Sutures and forces: a review

Biomechanics of conventional and miniscrew-assisted rapid palatal expansion

Posterior Crossbite is a common condition resulting because of transverse maxillary deficiency. The growth of the craniofacial complex finishes first in the transverse dimension, followed by sagittal and vertical dimensions. Conventional rapid palatal expansion (RPE) appliances are commonly used to correct transverse maxillary deficiency. Although RPE is efficient in correcting posterior crossbite, it results in dental side effects such as buccal tipping of maxillary molars, root resorption, bone dehiscence, and relapse. Mini-implant-assisted RPE has been introduced to increase the skeletal effects of expansion especially in patients with increased maturation and greater interdigitation of midpalatal suture. This article will review the biomechanics of RPE and mini-implant-assisted RPE. Additionally, the different designs of MARPE and the long-term clinical effects of expansion appliances will also be discussed in detail.

Environmental and climatic drivers of phenotypic evolution and distribution changes in a widely distributed subfamily of subterranean mammals

How environmental factors shape species morphology and distributions is a key issue in ecology, especially in similar environments. Species of Myospalacinae exhibit widespread distribution spanning the eastern Eurasian steppe and the extreme adaptation to the subterranean environment, providing an excellent opportunity for investigating species responses to environmental changes. At the national scale, we here use geometric morphometric and distributional data to assess the environmental and climatic drivers of morphological evolution and distribution of Myospalacinae species in China. Based on phylogenetic relationships of Myospalacinae species constructed using genomic data in China, we integrate geometric morphometrics and ecological niche models to reveal the interspecific variation of skull morphology, trace the ancestral state, and assess factors influencing interspecific variation. Our approach further allows us to project future distributions of Myospalacinae species throughout China. We found that the interspecific morphology variations were mainly concentrated in the temporal ridge, premaxillary-frontal suture, premaxillary-maxillary suture, and molars, and the skull morphology of the two current species in Myospalacinae followed the ancestral state; temperature and precipitation were important environmental variables influencing skull morphology. Elevation, temperature annual range, and precipitation of warmest quarter were identified as dominant factors affecting the distribution of Myospalacinae species in China, and their suitable habitat area will decrease in the future. Collectively, environmental and climate changes have an effect on skull phenotypes of subterranean mammals, highlighting the contribution of phenotypic differentiation in similar environments in the formation of species phenotypes. Climate change will further shrink their habitats under future climate assumptions in the short-term. Our findings provide new insights into effects of environmental and climate change on the morphological evolution and distribution of species as well as a reference for biodiversity conservation and species management.

Age-related transversal changes in craniofacial sutures of the anterior viscerocranium in growing rats

Objective: To evaluate the dimensional changes that occur in the internasal and nasopremaxillary sutures, and related transverse craniofacial dimensions, of rats from 4 to 38-weeks of age. Methods: Four groups of twelve male Wistar rats were sacrificed at different ages [4-weeks (immature), 16-weeks (adolescent), 26-weeks (young adult), 38-weeks (adult)]. The rats were scanned with a high-resolution micro-computed tomography imaging device with 90 µm voxel size and 45 mm × 45 mm field of view (FOV) to obtain images of the viscreocranium, and with 10 µm voxel size and 5 mm × 5 mm FOV to obtain images of the internasal and left nasopremaxillary sutures. The nasal bone width, transverse width between the nasopremaxillary sutures and interzygomatic width were measured as craniofacial measurements. The endocranial, ectocranial and mean suture widths (cross-sectional area between endocranial and ectocranial borders/suture height), and suture height were measured at 5 frontal planes with 1.2 mm intervals. Outcomes were compared at different ages, and correlation coefficients were used to assess the relationship between craniofacial and suture changes. Results: All transverse craniofacial dimensions increased significantly from 4-16 weeks of age (p < 0.001). After 16-weeks of age, the only significant increase was observed in interzygomatic width (p = 0.02), between 26 and 38 weeks. In both the internasal and nasopremaxillary sutures, the endocranial suture mean widths decreased from 4-16 weeks (p < 0.001 and p = 0.002, respectively), but did not show any significant change after 16-weeks of age. The ectocranial internasal suture width decreased from 4-16 weeks (p < 0.001), increased until 26-weeks (p = 0.035), and subsequently decreased (p < 0.001). The nasopremaxillary suture widths decreased from 4-38 weeks to varying degrees in different frontal planes. Except for the internasal ectocranial suture width, all suture measurements were found highly and negatively correlated with the transverse craniofacial dimensions. The height of the sutures increased with time, with the most significant changes occurring between 4 and 16 weeks of age (p < 0.001). Conclusion: Although the internasal and nasopremaxillary endocranial suture widths nearly reach their final widths during adolescence, the changes in the ectocranial and mean suture widths continue into early adulthood. These results may serve as a reference for future studies aiming to evaluate the effects of functional demands on suture development and dimensional changes of the viscerocranium.

Time course of sutural width during the physiological growth from birth to adulthood: CT quantitative and qualitative evaluations of sutural arches

PURPOSE

We performed a retrospective qualitative and quantitative evaluation of the sutural changes during the physiological growth to define the age-related ossification stages of major and minor skull sutures or synchondroses.

METHODS

A total of 390 healthy subjects, examined for cranio-facial trauma and whose CT scans turned out to be normal, were clustered into homogenous age-matched groups ranged from birth to 90 years. High-resolution CT was used to assess the degree of sutural closure according to a 3-grade scoring system, the sutural pattern, the width, and the density of the gap calculated as the average of two or three ROIs along each suture/synchondrosis.

RESULTS

The identification of a definite pattern depended on the suture's type, the closure degree, and the width of the gap (p < 0.001). The interdigitation process was more intricate for most of vault sutures than the skull base sutures/synchondroses. Closing grades 1, 2, and 3 were associated to an identifiable sutural pattern and the cutoff value of 1.45 mm of the gap width allowed to detect an identifiable sutural pattern with the best combination of sensitivity (97%) and specificity (98%). Age and sutural closing degree were inversely related to gap width while positively related to the gap density (p < 0.001).

CONCLUSION

The sutural ossification is an age-related process, distinctive for each suture, and synchondrosis; it occurs neither according to a predefined order along sutural arches nor following a sequential distribution in the cranial fossae, and some sutures continued their growth process during lifetime.

Short-term and long-term effects of miniscrew-assisted and conventional rapid palatal expansion on the cranial and circummaxillary sutures

INTRODUCTION

The objective of this study was to analyze the short-term and long-term effects of miniscrew-assisted rapid palatal expansion (MARPE) and conventional rapid palatal expansion (RPE) appliances on cranial and circummaxillary sutures as compared with a matched control group.

METHODS

One hundred and eighty cone-beam computed tomography scans for 60 subjects were evaluated for the 3 groups: (1) MARPE (n = 20; aged 13.7 ± 1.74 years), (2) RPE (n = 21; age 13.9 ± 1.14 years), and (3) control (n = 19; age 13.3 ± 1.49 years) at pretreatment (T1), postexpansion (T2), and posttreatment (T3) (T1 to T3: MARPE, 2 years 8 months; RPE, 2 years 9 months; control, 2 years 7 months). Frontonasal suture, frontomaxillary suture, zygomaticomaxillary suture, zygomaticofrontal suture, intermaxillary suture, pterygomaxillary suture, nasomaxillary suture, and zygomaticotemporal suture were measured on the right and left sides for all 3 time labels. In addition, midpalatal suture was measured at the incisor, canine, and molar levels.

RESULTS

Within-group analysis showed that MARPE and RPE led to a significant increase in the widths of frontonasal, frontomaxillary, intermaxillary, nasomaxillary, and midpalatal suture at incisor, canine, and molar levels at T2 compared with T1. Between-group analysis showed that MARPE and RPE significantly increased the width of the intermaxillary and midpalatal suture at the incisor, canine, and molar compared with controls at T2. In the long term, between-group comparisons showed no significant difference among the 3 groups except that MARPE led to a significant increase in the width of midpalatal suture at incisor, canine, and molar levels compared with RPE and controls at T3.

CONCLUSIONS

MARPE led to a significant increase in the width of the midpalatal suture at incisor, canine, and molar levels compared with RPE and controls in the long term. There was no difference in the width of other cranial and circummaxillary sutures among the 3 groups in the long term.

The comparison of the morphology of the mid-palatal suture between edentulous individuals and dentate jaws shows morphological differences

BACKGROUND

A profound understanding of the evolution and anatomy of the viscero- and neurocranium is quintessentially important for orthodontists. This particularly alludes to structures, which are directly targeted by orthodontic therapy such as the maxilla and the mid-palatal suture. The anatomy of the mid-palatal suture of toothed individuals is well described, whereas little is known about sutures' morphological changes after tooth loss. Therefore, the aim of this study was to evaluate the edentulous mid-palatal suture by means of histologic and histomorphometric analysis.

METHODS

Ten mid-palatal sutures of edentulous donors as well as six age- and sex matched dentulous controls were examined. For the histological and histomorphometric analysis (sutural width, obliteration, vascularization and interdigitation) conventional staining protocols (HE, Movat-Pentachrome, Sirius Red) and immunofluorescence (vWF, TRAP) were performed. Histomorphometric analysis was carried out using NIS-elements imaging software.

RESULTS

When compared to dentulous controls, the edentulous investigation group showed a decreased vascularization and sutural width as well as an increased sutural obliteration. Notably, a high variability and inhomogeneity within regard the histomorphometric parameters was seen in edentulous samples.

CONCLUSIONS

The mid-palatal suture of edentulous individuals showed significant morphological differences compared to individuals with toothed jaws. The loss of teeth and thereby functional loading seems to have a considerable impact on sutures' morphology.

The 27 Facial Sutures: Timing and Clinical Consequences of Closure

SUMMARY

Facial sutures contribute significantly to postnatal facial development, but their potential role in craniofacial disease is understudied. Since interest in their development and physiology peaked in the mid-twentieth century, facial sutures have not garnered nearly the same clinical research interest as calvarial sutures or cranial base endochondral articulations. In addition to reinforcing the complex structure of the facial skeleton, facial sutures absorb mechanical stress and generally remain patent into and beyond adolescence, as they mediate growth and refine the shape of facial bones. However, premature closure of these sites of postnatal osteogenesis leads to disrupted growth vectors and consequent dysmorphologies. Although abnormality in individual sutures results in isolated facial deformities, we posit that generalized abnormality across multiple sutures may be involved in complex craniofacial conditions such as syndromic craniosynostosis. In this work, the authors comprehensively review 27 key facial sutures, including physiologic maturation and closure, contributions to postnatal facial development, and clinical consequences of premature closure.

Buccal alveolar bone changes following rapid maxillary expansion and fixed appliance therapy

OBJECTIVES

To assess factors that may be associated with buccal bone changes adjacent to maxillary first molars after rapid maxillary expansion (RME) and fixed appliance therapy.

MATERIALS AND METHODS

Pretreatment (T1) and posttreatment (T2) cone-beam computed tomography scans were obtained from 45 patients treated with RME and preadjusted edgewise appliances. Buccal alveolar bone thickness was measured adjacent to the mesiobuccal root of the maxillary first molar 4 mm, 6 mm, and 8 mm apical to the cementoenamel junction, and anatomic defects were recorded. Paired and unpaired t-tests were used to compare alveolar bone thickness at T1 and T2 and to determine whether teeth with posttreatment anatomic defects had thinner initial bone. Correlation analyses were used to examine relationships between buccal alveolar bone thickness changes and amount of expansion, initial bone thickness, age at T1, postexpansion retention time, and treatment time.

RESULTS

There was a statistically significant reduction in buccal alveolar bone thickness from T1 to T2. Approximately half (47.7%) of the teeth developed anatomic defects from T1 to T2. These teeth had significantly thinner buccal bone at T1. Reduction in alveolar bone thickness was correlated with only one tested variable: initial bone thickness.

CONCLUSIONS

RME and fixed-appliance therapy can be associated with significant reduction in buccal alveolar bone thickness and an increase in anatomic defects adjacent to the expander anchor teeth. Anchor teeth with greater initial buccal bone thickness have less reduction in buccal bone thickness and are less likely to develop posttreatment anatomic defects of buccal bone.

The Morphological Grading and Comparison of Sutural Patency Among Cranial Sutures in Dry Human Skulls

OBJECTIVE

To investigate the degree of fusion (patency) among cranial sutures in human dry skulls in the Anatolia.

METHODS

One-hundred fifty-eight human dry skulls that were accepted as adults according to the teeth eruption were macroscopically examined and photographed with Canon 400B (55 mm objective). The grades of fusion of coronal, sagittal, and lambdoid were quantitatively analyzed by using the modified grading scale. According to the extent of patency, the sutures were graded as grade-0 (open), grade-1 (fused but not obliterated), grade-2 (50%< obliterated), grade-3 (50% > obliterated), and grade-4 (100% obliterated). The authors determined and compared the rate for each grade of sutural patency on coronal, sagittal, and lambdoid sutures.

RESULTS

The cranial sutures of 4 cranii (4/158; 2.53%) had grade-4 fusion, whereas there were no any cranii with sutures of grade-0 fusion. The number of each grade of fusion among cranial sutures of 158 skulls, in descending order, was as follows: 171 (grade-3), 145 (grade-1), 133 (grade-2), and 25 (grade-4). The grade-4 fusion was significantly less observed than the others. The grade-1 and grade-4 fusion of lambdoid sutures were established as the most (66/41.8%) and least (5/3.2%) common fusions among cranial sutures, respectively. The frequencies of each grade of fusion for each cranial suture were determined in a descending order: coronal (grade-3 > 2 > 1 > 4), sagittal (grade-3 > 2 > 1 > 4), and lambdoid sutures (grade-1 > 3 > 2 > 4). The frequency of grade-1 fusion of lambdoid suture (66/41.8%) was significantly different when compared with coronal (39/24.7%) and sagittal sutures (40/25.3%), respectively.

CONCLUSION

The grades of fusion (or sutural patency) vary among cranial sutures.

Evaluation of the palatal split pattern in surgically rapid maxillary expansion-comparison of two techniques

PURPOSE

Surgically assisted rapid maxillary expansion is performed to correct transverse deficiencies of the maxilla, and it is indicated in specific clinical situations. The literature presents different opinions in several aspects, mainly regarding the effect of disjunction of the pterygoid plates. The aim of this study was to evaluate the pattern of maxillary expansion obtained with two surgical techniques, with and without disjunction of the pterygoid plates.

METHODS

Twenty patients treated with surgically assisted rapid maxillary expansion for correction of transversal discrepancies were included in this retrospective study and divided into two groups: (G1) patients operated without disjunction of pterygoid plates and (G2) patients treated with release of the pterygoid plates.

RESULTS

There were seven male and 13 female patients, and the mean age was 29.9 years. Cone beam computed tomography images obtained after final activation of the expansion device were evaluated and complete disjunction of the midpalatal suture (type I) was present in 75 % of the patients whereas incomplete disjunction of the midpalatal suture (type II) was observed in 25 %. Chi-square test showed no statistically significant difference between groups (p = 0.606).

CONCLUSION

No difference was found in relation to the maxillary disjunction pattern irrespective of the treatment given to pterygoid plates.

Effect of maxillary expansion on orthodontics

OBJECTIVE

To explore the effect of maxillary expansion on orthodontics.

METHODS

Eight beagle dogs were randomly divided into two groups, with 4 dogs in each group. Dogs in group 1 were executed immediately and received the direct physical measurement. The magnetic expansion appliance was used in group 2 for the maxillary expansion. After the expansion, the model was taken again and they were executed after cone beam CT (CBCT) scanning. The model measurement method was adopted in group 1 to measure the dental measurement indicators and width of base bone arch. The CBCT measurement method was employed to measure the above dental indicators and bone indicators. The difference in the indicators measured by different methods was compared and analyzed.

RESULTS

Before the expansion, there was no significant difference in the bone measurement indicators between the CBCT measurement method and direct physical measurement method. After the expansion, there was no significant difference in indicators between the CBCT measurement method and direct physical measurement. But there was significant difference among the model measurement method, CBCT measurement method and direct physical measurement method. There was the significant difference in the dental indicators between the CBCT measurement method and model measurement, as well as the bone indicators of posterior marginal spacing of greater palatine foramen, posterior marginal spacing of incisive foramen, width of base bone arch and spacing of implant anchorage.

CONCLUSIONS

There is no significant difference between the effect of CBCT measurement method and direct physical measurement method, but CBCT is significantly better than the model measurement.

CBCT of skeletal changes following rapid maxillary expansion to increase arch-length with a development-dependent bonded or banded appliance

OBJECTIVE

To assess the three-dimensional (3D) skeletal response to a standardized 5 mm of rapid maxillary expansion (RME) in growing children (6-15 years) with maxillary width deficiency and crowding.

MATERIALS AND METHODS

A bonded appliance was used prior to the eruption of the maxillary first premolars (Mx4s), and a banded appliance was used thereafter. A consecutive sample of 89 patients (29 boys and 60 girls) from a large pediatric dentistry and orthodontics practice was divided into four groups: 1) 6-8 years old (n = 26), 2) 9-11 years old with unerupted Mx4s (n = 21), 3) 9-11 years with erupted Mx4s (n = 23), and 4) 12-15 years (n = 19). For all patients, the 3D evaluation of dental and skeletal effects was performed with cone-beam computed tomography (CBCT).

RESULTS

For both appliances in all patients, CBCT confirmed a triangular pattern of expansion in both the frontal and sagittal planes. Overall, both appliances produced significant maxillary expansion (>80% of the 5-mm activation), but older children showed a progressively more dental (less skeletal) response. Comparison of the two types of expanders in the crossover sample, children aged 9-11 years, showed that the bonded RME produced the most efficient skeletal expansion in the preadolescent sample. Increased maxillary width at the level of the zygomaticomaxillary suture was the best indicator for development of maxillary arch circumference.

CONCLUSION

Development-dependent appliances (bonded RPE before Mx4s erupt, and a banded device thereafter) provided optimal RME treatment for all children from age 6-15 years.

Effects induced after the use of maxillary protraction appliances: a literature review

OBJECTIVE: The present literature review, examined the effects of maxillary protraction in patients treated with different types of facial masks. METHODS: The review searched for relevant articles, including randomized controlled trials, controlled clinical trials and uncontrolled trials. Comparisons were made between eight different types of facial masks: Delaire; Grummons; Petit; Turley; Batista; "Sky Hook"; Nanda and Türbinger. Following aspects were evaluated: a) the type of anchorage; the origin, direction and magnitude of forces and b) the relevant results of following skeletal and dental measurements: angular (SNA and SNB), linear (AFAI); vertical angles (SN.GoGn, FMA); dental (IMPA) and linear (1-NA, 1-NB). CONCLUSION: The results showed that there was no uniformity in the choice of anchorage type and form of application of forces between the facial masks examined, but there were similarities in skeletal and dental aspects: Anterior displacement of the maxillary complex (increase in SNA) ; anterior displacement of the upper anterior teeth (increase of 1-NA), the lingual inclination of mandibular incisors (decrease of 1-NB), down and back rotation of the mandible (increase AFAI, SN.GoGn, FMA, decrease in SNB).

Effects of rapid maxillary expansion on the cranial and circummaxillary sutures

INTRODUCTION

The aim of this study was to determine whether the orthopedic forces of rapid maxillary expansion cause significant quantitative changes in the cranial and the circummaxillary sutures.

METHODS

Twenty patients (mean age, 12.3 ± 1.9 years) who required rapid maxillary expansion as a part of their comprehensive orthodontic treatment had preexpansion and postexpansion computed tomography scans. Ten cranial and circummaxillary sutures were located and measured on one of the axial, coronal, or sagittal sections of each patient's preexpansion and postexpansion computed tomography scans. Quantitative variables between the 2 measurements were compared by using the Wilcoxon signed rank test. A P value less than 0.05 was considered statistically significant.

RESULTS

Rapid maxillary expansion produced significant width increases in the intermaxillary, internasal, maxillonasal, frontomaxillary, and frontonasal sutures, whereas the frontozygomatic, zygomaticomaxillary, zygomaticotemporal, and pterygomaxillary sutures showed nonsignificant changes. The greatest increase in width was recorded for the intermaxillary suture (1.7 ± 0.9 mm), followed by the internasal suture (0.6 ± 0.3 mm), and the maxillonasal suture (0.4 ± 0.2 mm). The midpalatal suture showed the greatest increase in width at the central incisor level (1.6 ± 0.8 mm) followed by the increases in width at the canine level (1.5 ± 0.8 mm) and the first molar level (1.2 ± 0.6 mm).

CONCLUSIONS

Forces elicited by rapid maxillary expansion affect primarily the anterior sutures (intermaxillary and maxillary frontal nasal interfaces) compared with the posterior (zygomatic interface) craniofacial structures.

Trans-sutural distraction osteogenesis for alveolar cleft repair: an experimental canine study

OBJECTIVE

To explore a new method of repair of alveolar cleft by trans-sutural distraction osteogenesis.

DESIGN

Nine 8-week-old mongrel dogs were assigned randomly to two groups with three in the control group and six in the experimental group.

SETTING

First, an alveolar cleft model was created surgically in all animals. After 2 weeks, a U-shaped distractor, made of nickel-titanium (NiTi) shape memory alloy wire with 200 g tensile force, was inserted into the premaxilla of the experimental dogs to distract the mid-premaxillary suture for 3 weeks. Periosteoplasty of the alveolar cleft was performed when the premaxilla at the side of cleft approached the maxilla at the same side. The distractor was removed 2 weeks post periosteoplasty.

OUTCOME MEASURES

The results were evaluated clinically, radiographically, and morphologically.

RESULTS

The cleft model was stable and similar to the human alveolar cleft. No spontaneous bone union occurred in the control. In experimental dogs, the premaxilla was moved slowly toward the maxilla, and the cleft became gradually narrower and closed in the third week. Radiographically, the distracted mid-premaxillary suture showed a gradually widened triangle, with the tip of the triangle pointed posteriorly. The density of the distracted triangle suture was increased gradually. The alveolar cleft was completely bony 3 months post periosteoplasty. The morphology of the mid-premaxillary suture was also restored.

CONCLUSION

The alveolar cleft could be repaired by the technique of mid-premaxillary suture distraction using the elastic device of NiTi shape memory alloy.

[New perspectives on craniofacial growth]

There are subtle facial differences that make people unique. We can distinguish between individuals of different gender, age, ethnicity, race and face type. Traditionally, orthodontists have approached facial assessment using lateral skull and posterior/anterior radiographs which could be combined to build a three-dimensional assessment. The aim of this article is to present an outline for a new way of looking at facial growth.

The aponeurotic tension model of craniofacial growth in man

Craniofacial growth is a scientific crossroad for the fundamental mechanisms of musculoskeletal physiology. Better understanding of growth and development will provide new insights into repair, regeneration and adaptation to applied loads. Traditional craniofacial growth concepts are insufficient to explain the dynamics of airway/vocal tract development, cranial rotation, basicranial flexion and the role of the cranial base in expression of facial proportions. A testable hypothesis is needed to explore the physiological pressure propelling midface growth and the role of neural factors in expression of musculoskeletal adaptation after the cessation of anterior cranial base growth. A novel model for craniofacial growth is proposed for: 1. brain growth and craniofacial adaptation up to the age of 20; 2. explaining growth force vectors; 3. defining the role of muscle plasticity as a conduit for craniofacial growth forces; and 4. describing the effect of cranial rotation in the expression of facial form.Growth of the viscerocranium is believed to be influenced by the superficial musculoaponeurotic systems (SMAS) of the head through residual tension in the occipitofrontalis muscle as a result of cephalad brain growth and cranial rotation. The coordinated effects of the regional SMAS develop a craniofacial musculoaponeurotic system (CFMAS), which is believed to affect maxillary and mandibular development.

Assessment of the role of sutures in a lizard skull: a computer modelling study

Sutures form an integral part of the functioning skull, but their role has long been debated among vertebrate morphologists and palaeontologists. Furthermore, the relationship between typical skull sutures, and those involved in cranial kinesis, is poorly understood. In a series of computational modelling studies, complex loading conditions obtained through multibody dynamics analysis were imposed on a finite element model of the skull of Uromastyx hardwickii, an akinetic herbivorous lizard. A finite element analysis (FEA) of a skull with no sutures revealed higher patterns of strain in regions where cranial sutures are located in the skull. From these findings, FEAs were performed on skulls with sutures (individual and groups of sutures) to investigate their role and function more thoroughly. Our results showed that individual sutures relieved strain locally, but only at the expense of elevated strain in other regions of the skull. These findings provide an insight into the behaviour of sutures and show how they are adapted to work together to distribute strain around the skull. Premature fusion of one suture could therefore lead to increased abnormal loading on other regions of the skull causing irregular bone growth and deformities. This detailed investigation also revealed that the frontal-parietal suture of the Uromastyx skull played a substantial role in relieving strain compared with the other sutures. This raises questions about the original role of mesokinesis in squamate evolution.

Tensional Forces Influence Gene Expression and Sutural State of Rat Calvariae In Vitro

BACKGROUND

Theories regarding the cause of craniosynostosis that are more than 15 years old cite the role that tensional forces play in the normal and abnormal development of the cranial suture. These theories highlight the effect of stress bands originating from the skull base to the vertex, guiding sutural development.

METHODS

In this study, the normally fusing posterior intrafrontal suture of the rat was subjected to 3 mN of tensional force for 30 minutes per day. The suture was then assessed for patency, proliferation, apoptosis, and transforming growth factor (TGF)-beta signaling components.

RESULTS

Sutures that were subjected to tensional force were histologically patent at the end of 14 days. This was in contrast to sutures that were maintained without force. Proliferative and apoptotic activity was increased also in sutures maintained open artificially. Interestingly, levels of active TGF-beta-signaling components were also increased in force-maintained sutures.

CONCLUSIONS

Sutural maintenance by mechanical force is concurrent with modulation of cellular activity and protein expression reminiscent of the open suture. This study demonstrates the dynamic reciprocity existing between biochemical activity and morphologic state. Although it is known that changes in TGF-betas and fibroblast growth factors can cause sutural fusion, this is the first study to demonstrate that abrogation of sutural closure is responsible for growth factor signaling modulation.

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.

Remodeling the dentofacial skeleton: the biological basis of orthodontics and dentofacial orthopedics

Orthodontic tooth movement is dependent upon the remodeling of the periodontal ligament and alveolar bone by mechanical means. Facial sutures are also fibrous articulations, and by remodeling these joints, one can alter the positional relationships of the bones of the facial skeleton. As might be expected from the structure and mobility of the temporomandibular joint (TMJ), this articulation is more resistant to mechanical deformation, and whether functional mandibular displacement can alter the growth of the condyle remains controversial. Clinical investigations of the effects of the Andresen activator and its variants on dentofacial growth suggest that the changes are essentially dento-alveolar. However, with the popularity of active functional appliances, such as the Herbst and twin-block based on 'jumping the bite', attention has focused on how they achieve dentofacial change. Animal experimentation enables informed decisions to be made regarding the effects of orthodontic treatment on the facial skeleton at the tissue, cellular, and molecular levels. Both rat and monkey models have been widely used, and the following conclusions can be drawn from such experimentation: (1) Facial sutures readily respond to changes in their mechanical environment; (2) anterior mandibular displacement in rat models does not increase the mitotic activity of cells within the condyle to be of clinical significance, and (3) mandibular displacement in non-human primates initiates remodeling activity within the TMJ and can alter condylar growth direction. This last conclusion may have clinical utility, particularly in an actively growing child.

Cellular response to force application at craniofacial sutures

OBJECTIVES

To provide a comprehensive review of the literature describing research done on the responses of suture cells to force application in vitro and in vivo.

DESIGN AND RESULTS

This review outlines the types of forces that can be applied, methods of applying the forces, the sutures used in experiments, and the changes in morphology, molecular biology (gene and protein expression), and cell biology (proliferation, differentiation, apoptosis) in response to these forces.

CONCLUSION

The molecular response of sutures to force needs to be further investigated as these molecules can be used to enhance the way in which craniofacial sutures respond to mechanical force during orthopedic-orthodontic treatment.

Using finite-element analysis to investigate suture morphology: a case study using large carnivorous dinosaurs

Finite-element analysis (FEA) can be used to investigate the mechanical significance of sutures and regions of intracranial flexibility in skulls. By modeling the stress response to feeding forces in a finite-element skull model (with appropriate boundary conditions), one can compare the axis of distortion and orientation of stress and strain in the model to the degree of movement at actual sutural contacts in the real skull. Hypotheses detailing the effect of introducing patency or flexibility on mechanical performance can be constructed and subsequently tested. In this study, the correlation between stress environment, cranial strength, and sutural morphology and mobility is investigated in the cranium of the large theropod dinosaur Allosaurus fragilis. Theropods are an especially interesting model system as their skulls were massive (over 100 cm in some cases), may have generated extremely large bite forces, yet patent sutures persisted between many of the facial bones. In this analysis, it was discovered that Allosaurus cranial sutures appear generally capable of accommodating stress and strain patterns generated during biting. This study highlights the potential of FEA in devising and testing hypotheses of form and function and argues that useful information can be obtained from finite-element models of extinct animals, providing that adequate assumptions are made and appropriate questions asked.

Sutural Distraction Osteogenesis (SDO) Versus Osteotomy Distraction Osteogenesis (ODO) for Midfacial Advancement: A New Technique and Primary Clinical Report

A new technique of osteotomy distraction osteogenesis (ODO) and sutural distraction osteogenesis (SDO) by the use of bone-borne traction hooks is presented. The technique of osteotomy plus distraction osteogenesis is suitable for adult patients. The technique of sutural distraction osteogenesis is suitable for young patients, ages 6 through 12 years. The distraction system consists of a face-bow, orthodontic elastics, and bone-borne traction hooks. The bone-borne traction hooks are made of titanium, with two traction hooks running laterally or downwardly. When a Le Fort III osteotomy is needed, bone-borne traction hooks are inserted through the nostrils into a bone hole drilled at the lateral-inferior pyriform aperture. When no osteotomy is needed, only the bone-borne traction hooks are placed. Heavy elastics were used in the technique of osteotomy distraction osteogenesis for Le Fort III osteotomy adult patients, whereas light forces and thus light elastics were used for younger patients. Three adult patients and four children were treated by osteotomy distraction and sutural distraction, respectively. All seven patients with midfacial hypoplasia established a harmonious facial profile and normal occlusal relationships. Radiographic examination showed balanced advancement of the midfacial skeleton. It is suggested that the treatment of midfacial hypoplasia in children by the technique of sutural distraction osteogenesis is to be preferred because of its simplicity and relative noninvasiveness. Thus, the authors suggest that midfacial hypoplasia should be treated at a younger age by this technique, potentially eliminating the need for a Le Fort III osteotomy at an older age.

Cranial sutures and bones: growth and fusion in relation to masticatory strain

Cranial bones and sutures are mechanically loaded during mastication. Their response to masticatory strain, however, is largely unknown, especially in the context of age change. Using strain gages, this study investigated masticatory strain in the posterior interfrontal and the anterior interparietal sutures and their adjacent bones in 3- and 7-month-old miniature swine (Sus scrofa). Double-fluorochrome labeling of these animals and an additional 5-month group was used to reveal suture and bone growth as well as features of suture morphology and fusion. With increasing age, the posterior interfrontal suture strain decreased in magnitude and changed in pattern from pure compression to both compression and tension, whereas the interparietal suture remained in tension and the magnitude increased unless the suture was fused. Morphologically, the posterior interfrontal suture was highly interdigitated at 3 months and then lost interdigitation ectocranially in older pigs, whereas the anterior interparietal suture remained butt-ended. Mineralization apposition rate (MAR) decreased with age in both sutures and was unrelated to strain. Bone mineralization was most vigorous on the ectocranial surface of the frontal and the parietal bones. Unlike the sutures, with age bone strain remained constant while bone MARs significantly increased and were correlated with bone thickness. Fusion had occurred in the interparietal suture of some pigs. In all cases fusion was ectocranial rather than endocranial. Fusion appeared to be associated with increased suture strain and enhanced bone growth on the ectocranial surface. Collectively, these results indicate that age is an important factor for strain and growth of the cranium. .

Effects of masticatory muscle function on craniofacial morphology in growing ferrets (Mustela putorius furo)

Studying the effects of masticatory muscle function on craniofacial morphology in animal models with different masticatory systems is important for further understanding of related issues in humans. Forty 5-wk-old male ferrets were equally divided into two groups. One group was fed a diet of hard pellets (HDG) and the other group was fed the same diet but softened with water (SDG). Lateral and dorsoventral cephalograms were taken on each group after 6 months. Cephalometric measurements were performed by digital procedures. For SDG ferrets, the hard palate plane was more distant from the cranial base plane, and canines were more proclined compared with HDG ferrets. The SDG ferrets were also found to have smaller interfrontal and interparietal widths, and a slenderer zygomatic arch than the HDG ferrets. In the mandible, the coronoid process was generally shorter and narrower for the SDG ferrets. The effects of the altered masticatory muscle function on craniofacial morphology in growing ferrets seemed to differ from those previously reported in other animal models studied under similar experimental conditions. Such differences in the effects are presumably related to the differences in the mode of mastication, craniofacial anatomy and growth pattern in different animal models.

Brief communication: age and fractal dimensions of human sagittal and coronal sutures

The fractal dimensions of human sagittal and coronal sutures were calculated on 31 complete skulls from the Terry Collection. The aim was to investigate whether the fractal dimension, relying on the whole sutural length, might yield a better description of age-related changes in sutural morphology, as opposed to other methods of quantification, which generally rely on more arbitrary scoring systems. However, the fractal dimension did not yield better age correlations than other previously described methods. At best, the results reflected the general observation that young adults below age 40 years display an age-related development, but that it is impossible to arrive at any precise age determinations for older adults. It seems that for some individuals, suture obliteration simply does not take place, even at an advanced age, whereas for others, suture obliteration progresses rapidly. Until a better understanding of sutural biology is reached, this will render cranial sutures only marginally useful in age determination. This does not mean, however, that investigations should not be made to elucidate more unbiased methods of sutural morphology quantification.

Mechanobiology of craniofacial sutures

Craniofacial sutures are soft connective-tissue joints between mineralized skull bones. Suture mechanobiology refers to the understanding of how mechanical stimuli modulate sutural growth. This review's hypothesis is that novel mechanical stimuli can effectively modulate sutural growth. Exogenous forces with static, sinusoidal, and square waveforms induce corresponding waveforms of sutural strain. Sutural growth is accelerated upon small doses of oscillatory strain, as few as 600 cycles delivered 10 min/day over 12 days. Interestingly, both oscillatory tensile and compressive strains induce anabolic sutural responses beyond natural growth. Mechanistically, oscillatory strain likely turns on genes and transcription factors that activate cellular machinery via mechanotransduction pathways. Thus, sutural growth is determined by hereditary and mechanical signals via the common pathway of genes. It is concluded that small doses of oscillatory mechanical stimuli have the potential to modulate sutural growth effectively: either accelerating it or initiating net sutural bone resorption for various therapeutic objectives.

Accelerated chondrogenesis of the rabbit cranial base growth plate by oscillatory mechanical stimuli

How mechanical stimuli modulate chondral growth is not well understood. To test a hypothesis that chondral growth is accelerated by oscillatory mechanical stimuli rather than the peak magnitude of mechanical force, we delivered 2-N tensile forces with static (frequency = 0 Hz) and cyclic (f = 1 Hz) profiles noninvasively to the maxillae of growing New Zealand white rabbits for 20 minutes/day over 12 days. Computerized histomorphometry revealed significantly greater maximum height of the cranial base growth plate (GP) treated with cyclic forces (870 +/- 130 microm) than static forces (654 +/- 29 microm) and sham controls (566 +/- 47 microm). In addition, the average total GP area treated with cyclic forces (2.63 +/- 0.17 mm2) was significantly greater than static forces (2.12 +/- 0.99 mm2) and sham controls (1.65 +/- 0.13 mm2). The proliferating zone of GPs treated with cyclic forces (158 +/- 38.5 microm) was significantly longer than the corresponding zones of static forces (117 +/- 8.6 microm) and sham controls (54 +/- 14.9 microm). The average number of chondrocytes in the proliferating zone treated with cyclic forces (1045 +/- 127) was significantly greater than static forces (632 +/- 85) and sham controls (632 +/- 60) in standardized grids. Like natural GPs, the cartilage matrix treated with cyclic and static tensile forces consisted of abundant aggrecan-like proteoglycans. These findings indicate that oscillatory components of mechanical force rather than its peak magnitude are potent anabolic stimulus for chondral growth. A cascade of oscillatory mechanical stimuli is likely capable of engineering chondral growth beyond naturally occurring chondrogenesis.

Craniofacial sutures: morphology, growth, and in vivo masticatory strains

The growth and morphology of craniofacial sutures are thought to reflect their functional environment. However, little is known about in vivo sutural mechanics. The present study investigates the strains experienced by the internasal, nasofrontal, and anterior interfrontal sutures during masticatory activity in 4-6-month-old miniature swine (Sus scrofa). Measurements of the bony/fibrous arrangements and growth rates of these sutures were then examined in the context of their mechanical environment. Large tensile strains were measured in the interfrontal suture (1,036 microepsilon +/- 400 SD), whereas the posterior internasal suture was under moderate compression (-440 microepsilon +/- 238) and the nasofrontal suture experienced large compression (-1,583 microepsilon +/- 506). Sutural interdigitation was associated with compressive strain. The collagen fibers of the internasal and interfrontal sutures were clearly arranged to resist compression and tension, respectively, whereas those of the nasofrontal suture could not be readily characterized as either compression or tension resisting. The average linear rate of growth over a 1-week period at the nasofrontal suture (133.8 micrometer, +/- 50.9 S.D) was significantly greater than that of both the internasal and interfrontal sutures (39.2 micrometer +/- 11.4 and 65. 5 micrometer +/- 14.0, respectively). Histological observations suggest that the nasofrontal suture contains chondroid tissue, which may explain the unexpected combination of high compressive loading and rapid growth in this suture.

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.

Rapid palatal expansion. Part 2: Dentoskeletal changes in cats with patent versus synostosed midpalatal suture

Intercanine expansion (C-C) following rapid palatal expansion is made up of sutural displacement (Sd-Sd), tooth tip (Tt-Tt), tooth displacement (Td-Td), and alveolar process tipping and bending (At+b-At+b). The involvement of these four components was studied on 10 rapid palatal expansion treated and two control cats during an active phase (25 days), a retention phase (60 days), and a relapse phase (60 days). The midpalatal suture was analyzed for linear measurements, radiopaque versus radiolucent zones and optical density from occlusal radiographs. Nine treated cats exhibited sutural split and one treated cat showed no split as a result of synostosis of the suture. The contribution of the four constituents [(Sd-Sd):(Tt-Tt):(Td-Td):(At+b-At+b)] to the C-C expansion changed from active to relapse phase from [45%:15%:25%:15%] to [50%:25%:25%:0%] in the animals with sutural split and from [0%:40%:60%:0%] to [0%:0%:100%:0%] in the cat without sutural split, implying the major role of sutural displacement in patent suture, and tooth displacement in synostosed suture. The latter indicates the potential buccal corticalis fenestration, dehiscence or perforation in synostosed suture undergoing RPE. In patent suture (animals with sutural split), optical density increased during rapid palatal expansion (soft tissue build-up) and decreased during retention (remineralization) and relapse phases (medial convergence of the palatal processes). In the animal without sutural split, a continuous decrease in the optical density (predetermined ossification) was found. The progressive six-fold surge in coefficient of variation of C-C expansion during the relapse phase indicates limitation in predicting rapid palatal expansion stability. Clinically, the use of serial occlusal radiographs during rapid palatal expansion is recommended to evaluate patency and extent of retention period.

Principles of dentofacial orthopedics

The differences in the response of patients to the same orthodontic treatment are, to a great extent, the result of variability in the direction and rate of craniofacial growth. Furthermore, there is currently little scientific evidence that the temporary improvement of skeletal relationships from orthopedic appliances will alter the craniofacial skeleton on a permanent basis. However, contemporary literature is beginning to show that certain appliances may be more effective than others at a specific point in the growth process. Timing of treatment in a patient is becoming of increased clinical importance. A review of the anatomy of palatal expansion indicates that expansion is much greater in the anterior portion of the palate, in both horizontal and vertical planes. Assessment of skeletal maturity for treatment timing and growth prediction is most commonly performed with the hand/wrist radiograph. A new method is presented which uses epiphyseal and diaphyseal widths and fusion of selected phalanges to determine the relative position of the individual on the pubertal growth curve. Skeletal maturity assessment is a traditional attempt to judge physiological development. The future of craniofacial growth assessment lies in the development of physiological measurements which are both replicable and valid and clinically feasible. The data from these studies provides information to allow better quantitative diagnosis and treatment as well as objective assessment of the treatment outcome.

Palatal thickening and facial form in Paranthropus: examination of alternative developmental models

Paranthropus is distinctive among hominoids in its possession of a greatly thickened hard palate. Although traditionally considered a structural adaptation to counter high-magnitude masticatory stress, alternative developmental models are equally viable. Three models of palatal thickening were evaluated in this study. A mechanical model interprets palatal thickening as a compensatory response to increased instability of the midpalatal suture effected by an anterior placement of the masseteric muscle mass. This model predicts that palatal thickness is correlated with the length of the palate posterior to the masseteric tubercle. Two non-mechanical models consider the thickness of the hard palate to be structurally related to and therefore correlated with either 1) the degree to which the premaxilla overlaps the hard palate in the subnasal region or 2) the height of the posterior facial skeleton. The correlation of craniofacial variables was assessed intraspecifically in ontogenetic series of great ape and human crania. Tests of correlation were performed for each comparison using both residuals calculated from reduced major axis regression of the variable of interest against a measure of cranial size and shape ratios. A significant correlation of palatal thickness with posterior facial height in Pan suggests that the unusually thick hard palate of Paranthropus is directly related to the increased posterior facial height characteristic of this taxon. Further evaluation suggests that extreme palatal thickening in these specimens occurred by virtue of their possession of a nasal septum morphology in which the vomer extends onto the superior and nasal surface of the premaxilla. Such a morphology would have constrained the palatal nasal lamina to maintain the approximate level of the premaxillary nasal lamina throughout the growth process thereby promoting palatal thickening.

The role of sutures in normal and abnormal craniofacial growth

The paper is a shortened version of a paper read at the symposium on craniofacial growth, in which the literature on various aspects of sutures was reviewed. Suture development, structure, growth, and closure are covered, and the response of sutures to orthopedic forces and their role in craniosynostosis exemplified. Rather than being an extensive review, references are included preferably to present diversity in results and methods within the subtitle of the symposium, 'mechanisms and study methods'.

Tissue interactions with underlying dura mater inhibit osseous obliteration of developing cranial sutures

Cranial sutures play a critical role in calvarial morphogenesis, serving as growth centers during skull development. Both biomechanical tensile forces originating in the cranial base and biochemical factors present in dura mater have been postulated as determinants of suture morphogenesis and patency. A rat transplant model free of the putative biomechanical influence of the dura and cranial base was used to investigate the role of the dura mater in both the initial morphogenesis and maintenance of sutures during skull growth. Day 19 fetal presumptive (F19) and day 1 neonatal differentiated (N1) coronal sutures, including associated frontal and parietal bones, were transplanted with or without underlying dura mater to the center of adult parietal bones. After 1, 2, and 3 weeks, transplanted tissues were examined histologically and histomorphometrically to determine whether sutures formed and whether they were obliterated by ossification in the absence of dura mater. Both F19 and N1 sutures remained patent for 2 weeks either in the presence or the absence of transplant dura mater. However, at 3 weeks, in the absence of transplant dura mater, sutures were obliterated by bone, while in the presence of dura mater sutures resisted ossification, demonstrating an essential requirement for interactions with the transplant dura mater in maintaining functional sutures. Both F19 and N1 transplants showed comparable bone growth (cross-sectional surface area), regardless of the presence of transplant dura mater. These experiments suggest that tissue interactions of a biochemical nature, rather than biomechanical forces generated through the cranial base, are required to maintain the suture as a non-ossified growth center. Furthermore, while the presence of dura mater was essential for maintenance of suture patency, fetal dura mater was not required for initial suture formation.

Role of cranial bone mobility in cranial compliance

Increases in intracranial pressure are normally buffered by the displacement of blood and cerebrospinal fluid from the cranium when there is an increase in intracranial volume (ICV). How much pressure increases with an increase in ICV is expressed in the calculation of cranial compliance (delta ICV/delta P, where delta P is change in pressure) and elastance (delta P/delta ICV). Data reported here indicate that the movement of the cranial bones at their sutures is an additional factor defining total cranial compliance. Using controlled bolus injections of artificial cerebrospinal fluid into a lateral cerebral ventricle in anesthetized cats and a newly developed instrument to quantify cranial bone movement at the midline sagittal suture where the bilateral parietal bones meet, we show that these cranial bones move in association with increases in ICV along with corresponding peak intracranial pressures and changes in intracranial pressure. External restraints to the head restrict these movements and reduce the compliance characteristics of the cranium. We propose that total cranial compliance depends on the mobility of intracranial fluid volumes of blood and cerebrospinal fluid when there is an increase in ICV, but it also varies as a function of cranial compliance attributable to the movement of the cranial bones at their sutures. Our data indicate that although the cranial bones move apart even with small (nominally 0.2 ml) increases in ICV, total cranial compliance depends more on fluid migration from the cranium when ICV increases are less than approximately 3% of total cranial volume. Cranial bone mobility plays a progressively larger role in total cranial compliance with larger ICV increases.

Sutural biology and the correlates of craniosynostosis

The purpose of this paper is to provide a new perspective on craniosynostosis by correlating what is known about sutural biology with the events of craniosynostosis per se. A number of key points emerge from this analysis: 1) Sutural initiation may take place by overlapping, which results in beveled sutures, or by end-to-end approximation, which produces nonbeveled, end-to-end sutures. All end-to-end sutures occur in the midline (e.g., sagittal and metopic) probably because embryonic biomechanical forces on either side of the initiating suture tend to be equal in magnitude. A correlate appears to be that only synostosed sutures of the midline have pronounced bony ridging. 2) Long-term histologic observations of the sutural life cycle call into question the number of layers within sutures. The structure varies not only in different sutures, but also within the same suture over time. 3) Few, if any, of the many elegant experimental research studies in the field of sutural biology have increased our understanding of craniosynostosis per se. An understanding of the pathogenesis of craniosynostosis requires a genetic animal model with primary craniosynostosis and molecular techniques to understand the gene defect. This may allow insight into pathogenetic mechanisms involved in primary craniosynostosis. It may prove to be quite heterogeneous at the basic level. 4) The relationship between suture closure, cessation of growth, and functional demands across sutures poses questions about various biological relationships. Two conclusions are provocative. First, cessation of growth does not necessarily, or always lead to fusion of sutures. Second, although patent sutures aid in the growth process, some growth can take place after suture closure. 5) In an affected suture, craniosynostosis usually begins at a single point and then spreads along the suture. This has been shown by serial sectioning and calls into question results of studies in which the affected sutures are only histologically sampled. 6) Craniosynostosis is etiologically and pathogenetically heterogeneous. Known human causes are reviewed. Is craniosynostosis simply normal suture closure commencing too early?(ABSTRACT TRUNCATED AT 400 WORDS)

In vivo strain in cranial sutures: the zygomatic arch

Although cranial sutures presumably play a role in absorbing and/or transmitting loads applied to the skull, loading patterns on facial sutures are poorly understood. The zygomatic arch provides a comparatively isolated mechanical part of the skull containing a single suture, the zygomatico-squamosal. In pigs the zygomatico-squamosal suture has a short vertical segment located within the postorbital process and a longer horizontal segment which extends posteriorly. In anesthetized pigs single-element high-elongation strain gages were bonded over both segments of the suture. Strain was recorded during stimulation of the masseter muscles and while the lightly anesthetized animals masticated food pellets. The predominant strain patterns differed in the two segments of the suture. During mastication compressive strains predominated in the vertical segment, but tensile strains predominated in the horizontal segment. The same patterns were also produced by stimulation of the ipsilateral masseter muscle. Contraction of the contralateral masseter reversed the strain pattern, but strain levels were low and during mastication such reversals occurred only transiently. The two segments of the suture have contrasting morphologies. The vertical segment has broad, interdigitating contacts with fibers arranged in a compression-resisting orientation. The horizontal segment has a simple tongue and groove structure with fibers arranged to resist tension. Thus, the structure of the suture reflects the predominant strain pattern.