Painful Stimulation of the Temple Induces Nausea, Headache and Extracranial Vasodilation in Migraine Sufferers

To determine whether painful stimulation of the temple would induce nausea, ice was applied to the temple for 30 s, three times at 4-min intervals in 23 migraine sufferers and 22 age- and sex-matched controls. On one occasion, the ice was applied in the presence of residual motion sickness induced by optokinetic stimulation. On another occasion, the ice application was not preceded by optokinetic stimulation (the baseline condition). In the baseline condition, nausea had developed in migraine sufferers but not controls by the third application of ice. In the presence of residual motion sickness, each painful stimulus intensified nausea and headache in migraine sufferers whereas symptoms were minimal in controls. Changes in frontotemporal pulse amplitude were monitored with photoelectric pulse transducers. The extracranial blood vessels dilated in migraine sufferers but not controls before the first application of ice in the baseline condition, presumably due to anticipatory anxiety. In contrast, the ice application did not provoke extra-cranial vasodilation in either group after optokinetic stimulation. The findings show that susceptibility to nausea and stress-induced extracranial vascular hyper-reactivity are associated with the migraine predisposition. They also suggest that head pain might intensify gastrointestinal disturbances during attacks of migraine.

Enhanced Activation of Canonical Wnt Signaling Confers Mesoderm-Derived Parietal Bone with Similar Osteogenic and Skeletal Healing Capacity to Neural Crest-Derived Frontal Bone

Bone formation and skeletal repair are dynamic processes involving a fine-tuned balance between osteoblast proliferation and differentiation orchestrated by multiple signaling pathways. Canonical Wnt (cWnt) signaling is known to playing a key role in these processes. In the current study, using a transgenic mouse model with targeted disruption of axin2, a negative regulator of cWnt signaling, we investigated the impact of enhanced activation of cWnt signaling on the osteogenic capacity and skeletal repair. Specifically, we looked at two calvarial bones of different embryonic tissue origin: the neural crest-derived frontal bone and the mesoderm-derived parietal bone, and we investigated the proliferation and apoptotic activity of frontal and parietal bones and derived osteoblasts. We found dramatic differences in cell proliferation and apoptotic activity between Axin2^-/- and wild type calvarial bones, with Axin2^-/- showing increased proliferative activity and reduced levels of apoptosis. Furthermore, we compared osteoblast differentiation and bone regeneration in Axin2^-/- and wild type neural crest-derived frontal and mesoderm-derived parietal bones, respectively. Our results demonstrate a significant increase either in osteoblast differentiation or bone regeneration in Axin2^-/- mice as compared to wild type, with Axin2^-/- parietal bone and derived osteoblasts displaying a “neural crest-derived frontal bone-like” profile, which is typically characterized by higher osteogenic capacity and skeletal repair than parietal bone. Taken together, our results strongly suggest that enhanced activation of cWnt signaling increases the skeletal potential of a calvarial bone of mesoderm origin, such as the parietial bone to a degree similar to that of a neural crest origin bone, like the frontal bone. Thus, providing further evidence for the central role played by the cWnt signaling in osteogenesis and skeletal-bone regeneration.

Contrasting phase effects on vestibular evoked myogenic potentials (VEMPs) produced by air- and bone-conducted stimuli

We have studied the effects of stimulus phase on the latency and amplitude of cVEMPs and oVEMPs by reanalysing data from Lim et al. (Exp Brain Res 224:437-445, 2013) in which alternating phase was used. Responses for the different initial stimulus phase, either positive or negative, were separated and reaveraged. We found that the phase (compressive or rarefactive) of AC 500-Hz stimuli had no significant effect on either latency or amplitude of the responses. Conversely, phase (positive = motor towards subjects) did alter the effects of BC 500-Hz stimulation. For cVEMPs, phase consistently affected initial latency with earlier responses for positive stimuli, while, for stimulation at the mastoid, negative onset phase gave larger responses. For the oVEMP, effects were different for the two sites of BC stimulation. At the forehead, the response appeared to invert, whereas at the mastoid there appeared to be a delay of the initial response. Related to this, the effect of phase for the two sites was opposite: at the mastoid, positive responses were earlier but negative were larger (particularly for long stimuli). At the forehead, the effect was the opposite: negative onset stimuli evoked earlier responses, whereas positive onset evoked larger responses. These findings indicate a basic difference in the way that AC and BC stimuli activate vestibular receptors and also indicate that the effects of phase of BC stimulation depend on location. Stimulus alternation does little to affect the response to AC stimulation but obscures the effects of BC stimuli, particularly for the oVEMP.

Pre-activation and muscle activity during frontal impact in relation to whiplash associated disorders

OBJECTIVE

For the evaluation of neck injury the relative distance was observed between a marker placed on the forehead and a marker placed on the shoulder and also by change of the angle. To compare the severity of head injury a value of maximum head acceleration was used, HIC and a 3 ms criterion. All criteria were related to the activity of musculus sternocleidomastoideus and musculus trapezius in a situation of expected or unexpected impact.

MATERIALS AND METHODS

The situation was recorded using a Qualisys system, head acceleration of probands in three axes was recorded using the accelerometer, activity of neck muscles was monitored by a mobile EMG.

RESULTS

Maximum head acceleration was 12.1 g for non-visual and 8.2 g for visual. HIC36 was 5.7 non visual and 4.0 for visual. 3-ms criterion was 11.5 g for non-visual and 7.8 g for visual. The average time of muscle activation of the observed group without visual perception is 0.027 s after hitting an obstacle, with visual perception 0.127 s before the crash.

CONCLUSIONS

Kinematic values indicate more favourable parameters for neck injuries for visual. Head injury criteria show an average decrease of about 30% for visual. We can conclude that the visual perception means a significant increase in pre-activation of the observed muscle group of almost 400% and lower activation in both following phases of approximately 40%.

Stress and displacement patterns in the craniofacial skeleton with rapid maxillary expansion: A finite element method study

INTRODUCTION

The purpose of this finite element study was to evaluate stress distribution along craniofacial sutures and displacement of various craniofacial structures with rapid maxillary expansion (RME) therapy.

METHODS

The analytic model for this study was developed from sequential computed tomography scan images taken at 2.5-mm intervals of a dry young human skull. Subsequently, a finite element method model was developed from computed tomography images by using AutoCAD software (2004 version, Autodesk, Inc, San Rafael, Calif) and ANSYS software (version 10, Belcan Engineering Group, Downers Grove, Ill).

RESULTS

The maxilla moved anteriorly and downward and rotated clockwise in response to RME. The pterygoid plates were displaced laterally. The distant structures of the craniofacial skeleton--zygomatic bone, temporal bone, and frontal bone--were also affected by transverse orthopedic forces. The center of rotation of the maxilla in the X direction was somewhere between the lateral and the medial pterygoid plates. In the frontal plane, the center of rotation of the maxilla was approximately at the superior orbital fissure. The maximum von Mises stresses were found along the frontomaxillary, nasomaxillary, and frontonasal sutures. Both tensile and compressive stresses could be demonstrated along the same suture.

CONCLUSIONS

RME facilitates expansion of the maxilla in both the molar and the canine regions. It also causes downward and forward displacement of the maxilla and thus can contribute to the correction of mild Class III malocclusion. The downward displacement and backward rotation of the maxilla could be a concern in patients with excessive lower anterior facial height. High stresses along the deep structures and the various sutures of the craniofacial skeleton signify the role of the circummaxillary sutural system in downward and forward displacement of the maxilla after RME.

What Wrapped Perichondrial and Periosteal Grafts Offer as Regenerators of New Tissue

The major goals in contour restoration procedures are to re-establish the desired contour with the use of resilient and durable materials that can be easily found and harvested. Cartilage grafts are commonly used for these purposes though they often possess a problem of donor site morbidity and shortage of quantity. The neo-cartilage formation capacities of both perichondrium and periosteum are well-known. We aimed to optimize both the amount and quality of the newly forming tissue from perichondrial and periosteal grafts. For this purpose the grafts were wrapped on themselves. Placement of oxidized regenerated cellulose (ORC) within graft layers was performed in two groups with the aim of giving support to the regenerating tissue, and increasing the connective tissue formation within the graft layers. Three-month-old New Zealand white rabbits were used. Group 1 ear perichondrial, and Group 2 calvarium periosteal grafts of 1.4 x 2.4 cm were harvested, folded on themselves, and sutured at the edges to create closed pockets. 0.8 x 0.8 cm sized ORC sheets were placed inside the pockets before wrapping in Group 3 perichondrial and Group 4 periosteal grafts. 0.2-mL autogenous blood was injected in each pocket. All grafts were transplanted under the abdominal muscle fascia, and harvested after 6 weeks. Volumes and weights of wrapped perichondrial grafts were higher than their periosteal counterparts either with or without the inclusion of ORC. Grafts with ORC (Groups 3 and 4) were heavier than the grafts lacking ORC (Groups 1 and 2), in a statistically significant manner (P </= 0.01). Histologically, the inclusion of ORC in both perichondrial and periosteal grafts resulted in an increased amount of fibrosis, yet did not preclude neo-cartilage formation.

Stresses at the cranial base induced by rapid maxillary expansion

OBJECTIVE

An analysis of the distribution of stresses at the juvenile and adult cranial base after implementation of a rapid palatal suture expansion was the goal of this study. Of particular interest were stresses occurring near the cranial foramina containing vulnerable structures.

MATERIALS AND METHODS

The stresses were simulated and analyzed using a finite elements model of the human cranial base. The model consisted of several skull bones (sphenoid, frontal bone, occipital bone, and the two temporal bones) with a total of 41,556 finite elements. To illustrate the differences between reactions in the juvenile and the adult, the differing bone elasticity was depicted as variations in the modulus of elasticity.

RESULTS

At the juvenile cranial base only moderate stresses occurred during rapid palatal suture expansion, apparently precluding the likelihood of any serious complications in the area of the foramina. The situation in the adult, however, was different. Because of the reduced elasticity of the bony structures, considerable stress already occurred on light bending of the pterygoid process, especially in the area of the round foramen, the oval foramen, and the superior orbital fissure, all of which might lead to microfractures with injury of nervous and vascular structures.

CONCLUSIONS

The lower the bone elasticity on carrying out a rapid palatal suture expansion, the more important safety measures are for protecting the cranial base. For this reason the pterygomaxillary connection should be severed on both sides in adults when carrying out a surgically assisted palatal suture expansion.

Nanomechanical properties of facial sutures and sutural mineralization front

The mechanical properties of craniofacial sutures have rarely been investigated. Three facial sutures-the pre-maxillomaxillary (PMS), the nasofrontal (NFS), and the zygomaticotemporal (ZTS)-and their corresponding sutural mineralization fronts in 8 young New Zealand White rabbits were subjected to nano-indentation with atomic force microscopy as a test of the hypothesis that they have different mechanical properties. The average elastic modulus of the PMS was 1.46 +/- 0.24 MPa (mean +/- SD), significantly higher than both the ZTS (1.20 +/- 0.20) and NFS (1.16 +/- 0.18). The average elastic moduli of sutural mineralization fronts 30 micro m away were significantly higher than their corresponding sutures and had the same distribution pattern: the PMS (2.07 +/- 0.24 MPa) significantly higher than both the ZTS (1.56 +/- 0.29) and NFS (1.71 +/- 0.22). Analysis of these data suggests that facial sutures and their immediately adjacent sutural mineralization fronts have different capacities for mechanical deformation. The elastic properties of sutures and sutural mineralization fronts are potentially useful for improving our understanding of their roles in development.

Msx2 and Twist cooperatively control the development of the neural crest-derived skeletogenic mesenchyme of the murine skull vault

The flat bones of the vertebrate skull vault develop from two migratory mesenchymal cell populations, the cranial neural crest and paraxial mesoderm. At the onset of skull vault development, these mesenchymal cells emigrate from their sites of origin to positions between the ectoderm and the developing cerebral hemispheres. There they combine, proliferate and differentiate along an osteogenic pathway. Anomalies in skull vault development are relatively common in humans. One such anomaly is familial calvarial foramina, persistent unossified areas within the skull vault. Mutations in MSX2 and TWIST are known to cause calvarial foramina in humans. Little is known of the cellular and developmental processes underlying this defect. Neither is it known whether MSX2 and TWIST function in the same or distinct pathways. We trace the origin of the calvarial foramen defect in Msx2 mutant mice to a group of skeletogenic mesenchyme cells that compose the frontal bone rudiment. We show that this cell population is reduced not because of apoptosis or deficient migration of neural crest-derived precursor cells, but because of defects in its differentiation and proliferation. We demonstrate, in addition, that heterozygous loss of Twist function causes a foramen in the skull vault similar to that caused by loss of Msx2 function. Both the quantity and proliferation of the frontal bone skeletogenic mesenchyme are reduced in Msx2-Twist double mutants compared with individual mutants. Thus Msx2 and Twist cooperate in the control of the differentiation and proliferation of skeletogenic mesenchyme. Molecular epistasis analysis suggests that Msx2 and Twist do not act in tandem to control osteoblast differentiation, but function at the same epistatic level.

Electronic removal of encrustations inside the Steinheim cranium reveals paranasal sinus features and deformations, and provides a revised endocranial volume estimate

Features in the endocranium, as revealed by computed tomography (CT) scans of largely complete mid-Pleistocene crania, have helped elucidate unexpected affinities in the genus Homo. Because of its extensive encrustations and deformations, it has been difficult to repeat such analyses with the Steinheim cranium. Here, we present several advances in the analysis of this Homo heidelbergensis cranium by applying filter algorithms and image editing techniques to its CT scan. First, we show how the encrustations have been removed electronically, revealing interesting peculiarities, particularly the many directions of the deformations. Second, we point out similarities and differences between the frontal and sphenoidal sinuses of the Steinheim, Petralona, and Broken Hill (Kabwe) crania. Third, we assess the extent of the endocranial deformations and, fourth, their implications for our estimation of the braincase volume.

Transmission of bone strain in the craniofacial bones of edentulous human skulls upon dental implant loading

STATEMENT OF PROBLEM

Little is known about how craniofacial bones that are distant from dental implants are loaded. Whether bone experiences different strain when implants of different diameters are loaded is unknown.

PURPOSE

This study was designed to (1) characterize bone strain both adjacent to and distant from dental implants and (2) compare bone strain in response to the same loads on small-diameter and large-diameter implants.

MATERIAL AND METHODS

On 4 edentulous, dry adult human skulls, the buccopalatal midpoint of the edentulous occlusal surface was marked unilaterally in the maxillary first molar area with a round bur. A hole for implant placement was prepared, and 2 self-tapping titanium implants (3.75 x 7 mm and 4 x 7 mm) were placed in the same location and at the same orientation, one after the other. A 4-mm-long titanium abutment was connected to the implant. Each implant was loaded 10 degrees lateral to its longitudinal axis, simulating a lateral occlusal force in 3 of the skulls. In skull 2, loading was along the longitudinal axis of the implant and simulated a vertical occlusal force. The magnitude of the ramp forces was 0 to 100 N. Uniaxial strain gages and/or 3-element strain rosettes were implanted in the supramolar cortical bone, the supraincisor cortical bone, the zygomaticomaxillary suture, and the zygomaticotemporal suture. All strain gages/rosettes were excited with 500 mV DC, and the output signals were recorded with a strain conditioner. Tensile strain was expressed as positive values and compressive strain as negative values. Student t tests were used to test for normal distribution of bone strain within each skull; Wilcoxon tests were applied for skewed distribution between small- and large-diameter implants and between 50-N and 100-N loads (P<or=.05).

RESULTS

Bone strain both adjacent to and distant from the implants was complex: compressive strain in the buccal cortical bone superior to the implants; tensile strain in the ipsilateral supraincisor cortical bone but compressive strain in the contralateral supraincisor cortical bone; and tensile strain anterior to the zygomaticotemporal suture but compressive strain posterior to the suture. With the same applied loads, bone strain was higher for large-diameter implants than for small-diameter implants for all the above cortical locations (P<.01 to.001) except posterior to the zygomaticotemporal suture.

CONCLUSION

Within the limitations of this study, bone strain resulting from dental implant loading was distributed to cortices not only adjacent to but also distant from dental implants. The large-diameter implant was more facilitative of stress transfer to cortical bone than the small-diameter implant tested.

The morphology of the European miocene hominid frontal bone: functional, developmental and phylogenetic considerations

This paper re-interprets the morphology of fossil and extant hominid frontal bones in light of development, functional and phylogenetic considerations. It is argued that the suggested inclusion of Hispanopithecus and Ankarapithecus as members of the Ponginae (which has partly been based on frontal bone morphology) remains problematic as their similarity with other members of the Ponginae is likely the result of distinct developmental processes resulting in Hispanopithecus and Ankarapithecus sharing an anatomical analogy with this subfamily. Whether this can be used to argue against their inclusion within the Ponginae remains debatable, as we still do not appreciate degrees of developmental variability within and between taxa, nor their phylogenetic significance in closely related taxa. The frontal bone morphology as observed in Hispanopithecus and Ankarapithecus, however, suggests that they share a sister-group relationship. In terms of the Homininae, Graecopithecus is supported as a likely member of this subfamily, while Dryopithecus is considered as a primitive member of the Hominidae.

The timing of physiologic closure of the metopic suture: a review of 159 patients using reconstructed 3D CT scans of the craniofacial region

PURPOSE

The purpose of this study was to determine the normal physiologic timing of the closure of the metopic suture in non-craniosynostotic patients.

METHODS

This clinical study involved a consecutive series of infants and young children who underwent 3D CT-scan evaluation for deformational plagiocephaly or suspected traumatic head injury. All patients with evidence of craniosynostosis were excluded from the study. Every infant and child referred to our Craniofacial Team for deformational plagiocephaly between 1997 and 2000 (n = 84) received a baseline pre-treatment 3D CT-scan of the head. Our study also included a series of selected pediatric trauma patients (1 to 24 months of age) between 1997 and 2000 (n = 75) who received CT-scan to rule out head injury. The CT scan results were reviewed for closure of metopic suture by a single observer.

RESULTS

The earliest evidence of metopic suture closure was at 3 months, the age at which 33% of patients (4/12) were closed. At 5 months of age, 59% (13/22) of sutures were closed. At 7 months of age, 65% (15/23) were closed. At 9 months of age, 100% (10/10) were closed. All patients greater than 9 months of age within the study had complete metopic suture closure.

CONCLUSION

Our findings suggest that normal or physiologic closure of the metopic suture occurs much earlier than what has been previously described. This study establishes that metopic fusion may normally occur as early as 3 months of age, and that complete fusion occurred by 9 months of age in all patients in our series. Therefore, 3-D CT scans showing complete closure of the metopic suture at an early age (3 to 9 months) cannot be considered as evidence of metopic synostosis, and thus, should not be the decisive factor for early surgical intervention.

Absolute and relative facial pressure-pain thresholds in healthy individuals

AIMS

To investigate and compare absolute pressure-pain threshold (PPT) levels and ratios between craniofacial test and reference sites during consecutive PPT recordings, as well as over a 6-month period, in healthy individuals. This study also investigated PPT differences between genders and the clinical usefulness of different reference sites in the craniofacial region.

METHODS

Twelve female and 12 male healthy individuals participated in the first examination. Six months later, 9 females and all of the males returned for a second examination. An electronic algometer was used to make 5 consecutive recordings of PPTs with a 2-minute interval at 3 reference sites: mental protuberance (PRO), first metacarpal bone (MET), and frontal bone (FRO), as well as at 3 test sites: temporomandibular joint, masseter muscle, and temporalis muscle.

RESULTS

Absolute PPTs decreased significantly for all test sites during the 5 recordings, while they increased significantly between the examinations. No ratio with FRO as a reference site changed significantly. The males had significantly higher absolute PPTs than the females at PRO and FRO sites.

CONCLUSION

This study shows that absolute PPT levels in healthy individuals change significantly during consecutive PPT recordings, as well as over a 6-month period; this limits the usefulness of such measurements. This study also shows that the use of relative PPTs with the FRO as a reference site is useful, both for comparison between groups and for longitudinal studies.

The load-displacement characteristics of neonatal rat cranial sutures

OBJECTIVE

Recently several centers have attempted to distract the craniofacial skeleton in infants with craniosynostosis. To effectively achieve this goal, we must first understand the normal sutural response to tensile forces. The objective of this study was to determine the load-displacement characteristics of neonatal rat sutures.

METHODS

Thirty cranial sutures were harvested from 1-week-old Wistar rats (10 each coronal, posterior frontal, and sagittal). The width of the harvested bone-suture-bone construct was standardized to 4 mm. The specimens, kept moist, were mounted fresh and distracted at 10 microm/sec until rupture using a Vitrodyne V1000 universal tester. Standard load-displacement curves were constructed. The stiffness, defined as tensile force/change in suture length, and the ultimate stress, defined as tensile force at suture rupture/cross sectional area, were calculated.

RESULTS

These sutures demonstrated classical viscoelastic behavior. During the elastic phase, they elongated approximately 1 microm for every 1 g of force (10(4) N/m). The ultimate tensile stress was approximately 4 MN/m2. The estimated mean elastic modulus was 10 megapascals. The posterior frontal sutures were significantly less stiff than the other two sutures (Kruskal-Wallis nonparametric analysis of variance, p = .0023). The difference in the ultimate stress was also significant (p = .0201).

CONCLUSIONS

This study provides data regarding the basic mechanical behavior of neonatal cranial sutures in a mammalian system.

Strain gauge analysis of the frontozygomatic region of the zygomatic complex

PURPOSE

This study evaluates the biomechanical consequences of physiologic forces acting on the frontozygomatic suture region, with the ultimate goal of defining appropriate fixation techniques and improving the surgical management of this complex anatomic region.

MATERIALS AND METHODS

Single foil strain gauges were bonded to the cortical surface of the frontal process of the zygoma in 13 subadult Cercopithecus africanus. Subdermal electrodes were used to induce tetanic contractions of the jaw elevator muscles, and bite force was measured using a twin-beam bite force transducer placed between the teeth. Microstrain was simultaneously measured and recorded.

RESULTS

Tensile strains predominated in the region of the frontal process of the zygoma, with balancing side strains twice as large as working side strains; incisal strains were intermediate.

CONCLUSIONS

The tensile strains observed in the frontozygomatic region contradict the concept of this area as a "stress riser" for compressive occlusal forces, and supports the use of compression plate osteosynthesis for improved stabilization of fractures in this region.

Cranial bone apposition and ingrowth in a porous nickel-titanium implant

A 5 x 5 x 1-mm uncoated porous nickel-titanium (nitinol) implant was placed 4 mm to either side of the midsection of the frontal bone and 4 mm anterior to the coronal suture of the cranial bone of New Zealand White rabbits. In the other frontal location, a 5 x 5 x 1-mm coralline hydroxyapatite (HA) (Interpore 200, a well-known craniofacial implant material) implant was fitted. Rabbits were killed at each of three postsurgical intervals (2, 6, and 12 weeks), and the implants were evaluated for gross biocompatibility, bony contact, and ingrowth. No adjacent macrophage cells were observed for either implant type, and overlaying soft tissues and connective tissues readily adhered to the implants even after 2 weeks. Both materials made bone contact with the surrounding cranial hard tissue, and percent ingrowth increased with surgical recovery time. Measurements of microhardness and bone histologic parameters indicated that bone in contact with and grown into the implants was similar in properties to the surrounding cranial bone. Porous nitinol implants therefore appear to allow for significant cranial bone ingrowth after as few as 12 weeks, and thus nitinol appears to be suitable for craniofacial applications. Compared to HA, the nitinol implants demonstrated a trend for less total apposition and more total ingrowth after 6 and 12 weeks of implantation.

Controlled bending of cranial bone grafts: a simple surgical technique

The cranium serves as a primary bone graft donor site in reconstructive craniofacial surgery. However, the mechanical properties of cranial bone predispose to fragmentation when excessive bending forces are applied, or to a return to the original shape when bending forces are insufficient. The precise and sustained contouring of cranial bone therefore remains a practical clinical problem. This paper describes a simple surgical technique which relies upon the application of a miniplate to the cortical surface of the cranial bone segment prior to bending. The miniplate serves to reinforce the segment, allowing accurate shaping of cranial bone and maintenance of the newly acquired contour.

Elastic properties of human supraorbital and mandibular bone

Elastic constants, including the elastic modulus, the shear modulus, and Poisson's ratio, were measured on human craniofacial bone specimens obtained from the supraorbital region and the buccal surfaces of the mandibles of unembalmed cadavers. Constants were determined using an ultrasonic wave technique in three directions relative to the surface of each sample: 1) normal, 2) tangential, and 3) longitudinal. Statistical analysis of these elastic constants indicated that significant differences in the relative proportions of elastic properties existed between the regions. Bone from the mandible along its longitudinal axis was stiffer than bone from the supraorbital region. Directional differences in both locations demonstrated that cranial bone was not elastically isotropic. It is suggested that differences in elastic properties correspond to regional differences in function.

Masticatory-stress hypotheses and the supraorbital region of primates

The purpose of this study is to test various masticatory-stress hypotheses about the evolution and function of well-developed browridges of higher primates. This was done by measuring and analyzing patterns of in vivo bone strain recorded from three-element rosette strain gages bonded to the supraorbital region and to other portions of the bony face of Macaca fascicularis and Papio anubis during mastication and incision. The magnitude and direction of the principal strains recorded support Endo's hypothesis that the supraorbital region during mastication and incision is bent in the frontal plane (Endo, 1966). Our data do not, however, support his hypothesis that the supraorbital region is bent more during incision than during mastication. The data also demonstrate that overall levels of supraorbital strain are not larger in more prognathic subjects. Most importantly, the data indicate that the supraorbital region of nonhuman catarrhines is strained very little during mastication and incision. This indicates that there is much more supraorbital bone than is necessary both to counter masticatory loads and to provide an adequate safety factor to failure for these loads. This in turn suggests that the macaque and baboon browridges can be considerably reduced in size and still maintain these required structural characteristics. Thus, our experiments provide no support whatsoever for those hypotheses that directly link browridge morphology to masticatory stress (cf. Endo, 1966; Russell, 1983, 1985). A recent review of Endo's original work indicates that this latter statement is also true for humans (Picq and Hylander, 1989). We conclude, therefore, that there is no good reason to believe that enlarged browridges in living and/or fossil primates are structural adaptations to counter intense masticatory forces. The evolution of browridge morphology in primates is best explained on the basis of factors related to the position of the brain relative to the orbits (Moss and Young, 1960). When these structures are widely separated, as in gorillas, the large intervening space must be bridged with bone. In addition, enough bone must be present within the supraorbital and bridged regions to prevent structural failure due to non-masticatory external forces associated with highly active primates (e.g., accidental traumatic forces applied to the orbits and neurocranium). This requirement results in both pronounced browridges and in much more supraorbital bone than is necessary to counter routine cyclical stress during mastication and incision. This in turn explains why bone strains recorded from the supraorbital region are extremely small relative to other portions of the primate face during mastication and incision.

[Mechanical impedance of the human mastoid and forehead--a critique of the mechanical coupler of the IEC373]

Mechanical impedances of human mastoids and foreheads were measured on frequencies from 250 to 6300 Hz for 80 young adults by means of B&K impedance head (#8000) and shaker (#4810) as main parts of the measuring setup. The measurements revealed the following problems in the IEC373 (1971/1981) which had defined the mechanical impedance characteristics of the mechanical coupler for calibration of bone vibrators in audiometric use. The average impedance levels of the mastoids differ significantly from those of the foreheads in middle and high frequencies. The impedance levels of the IEC373 mechanical coupler are higher than those of the present measurements of the mastoids and the foreheads. The differences exceeded the tolerance limits of IEC373 (1981) in every frequency. These findings strongly suggest that the coupler is neither the artificial mastoid nor the artificial forehead but a coupler having a specified impedance, therefore, disregard for effect of the type of bone vibrator on the Reference Equivalent Threshold Force Level, as seen in ISO7566, should be revised and that the RETFL should be determined for an each type of bone vibrator.

Frontal distribution of early cortical somatosensory evoked potentials to median nerve stimulation

The topography of early frontal SEPs (P20 and N26) to left median nerve stimulation was studied in 30 normal subjects and 3 patients with the left frontal bone defect. The amplitudes of P20 and N26 were maximum at the frontal electrode (F4) contralateral to the stimulation and markedly decreased at frontal electrodes ipsilateral to the site of stimulation. There was, however, no latency difference of P20 and N26 between ipsilateral and contralateral frontal electrodes. These results suggest that the origin of the ipsilateral and contralateral P20 and N26 is the same. The wide distribution of P20 and N26 over both frontal areas could be explained by assuming a smearing effect from generators actually located in the rolandic fissure and motor cortex.

Biomechanical effects of maxillary protraction on the craniofacial complex

The deformational effects on the human skull resulting from maxillary protraction were examined by means of strain gauges and displacement transducers. A maxillary protraction appliance was used that included a reverse headgear attached to the maxillary first molars. The protraction forces that were applied to this appliance were parallel to the occlusal plane at the following locations: the height of the maxillary arch, 5 mm above the palatal plane, and 10 mm above the Frankfort horizontal plane. The results indicated that protraction forces at the level of the maxillary arch produced an anterior rotation and forward movement of the maxilla, protraction forces 10 mm above the Frankfort horizontal plane produced a posterior rotation of the maxilla with a forward movement of nasion, and protraction forces 5 mm above the palatal plane produced a combination of parallel forward movement and a very slight anterior rotation of the maxilla. Moreover, constriction of the anterior part of the palate occurred in all cases.

A contribution on revisional and drainage of the frontal sinus by osteoplastic operation

Osteoplasty of the frontal sinus (bone lid operation) consists of the excision of a piece of bone from the anterior surface of the frontal sinus. A circular saw with an extremely fine saw blade is used. The ensuing cut is thus extremely narrow and the excised bone lid can be reimplanted exactly, flush with the neighbouring bone from which it was excised. Primary healing takes place without the development of intermediary connective or cartilagenous tissue. Only circumscribed pathological lesions of the diseased mucous membrane are removed. Otherwise, healing is promoted by improved drainage and ventilation. For this purpose a channel leading to the nose is created. In order to ensure that this channel stays open it is lined by dura or mucous membrane. The latter is put into place and fixed by an inflatable balloon acting as a tampon. The balloon is traversed by a tube which guarantees adequate drainage and ventilation during healing of the lining material in the channel.

Calvarial and sutural re-development following craniectomy in the neonatal rabbit

In the present investigation extensive calvariectomy was performed on neonatal rabbits and the subsequent regeneration of the calvarium was followed grossly, radiographically and histologically. The results indicate that regeneration of the calvarium is a gradual process which exhibits a definite pattern and rate. Furthermore, although the sutural articulations re-develop in their proper anatomical positions and exhibit normal histological structure, they tend to synostose earlier than controls. Of perhaps greater biological significance is the apparent importance of the periosteal envelope during the regenerative process. Maintenance of dural integrity during operation, and the re-establishment of pericranial continuity post-operatively, seem to be essential for restoration of normal sutural and skeletal architecture.

Role of periosteum on the fate of pedicle osteocutaneous grafts

Recent studies on the fate of pedicle osteocutaneous grafts have shown that they remain viable and may be actively involved in the mechanics of bone repair. This communication reports on a series of experiments aimed to clarify the role of periosteum in the survival of pedicle-assisted bone grafts. Osteocutaneous grafts were developed in dogs in such a manner as to isolate the implant from normal recipient bone. Free bone grafts were used as controls and a group of pedicle periosteal grafts were studied as potential sources of bone formation. Specimens were evaluated at regular intervals over a 40-week period. The pedicle bone grafts maintained their viability and developed vigorous osteoneogenesis. The process was progressive and eventually resulted in partial substitution of the original graft by new bone of periosteal origin. The free bone grafts were resorbed and no bone formation was obtained in pedicle periosteum specimens. The study provides clear evidence that under experimental conditions no bone contact is needed to maintain the viability of pedicle osteocutaneous grafts. It also shows that the periosteum has the leading role in the restructuring process of these grafts.

Effects of orthodontic intermaxillary Class III mechanics on craniofacial structures. Part I - photoerlastic analysis

The relation between active growth and induced anatomic changes was examined using photoelastic stress techniques. The following can be concluded from this investigation: 1. Utilization of Class III mechanics on the photoelastic skull affected the zygomaticotemporal, zygomaticofrontal and frontomaxillary sutures. 2. The stress trajectories observed in the mandible lead to the conclusion that Class III traction affects mandibular growth and opening, as well as condylar repositioning. 3. Evidence of stress was observed in a section of the condyle due to the external pterygoid muscle. 4. The stress concentrated at the outer surface of the pterygoid plate was due to the action of the external pterygoid muscle. 5. The effect of the simulated Class III traction created concentrations of stress mesial and distal of the second molars and at the apical and midroot areas of first molars.

Remodeling of cancellous bone in young monkeys

Remodeling of the trabeculae in cancellous bone was studied in young monkeys that received multiple weekly injections of lead acetate as a marker. Resorption of old bone and deposition of new bone were demonstrated. The rate of deposition of new bone varied at different sites of the same trabeculae and also at different time intervals of the same site. The total formation time of new bone to fill the trabecular space was estimated.

Sutural development: structure and its response to rapid expansion

This fine structural study of the suture, its development, structure, and response to rapid expansion has shown that the sutural complex is best described in terms of the functional activity of two cell populations, namely, the osteocytic and fibrocytic series, which have the ability to remodel the tissues which they form. It is suggested that the previous detailed descriptions of differences in fiber orientation and vascular distribution reflect functional activity of a suture at any given time rather than immutable anatomic characteristics. Development of the suture and its rapid expansion showed many similarities in that growth during development and orthopedic expansion both separate the joint. If the initial inflammatory aspect of rapid expansion is ignored, the response of the suture is one of osteogenesis and fibrillogenesis, followed finally by remodeling. It is also suggested that sutural expansion involves injury followed by a proliferative repair phenomenon which, in other tissues, usually leads to the formation of scar tissue. However, the ability of sutural connective tissue fibroblasts to remodel ultimately leads to regeneration of the suture. Finally, programmed cell death has been shown to be an important feature in the development of the suture.

[Bone statics of the face: the frontal-sphenoid-pterygoid bone pillars as biomechanic equivalents of the mandible]

In general biomechanics, trabecular osteo-architectonics is considered as a response to the mechanical strains present in the bone (compression or traction). The facial and cephalic skeleton is no exception to this law. The study of the bony architectionic provides the proof, since we have demonstrated in the fixed facial bone mass (at the limits of the facial skeleton and the skeleton of the base of the skull) the biomechanical equivalent of the mandible: the cranio-facial pterygo-spheno-frontal bony pillars. Paired, symmetrical and with a medio-frontal junction, they represent an embryological, anatomical and functional entity. Their ossification (mixed) may be compared to that of the mandible. They are made up of directional trabecular bone which may be analysed by stereology, electron microscope scanning and by strain gauges. Each pillar is made up of: - A part free of musculature corresponding to the supra-orbital frontal arch, which receives the four vertical pillars (naso-maxillary and maxillo-malo-frontal) of the superficial system of the face which transmit to the supra-orbital frontal arch the ascending mechanical strains of mastication registered in the spongy hard palate. The supra-orbital frontal arch is the biomechanical homologue in the fixed facial mass of the tooth bearing bony base of the mandible. - A spheno-pterygoid part, into which are inserted the alimentary muscles of the cephalic region (masticators, velar and superior pharyngeal). There is further functional homology between the ascending ramus of the mandible and the pterygoid greater wings and apophyses complex of the sphenoid. The 2 pterygo-spheno-frontal pillars also participate in the osseous statics of the orbit and the osseous statics of the temporo-mandibular joint. The basi-sphenoid plays a role of first importance in the general statics of the cephalic region. Thus the two pterygo-spheno-frontal pillars, biomechanical homologues of the mandible in the fixed facial mass, underline the functional interdependence of the osseous, dental and muscular systems of the cephalic region, a region which should be viewed as being in a stade of permanent dynamic equilibrium during growth and in the adult.

The effect of heavy orthopedic forces on the sutures of the facial bones

The effect of heavy continuous orthopedic forces was studied in three Saimiri Sciureus (squirrel) monkeys. Two additional monkeys served as controls. The maxillary sutures were investigated microscopically. In addition, the bone markers (tetracycline, Procion Red H-8 BS) served for quantitative evaluation under ultraviolet light. After two weeks slight remodeling activity could be observed. After one month a tremendous activity was found in the sutures. The width of the sutures was two to three times enlarged. The regular tissue pattern of the sutures had changed to a mixture of precollagen and collagen fibers running in all directions with plenty of active cells. In the ultraviolet light there is a take up of markers at the sutural margins. After three months of treatment though, the sutures showed a similar pattern. The three zones of the sutures began to form again; osteoblasts were attached to the sutural margins and reorganization was relatively complete.

Association between the direction of orthopedic headgear force and sutural responses in the nasomaxillary complex

This study was designed to investigate biomechanical responses of the sutures in the nasomaxillary complex to orthopedic headgear forces applied in various directions. A three-dimensional analytic model of the craniofacial complex was used for finite element analysis. A posteriorly-directed force of 1.0 Kgf was applied to the maxillary first molars in 30 degrees inferior, parallel, and 30 degrees, 52.4 degrees and 60 degrees superior directions to the functional occlusal plane. Mean principal and shear stresses were evaluated at the sphenozygomatic, temporozygomatic, sphenomaxillary, frontomaxillary and frontozygomatic sutures and lamina cribrosa. As the force direction passed closer to the center of resistance (CRe) of the complex (52.4 degrees superior direction). normal stresses approached a certain level of uniform compressive stress (-2.5 gf/mm2) with gradual decrease in shear stresses, whereas variation in these stresses produced by the forces applied in other horizontal and inferior directions was greater. It is shown that stresses in the nasomaxillary sutures are varied by the direction of headgear force. Directing the line of force closer the CRe may produce the most optimal sutural modification effective for controlling forward and downward maxillary growth.