High mobility group AT-hook 2 regulates osteoblast differentiation and facial bone development

The mutation and deletion of high mobility group AT-hook 2 (Hmga2) gene exhibit skeletal malformation, but almost nothing is known about the mechanism. This study examined morphological anomaly of facial bone in Hmga2-/- mice and osteoblast differentiation of pre-osteoblast MC3T3-E1 cells with Hmga2 gene knockout (A2KO). Hmga2-/- mice showed the size reduction of anterior frontal part of facial bones. Hmga2 protein and mRNA were expressed in mesenchymal cells at ossification area of nasal bone. A2KO cells differentiation into osteoblasts after reaching the proliferation plateau was strongly suppressed by alizarin red and alkaline phosphatase staining analyses. Expression of osteoblast-related genes, especially Osterix, was down-regulated in A2KO cells. These results demonstrate a close association of Hmga2 with osteoblast differentiation of mesenchymal cells and bone growth. Although future studies are needed, the present study suggests an involvement of Hmga2 in osteoblast-genesis and bone growth.

Developmental changes of the facial skeleton from birth to 18 years within a South African cohort (A computed tomography study)

Skeletal remains are often found on a crime scene in which a forensic anthropologist is then consulted to create a biological profile, which includes the estimation of age, sex, ancestry and stature. The viscerocranium plays an important role in the formation of a biological profile. However, to utilise the viscerocranium for age estimation, population specific normative data and knowledge of the development of the viscerocranium is required. Therefore, this study aimed to investigate the developmental changes from birth to 18 years of age of the facial skeleton of individuals from a South African cohort. This study comprised of 239 computed tomography (CT) scans (128 males; 111 females). The viscerocranium was subdivided into five regions viz.: orbital, nasal, midfacial, maxillary and mandibular. The linear parameters in each region were correlated to age to identify the developmental growth patterns of the viscerocranial regions according to male and female. The measurements which displayed the highest correlations with age were used to develop formulas which could be used for age estimation. The results of this study showed that the measurements in the orbital, midfacial, maxillary and mandibular regions experienced rapid growth between 0 and 5 years of age, with the nasal region increasing steadily over time. It was noted that males displayed overall larger measurements than females except for the anterior interorbital distance and both right and left zygomatic arch lengths (ZAL). Although only the left orbital height, nasal aperture height and mandible width displayed statistically significant size differences according to sex (p ≤ 0.05). The measurements which showed the highest correlations to age were the zygomatic arch distance (r = 0.8842, p < 0.001), ZAL (right: r = 0.8929, p < 0.001; left: r = 0.8656, p < 0.001) and the mandible width (r = 0.8444, p < 0.001). Formulas were derived for the measurements that could be used to forensically estimate age within a subadult cohort.

Effects of 4-Hexylresorcinol on Craniofacial Growth in Rats

4-Hexylresorcinol (4HR) has been used as a food additive, however, it has been recently demonstrated as a Class I histone deacetylase inhibitor (HDACi). Unlike other HDACi, 4HR can be taken through foods. Unfortunately, some HDACi have an influence on craniofacial growth, therefore, the purpose of this study was to evaluate the effects of 4HR on craniofacial growth. Saos-2 cells (osteoblast-like cells) were used for the evaluation of HDACi and its associated activities after 4HR administration. For the evaluation of craniofacial growth, 12.8 mg/kg of 4HR was administered weekly to 4 week old rats (male: 10, female: 10) for 12 weeks. Ten rats were used for untreated control (males: 5, females: 5). Body weight was recorded every week. Serum and head samples were collected at 12 weeks after initial administration. Craniofacial growth was evaluated by micro-computerized tomography. Serum was used for ELISA (testosterone and estrogen) and immunoprecipitation high-performance liquid chromatography (IP-HPLC). The administration of 4HR (1-100 μM) showed significant HDACi activity (p < 0.05). Body weight was significantly different in male rats (p < 0.05), and mandibular size was significantly smaller in 4HR-treated male rats with reduced testosterone levels. However, the mandibular size was significantly higher in 4HR treated female rats with increased growth hormone levels. In conclusion, 4HR had HDACi activity in Saos-2 cells. The administration of 4HR on growing rats showed different responses in body weight and mandibular size between sexes.

A model of developmental canalization, applied to human cranial form

Developmental mechanisms that canalize or compensate perturbations of organismal development (targeted or compensatory growth) are widely considered a prerequisite of individual health and the evolution of complex life, but little is known about the nature of these mechanisms. It is even unclear if and how a “target trajectory” of individual development is encoded in the organism’s genetic-developmental system or, instead, emerges as an epiphenomenon. Here we develop a statistical model of developmental canalization based on an extended autoregressive model. We show that under certain assumptions the strength of canalization and the amount of canalized variance in a population can be estimated, or at least approximated, from longitudinal phenotypic measurements, even if the target trajectories are unobserved. We extend this model to multivariate measures and discuss reifications of the ensuing parameter matrix. We apply these approaches to longitudinal geometric morphometric data on human postnatal craniofacial size and shape as well as to the size of the frontal sinuses. Craniofacial size showed strong developmental canalization during the first 5 years of life, leading to a 50% reduction of cross-sectional size variance, followed by a continual increase in variance during puberty. Frontal sinus size, by contrast, did not show any signs of canalization. Total variance of craniofacial shape decreased slightly until about 5 years of age and increased thereafter. However, different features of craniofacial shape showed very different developmental dynamics. Whereas the relative dimensions of the nasopharynx showed strong canalization and a reduction of variance throughout postnatal development, facial orientation continually increased in variance. Some of the signals of canalization may owe to independent variation in developmental timing of cranial components, but our results indicate evolved, partly mechanically induced mechanisms of canalization that ensure properly sized upper airways and facial dimensions.

Developmental mechanisms that canalize or compensate perturbations of organismal development are a prerequisite of individual health and the evolution of complex life. However, surprisingly little is known about these mechanisms, partly because the “target trajectories” of individual development cannot be directly observed. Here we develop a statistical model of developmental canalization that allows one to estimate the strength of canalization and the amount of canalized variance in a population even if the target trajectories are unobserved. We applied these approaches to data on human postnatal craniofacial growth. Whereas overall craniofacial size was strongly canalized during the first 5 years of age, frontal sinus size did not show any signs of canalization. The relative dimensions of the nasopharynx showed strong canalization and a reduction of variance throughout postnatal development, whereas other shape features, such as facial orientation, continually increased in variance. Our results indicate evolved, partly mechanically induced mechanisms of canalization that ensure properly sized upper airways and facial dimensions.

The Special Developmental Biology of Craniofacial Tissues Enables the Understanding of Oral and Maxillofacial Physiology and Diseases

Maxillofacial hard tissues have several differences compared to bones of other localizations of the human body. These could be due to the different embryological development of the jaw bones compared to the extracranial skeleton. In particular, the immigration of neuroectodermally differentiated cells of the cranial neural crest (CNC) plays an important role. These cells differ from the mesenchymal structures of the extracranial skeleton. In the ontogenesis of the jaw bones, the development via the intermediate stage of the pharyngeal arches is another special developmental feature. The aim of this review was to illustrate how the development of maxillofacial hard tissues occurs via the cranial neural crest and pharyngeal arches, and what significance this could have for relevant pathologies in maxillofacial surgery, dentistry and orthodontic therapy. The pathogenesis of various growth anomalies and certain syndromes will also be discussed.

Mutant COMP shapes growth and development of skull and facial structures in mice and humans

BACKGROUND

Cartilage oligomeric matrix protein (COMP) is an important extracellular matrix protein primarily functioning in the musculoskeletal tissues and especially endochondral bone growth. Mutations in COMP cause the skeletal dysplasia pseudoachondroplasia (PSACH) that is characterized by short limbs and fingers, joint laxity, and abnormalities but a striking lack of skull and facial abnormalities.

METHODS

This study examined both mice and humans to determine how mutant-COMP affects face and skull growth.

RESULTS

Mutant COMP (MT-COMP) mice were phenotypically distinct. Snout length and skull height were diminished in MT-COMP mouse and the face more closely resembled younger controls. Three-dimensional facial measurements of PSACH faces showed widely spaced eyes, reduced lower facial height, and decreased nasal protrusion, which correlated with a more juvenile appearing face. Neither MT-COMP mice nor PSACH individuals show midface hypoplasia usually associated with abnormal endochondral bone growth. MT-COMP mice do show delayed endochondral and membranous skull ossification that normalizes with age.

CONCLUSION

Therefore, mutant-COMP affects both endochondral and intramembranous bones of the skull resulting in a reduction of the nose and lower facial height in mice and humans, in addition to its well-defined role in the growth plate chondrocytes.

Autophagy Regulates Craniofacial Bone Acquisition

Increasing evidence has demonstrated the important role of autophagy in skeletal homeostasis; however, the role of autophagy in craniofacial bone development and acquisition is largely unknown. In this study, we investigated the effect of autophagy suppression on craniofacial bone acquisition by deleting Fip200 or Atg5, two essential autophagy genes, using Osterix-Cre (Osx-Cre). We found that the Osx-Cre transgene mildly decreased the bone mass of parietal bone but not frontal bone, and did not affect cranial base bone mass in adult mice. In the cranial vault, Fip200 or Atg5 deletion similarly decreased 50% bone mass of neural crest-derived frontal bone; Atg5 deletion decreased 50% and Fip200 deletion decreased 30% bone mass of mesoderm-derived parietal bone. In the cranial base, Fip200 or Atg5 deletion similarly decreased 30% bone mass of neural crest-derived presphenoid bone; Atg5 deletion decreased 30% and Fip200 deletion decreased 16% bone mass of mesoderm-derive basioccipital bone. Lastly, we used doxycycline treatment to inhibit the Osx-Cre expression until 2 months of age and showed that postnatal Fip200 deletion led to cranial vault bone mass decrease in association with a small increase in both bone volume/tissue volume and tissue mineral density. Altogether, this study demonstrated the important role of autophagy in craniofacial bone acquisition during development and postnatal growth.

p63 establishes epithelial enhancers at critical craniofacial development genes

The transcription factor p63 is a key mediator of epidermal development. Point mutations in p63 in patients lead to developmental defects, including orofacial clefting. To date, knowledge on how pivotal the role of p63 is in human craniofacial development is limited. Using an inducible transdifferentiation model, combined with epigenomic sequencing and multicohort meta-analysis of genome-wide association studies data, we show that p63 establishes enhancers at craniofacial development genes to modulate their transcription. Disease-specific substitution mutation in the DNA binding domain or sterile alpha motif protein interaction domain of p63, respectively, eliminates or reduces establishment of these enhancers. We show that enhancers established by p63 are highly enriched for single-nucleotide polymorphisms associated with nonsyndromic cleft lip ± cleft palate (CL/P). These orthogonal approaches indicate a strong molecular link between p63 enhancer function and CL/P, illuminating molecular mechanisms underlying this developmental defect and revealing vital regulatory elements and new candidate causative genes.

Geometric morphometric analysis of craniofacial growth between the ages of 12 and 14 in normal humans

Aim

There is great variation of growth among individuals. The question whether patients with different skeletal discrepancies grow differently is biologically interesting but also important in designing clinical trials. The aim of the present study was to evaluate whether growth direction depends on the initial craniofacial pattern.

Subjects and method

The sample consisted of 350 lateral cephalograms of 175 subjects (91 females and 84 males) followed during normal growth without any orthodontic treatment. The examined ages were 12 (T1) and 14 (T2) years. The cephalograms were obtained from the American Association of Orthodontists Foundation (AAOF) Craniofacial Growth Legacy Collection (Burlington, Fels, Iowa, and Oregon growth studies). We digitally traced 15 curves on each cephalogram, comprehensively covering the craniofacial skeleton, and located 127 points on the curves, 117 of which were sliding semilandmarks and 10 fixed. Procrustes alignment, principal component analysis and two-block partial least squares analysis were performed, after sliding the semilandmarks to minimize bending energy.

Results

The first 10 principal components (PCs) described approximately 71 per cent of the total shape variance. PC1 was related to shape variance in the vertical direction (low/high angle skeletal pattern) and PC2 was mainly related to shape variance in the anteroposterior direction (Class II/Class III pattern). PC3 was mainly related to the shape variance of the mandibular angle. All subjects shared a similar growth trajectory in shape space. We did not find any correlation between the initial shape and the magnitude of shape change between T1 and T2, but males showed a greater shape change than females. The direction of shape change was moderately correlated to the initial shape (RV coefficient: 0.14, P < 0.001).

Conclusions

The initial shape of the craniofacial complex covaried weakly with the direction of shape change during growth.

Role of Matrix Gla protein in midface development: Recent advances

Craniofacial development is a delicate process that involves complex interactions among cells of multiple developmental origins, their migration, proliferation, and differentiation. Tissue morphogenesis of the craniofacial skeleton depends on genetic and environmental factors, and on specific signaling pathways, which are still not well understood. Developmental defects of the midface caused by the absence, delays, or premature fusion of nasal and maxillary prominences vary in severity; leading to clefts, hypoplasias, and midline expansion. In the current review, we focus on the importance of the chondrocranium in craniofacial growth and how its impaired development leads to midface hypoplasia. More importantly, we reported how Matrix Gla protein (MGP), a potent inhibitor of extracellular matrix mineralization, facilitates midface development by preventing ectopic calcification of the nasal septum. In fact, MGP may act as a common link in multiple developmental pathologies all showing midface hypoplasia caused by abnormal cartilage calcification. This brief review discusses the gap in knowledge in the field, raises pertinent questions, which remain unanswered, and sheds light on the future research directions.

Ethnic differences in craniofacial and upper spine morphology in children with skeletal Class II malocclusion

OBJECTIVES

To analyze differences in upper cervical spine and craniofacial morphology, including posterior cranial fossa and growth prediction signs, between Danish and South Korean pre-orthodontic skeletal Class II children and to analyze associations between upper cervical spine morphology and craniofacial characteristics.

MATERIALS AND METHODS

One hundred forty-six skeletal Class II children-93 Danes (54 boys and 39 girls, mean age 12.2 years) and 53 Koreans (27 boys and 26 girls, mean age 10.8 years)-were included. Upper spine morphology, Atlas dimensions, and craniofacial morphology, including posterior cranial fossa and growth prediction signs, were assessed on lateral cephalograms. Differences and associations were analyzed by multiple linear and logistic regression analyses adjusted for age and gender.

RESULTS

Significant differences between the ethnic groups were found in the sagittal and vertical craniofacial dimensions ( P < .001), mandibular shape ( P < .01), dental relationship ( P < .01), posterior cranial fossa ( P < .05), and growth prediction signs ( P < .001). No significant differences were found in upper spine morphology and Atlas dimensions between the groups. Upper spine morphology/dimensions were significantly associated with the cranial base angle ( P < .01), sagittal craniofacial dimensions ( P < .001), posterior cranial fossa ( P < .001), and growth prediction signs ( P < .05).

CONCLUSIONS

Upper spine morphology/dimensions may be valuable as predictive factors in treatment planning for growing Class II children.

Three-Dimensional Analysis of Maxillary and Mandibular Growth Increments

Objective

To analyze changes in the facial, maxillary, and mandibular skeleton in the vertical, sagittal, and transverse dimensions during an orthodontically relevant period of dentofacial development (i.e., between 7 and 15 years of age).

Subjects and Method

This longitudinal study comprised posteroanterior (PA) and lateral cephalograms at 7, 9, 11, 13, and 15 years of 18 untreated Class I subjects with good occlusion. Transverse growth (width) was analyzed on the basis of PA cephalograms and sagittal (depth) and vertical (height) growth by means of lateral cephalograms. For each linear measurement, mean percentage increases were calculated relative to the size at 7 years of age.

Results and Conclusions

Between 7 and 15 years of age, in the whole facial skeleton and the maxilla, percentage increases were most pronounced in the vertical dimension when compared with the sagittal and transverse dimensions. In the mandible, the largest percentage increases were found in both sexes for vertical growth of the ramus, followed by sagittal growth (body length) and then mandibular width. In the sagittal dimension, development was more pronounced in the mandible (at pogonion more than at B point) than in the maxilla (A point). With respect to vertical growth, percentage increases in posterior face height exceeded the increases in anterior face height. When facial shape changes were analyzed between 7 and 15 years of age in both sexes, the ratio facial height/facial width increased and the ratio facial depth/ facial height decreased, which points toward an age-related increasing influence of vertical development.

Long-Term Effects of Palate Repair on Craniofacial Morphology in Patients with Unilateral Cleft Lip and Palate

Objective

To identify the long-term effects of palate repair on craniofacial growth in patients with unilateral cleft lip and palate (UCLP).

Design

Retrospective cross-sectional study.

Setting

Sri Lankan Cleft Lip and Palate Project.

Subjects

Forty-eight adults with nonsyndromic unilateral cleft lip and palate, 29 men and 19 women, had lip repair only (LRO group). Fifty-eight adults with nonsyndromic unilateral cleft lip and palate, 35 men and 23 women, had lip and palate repairs by the age of 9 (LPR group).

Main Outcome Measures

Clinical notes were used to record surgical treatment histories. Cephalometry was used to determine craniofacial morphology.

Results

In the lip and palate repair group, the depth of the bony pharynx (Ba-PMP), the maxillary length at the alveolar level (PMP-A), the effective length of the maxilla (Ar-IZ, Ar-ANS, Ar-A), the maxillary protrusion (S-N-ANS, SNA), the anteroposterior jaw relation (ANS-N-Pog, ANB), and the overjet were smaller than in the lip repair only group. There were no significant differences in the maxillary length at the basal level (PMP-IZ, PMP-ANS) and the anterior and posterior maxillary heights (N-ANS and R-PMP, respectively) in the two groups.

Conclusion

Palate repair inhibits the forward displacement of the basal maxilla and anteroposterior development of the maxillary dentoalveolus in patients with unilateral cleft lip and palate. Palate repair has no detrimental effects on the downward displacement of the basal maxilla or on palatal remodeling in patients with unilateral cleft lip and palate.

Dentocraniofacial Morphology of 21 Patients with Unilateral Cleft Lip and Palate: A Cephalometric Study

Objective

To assess the skeletal and dental craniofacial proportions of unilateral cleft lip and palate patients who were operated upon using the Malek technique, and compare them with a normal group to highlight the effect of surgical correction on craniofacial development during growth.

Design

Retrospective.

Methods

The cleft palate was closed using the Malek technique in a single operation at 3 months for 11 patients (complete closure of lip and palate) and in a two-stage operation for 10 patients (soft palate at 3 months, lip and hard palate at 6 months). Comparisons were made with a normal control group. Angular and linear measurements of anterior and posterior dimensions of the upper and lower compartments of the face were measured in the 7th and 12th years.

Results and Conclusion

No significant differences were observed between the two groups of palate technique repair, although significant differences were observed between craniofacial dimensions of normal versus cleft lip and palate patients. At a skeletal level, the maxilla and mandible were retrusive relative to the cranial base in the cleft lip and palate group. In fact, there was a backward rotation of the palatal plane with repercussions on the maxillo-mandibular complex position. Furthermore, the maxilla was shorter than in normal patients, whereas the mandible was normally shaped. The upper incisors were retroclined and they locked the lower incisors in linguoversion. There was a posterior skeletal deficit of the respiratory compartment, compensated by more marked posterior maxillary alveolar growth. Facial growth in cleft lip and palate patients followed the same pattern, but was delayed compared with normal patients.

[THE RAPID TEST METHOD OF IDENTIFICATION OF THE TYPE OF GROWTH OF THE JAW BONE ON THE ORTHOPANTOMOGRAM]

The roentgenological methods of research take the lead in the diacrisis of dentofacial anomalies, they are of the utmost importance as for the identification of the jaws' growth character, so too for the generation of the treatment planning and of the expected response to the treatment. The type of the jaw growth is identified by the means of a basal angle on the teleroentgenography (TRG). The objective of the research was to develop a rapid test method of identification of the type of growth by means of a basal angle on the orthopantomogram (OPTG). The comparison of <B and of <G was conducted during the roentgenological research of 28 patients at the age from 13 to 29 years with the different forms of the dentofacial anomalies by means of the methods of dental x-rays, made through the use of TRG and OPTG. The dissimilarities are statistically insignificant (p>0,05) during the comparison of angles' indexes on the TRG and OPTG. The proposed rapid test method allows to identify the type of growth of the mandibular bones by the means of basal angle <B on the OPTG and to make allowance for the anatomic peculiarities of the structure of jaws on both sides in contradistinction from the TRG. The value <B is more than 25° on the OPTG - it denotes the retroinclination of the lower jaw bone and the vertical direction of growth, the index, which is lower than 15° bears record to the inclination of the lower jaw bone in an anteriad direction and in the horizontal direction of the growth.

Effects of the subcranial approach on facial growth and development

OBJECTIVE: To analyze the long-term effects of subcranial surgery for anterior skull base tumors on facial growth.

STUDY DESIGN AND SETTING: Retrospective study (1994 to 2004) in a university-affiliated hospital. Of 108 patients who underwent a subcranial surgical approach for anterior skull base tumors, six adolescents and five young adults fulfilled study entry criteria for age and follow-up data availability (mean, 3.2 ± 2 years). Cephalometric x-ray films monitored postoperative facial growth. Anteriorly and posteriorly measured horizontal and vertical maxillary growth were compared with normal values.

RESULTS: All subjects had superiorly positioned maxillae (shorter in patients with long-standing pathologies). The upper incisor teeth were proclined relative to the cranial base reference planes. All cephalometric changes were within a 10 percent deviation of normal values.

CONCLUSIONS: Subcranial surgery for these tumors minimally affects vertical facial skeleton growth. Early surgery is essential for unaffected horizontal growth.

SIGNIFICANCE: Guidelines for anterior skull base tumor surgery in adolescents and young adults.

© 2007 American Academy of Otolaryngology-Head and Neck Surgery Foundation. All rights reserved.

Vertical and sagittal morphology of the facial skeleton and the pharyngeal airway

AIM

The aim of this study was to evaluate the relationship between sagittal and vertical facial skeletal morphology, and the morphology of the upper and lower pharyngeal airway.

MATERIAL AND METHODS

Pharyngeal airway structures were studied in 101 healthy children (36 boys and 65 girls) aged 7-17 years who were referred for orthodontic treatment. The sample was divided into two groups: according size of the ANB angle group Class I: angle till 4º was considered as skeletal Angle Class I; group Class II: ANB angle more than 4º, considered as skeletal Angle Class II. The vertical pattern was classified using the SN-MP angle, with angle less than 34 taken as normal, and more than 34 - as high vertical growth patterns. The linear measurements and angles were calculated using special purpose software (Dolphin v. 11.0). Pharyngeal width was measured at different point levels using Arnett/Gunson airway analysis.

RESULTS

A statistically significant difference between the two groups, and airway width on all levels was statistically significantly narrower in Angle Class II. Pearson's correlation coefficient showed a negative statistically significant dependence between nasopharyngeal airway, oropharyngeal airway space, and SN-MP angle.

CONCLUSION

Statistically significantly narrower airways were found in patients with ANB more than 4°. In groups divided by SN-MP angle statistically significant difference have not found. Nasopharyngeal airway and oropharyngeal airway spaces statistically significantly negatively correlated with the SN-MP angle: the bigger the SN-MP angle, the smaller were nasopharyngeal and oropharyngeal airway spaces.

[PECULIARITIES OF THE STRUCTURE OF THE TEMPOROMANDIBULAR JOINT IN INDIVIDUALS WITH DIFFERENT DIRECTION OF GROWTH OF THE FACIAL PART OF THE SKULL]

The characteristics of the structure of the temporomandibular joint (TMJ) in individuals with different direction of growth of the facial part of the skull were studied. Cone beam computed tomography data were analyzed in 16 young (mean age 29±7 years) orthodontic patients (32 joints) before treatment, which had class II dentition ratio. The patients were divided into 2 groups (4 men and 4 women in each): with strongly expressed vertical and horizontal types of facial growth. In patients with a vertical type of facial growth, the reduction of the size of joint spaces was noted in anterior, posterior, upper, oral and buccal parts of TMJ. In patients with a vertical type of facial growth anterior articular angle was smaller than in those with a horizontal growth type. The data obtained indicate the relationship of the structure of TMJ and the direction of growth of the facial part of the skull.

Is There a Relationship between Nutrition, Facial Development, and Crowding of the Teeth?

Nutrition plays an important role, especially key vitamins D3 and K2 which are necessary for proper dentofacial development and food consistency influence on crowding and dental arches narrowing. Changes in our dentition and facial appearance are caused by changing our diet from primitive hunter gatherer to a more modern industrialized agriculture. Nutrition and its impact on epigeneticaly- mediated mechanisms continuously shape our phenotype which impacts overall health and can reverse the path for overall health and facial bone development. Orthodontics and nutrition both play a role in following nature's path to reestablishing facial balance and dental arches proportions to accommodate all 32 teeth.

[Mechanisms of growth, development and disease of the craniofacial skeleton]

Craniofacial skeleton is derived from several pieces of bone, which hold the brain and house the sensory organ of vision, hearing, taste and smell. It also serves as an entrance of the digestive and respiratory tracts. Hence, craniofacial complex develops under sophisticated balance between the shape and the function. Disruption of such balance leads to various types of malformation and/or deformation of the face. This review focuses on the molecular aspects of growth and developments of the craniofacial structures and also on the genetic basis of congenital craniofacial malformations.

Interactions of hard tissues, soft tissues, and growth over time, and their impact on orthodontic diagnosis and treatment planning

The approach to orthodontic diagnosis has changed gradually but steadily over the past 2 decades. The shift away from diagnosis based entirely on hard tissue evaluations has been a result of a broadened recognition of the importance of facial and smile appearance to our patients, and how they change over time. The purpose of this article is to describe and illustrate the integration of the new soft tissue paradigm into long-term treatment planning, with a focus on the esthetic goals of treatment.

Heritability of the Human Craniofacial Complex

Quantifying normal variation and the genetic underpinnings of anatomical structures is one of the main goals of modern morphological studies. However, the extent of genetic contributions to normal variation in craniofacial morphology in humans is still unclear. The current study addresses this gap by investigating the genetic underpinnings of normal craniofacial morphology. The sample under investigation consists of 75 linear and angular measurements spanning the entire craniofacial complex, recorded from lateral cephalographs of 1,379 participants in the Fels Longitudinal Study. Heritabilities for each trait were estimated using SOLAR, a maximum-likelihood variance components approach utilizing all pedigree information for parameter estimation. Trait means and mean effects of the covariates age, sex, age(2) , sex × age, and sex × age(2) were simultaneously estimated in the analytic models. All traits of the craniofacial complex were significantly heritable. Heritability estimates ranged from 0.10 to 0.60, with the majority being moderate. It is important to note that we found similar ranges of heritability occurring across the different functional/developmental components of the craniofacial complex, the splanchnocranium, the basicranium, and the neurocranium. This suggests that traits from different regions of the craniofacial complex are of comparable utility for the purposes of population history and phylogeny reconstruction. At the same time, this genetic influence on craniofacial morphology signals a caution to researchers of nongenetic studies to consider the implications of this finding when selecting samples for study given their project design and goals.

Contemporary skull development - palatal angle analysis

OBJECTIVES

The palatal angle is an important angle of the craniofacial complex. It is significant for the diagnosis of craniofacial disorders mainly for nasopharyngeal soft-tissue patterns.Background The dentists and otorhinolaryngologists use this relationship to establish proper treatment mechanics and evaluate facial profile. The aims of this study were to provide comparative cephalometric analyses of historical and contemporary skulls.

MATERIALS AND METHOD

A total of 190 cephalograms of 2 groups of subjects were evaluated. Dolphin Imaging 11.0 - Cephalometric Tracing Analysis was used for the analysis. Unpaired two-tailed t-test assuming equality of variances was used for all variables (at the significance level p = 0.0001).

RESULTS

The -modern forensic skulls had larger palatal angle at average value of 8.60 degrees ± 4.35, than that of archeological ones, the average value of which was 6.50 degrees ± 3.92. The difference was found significant. Unpaired two-tailed t-test assuming equality of variances showed that historical and contemporary skulls had statistically significant results. The difference was -2.09 with standard error of 0.60 (95% confidence interval from -3.29 to -0.89). Two-tailed probability attained value of P was less than 0.0001.

CONCLUSION

The difference between both groups was found significant. An increase in the palatal angle can be directly connected with anterior rotation of upper jaw(Tab. 2, Fig. 5, Ref. 19).

Late adult skeletofacial growth after adolescent Herbst therapy: a 32-year longitudinal follow-up study

INTRODUCTION

The aim of this longitudinal 32-year follow-up investigation was to analyze the very long-term effects of Herbst treatment on the dentoskeletal structures. We followed 14 patients from a sample of 22 with Class II Division 1 malocclusions who were consecutively treated with the banded Herbst appliance at ages 12 to 14 years. The subjects were reexamined after therapy at the ages of 20 years (when the radius epiphysis/diaphysis plate was closed) and 46 years.

METHODS

Lateral head films were analyzed from before (T1) and after (T2) treatment, and at 6 years (T3) and 32 years (T4) after treatment.

RESULTS

(1) In the standard analysis (angular measurements) during the T2 to T3 period of 6 years, significant skeletal changes were the following: increase of the SNB (1.0°; P <0.01), decrease of the ANB (0.9°; P <0.01), and decrease of the ML/NSL (2.5°; P <0.001). During the T3 to T4 period of 24 years, no further significant angular changes occurred. (2) In the analysis of the sagittal changes in the occlusion (linear measurements) during the T2 to T3 period of 6 years, the mandible (6.1 mm; P <0.001) and the maxilla (3.0 mm; P <0.01) grew forward. During the T3 to T4 period of 24 years, the mandible (2.8 mm; P <0.01) and the maxilla (3.1 mm; P <0.01) continued to grow forward. Thus, during the total posttreatment (T2-T4) period of 32 years, there was continuous forward growth of the mandible (8.9 mm; P <0.001) and the maxilla (6.1 mm; P <0.001). (3) The analysis of superimposed lateral head films showed in all 14 subjects large amounts of sagittal and vertical skeletofacial growth during T3 to T4.

CONCLUSIONS

In all 14 subjects, large amounts of sagittal and vertical skeletofacial growth occurred after the age of 20 years. However, the question of when, during the period from 20 to 46 years, growth had come to an end remains open. Closure of the radius epiphysis/diaphysis plate is not useful as an indicator for completed skeletofacial growth. Our findings indicate the importance of considering late adult skeletofacial growth in dentofacial orthopedics, orthognathic surgery, and tooth implantology with respect to treatment timing, posttreatment retention, and relapse.

Beyond the functional matrix hypothesis: a network null model of human skull growth for the formation of bone articulations

Craniofacial sutures and synchondroses form the boundaries among bones in the human skull, providing functional, developmental and evolutionary information. Bone articulations in the skull arise due to interactions between genetic regulatory mechanisms and epigenetic factors such as functional matrices (soft tissues and cranial cavities), which mediate bone growth. These matrices are largely acknowledged for their influence on shaping the bones of the skull; however, it is not fully understood to what extent functional matrices mediate the formation of bone articulations. Aiming to identify whether or not functional matrices are key developmental factors guiding the formation of bone articulations, we have built a network null model of the skull that simulates unconstrained bone growth. This null model predicts bone articulations that arise due to a process of bone growth that is uniform in rate, direction and timing. By comparing predicted articulations with the actual bone articulations of the human skull, we have identified which boundaries specifically need the presence of functional matrices for their formation. We show that functional matrices are necessary to connect facial bones, whereas an unconstrained bone growth is sufficient to connect non-facial bones. This finding challenges the role of the brain in the formation of boundaries between bones in the braincase without neglecting its effect on skull shape. Ultimately, our null model suggests where to look for modified developmental mechanisms promoting changes in bone growth patterns that could affect the development and evolution of the head skeleton.

Facial transplants in Xenopus laevis embryos

Craniofacial birth defects occur in 1 out of every 700 live births, but etiology is rarely known due to limited understanding of craniofacial development. To identify where signaling pathways and tissues act during patterning of the developing face, a 'face transplant' technique has been developed in embryos of the frog Xenopus laevis. A region of presumptive facial tissue (the "Extreme Anterior Domain" (EAD)) is removed from a donor embryo at tailbud stage, and transplanted to a host embryo of the same stage, from which the equivalent region has been removed. This can be used to generate a chimeric face where the host or donor tissue has a loss or gain of function in a gene, and/or includes a lineage label. After healing, the outcome of development is monitored, and indicates roles of the signaling pathway within the donor or surrounding host tissues. Xenopus is a valuable model for face development, as the facial region is large and readily accessible for micromanipulation. Many embryos can be assayed, over a short time period since development occurs rapidly. Findings in the frog are relevant to human development, since craniofacial processes appear conserved between Xenopus and mammals.

Craniofacial catch-up growth in intrauterine growth retarded rats following postnatal nutritional rehabilitation

PURPOSE

The aim of the study was to analyze the effect of postnatal nutritional rehabilitation on the craniofacial growth in rats with intrauterine growth retardation (IUGR).

MATERIALS AND METHODS

Wistar rats were assigned to one of the following groups: control, Sham-operated, and IUGR. The IUGR was produced by uterine vessels bending (day 14 of pregnancy). At days 1, 21, 42, 63, and 84 of postnatal life, each animal was X-rayed, and neural and facial length, width and height were measured. Volumetric and morphometric indices were calculated.

RESULTS

The decreased maternal-fetal blood flow during the last-third of the gestation period modified cranial size and shape of both sexes at birth.

DISCUSSION

Postnatal nutritional rehabilitation is not fully sufficient to reverse the prenatal growth retardation. There are specific responses depending on the sex and the age of the IUGR pups. Regardless of the changes in size, the shape is not modified during all the postnatal period.

Illustrated review of the embryology and development of the facial region, part 2: Late development of the fetal face and changes in the face from the newborn to adulthood

The later embryogenesis of the fetal face and the alteration in the facial structure from birth to adulthood have been reviewed. Part 3 of the review will address the molecular mechanisms that are responsible for the changes described in parts 1 and 2.

Comparing phototoxicity during the development of a zebrafish craniofacial bone using confocal and light sheet fluorescence microscopy techniques

The combination of genetically encoded fluorescent proteins and three-dimensional imaging enables cell-type-specific studies of embryogenesis. Light sheet microscopy, in which fluorescence excitation is provided by a plane of laser light, is an appealing approach to live imaging due to its high speed and efficient use of photons. While the advantages of rapid imaging are apparent from recent work, the importance of low light levels to studies of development is not well established. We examine the zebrafish opercle, a craniofacial bone that exhibits pronounced shape changes at early developmental stages, using both spinning disk confocal and light sheet microscopies of fluorescent osteoblast cells. We find normal and aberrant opercle morphologies for specimens imaged with short time intervals using light sheet and spinning disk confocal microscopies, respectively, under equivalent exposure conditions over developmentally-relevant time scales. Quantification of shapes reveals that the differently imaged specimens travel along distinct trajectories in morphological space.

Patterns of vertical facial growth in Korean adolescents analyzed with mixed-effects regression analysis

INTRODUCTION

To understand the growth patterns of skeletal open bite and deepbite, we present observations from 9 years of pure longitudinal data based on lateral cephalometric radiographs using mixed-effects regression model analysis.

METHODS

In total, 51 children (14 years old) with extreme values for the ratio of lower anterior facial height to total anterior facial height were assigned to 1 of 2 groups: a skeletal open-bite group (11 boys, 14 girls) or a skeletal deepbite group (14 boys, 12 girls). Measurements of total anterior facial height, upper anterior facial height, lower anterior facial height, total posterior facial height, ramus height, and ratio of lower anterior facial height to total anterior facial height were obtained for all subjects. All data were analyzed and interpreted using a mixed-effects regression model analysis with random effects.

RESULTS

From these 4 groups at 14 years old, statistically significant differences were observed between the groups when subjects of the same sex were compared; however, statistical significance was not reached between subjects of opposite sexes in each group. Morphologic differences were clearly evident from the start and became more pronounced with age. There were statistical significances in the initial values and increases with age in all 6 variables except for increases with age in the ratio of lower anterior facial height to total anterior facial height. Statistical significance was also reached for morphologic differences between the annual increases in the ratio of lower anterior facial height to total anterior facial height and lower anterior facial height. In general, individual random variability was high in all variables when compared with the annual changes over time.

CONCLUSIONS

Divergent patterns were established early and became more pronounced with age, with anterior facial height dimensions primarily contributing to these differences. Individual variations were so pronounced that caution is recommended for all clinical decisions.

Cephalometric assessment of human fetal head specimens

BACKGROUND

Past investigations of prenatal craniofacial growth have largely relied on histological sections. Few studies have taken measurements on three-dimensional representations (3D reconstruction, 3D CT, postmortem) or varying depth levels (ultrasound), and we know of no craniofacial growth studies done on cleared-and-stained specimens of whole fetal heads.

MATERIALS AND METHODS

This study comprised 14 human fetal head specimens cleared and stained with alizarin red and alcian blue. They had been stored in glycerol and represented weeks 8-12 of gestation, with crown-rump lengths ranging from 23-145 mm. These specimens were cephalometrically analyzed in norma frontalis and norma lateralis, which notably included the opportunity for side-to-side comparison.

RESULTS

As the cranial membrane bones progressively approached each other, the orbits, maxilla, and mandible gradually grew wider. Likewise, the sagittal dimensions of the maxilla and mandible increased continuously and synchronically. We noted side-to-side differences ranging from 2-5 mm. Another notable finding concerned the inclination of the maxilla relative to the cranial base, which increased more on the right than on the left side.

CONCLUSION

This is the first investigation presenting side-to-side comparative measurements of human fetal head specimens. Such measurements are essential in the quest toward validating the findings of other imaging techniques such as CT or MRI and-most importantly-intrauterine sonography.

Comparison of skeletal changes between female adolescents and adults with hyperdivergent Class II Division 1 malocclusion after orthodontic treatment

OBJECTIVE

To compare the skeletal changes between female hyperdivergent adolescents and adults with Class II Division 1 malocclusion after orthodontic treatment.

METHODS

Thirty adolescent girls and 30 adult women both with hyperdivergent Class II Division 1 malocclusions were selected. The 2 groups were matched by both treatment period and treatment method. Cephalometric radiographs taken before and after treatment were traced and measured. Data were statistically examined.

RESULTS

After treatment, SNA decreased significantly in both groups. SNB remained unchanged in the adolescent group, while it decreased in the adult group. ANB decreased significantly only in the adolescent group and remained unchanged in the adult group. Obvious growth was found in the adolescent group. Ar-Gn, Ar-Go, N-Me and S-Go increased significantly in adolescents. In the adult group, N-Me and ANS'-Me increased after treatment, but with less magnitude than those in the adolescent group. All the angular measures (MP-SN, PP-SN, Ar- Go-Gn and N-S-Ba) remained quite stable in both the adolescent and adult groups.

CONCLUSION

Although obvious vertical growth was found in the female hyperdivergent adolescent Class II Division 1 group, no clockwise rotation of the mandible and no mandibular catch-up growth were found. Vertical growth of the mandible was helpful in maintaining the MP-SN angle with conventional orthodontic mechanism in the adolescent group.

A genome-wide linkage scan for quantitative trait loci influencing the craniofacial complex in humans (Homo sapiens sapiens)

The genetic architecture of the craniofacial complex has been the subject of intense scrutiny because of the high frequency of congenital malformations. Numerous animal models have been used to document the early development of the craniofacial complex, but few studies have focused directly on the genetic underpinnings of normal variation in the human craniofacial complex. This study examines 80 quantitative traits derived from lateral cephalographs of 981 participants in the Fels Longitudinal Study, Wright State University, Dayton, Ohio. Quantitative genetic analyses were conducted using the Sequential Oligogenic Linkage Analysis Routines analytic platform, a maximum-likelihood variance components method that incorporates all familial information for parameter estimation. Heritability estimates were significant and of moderate to high magnitude for all craniofacial traits. Additionally, significant quantitative trait loci (QTL) were identified for 10 traits from the three developmental components (basicranium, splanchnocranium, and neurocranium) of the craniofacial complex. These QTL were found on chromosomes 3, 6, 11, 12, and 14. This study of the genetic architecture of the craniofacial complex elucidates fundamental information of the genetic architecture of the craniofacial complex in humans.

Guiding atypical facial growth back to normal. Part 1: Understanding facial growth

Many practitioners find the complexity of facial growth overwhelming and thus merely observe and accept the clinical features of atypical growth and do not comprehend the long-term consequences. Facial growth and development is a strictly controlled biological process. Normal growth involves ongoing bone remodeling and positional displacement. Atypical growth begins when this biological balance is disturbed With the understanding of these processes, clinicians can adequately assess patients and determine the causes of these atypical facial growth patterns and design effective treatment plans. This is the first of a series of articles which addresses normal facial growth, atypical facial growth, patient assessment, causes of atypical facial growth, and guiding facial growth back to normal.

Epigenetic orthodontics: facial and airway development

It is the purpose of this article to introduce a functional orthopedic/orthodontic appliance, the Homeoblock (Figure 1), which, when worn at night (3 p.m. to 8 a.m.), alters oral function and produces a gene environmental interaction that results in an epigenetic response, namely, the expression of unexpressed genes in adult patients. The results of the case studies presented are evaluated using state-of-the-art, three-dimensional technologies: cone beam computerized tomography combined with Dolphin and Analyze 10.0 software (Mayo Clinic). The results, in so-called non-growing adult patients, can only be attributed to gene expression.

Changes on craniofacial structures in children with growth-hormone-deficiency

OBJECTIVE

To describe the growth of craniofacial structures in growth-hormone deficiency (GHD) children during growth-hormone therapy (GHT).

METHODS

A cross-sectional sample of 46 subjects (n = 14 girls, 32 boys) aged 4-18 years was obtained. They were categorized into two paired groups: the reference group, for comparing the cephalograms, consisted in 23 healthy subjects, and the study group (23 patients) with GHD under GHT. Differences between groups were assessed by independent t-tests.

RESULTS

The boys showed smaller measurements for all facial structures presenting significant differences in total mandibular length (Co-Pg p < 0.03), lower anterior facial height (ANS-Me p < 0.03) and total anterior facial height (N-Me p < 0.02) as well as retrognathic facial type. In girls the posterior cranial base length was shortened (S-Ba 29.14 ± 3.02 mm) and show a high mandibular plane angle (40 ± 5.50°) a wide relation anterior maxillo-mandibular (5.86 ± 1.57°) with a statistical difference (p < 0.05 and p < 0.04) compared with the reference group.

CONCLUSIONS

We suggest considering the cephalometric morphology at the beginning of GHT.

The airway, breathing and orthodontics

Dentists need to play a bigger role in managing airway development and craniofacial formation even though the relationship between the airway, breathing and malocclusion remains quite controversial. Certainly the airway, the mode of breathing and craniofacial formation are so interrelated during growth and development that form can follow function and function can follow form. So, it is imperative to normalize form and function as early as possible so that function is optimized for life.

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.

ALX4 dysfunction disrupts craniofacial and epidermal development

Genetic control of craniofacial morphogenesis requires a complex interaction of numerous genes encoding factors essential for patterning and differentiation. We present two Turkish families with a new autosomal recessive frontofacial dysostosis syndrome characterized by total alopecia, a large skull defect, coronal craniosynostosis, hypertelorism, severely depressed nasal bridge and ridge, bifid nasal tip, hypogonadism, callosal body agenesis and mental retardation. Using homozygosity mapping, we mapped the entity to chromosome 11p11.2-q12.3 and subsequently identified a homozygous c.793C-->T nonsense mutation in the human ortholog of the mouse aristaless-like homeobox 4 (ALX4) gene. This mutation is predicted to result in a premature stop codon (p.R265X) of ALX4 truncating 146 amino acids of the protein including a part of the highly conserved homeodomain and the C-terminal paired tail domain. Although the RNA is stable and not degraded by nonsense-mediated RNA decay, the mutant protein is likely to be non-functional. In a skin biopsy of an affected individual, we observed a hypomorphic interfollicular epidermis with reduced suprabasal layers associated with impaired interfollicular epidermal differentiation. Hair follicle-like structures were present but showed altered differentiation. Our data indicate that ALX4 plays a critical role both in craniofacial development as in skin and hair follicle development in human.

A cross-sectional study of human craniofacial growth

It is generally accepted that different cranial regions do not follow the same growth pattern. In this study, size changes of the functional cranial components (FCCs) in 228 human skulls of age at death between 0 and 20 years were evaluated. The skull is considered as divided into anteroneural, midneural, posteroneural, otic, optic, respiratory, masticatory and alveolar FCCs. Age-related changes of FCCs were assessed by fitting curves with the smoothing spline method, and quantifying the proportional increments at different stages. All FCCs show a high growth rate in the first 3-5 years of life. Two groups of growth trajectories can be distinguished. The anteroneural, midneural, posteroneural and optic FCCs are more advanced at all stages; they show a high growth rate before 3-5-years-old and a low rate later. This difference is less pronounced in the group comprising the respiratory, masticatory and otic FCCs. The alveolar FCC shows an independent pattern. The similarities among FCCs of the two groups are best explained by their common embryological origin. In contrast, the participation in a common function cannot be associated with the co-ordinated variation, given that the masticatory and alveolar FCCs show independent trajectories.

Krox-20 gene expression: influencing hindbrain-craniofacial developmental interactions

Krox-20 is a C(2)H(2)-type zinc-finger transcription factor that plays an essential role in hindbrain development. The Krox-20 null mutation results in hindbrain anomalies that result in neonatal death due to respiratory and feeding deficits. Here we review our studies of how the Krox- 20 null mutation impacts the development of motor and sensory systems critical for the production of consummatory behaviors (suckling/chewing). First, we demonstrated that Krox-20 null mutants suffer a selective loss of primary jaw-opening muscles during prenatal development. In vivo and in vitro studies are reviewed that highlight intrinsic defects in mutant jaw-opener muscles that contribute to muscle degeneration. Next we focus on the impact of the mutation on proprioceptive neurons activated during consummatory behaviors. Mesencephalic trigeminal (Me5) neurons are primary sensory neurons that relay jaw proprioception to the central nervous system. These cells are unique because their cell bodies are located in the central as opposed to the peripheral nervous system. Data are reviewed that demonstrate the impact of the mutation on Me5 neurons, a cell group traditionally thought to emerge from the mesencephalon. We show that Krox-20 null mutants have twice as many Me5 neurons relative to wildtypes at E15, but by birth have half the number of Me5 cells as wildtypes. TUNEL assays performed in each set of studies reveal that Krox-20 expression acts to protect both muscle and mesencephalic trigeminal neurons against apoptosis, suggesting that Krox-20, in addition to its role in hindbrain patterning, has a broader, long-lasting role in development.

Effects of tongue volume reduction on craniofacial growth: A longitudinal study on orofacial skeletons and dental arches

The interaction between tongue size/volume and craniofacial skeletal growth is essential for understanding the mechanism of specific types of malocclusion and objectively measuring outcomes of various surgical and/or orthodontic treatments. Currently available information on this interaction is limited. This study was designed to examine how tongue body volume reduction affects craniofacial skeleton and dental arch formation during the rapid growth period in five 12-week-old Yucatan minipig sibling pairs. One of each pair received a standardized reduction glossectomy to reduce tongue volume by 15-17% (reduction group), and the other had the reduction glossectomy incisions without tissue removal (sham group). Before surgery, five stainless steel screws were implanted into standardized craniofacial skeletal locations. A series of cephalograms, lateral and axial, were obtained longitudinally at 1 week preoperative, and 2 and 4 weeks postoperative. These images were traced using superimposition, and linear and angular variables were measured digitally. Upon euthanasia, direct osteometric measurements were obtained from harvested skulls. Five en-bloc bone pieces were further cut for bone mineral examination by dual photon/energy X-ray absorptiometry (DEXA). The results indicate that: (1) while daily food consumption and weekly body weight were not significantly affected, tongue volume reduction showed an overall negative effect on the linear expansion of craniofacial skeletons; (2) premaxilla and mandibular symphysis lengths, and anterior dental arch width were significantly less in reduction than sham animals at 2 and/or 4 weeks after the surgery; (3) both premaxilla/maxilla and mandible bone mineral density and content were lower in reduction than sham animals, significantly lower in anterior mandible; (4) craniofacial skeletal and dental arch size were significantly smaller in reduction than sham animals, being most significant in the mandibular anterior length and ramus height, the anterior dental arch and midface width. These results suggest that reducing tongue body volume in young animals slows craniofacial skeletal growth and anterior dental arch expansion during rapid growth. The mandible, in particular its symphysis portion, and the anterior dental arch width are most affected. These effects may in part contribute to the decrease of functional loads in the anterior mouth by a volume-reduced tongue.

Development of craniofacial structures in transgenic mice with constitutively active PTH/PTHrP receptor

Parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP) regulate calcium homeostasis, and PTHrP further regulates growth and development. A transgenic mouse carrying the constitutively active PTH/PTHrP receptor (HKrk-H223R) under the control of the mouse bone and odontoblast-specific alpha1(I) collagen promoter (Col1-caPPR) has been developed to demonstrate the complex actions of this mutant receptor in hard tissue formation. We have further characterized Col1-caPPR mice abnormalities in the craniofacial region as a function of development. Col1-caPPR mice exhibited a delay in embryonic bone formation, followed by expansion of a number of craniofacial bones including the maxilla and mandible, delay in tooth eruption and teratosis, and a disrupted temporomandibular joint (TMJ). These findings suggest that the Col1-caPPR mouse is a useful model for characterization of the downstream effects of the constitutively active receptor during development and growth, and as a model for development of treatments of human diseases with similar characteristics.

[Embryonic odontogenesis in vertebrates. A mini-review]

Although the molecular cascades that control craniofacial development are still largely unknown, the generation of mutant animal models and the identification of gene mutations that cause human craniofacial syndromes have recently given significant insight into how the unique structure of the head develops. Craniofacial structures are formed from the prechordal mesoderm, the craniofacial ectoderm as well as the neural crest cells which develop on the dorsal side of the neural tube. Normal craniofacial morphology as well as normal (in number and in morphology) tooth organs develop as a consequence of complex interactions between these embryonic tissues. A series of inductive and reciprocal signals between the epithelium and mesenchyme determine the growth, the form and the ultimate differentiation of tissues and organs. Genetic research has shown the involvement of numerous developmental genes encoding a variety of transcription factors, growth factors and receptors. Mutations have been associated with, among others, non-syndromal forms of cleft palate, agenesis of tooth organs and abnormalities in the cranial bones.

Using zebrafish to investigate cypriniform evolutionary novelties: functional development and evolutionary diversification of the kinethmoid

Although the zebrafish has become a popular model organism for biomedical studies, we propose that the wealth of morphological novelties that characterize this cypriniform fish makes it well suited for investigating the development of evolutionary innovations. Morphological novelties associated with feeding in cypriniform fishes include: a unique structure of the pharyngeal jaws in which the lower pharyngeal jaws are enlarged and opposed to a pad on the basioccipital process; a palatal organ found on the roof of the buccal chamber that is thought to help process detrital food within the buccal chamber; and, the kinethmoid, a novel ossification that effects a unique means of premaxillary protrusion. We present new morphological and developmental data and review functional data regarding the role of the kinethmoid in premaxillary protrusion in the zebrafish. Premaxillary protrusion plays an important role in effective prey acquisition in teleosts and the evolution of a unique means of premaxillary protrusion within Cypriniformes may have led to a number of trophic radiations within this clade. Ontogenetic data from zebrafish show that substantial premaxillary protrusion is not seen until these fish have undergone metamorphosis at which point the adductor mandibulae musculature becomes divided and all ligamentous attachments become established. A comparative study of families within Cypriniformes shows diverse morphologies of the kinethmoid. The morphological diversification that characterizes the kinethmoid suggests that this feeding structure has played a role in trophic radiations within Cypriniformes, since the morphology of this feature is correlated with feeding habits.

An in vitro model of radiation-induced craniofacial bone growth inhibition

Radiation-induced craniofacial bone growth inhibition is a consequence of therapeutic radiation in the survivors of pediatric head and neck cancer. Previously, the infant rabbit orbitozygomatic complex (OZC) was established as a reliable animal model. The purpose of this study was to develop a cell culture model from the rabbit OZC to study the effects of radiation in the craniofacial skeleton. Infant (7-week-old) New Zealand white rabbits were used in this study. Periostea from both OZC were harvested in sterile conditions, introduced into cell culture by way of sequential digestion, and subcultured at confluence. Cultures were analyzed for cellular proliferation (methylthiazoletetrazolium assay), alkaline phosphatase activity, collagen type I expression, and mineralization. Electron microscopy was performed to reveal the in vitro ultrastructure. Subsequently, rabbits were irradiated with sham or 15 Gy radiation, and cell cultures were developed and analyzed for cell numbers. Cell cultures, grown from OZC periostea, expressed osteoblast-like phenotype, with high alkaline phosphatase activity, collagen type 1 expression, and mineralization in an osteogenic environment. Electron microscopy confirmed the characteristic ultrastructural features of osteogenesis in vitro. Finally, significantly (P < 0.01) fewer cells were obtained from animals treated with 15 Gy radiation compared with those from control animals.A primary cell culture with osteoblast-like cellular phenotype was developed from infant rabbit OZC periosteum. This cell culture system responded to in vivo administered radiation by a significant decrease in cell numbers. This in vitro model will be subsequently used to study the cellular mechanisms of radiation and radioprotection in craniofacial osteoblast-like cells.