Effect of unilateral partial facial paralysis on periosteal growth at the muscle-bone interface of facial muscles and facial bones

In a previous study, the influence of the midfacial musculature upon growth and development of the maxilla and mandible was established macroscopically. Dry skull measurements revealed a reduced premaxillary, maxillary, mandibular, and anterior corpus length with a simultaneous increase in mandibular ramal height on the paralyzed side. It was demonstrated that these reduced premaxillary and maxillary lengths were among others the result of reduced nasofrontal growth, whereas the increased ramal height was accompanied by condylar growth alterations. This study investigated whether the growth alterations at the mandibular corpus region could be explained by altered periosteal growth at the muscle-bone interface of the zygomatico-auricular muscle and the mandibular corpus, caused by altered muscle activity acting upon the periosteal sleeve. Fifty-six 12-day-old New Zealand White rabbits were randomly assigned to either a control or an experimental group. In the experimental group, left-sided partial facial paralysis was induced surgically when the animals were 12 days old. To study the muscle-bone interface, seven follow-up time intervals were defined between 3.5 and 60 days following the surgery. At these time intervals, four randomly selected control animals and four randomly selected experimental animals were killed. The anterior mandibular corpus region with the muscle-bone interface of the left control hemimandible and the left and right experimental hemimandibles was processed for undecalcified tissue preparation. Quantitative analysis of the total bone area at the muscle-bone interface revealed no significant differences between the left control hemimandible and the left and right experimental hemimandibles. Also, qualitative study of the histologic sections showed no major changes in the appearance or development of the trabecular pattern between the groups. However, slight differences in the distribution pattern of osteoblasts and osteoclasts along the bony surface were found between the left control hemimandible and the left and right experimental hemimandibles, which seemed to explain the alterations in mandibular corpus shape between these groups. It was suggested that these changes in the distribution pattern of osteoblasts and osteoclasts were the result of changes in the loading distribution pattern acting upon the mandible, caused by an altered neuromuscular recruitment pattern of the remaining functionally intact, mandibularly attached muscles. The latter was probably the result of adaptive mandibular positioning in response to an altered occlusal relationship, which was induced by the abnormal maxillary growth as a result of the unilateral partial facial paralysis.     

Relationships between the size and spatial morphology of human masseter and medial pterygoid muscles, the craniofacial skeleton, and jaw biomechanics

The relationship between human craniofacial morphology and the biomechanical efficiency of bite force generation in widely varying muscular and skeletal types is unknown. To address this problem, we selected 22 subjects with different facial morphologies and used magnetic resonance imaging, cephalometric radiography, and data from dental casts to reconstruct their craniofacial tissues in three dimensions. Conventional cephalometric analyses were carried out, and the cross-sectional sizes of the masseter and medial pterygoid muscles were measured from reconstituted sections. The potential abilities of the muscles to generate bite forces at the molar teeth and mandibular condyles were calculated according to static equilibrium theory using muscle, first molar, and condylar moment arms. On average, the masseter muscle was about 66% larger in cross section than the medial pterygoid and was inclined more anteriorly relative to the functional occlusal plane. There was a significant positive correlation (P less than 0.01) between the cross-sectional areas of the masseter and medial pterygoid muscles (r = 0.75) and between the bizygomatic arch width and masseter cross-sectional area (r = 0.56) and medial pterygoid cross-sectional area (r = 0.69). The masseter muscle was always a more efficient producer of vertically oriented bite force than the medial pterygoid. Putative bite force from the medial pterygoid muscle alone correlated positively with mandibular length and inversely with upper face height. When muscle and tooth moment arms were considered together, a system efficient at producing force on the first molar was statistically associated with a face having a large intergonial width, small intercondylar width, narrow dental arch, forward maxilla, and forward mandible. There was no significant correlation between muscle cross-sectional areas and their respective putative bite forces. This suggests that there is no simple relationship between the tension-generating capacity of the muscles and their mechanical efficiency as described by their spatial arrangement. The study shows that in a modern human population so many combinations of biomechanically relevant variables are possible that subjects cannot easily be placed into ideal or nonideal categories for producing molar force. Our findings also confirm the impression that similar bite-force efficiencies can be found in subjects with disparate facial features.     

A comparative analysis of temporomandibular joint morphology in the African apes

A number of researchers have suggested a functional relationship between dietary variation and temporomandibular joint (TMJ) morphology, yet few studies have evaluated TMJ form in the African apes. In this study, I compare TMJ morphology in adults and during ontogeny in Gorilla (G.g. beringei, G.g. graueri, and G.g. gorilla) and Pan (P. paniscus, P. troglodytes troglodytes, P.t. schweinfurthii, and P.t. verus). I test two hypotheses: first, compared to all other African apes, G.g. beringei exhibits TMJ morphologies that would be predicted for a primate that consumes a diet comprised primarily of moderately to very tough, leafy vegetation; and second, all gorillas exhibit the same predicted morphologies compared to Pan. Compared to all adult African apes, G.g. beringei has higher rami and condyles positioned further above the occlusal plane of the mandible, relative to jaw length. Thus, mountain gorillas have the potential to generate relatively more muscle force, more evenly distribute occlusal forces along the postcanine teeth, and generate relatively greater jaw adductor moment. G.g. beringei also exhibits relatively wider mandibular condyles, suggesting these folivorous apes are able to resist relatively greater compressive loads along the lateral and/or medial aspect of the condyle. All gorillas likewise exhibit these same shape differences compared to Pan. These morphological responses are the predicted consequences of intensification of folivory and, as such, provide support for functional hypotheses linking these TMJ morphologies to degree of folivory. The African apes to not, however, demonstrate a systematic pattern of divergence in relative condylar area as a function of intensification of folivory. The ontogenetic trajectories for gorillas are significantly elevated above those of Pan, and to a lesser but still significant degree, mountain gorillas similarly deviate from lowland gorillas (G.g. gorilla and G.g. graueri). Thus, adult shape differences in ramal and condylar heights do not result from the simple extrapolation of common growth allometries relative to jaw length. As such, they are suggestive of an adaptive shift towards a tougher, more folivorous diet. However, the allometric patterning for condylar area and condylar width does not systematically conform to predictions based on dietary specialization. Thus, while differences in condylar shapes may confer functional advantages both during growth and as adults, there is no evidence to suggest selection for altered condylar proportions, independent of the effects of changes in jaw size.     

Craniofacial sequelae of lesions to facial and trigeminal motor nuclei in growing rats

Unilateral electrolytic lesions were made in the left-side facial motor nucleus (FMNu) of six Sprague-Dawley rats at 35 days of age in order to correlate craniofacial sequelae with changed motoneuron function. Experimental and control rats were killed at 22, 32, 42, and 52 days postoperatively to provide muscle weight, brain histology, and dry skull preparations for analyses. Dissection, muscle weight, motoneuron count, and osteometric data revealed that lesion-side facial and masticatory muscles were affected by the lesions. Paired t-tests indicated that significant differences existed between weights of experimental lesion- and nonlesion-side anterior digastric, temporalis, masseteric complex, and medial pterygoid muscles, numbers of facial and trigeminal motoneurons, and several skeletal dimensions of the skull. Basi-cranial dimensions of experimental animals were least affected by the lesion, whereas zygomatic arch, dorsal facial region, and mandibular condyle dimensions were most affected. Statistical analyses also detected significant differences between experimental and control groups for several skeletal dimensions of the skull. Data indicated that damage to the trigeminal motor nucleus (TMNu) was secondary to the primary lesion in the FMNu. Motoneurons within the facial and trigeminal neuromuscular complexes (FNC and TNC) play an important role in craniofacial growth and development.     

Craniofacial alterations following electrolytic lesions of the trigeminal motor nucleus in actively growing rats

The objective of this study was to define further the role of the trigeminal motor nucleus (TMNu) in the postnatal ontogeny of the mammalian craniofacial skeleton. To that end, 42 male Sprague-Dawley rats underwent stereotaxic surgery at 40 days of age; 21 received small electrolytic lesions to their left-side TMNu (lesioned group) while 21 had TMNu stimulation with no actual electrolytic lesion produced (sham group). Seven rats from each group were killed at 28, 56, and 84 days postoperative to analyze trigeminal motoneuron (TMNe) count, masticatory muscle weight, and osteological growth vector data. At all three time periods, lesioned animals showed significant differences 1) between the surgery and nonsurgery sides, and 2) from sham animals. However, sham animals also demonstrated significant between-side differences for medial pterygoid muscle weight (56 days), mandibular height (28 and 56 days), and mandibular length data (84 days); these data suggested that even relatively slight damage to TMNe can create morphological changes within the craniofacial complex. Snout deviation in a lesioned rat towards the opposite side from all other lesioned animals was correlated with unique damage to its pontine reticular formation; this suggested that the observed morphological alterations of the craniofacial complex may have been due not only to TMNu damage, but also to changed expressions of the masticatory central pattern generator (CPG). Morphological alterations of the craniofacial skeleton resulting from lesions to the TMNu were likely due to changed neuromuscular activity patterns of the masticatory muscles and their biomechanical effects upon bone.     

Size and shape of the mandibular condyle in primates

The relationships between the size of the articular surface of the mandibular condyle and masticatory muscle size, tooth size, diet, and biomechanical variables associated with mastication were studied by taking 12 measurements on skulls of 253 adult female anthropoid primates, including three to ten specimens from each of 32 species. In regressions of condylar length, width, or area against body weight, logarithmic transformations substantially improve the fit of the equations compared with untransformed data. There is a strong relationship between condylar measurements and body weight, with all correlations being .94 or higher. The slopes of the allometric regressions of length, width, and area of the condylar head indicate slight positive allometry with body size. Folivorous primates have smaller condyles than frugivorous primates, and colobines have smaller condyles than cebids, cercopithecines, or hominoids. When colobines are eliminated, the differences between frugivores and folivores are not significant. However, the two species with the relatively largest condyles are Pongo pygmaeus and Cercocebus torquatus, suggesting that there may be a relationship between unusually large condylar dimensions and the ability to crack hard nuts between the teeth. Cranial features having strong positive correlations with condylar dimensions include facial prognathism, maxillary incisor size, maxillary postcanine area, mandibular ramus breadth, and temporal fossa area. These data are interpreted as indicating that relatively large condyles are associated with relatively large masticatory muscles, relatively inefficient mandibular biomechanics, and a large dentition. These relationships support the growing evidence that the temporomandibular joint is a stress-bearing joint in normal function.     

The effect of unilateral partial facial paralysis on nasofrontal sutural growth: an experimental study in the rabbit.

In a previous study in the rabbit, it was demonstrated that paralysis of the midfacial musculature results in decreased anteroposterior growth of the snout. At the end of growth, these animals showed macroscopically striking similarities to animals with unilateral fusion of the nasofrontal suture. In this study, whether nasofrontal sutural growth is unilaterally restricted in animals with unilateral partial facial paralysis was investigated. A left-sided partial facial paralysis was induced in sixteen 12-day-old New Zealand White rabbits. At the ages of 5, 9, 12, and 17 weeks, four animals were randomly assigned to be killed for analysis of nasofrontal sutural growth. In each animal, the left experimental side was compared with the right control side. By means of histomorphometric measurements, it was shown that diminished sutural growth activity was present on the left paralyzed side in periods of rapid growth. On the other hand, no significant alterations in sutural width were found. These findings seem to explain some of the macroscopic growth alterations (i.e., diminished anterior maxillary length) observed in rabbits with unilateral partial facial paralysis.     

The incidence and expression of the subcondylar tubercle of the mandible in early Polynesians, modern Indians and modern Europeans

A sample of pre-European Polynesian and Melanesian mandibles, modern Asian Indians and cadaveric European mandibles were investigated to establish the prevalence of a subcondylar tubercle and to attempt to relate its presence to mandibular function. Among the three population samples, the subcondylar tubercle appeared 1.5 times more frequently among the Polynesians/Melanesians, than either the Indian or European groups. It was fairly equally present on both sides in all three groups. Where it was present unilaterally, it was far more likely to be present on the left side. This left-side presence coincided with a significantly greater right-side condylar height and ramal width.     

Biomechanical scaling of mandibular dimensions in New World Monkeys

Previous studies show that folivorous Old World monkeys have shorter, deeper mandibles and shorter, wider condyles than frugivorous ones. These morphologies have been related to leaf mastication in colobines and ingestion of large, tough fruits in cercopithecines. This study examines New World monkeys in order to determine whether they exhibit similar adaptations to diet. New World monkeys have relatively long, transversely thin mandibles and somewhat deep mandibles and narrow condyles. Except for their deep mandibles, folivorous New World monkeys (i.e., Alouatta) do not exhibit the mandibular and condylar specializations typical of cercopithecid folivores. Reliance on comparatively nonfibrous foods plus alterations in masticatory muscle ratios among New World monkeys partially accounts for observed differences between folivorous New and Old World monkeys. In addition, adaptations for howling in Alouatta appear to have a significant effect on mandibular morphology. A biomechanical interpretation of craniofacial scaling patterns suggests that the mandibles of New World monkeys are subjected to lower condylar loads and considerably less twisting of the mandibular corpus than those of comparable Old World monkeys.     

Correlations between the cross-sectional area of the jaw muscles and craniofacial size and shape

In adult human subjects, the correlations were determined between the cross-sectional areas of the jaw muscles (measured in CT scans) and a number of facial angles and dimensions (measured from lateral radiographs). Multivariate statistical analysis of the skeletal variables in a group of 50 subjects led to the recognition of six independent factors determining facial shape, i.e., cranial base length, lower facial height, cranial base flexure and prognathism, facial width, mandibular length, and upper facial height. In 29 of these subjects, the cross-sectional areas of the jaw muscles were determined, and correlations between these areas and the scores on the above-mentioned factors were calculated. It appeared that the cross-sectional areas of temporalis and masseter muscles correlated positively with facial width, whereas the areas of masseter and both pterygoid muscles did so with mandibular length. It has been shown experimentally that a decrease in jaw muscle size in various animals likewise has an effect on facial width and mandibular length. Our results therefore support the hypothesis that in man too the jaw muscles affect facial growth and partly determine the final facial dimensions. They also hint that the role of each muscle is different.     

Mechanical stress promotes matrix synthesis of mandibular condylar cartilage via the RKIP-ERK pathway

Mandibular hypoplasia is a common jaw deformity that affects breathing, occlusal function and facial aesthetics. Stimulating mandibular condylar growing with functional appliances is an ordinary but controversial treatment method in orthodontics. Therefore, it is vital to clarify how functional appliances affect condylar growing. Raf-1 kinase inhibitor protein (RKIP), as an endogenous inhibitory molecule of the ERK signaling, is postulated to involve in stress-induced response to articular cartilage. This study was to reveal the role of RKIP in regulating cartilage matrix synthesis with functional appliance treatment. Here, position rat mandibular forward simulating functional appliance effect to examine the stress-induced modification of mandibular condylar in vivo, meanwhile rat mandibular condylar chondrocytes (Mccs) were subjected to cyclic tensile stress (CTS, 16%, 1 HZ). The results showed that mandibular forward therapy enhanced condylar cartilage growth. The thicknesses of all layers of condylar cartilage were increased significantly. RKIP expression was also increased in the mature cartilage layer. In addition, CTS could enhance extracellular matrix formation and cartilage marker expression (aggrecan and collagen II), which shared a similar expression pattern with RKIP in Mccs. However, CTS induced up-regulation of collagen II and aggrecan was blocked by RKIP knockdown. Nuclear p-ERK, targeting downstream of RKIP, showed a decrease after CTS,which was disappeared in RKIP-knockdown Mccs. Taken together, physiological mechanical stimulation promotes cartilage growth modification by up-regulating RKIP through inhibiting ERK signaling pathway.     

Correction of unilateral coronal synostosis leads to resolution of mandibular asymmetry in rabbits

Mandibular dysmorphology in unilateral coronal synostosis has been recognized clinically. In patients with unilateral coronal synostosis, the chin point deviates away from the affected side. To investigate whether this mandibular asymmetry resolves after correction of unilateral coronal synostosis, familial nonsyndromic rabbits were used. Rabbits with unilateral coronal synostosis that underwent "correction" with resection of the affected suture were compared with "uncorrected" rabbits with unilateral coronal synostosis and normal, wild-type rabbits (n = 36; three equal groups of 12). Serial lateral cephalograms obtained at 10, 25, 42, and 84 days showed no asymmetries in wild-type rabbits and progressive asymmetries in the ramal height and mandibular length in uncorrected unilateral coronal synostosis rabbits. However, in corrected unilateral coronal synostosis rabbits, existing asymmetries at 10 and 25 days improved by 42 days and were not seen by maturity, at 84 days. In dry, mature, mandibular specimens, wild-type rabbits showed equal side-to-side measurements and uncorrected unilateral coronal synostosis rabbits showed the following on the affected side: longer ramal height (15 percent), shorter ramal width (13 percent), longer body height (10 percent), and shorter body width (13 percent). By contrast, the corrected unilateral coronal synostosis specimens showed no side-to-side differences in 10 of 11. There were no asymmetries in condylar shape or condylar volume in any of the three groups. Cranial base measurements showed asymmetries of the uncorrected unilateral coronal synostosis specimens that were consistent with an anteriorly positioned glenoid fossa on the affected side. However, only one of 11 corrected unilateral coronal synostosis specimens showed similar cranial base asymmetries. The data showed that mandibular asymmetries in nonsyndromic, familial rabbits with unilateral coronal synostosis are progressive with growth but improve after correction of synostosis.     

Condylar translation and the function of the superficial masseter muscle in the rhesus monkey (M. mulatta).

The relationship between translation of the mandibular condyle during symmetrical mandibular rotation, i.e., symmetrical jaw depression and elevation, and the function of the superficial masseter muscle was examined in light of relative torque and the length-tension relationship for muscle. Lateral cephalograms of live adult rhesus monkeys (Macaca mulatta) were analyzed using two models: (1) Model A, normal symmetrical jaw rotation accompanied by condylar translation; and (2) Model B, mandibular rotation about an axis fixed at the position of the condyles during centric occlusion. The decrease in relative torque and the excursion of the superficial masseter at mouth-open positions are significantly greater in Model B than in Model A. Symmetrical rotation of the jaw about a fixed axis would result in a 35% greater loss of maximum producible tension at maximum gape than rotation associated with condylar translation. These results suggest that condylar translation during mandibular depression and elevation functions to minimize reduction in relative torque and excursion of superficial masseter muscle, thereby maintaining optimal potential for exerting maximum tension during jaw closure.     

Time-Dependent Effects of a Functional'-Type Orthopedic Appliance on the Rat Mandible Growth

The modus operandi and the time-dependent variations in the effects of the LSU-activator, an orthopedic appliance currently used in human orthodontic therapy, was experimentally analyzed in growing rats. This appliance causes a forward positioning of the lower jaw and a restriction of mandibular motility. After a 4-week treatment, the following changes were observed:

(i) the growth rate of the condylar cartilage was accelerated, this growth-promoting effect being more pronounced when the LSU-activator was worn during the animal's rest span.

(ii) the direction of condylar growth became more backward-oriented; no significant difference between day and night treatment, i.e. during the rest and activity spans could be detected;

(iii) the supplementary lengthening of the mandible was greater in rats treated during rest than in rats treated during waking and

(iv) the number of serial sarcomeres in the lateral pterygoid muscle was smaller. This growth retardation of the muscle was greater in rest-time than in waking-time treated individuals.

The LSU-type activator's action implies a two-step effect: during the time of wearing the appliance, the more forward positioning of the mandible causes a reduced growth of the lateral pterygoid muscle; during the time the LSU-type activator is not worn, the mandible is functioning in a more forward position in such a way that it stimulates the growth rate of the condylar cartilage and the subperiosteal ossification of the posterior border of the ramus. It is therefore essential, for a few hours every day, that the mandible be allowed to move freely from the appliance in a more forward position.     

Surgical correction of hemifacial microsomia in the growing child

This is a follow-up study of 20 children who had surgical correction of hemifacial microsomia in an effort to improve facial growth and minimize secondary distortion. In group 1 (skeletal types I and IIA), 10 children underwent elongation and lengthening of the mandible. In group 2 (skeletal types IIB and III), 10 children had total construction of a new temporomandibular joint and mandibular ramus with rib grafts and costochondral junction. In both groups, an open bite was created on the affected side to provide space for tooth eruption and downward growth of the middle face. The mean follow-up was 50.9 months (18 to 117 months) in group 1 and 45 months (18 to 50 months) in group 2. Analysis of our early results showed that all patients have had downward growth of the midface on the affected side. All five patients in group 1, followed to complete closure of the surgically created open bite, have maintained a level occlusal plane. In group 2, the one patient followed to completion of facial growth continues to have a level occlusal plane and facial symmetry. Appropriately timed mandibular construction and/or elongation in children with hemifacial microsomia is safe and effective. There is a decrease in secondary deformity on the affected side, and the eventual overall facial growth is optimized. Some group 2 children will need secondary elongation and augmentation of the mandible. Nevertheless, this study demonstrates that early mandibular correction may obviate the need for maxillary and orbital procedures in adulthood.     

The effect of muscle transplantation after unilateral partial facial paralysis on craniofacial growth and development: relationship between muscle and nerve histomorphometric findings

Muscle transplantation has become an indispensable tool to restore the smile in patients with long-standing or congenital facial paralysis. However, little is known of the effect of this surgical intervention on craniofacial growth and development or of the adaptation of the transplant to its recipient site under circumstances of growth. The present study investigates these phenomena in the rabbit model. Twelve-day-old New Zealand White rabbits were randomly assigned to three experimental groups. The control group was used to study normal craniofacial growth and development (n = 15). In the nerve ablation group, unilateral paralysis of the buccal branches of the facial nerve was surgically induced (n = 15). In the transplant group, the surgically induced unilateral paralysis of the buccal branches was immediately followed by a neuromuscular graft (n = 12). All animals were operated on at the age of 12 days, and follow-up evaluations were performed at the ages of 2 months and 6 months. Computerized dorsoventral roentgencephalometric and computed tomography investigations were performed at both ages. Nerve and muscle histomorphometric measurements were performed at the age of 6 months to relate the quality of nerve and muscle regeneration to the growth parameters. The roentgencephalometric measurements revealed that analogous disturbed parameters were present in the nerve ablation and the transplant groups. However, in the transplant group, an additional significant effect of time between 2 and 6 months was seen for some parameters. This resulted in significant differences between the nerve ablation and transplant groups at 6 months for these parameters. Computed tomography measurements showed no significant differences in maxillary or mandibular volume in the transplant group compared with the control or nerve ablation groups. However, a significantly diminished increase in bone volume existed in the transplant group for the time period between 2 and 6 months in comparison with the control and nerve ablation groups. Muscle histomorphometric findings revealed a significant change in muscle fiber composition in the graft compared with the normal latissimus dorsi muscle; this was due to a major decrease in type IIB fibers, with an increase in type I and type IIA fibers. Compared with the normal zygomaticoauricular muscle, the amount of type I fibers was significantly increased. No fiber atrophy was found. Macroscopically, the transplanted muscle failed to increase its length during growth. Nerve histomorphometric findings demonstrated a normal amount of nerve fibers; however, they had significantly decreased diameters and reduced myelin areas. The nerve histomorphometric parameters were related to the muscle histomorphometric findings, which in turn were related to craniofacial growth disturbances. These findings suggested that the main growth differences between the transplant group and the control group may have been due to altered nerve function influencing muscle function. Scar tissue formation and the development of more intense muscle activity later are suggested as the causes of the additional effect of time between 2 and 6 months for the several parameters in the transplant group. Reasons for the failure of complete conversion of the graft to a fast muscle and the failure of the transplant to elongate during growth are discussed.     

Reconstruction of the cranial musculature and masticatory function of the Pleistocene panamerican ground sloth Eremotherium laurillardi (Mammalia,Xenarthra, Megatheriidae)

Cranial musculature, dental function and mandibular movement patterns in Eremotherium laurillardi were reconstructed from the examination of crania and dentitions. Size, shape and pattern of muscle divisions were reconstructed from the examination of bony rugosities indicating muscle attachments. Details of masticatory muscle structure and function were based on dissections of the tree sloths Bradypus and Choloepus. Among sloths, masticatory muscles in E. laurillardi demonstrate a different synergist–antagonist pattern, reflecting greater emphasis on mediolateral mandibular movements. Eight cranial character complexes (anterior facial, zygomatic arch, superficial masseter, deep masseter–zygomaticomandibularis, pterygoid, temporal, occipital and occlusal) determined by interrelated contributions of each component made to group functions were identified. An elongate anterior face and predental spout in E. laurillardi allowed protrusion of a long narrow tongue at small degrees of gape, reflecting a probably ancestral xenarthran condition. Gape minimisation, in conjunction with the mediolaterally directed masticatory stroke in E. laurillardi, was a unique solution to increase masticatory efficiency by permitting molariform tooth shearing surfaces to remain in or near occlusion for a greater percentage of each chewing cycle.     

Evolution of anthropoid jaw loading and kinematic patterns

Major transformations in the skull and masticatory system characterized the evolution of crown anthropoids. To offer further insight into the phylogenetic and arguably adaptive significance of specific primate mandibular loading and kinematic patterns, allometric analyses of metric parameters linked to masticatory function are performed within and between 47 strepsirhine and 45 recent anthropoid species. When possible, basal anthropoids are considered. These results are subsequently integrated with prior experimental and morphological work on primate skull form. As compared to strepsirhines, crown anthropoids have a vertically longer ascending ramus linked to a glenoid and condyle positioned relatively higher above the occlusal plane. Interestingly, anthropoids and strepsirhines do not exhibit different mean ratios of condylar to glenoid height, which suggests that both clades are similar in their ability to evenly distribute occlusal contacts and perhaps forces along the postcanine teeth. Thus, given the considerable suborder differences in the scaling of both glenoid and condylar height, we argue that much of this variation in jaw-joint height is linked to suborder differences in relative facial height due in turn to increased encephalization, basicranial flexion, and facial kyphosis in anthropoids. Due to a more elongate ascending ramus, anthropoids evince more vertically oriented masseters than like-sized strepsirhines. Having a relatively longer ramus and a more medially displaced lateral pterygoid plate, crown anthropoids exhibit medial pterygoids oriented similar to those of strepsirhines, but with a variably longer lever arm. As anthropoid masseters are less advantageously placed to effect transverse movements/forces, we argue that balancing-side deep-masseter activity underlying a wishboning loading regime serves to increase, or at least maintain, transverse levels of jaw movement and occlusal force at the end of the masticatory power stroke. Crown anthropoids are also more isognathic and isodontic than strepsirhines. A consideration of early anthropoids suggests that the crown anthropoid masticatory pattern, i.e., more vertical masseters due to a high condyle as well as greater isognathy and isodonty, occurred stepwise during stem anthropoid evolution. This appears to correspond to a more transverse, and perhaps progressively larger, power stroke across oligopithecids, parapithecids, and propliopithecids.     

Craniofacial abnormalities in osteopetrosis with precocious manifestations: report of a case with serial cephalometric roentgenograms

Serial roentgencephalograms were taken (from the age of 2 to 8 years) of a female patient with malignant osteopetrosis. The roentgencephalograms were compared to those of a control patient with cleft lip and to other normative data. The calvaria of the osteopetrosis patient was very thick, increasing with age. The intracranial space was reduced in volume, resulting in compression of the brain. Roentgencephalometric characteristics of the facial skeleton included orbital hypertelorism, defective horizontal and vertical growth of the middle and lower face, and poorly developed dentoalveolar structures. The mandibular body was short in contrast to the wide ramus, both resulting from defective resorption of the anterior ramal border. A cone-shaped structure in the mandible extending from the condylar process into the ramus was noted. This was believed to consist of remnants of unresorbed, heavily calcified secondary cartilage constituting part of the condylar process present since intrauterine life. Recent treatment of malignant osteopetrosis by bone marrow transplantation early in life has resulted in some cases in normalization of bone structure and marrow. Serial roentgencephalometry provides a sensitive method of assessing craniofacial development in cases of osteopetrosis and presumably can be used to evaluate the effects of therapy.     

Microscopic study of the rabbit mandibular periosteum and attached structures.

The structure of the mandibular periosteum in rabbits of different ages has been studied by different histological staining techniques and polarization microscopy. The periosteum consisted of two layers. From the inner, cellular layer the functional state could be determined. A reproducible pattern of resorptive and depository areas was found on the bony surface. In the outer, fibrous periosteal layer, collagenous and elastin fibers were running in distinct directions. The masticatory muscles appeared to be attached directly endomysially or indirectly endomysially, via the perimysium or tendinous attachment. From the periosteal structures and the characteristics of muscular fiber attachments to the bone and periosteum, especially in the ramal and condylar areas, it could be concluded that a mechanical influence of the periosteum on condylar growth is very well possible, which will probably vary during life. The masticatory muscles seemed to be only of minor influence in condylar activity.