Functional influence on sutural bone apposition in the growing rat

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.

Effects on Facial Growth Following Masseter Muscle Resection in Growing Rats-A Systematic Review

An individual's facial appearance is heavily influenced by facial symmetry. In the asymmetric mandible, periosteal apposition and endochondral ossification in one of the condyles may stimulate asymmetric growth of the body. Our aim was to review the impact on the growth following masseter resection. Relevant studies up to October 2022 were retrieved from PubMed, Scopus, and Web of Science. The PICOS method was utilized to determine eligibility, and the SYRCLE risk of bias tool was utilized to provide an estimate of potential bias. A predetermined algorithm was used to search the databases. The results of our systematic review of seven studies indicate that the masseter muscle strongly impacts craniofacial growth and development. Resection of the masseter muscle significantly reduces the sagittal and vertical development of the jaw in rats. In addition, the masseter muscle excision influences the mandibular morphology, including the condylar area, angle, and development direction of the jaw.

The histology of sutures in chicken skulls: Types, conservation, and ontogeny

Sutures are fibrous joints that occur between bone elements in vertebrate skulls, where they play a variety of roles including facilitating skull growth and function. In addition, a variety of studies examining sutures from diverse perspectives in many taxa have enabled the determination of anatomical homologs. Surprisingly, one important aspect of sutures-histology-remains unknown in the key model organism of the chicken. To fill this gap in our knowledge, we generated histological sections of six different cranial sutures across a range of developmental stages in embryonic chicken. Despite having a skull that is largely co-ossified or fused as an adult, we found that the types, components, and ontogeny of sutures in chicken skulls are very similar to sutures in other vertebrates. We did, however, find a new transient stage in the ontogeny of sutures between endochondral bone elements, in which one element has ossified and one was still cartilaginous. Moreover, to better understand the morphogenetic events at the onset of suture formation, we compared the developmental histology of six sutures with that of the space between the two ossification centers of the frontal-a location expected to be void of suture structures. We found that the mesenchymal cells in sutures condense and form a middle vascular layer. This was not found to be the case in the space between the two ossifications of the frontal, where instead only osteoid occurs.

Effects of masticatory muscle function affected by BTX on maxillofacial bone growth through the sutural modification

OBJECTIVES

To evaluate the effect of botulinum toxin type A (BTX)-induced masticatory muscle hypofunction on the maxillofacial suture bone growth of growing rats.

SETTING AND SAMPLE POPULATION

Department of Orthodontics at Taipei Medical University. Forty-eight male 4-week-old Wistar rats were divided into four groups. The N group received injections of normal saline into each of the masseter and temporalis muscles. The M group received injections of normal saline into each of the temporalis muscle and injections of BTX into each of the masseter muscle. The T group received injections of normal saline into each of the masseter muscle and injections of BTX into each of the temporalis muscle. The MT group received injections of BTX into each of the masseter and temporalis muscles.

MATERIAL & METHODS

Rats were sacrificed after 42 days of growth. Changes in body and muscle weight were measured. Anthropometric measurements of the maxillary arch, sutural bone mineral density and sutural bone deposition distances were recorded. Statistical comparisons were performed using analysis of variance.

RESULTS

No significant change in body weight was found across groups. However, significant decreases were observed in muscle weight, anthropometric measurements, sutural bone mineral density and bone apposition distance in the BTX-injected group.

CONCLUSIONS

Reduced masticatory muscle function in growing rats can affect maxillofacial suture bone growth.

Assessment of midpalatal suture ossification using cone-beam computed tomography

BACKGROUND AND OBJECTIVE

The degree of ossification of the midpalatal suture is an important factor in the selection of treatment procedure, especially in young individuals. Considering the discrepancies in the results of studies on the exact time of the closure of this suture, the present study was undertaken to evaluate ossification and morphology of the suture with the use of CBCT.

METHODS

In the present cross-sectional study, the CBCT images of the maxilla in 144 Iranian subjects (72 males, 72 females) with an age range of 10 to 70 years, referring to a private radiology center in Sari, Iran, were evaluated. The CBCT images were evaluated in the axial cross-sectional slice at 1 mm intervals to determine morphology and the maturation stage of the suture and its degree of ossification. The six developmental stages that were observed were as follows: stage A, a direct line without disturbances; stage B, a scalloped appearance in the suture; stage C, two parallel lines with a scalloped appearance that were connected at some points; stage CD, the anterior portion was similar to stage C, and the posterior region was similar to stage D; stage D, ossification only in the palatine bone; stage E, complete ossification of the suture. The degree of ossification of the suture was calculated with the use of the ratio of the length of the ossified segment to the entire length of the suture. Data were analyzed with Spearman's correlation test, Chi-squared test, t-test, ANOVA, Mann-Whitney U, and Kruskal-Wallis test. Intra-observer agreement was calculated with the use of weighted kappa coefficient. Data were analyzed with SPSS 17.

RESULTS

There was a strong correlation between the age groups and the developmental stages of the midpalatal suture in both genders (r=0.681, p<0.001). The ossification process occurred in the posterior to anterior direction in 98% of the cases. There was a significant relationship between aging and the degree of ossification (p<0.001); however, the difference was not significant between the two genders (p=0.193).

CONCLUSION

Although the rate of suture closure increased with aging, age was not a reliable factor alone to determine the developmental stage of the suture. Use of CBCT is necessary in all the patients to determine the degree of ossification and morphology of the midpalatal suture.

Orthodontic skeletal anchorage using a palatal external plate

We have developed the Anchor-Lock external plate system, which is fitted on the palate for the purpose of orthodontic skeletal anchorage. The aim of this study was to introduce the Anchor-Lock and assess its success rate. The Anchor-Lock is composed of titanium screws of 2·0-mm diameter and a titanium plate of 1·0-mm thickness. The external plate is rigidly interlocked with the heads of the screws, which are implanted trans-mucosally into palatal bone. Three types of Anchor-Lock are available. These were applied to 137 orthodontic patients (104 females and 33 males) aged 10-54 years. Two types of plate were used, a straight-shaped plate applied to the hard palate and to the anterior palate and a double-Y-shaped plate applied after tooth-borne rapid maxillary expansion. Success rate of the Anchor-Lock was 92·0% overall. No significant difference in success rate was found by age or sex of patients. Type or screw length of the Anchor-Lock did not affect success rate significantly. Success rate was significantly increased by the use of the surgical stent. The Anchor-Lock was effectively applied to distalize and/or intrude the upper molars. The Anchor-Lock system appears suitable for clinical use as an alternative to conventional screw- and plate-type orthodontic implants.

Measurement of the midpalatal suture width

OBJECTIVE

To conduct a pilot study to investigate the potentiality to determine the midpalatal sutural width radiographically with a flat-panel volume computed tomography (fpVCT) in a porcine model.

MATERIALS AND METHODS

Bone samples from the midpalatal suture of five young (16 weeks) and five old (200 weeks) sus scrofa domestica were gathered. The midpalatal suture width was measured via fpVCT and compared to respective histological preparations. Results with P < .05 were considered significant.

RESULTS

The data obtained by fpVCT and by histomorphometric analysis reveal a highly significant age dependency of the measured suture width (both P < .0001), with lower suture width values in older subjects compared to the younger group. The averaged suture widths measured in the fpVCT images shows a distinctively higher mean compared to the histomorphometric data with high statistical significance (P < .0001). The evaluated difference between both methods was almost constant.

CONCLUSION

fpVCT is a powerful tool for determining midpalatal sutural width.

Nasal septal and premaxillary developmental integration: implications for facial reduction in Homo

The influence of the chondrocranium in craniofacial development and its role in the reduction of facial size and projection in the genus Homo is incompletely understood. As one component of the chondrocranium, the nasal septum has been argued to play a significant role in human midfacial growth, particularly with respect to its interaction with the premaxilla during prenatal and early postnatal development. Thus, understanding the precise role of nasal septal growth on the facial skeleton is potentially informative with respect to the evolutionary change in craniofacial form. In this study, we assessed the integrative effects of the nasal septum and premaxilla by experimentally reducing facial length in Sus scrofa via circummaxillary suture fixation. Following from the nasal septal-traction model, we tested the following hypotheses: (1) facial growth restriction produces no change in nasal septum length; and (2) restriction of facial length produces compensatory premaxillary growth due to continued nasal septal growth. With respect to hypothesis 1, we found no significant differences in septum length (using the vomer as a proxy) in our experimental (n = 10), control (n = 9) and surgical sham (n = 9) trial groups. With respect to hypothesis 2, the experimental group exhibited a significant increase in premaxilla length. Our hypotheses were further supported by multivariate geometric morphometric analysis and support an integrative relationship between the nasal septum and premaxilla. Thus, continued assessment of the growth and integration of the nasal septum and premaxilla is potentially informative regarding the complex developmental mechanisms that underlie facial reduction in genus Homo evolution.

Rehabilitation of masticatory function improves the alveolar bone architecture of the mandible in adult rats

Masticatory functional changes have been shown to influence the quantity and quality of the alveolar bone during growth. This study was designed to investigate the effect of masticatory function rehabilitation on the morphology and the trabecular architecture of the mandibular alveolar bone after cessation of growth. Forty-four Sprague-Dawley male rats received soft diet in order to develop masticatory muscle hypofunction. After 21 weeks, after cessation of growth, the animals were divided into two groups: the first group continued receiving soft diet for six more weeks (hypofunction group), while the second group changed to ordinary (hard) diet with the aim to restore a normal masticatory function (rehabilitation group). A third group of 16 male rats (normal group) received ordinary (hard) diet during the whole experimental period and served as control. Micro-tomographic histomorphometry was used to evaluate the architecture of the mandibular alveolar bone (e.g. bone volume fraction, trabecular thickness, trabecular separation, etc.) at the end of the experiment (27 weeks). The height and width of the alveolar process were measured as well. The alveolar process trabecular bone volume fraction (BV/TV) was lower for the animals of the hypofunctional group as compared to those of the normal (p<0.01) and the rehabilitation (p<0.05) groups. Despite the significant improvement observed in the rehabilitation group, their BV/TV was lower in comparison to the normal group (p<0.05) at the end of this experiment. All the other micro-tomographic parameters followed the same pattern of change between groups; values of the rehabilitation group were between the values of the two other groups, differing significantly from both of them. The alveolar process was significantly shorter in the normal group in comparison to both the hypofunctional and rehabilitation groups (p<0.05). On the other hand, both the normal and rehabilitation groups were had a wider alveolar process than the hypofunctional group (p<0.05). Both alveolar height and width were significantly correlated with all micro-tomographic parameters under study. The rehabilitation of masticatory function led to a significant improvement of alveolar bone architecture in adult rats, although the negative effects of hypofunction were not totally reversed during the period under study.

Dietary consistency and the midline sutures in growing pigs

OBJECTIVES

The purpose of this study was to investigate the effects of reduced masticatory function on midline suture growth and morphology in growing pigs.

SETTING AND SAMPLE POPULATION

The sample was 20 pigs separated into two dietary groups and raised at the Department of Anthropology, Harvard University. Midline suture specimens were analyzed at the Department of Orthodontics, University of Washington.

MATERIALS AND METHODS

Ten farm pigs and 10 minipigs, all male, were randomly assigned to hard (n = 9) and soft-diet (n = 11) groups. Fluorochromic mineral labels were administered to document bone apposition, and the animals were killed after 12 weeks. Undecalcified sections of the interfrontal, interparietal, internasal, and intermaxillary sutures were evaluated for bone quantity and sutural thickness, interdigitation ratio and growth rate.

RESULTS

Soft-diet pigs were characterized by a slower rate of weight gain and less bone than their hard-diet counterparts. Even after correction for weight gain, soft-diet pigs had reduced suture growth rate and thickness. However, no difference in interdigitation ratio was detected between dietary groups.

CONCLUSIONS

Restriction to a soft diet reduces midline suture growth and bone apposition in the growing pig.

Three-dimensional craniomaxillary characteristics of the mouse with spontaneous malocclusion using micro-computed tomography

The aim of this study was to clarify the morphological characteristics of craniomaxillary deviations in BALB/c-bm/bm mice with a spontaneous malocclusion (incisal transverse crossbite) using three-dimensional (3D) morphological measurements. Sixty female mice aged 13 and 25 weeks were divided into the following groups: control (BALB/c-+/+ mice, n = 20), norm (BALB/c-bm/bm mice with a normal occlusion, n = 20), and mal (BALB/c-bm/bm mice with a malocclusion, n = 20). Various points in the skull were selected and the distances between two points were measured using 3D micro-computed tomography (CT) images. Statistically significant differences in measurement values among the three groups were evaluated by one-way analysis of variance with a probability level of P < 0.05 considered statistically significant. At both ages, the lengths of almost all measurements in the norm and mal groups were significantly shorter than those in the control group. Comparison between the shifted and non-shifted sides in the mal group showed that significant lateral deviation at the maxilla and nasal bone had occurred. Using 3D micro-CT images, the results of this study quantitatively showed that the craniomaxillary complex of BALB/c-bm/bm mice was significantly smaller than that of BALB/c-+/+ mice and that BALB/c-bm/bm mice have a spontaneous transverse crossbite due to lateral deviation of the maxilla and nasal bone.

Changes in bone mineral and matrix in response to a soft diet

Alterations in the magnitude of habitual mechanical loads upon the skeleton may not only affect bone architecture, but also influence the nature of the bone matrix. We tested the hypothesis that changing the mechanical consistency of the diet affects both the mineral and non-mineralized moieties of bone matrix. Female rats were fed a soft diet (powdered chow as a paste), while control animals were fed the standard chow. After 8 or 20 wks, animals were killed. Cranial (mandible, maxilla, parietal, and frontal) bones and ulnae were analyzed for mineralization density by quantitative backscattered electron microscopy, and sulphated glycosaminoglycan levels with alcian blue staining were measured by microdensitometry. The soft diet group showed a significant increase in mineralization density distribution at almost all cranial sites and a reduction in alcian blue staining in alveolar bone. Altering the consistency of the diet significantly affects mineral concentration and glycosaminoglycan content of alveolar bone.

Sutural growth restriction and modern human facial evolution: an experimental study in a pig model

Facial size reduction and facial retraction are key features that distinguish modern humans from archaic Homo. In order to more fully understand the emergence of modern human craniofacial form, it is necessary to understand the underlying evolutionary basis for these defining characteristics. Although it is well established that the cranial base exerts considerable influence on the evolutionary and ontogenetic development of facial form, less emphasis has been placed on developmental factors intrinsic to the facial skeleton proper. The present analysis was designed to assess anteroposterior facial reduction in a pig model and to examine the potential role that this dynamic has played in the evolution of modern human facial form. Ten female sibship cohorts, each consisting of three individuals, were allocated to one of three groups. In the experimental group (n = 10), microplates were affixed bilaterally across the zygomaticomaxillary and frontonasomaxillary sutures at 2 months of age. The sham group (n = 10) received only screw implantation and the controls (n = 10) underwent no surgery. Following 4 months of post-surgical growth, we assessed variation in facial form using linear measurements and principal components analysis of Procrustes scaled landmarks. There were no differences between the control and sham groups; however, the experimental group exhibited a highly significant reduction in facial projection and overall size. These changes were associated with significant differences in the infraorbital region of the experimental group including the presence of an infraorbital depression and an inferiorly and coronally oriented infraorbital plane in contrast to a flat, superiorly and sagittally infraorbital plane in the control and sham groups. These altered configurations are markedly similar to important additional facial features that differentiate modern humans from archaic Homo, and suggest that facial length restriction via rigid plate fixation is a potentially useful model to assess the developmental factors that underlie changing patterns in craniofacial form associated with the emergence of modern humans.