density and body mass. We also confirm that lamellar bone is an incremental tissue, one lamella formed in the species-specific time dependency of striae of Retzius formation. We conclude by contextualizing our morphological research with a current understanding of autonomic regulatory control of the skeleton and body mass, suggesting a central contribution to the coordination of organismal life history and body mass.

Regional variability in secondary remodeling within long bone cortices of catarrhine primates: the influence of bone growth history.

Secondary intracortical remodeling of bone varies considerably among and within vertebrate skeletons. Although prior research has shed important light on its biomechanical significance, factors accounting for this variability remain poorly understood. We examined regional patterning of secondary osteonal bone in an ontogenetic series of wild-collected primates, at the midshaft femur and humerus of Chlorocebus (Cercopithecus) aethiops (n = 32) and Hylobates lar (n = 28), and the midshaft femur of Pan troglodytes (n = 12). Our major objectives were: 1) to determine whether secondary osteonal bone exhibits significant regional patterning across inner, mid-cortical and outer circumferential cortical rings within cross-sections; and if so, 2) to consider the manner in which this regional patterning may reflect the influence of relative tissue age and other circumstances of bone growth. Using same field-of-view images of 100-microm-thick cross-sections acquired in brightfield and circularly polarized light microscopy, we quantified the percent area of secondary osteonal bone (%HAV) for whole cross-sections and across the three circumferential rings within cross-sections. We expected bone areas with inner and middle rings to exhibit higher %HAV than the outer cortical ring within cross-sections, the latter comprising tissues of more recent depositional history. Observations of primary bone microstructural development provided an additional context in which to evaluate regional patterning of intracortical remodeling. Results demonstrated significant regional variability in %HAV within all skeletal sites. As predicted,%HAV was usually lowest in the outer cortical ring within cross-sections. However, regional patterning across inner vs. mid-cortical rings showed a more variable pattern across taxa, age classes, and skeletal sites examined. Observations of primary bone microstructure revealed that the distribution of endosteally deposited bone had an important influence on the patterning of secondary osteonal bone across rings. Further, when present, endosteal compacted coarse cancellous bone always exhibited some evidence of intracortical remodeling, even in those skeletal sites exhibiting comparatively low %HAV overall. These results suggest that future studies should consider the local developmental origin of bone regions undergoing secondary remodeling later in life, for an improved understanding of the manner in which developmental and mechanical factors may interact to produce the taxonomic and intraskeletal patterning of secondary bone remodelling in adults.

Craniofacial architectural constraints and their importance for reconstructing the early Homo skull KNM-ER 1470.

OBJECTIVE: Our objective is to exploit architectural constraint for the analysis and interpretation of craniofacial form, which we apply here to the reconstruction of the early Homo cranium KNM-ER 1470. We are motivated to perform this study because in the absence of biological criteria our preconceptions are likely to govern our concept of craniofacial form. STUDY DESIGN: We reassembled the fragmented parts--left and right halves of the calvaria and the face--according to mammalian craniofacial architectural constraints described by Donald H. Enlow and colleagues. RESULTS: When evaluated on a biological premise, KNM-ER 1470 is found to have a more prognathic midface than commonly appreciated. The relationship between facial prognathism and cranial capacity also provides an estimate downward for this specimen, from 752cc to ca. 700cc. CONCLUSION: Awareness of our preconceptions is critical to the performance of relatively unbiased research in fields characterized by interpretations of morphology. When perceptual bias is relatively minimized, applied here as an architecturally constrained of KNM-ER 1470 craniofacial skeleton, we are able to provide the scientific community with a more tractable Gestalt perspective of form.

Collagen Fiber Orientation in Primate Long Bones.

Studies of variation in orientation of collagen fibers within bone have lead to the proposition that these are preferentially aligned to accommodate different kinds of load, with tension best resisted by fibers aligned longitudinally relative to the load, and compression best resisted by transversely aligned fibers. However, previous studies have often neglected to consider the effect of developmental processes, including constraints on collagen fiber orientation (CFO), particularly in primary bone. Here we use circularly polarized light microscopy to examine patterns of CFO in cross-sections from the midshaft femur, humerus, tibia, radius, and ulna in a range of living primate taxa with varied body sizes, phylogenetic relationships and positional behaviors. We find that a preponderance of longitudinally oriented collagen is characteristic of both periosteal primary and intracortically remodeled bone. Where variation does occur among groups, it is not simply understood via interpretations of mechanical loads, although prioritized adaptations to tension and/or shear are considered. While there is some suggestion that CFO may correlate with body size, this relationship is neither consistent nor easily explicable through consideration of size-related changes in mechanical adaptation. The results of our study indicate that there is no clear relationship between CFO and phylogenetic status. One of the principle factors accounting for the range of variation that does exist is primary tissue type, where slower depositing bone is more likely to comprise a larger proportion of oblique to transverse collagen fibers. Anat Rec, 300:1189-1207, 2017. © 2017 Wiley Periodicals, Inc.

Assessment of mandibular growth and response to orthopedic treatment with 3-dimensional magnetic resonance images.

INTRODUCTION: Three-dimensional (3D) craniofacial images are commonly used in clinical studies in orthodontics to study developmental and morphologic relationships. METHODS: We used 3D magnetic resonance imaging to study relationships among craniofacial components during the pubertal growth spurt and in response to Fränkel appliance therapy. The sample for this prospective study was 156 high-resolution magnetic resonance images with 1 mm isotropic voxel resolution of 78 subjects taken initially (T1) and 18 +/- 1 months (T2) after treatment or an observation period. The subjects were Brazilian children; 28 were treated and 25 were untreated for Class II malocclusion, and 25 were untreated with normal occlusions. A Procrustes geometric transformation of 3D skeletal landmarks was used to assess growth or treatment alterations from T1 to T2. The landmarks were located on the mandibular rami and the other craniofacial parts specifically related to the mandibular growth (the middle cranial fossae and the posterior part of the bilateral nasomaxilla). This allowed visualization of the entire volumetric dataset with an interactive 3D display. RESULTS: Statistically significant differences were found in the relative 3D skeletal growth directions from T1 to T2 for treated vs untreated Class II children (Bonferroni-adjusted P < .001) and for treated Class II vs normal-occlusion subjects ( P < .001). The major differences in the treated group were increased mandibular rami vertical dimensions and more forward rami relative to the posterior nasomaxilla and the middle cranial fossae. Principal component analysis made it possible to show individual variability and group differences in the principal dimensions of skeletal change. CONCLUSIONS: These methods are generalizable to other imaging techniques and 3D samples, and significantly enhance the potential of systematically controlled data collection and analysis of bony structures in 3 dimensions for quantitative assessment of patient parameters in craniofacial biology.

Comparison of relative mandibular growth vectors with high-resolution 3-dimensional imaging.

INTRODUCTION: The mandibular rami and their endochondrally growing condyles develop in many directions relative to the variable anatomic patterns of the nasomaxilla and middle cranial fossae during growth and response to orthopedic treatment. METHODS: High-resolution magnetic resonance images were used to compare 3-dimensional (3D) growth vectors of skeletal displacement and bone remodeling in 25 untreated subjects with Class II malocclusions, 28 subjects with Class II malocclusions who were treated with Fränkel appliance therapy, and 25 subjects with normal occlusions. Marked differences were noted over an 18-month observation period. The 3D coordinates of anatomic landmarks were registered by Procrustes fit to control for rotation, translation, and scale differences. RESULTS: Compared with untreated Class II and normal-occlusion subjects, the treated group showed highly significant differences in the 3D displacement/remodeling vectors of gonion and pterygomaxillary fissure relative to condylion and middle cranial fossae bilateral skeletal landmarks, by using both permutation tests ( P < .001) and a general linear multivariate model ( P < .0001). CONCLUSIONS: In a prospective and systematically controlled study, we quantitatively described significant 3D rami skeletal compensations in the structural assembly of facial morphogenesis at the beginning of the adolescent growth spurt using novel modeling techniques. These techniques have facilitated quantification of relative 3D growth vectors to illustrate skeletal changes with Fränkel appliance therapy. Future studies are required to assess the long-term clinical significance of our findings.

Clinical outcomes of Fränkel appliance therapy assessed with a counterpart analysis.

To evaluate whether the Fränkel Regulator-II (FR-II) induced mandibular growth rotations relative to the nasomaxilla and the middle cranial fossae, cephalometric changes in 28 treated Brazilian children were compared with changes in 28 untreated Class II children and in 28 children with normal occlusion. According to Enlow's counterpart analysis, the 3 groups were not significantly different initially in ramus alignment or relative ramus vertical dimension. These jaw relationships were maintained in both untreated groups. In the treated group, all children had overjet reduction, with correction of the dental arch relationship in 26 of the 28, and there was a significant trend toward a more forward ramus alignment (P =.002) and increased ramus relative vertical dimension (P =.0002). These treatment-induced changes showed a negative correlation with ramus alignment; ie, greater improvement was more likely in children who had backward ramus alignment before treatment and whose Class II malocclusion had not already been intrinsically compensated. Changes in the treated children were similar to but greater than those in the normal children, and different from those in the untreated Class II group. The data suggest that studies of skeletal variations with counterpart analysis can show ramus remodeling compensations from treatment that are missed with conventional cephalometrics.

Mesial drift as a function of growth

Migration of teeth in apparent mesial directions through maxillary and mandibular alveolar bone is a well known process. Such drifting of teeth has been presumed to function in maintenance of firm contact between teeth in order to compensate for wear on contact surfaces. Histological changes associated with this process involve differential deposition and resorption of bone on selective surfaces of alveolar walls. Although this functional interpretation of mesial drift is sound in principle, other equally important factors also appear to be involved. As the maxilla and mandible grow in size, a continuous remodelling process takes place that involves successive relocations of all areas into new positions within the entire bone. The purpose of such relocation is to maintain the constant shape, proportions, and relationship of the bone as a whole. The process involves localized additions and removal of bone in order to adjust the shape and size of each area as it is relocated into successive new positions. For example, a molar area at a given growth level is actually occupied by a premolar region at a later stage of growth. The remodelling movements of all such areas within the whole bone also requires corresponding movements of teeth inorder to maintain the constant positions of each tooth relative to its location in the growing bone. Since bone is a hard, calcified tissue, such tooth movements involve deposition and resorption of bone on selective surfaces of the alveolar wall, thereby resulting in the histological picture characteristic of mesial drift. It is suggested that these growth and remodelling movements represent the actual basis for drift, and that the maintenance of functional contact between teeth is a secondary but nevertheless important function of the same process (AU)

Wolff's law and the problem of muscle attachment on resorptive surfaces of bone

During the growth of a bone, outer (periosteal) surfaces in many areas undergo normal remodeling processes involving resorptive removal. Attachments of muscles commonly occur on such outer resorptive surfaces.The cortex in these regions grows in an inward direction by bone deposition on endosteal surfaces. In some areas of a bone, a portion of muscle can be inserted onto adepository surface, but other parts of the same muscle may be attached on to an adjacent resorptive surface. It has been generally assumed that the pull of a muscle acts to directly stimulate deposition of new bone, and that attachments of muscle are thereby responsible for determining the gross morphology of a whole bone. In view of the foregoing considerations, a re-evaluation and an expansion of this concept is now needed. Muscle pull, in many regions of a bone, can be associated with normal cortical recession (involving surface resorption) as well as with outward bone deposition. (AU)