Extensive phenotyping of the orofacial and dental complex in Crouzon syndrome

Influence of bone morphogenetic protein (BMP) signaling and masticatory load on morphological alterations of the mouse mandible during postnatal development

OBJECTIVE

Bone homeostasis relies on several contributing factors, encompassing growth factors and mechanical stimuli. While bone morphogenetic protein (BMP) signaling is acknowledged for its essential role in skeletal development, its specific impact on mandibular morphogenesis remains unexplored. Here, we investigated the involvement of BMP signaling and mechanical loading through mastication in postnatal mandibular morphogenesis.

DESIGN

We employed conditional deletion of Bmpr1a in osteoblasts and chondrocytes via Osterix-Cre. Cre activity was induced at birth for the 3-week group and at three weeks for the 9-week and 12-week groups, respectively. The conditional knockout (cKO) and control mice were given either a regular diet (hard diet, HD) or a powdered diet (soft diet, SD) from 3 weeks until sample collection, followed by micro-CT and histological analysis.

RESULTS

The cKO mice exhibited shorter anterior lengths and a posteriorly inclined ramus across all age groups compared to the control mice. The cKO mice displayed an enlarged hypertrophic cartilage area along with fewer osteoclast numbers in the subchondral bone of the condyle compared to the control group at three weeks, followed by a reduction in the cartilage area in the posterior region at twelve weeks. Superimposed imaging and histomorphometrical analysis of the condyle revealed that BMP signaling primarily affects the posterior part of the condyle, while mastication affects the anterior part.

CONCLUSIONS

Using 3D landmark-based geometric morphometrics and histological assessments of the mandible, we demonstrated that BMP signaling and mechanical loading reciprocally contribute to the morphological alterations of the mandible and condyle during postnatal development.

Strategic treatment planning for anterior open bite: A comprehensive approach

Anterior open bite (AOB), characterized by the lack of vertical overlap between upper and lower anterior teeth, poses a considerable challenge in orthodontics. The condition depends on many factors that combine to render it difficult to achieve post treatment stability. AOB is commonly classified as dental, skeletal, or functional on the basis of the clinical presentation and causative factors. Traditionally, skeletal AOB necessitates surgical intervention, whereas nonsurgical approaches such as extrusion arches and the Multiloop Edgewise Archwire Technique (MEAW) can be employed in more straightforward cases. Functional appliances are reserved for situations in which a patient's growth potential offers the possibility of effectively addressing AOB. This review presents a strategic treatment approach for addressing AOB, taking into account the classification and severity of the condition. The proposed SHE framework describes the use of mini-screws (S) for anchorage and vertical control, encouragement to correct habits (H), and the utilization of extractions and elastics (E). By incorporating extra-radicular mini-screws, AOB closure is achieved through anterior retraction in extraction cases or whole arch distalization of dentition with elastics in non-extraction cases. This framework emphasizes habit correction through a regimen of oral myofunctional therapy (OMT) and habit-correcting appliances to enhance posttreatment stability. This review suggests that nonsurgical correction is viable in the majority of cases, whereas surgical intervention should be reserved for severe cases of skeletal vertical overgrowth or horizontal discrepancies.

Craniofacial anomalies in a murine model of heterozygous fibroblast growth factor 10 gene mutation

OBJECTIVE

Dysregulation of Fibroblast Growth Factor 10 (FGF10), a member of the family of Fibroblast Growth Factor (FGF) proteins, has been implicated in craniofacial and dental anomalies, including craniosynostosis, cleft palate, and Lacrimo-Auriculo-Dento-Digital Syndrome. The aim of this murine study was to assess the craniofacial and dental phenotypes associated with a heterozygous FGF10 gene (FGF10+/- ) mutation at skeletal maturity.

METHODS

Skulls of 40 skeletally mature mice, comprising two genotypes (heterozygous FGF10+/- mutation, n = 22; wildtype, n = 18) and two sexes (male, n = 23; female, n = 17), were subjected to micro-computed tomography. Landmark-based linear dimensions were measured for the cranial vault, maxilla, mandible, and first molar teeth. Multivariate analysis of variance was performed to assess whether there were significant differences in the craniofacial and dental structures between genotypes and sexes.

RESULTS

The craniomaxillary skeleton and the first molar teeth were smaller in the FGF10+/- mice (P < .05), but the mandible was unaffected. Sex did not have a significant effect on these structures (P > .05). Cranial sutural defects were noted in 5/22 (22.7%) mutant versus 2/18 (11.1%) wildtype mice, and cleft palate in only one (4.5%) mutant mouse. None of the mice displayed craniosynostosis, expansive bony lesions, bifid condyles, or impacted teeth.

CONCLUSION

The FGF10+/- mutation was associated with craniomaxillary skeletal hypoplasia that probably arose from deficient (delayed) intramembranous ossification of the sutured bones. Overall, the skeletal and dental data suggest that the FGF10 gene plays an important role in the aetiology of craniofacial dysmorphology and malocclusion.

Candidate genes for obstructive sleep apnea in non-syndromic children with craniofacial dysmorphisms - a narrative review

Pediatric obstructive sleep apnea (POSA) is a complex disease with multifactorial etiopathogenesis. The presence of craniofacial dysmorphisms influencing the patency of the upper airway is considered a risk factor for POSA development. The craniofacial features associated with sleep-related breathing disorders (SRBD) - craniosynostosis, retrognathia and micrognathia, midface and maxillary hypoplasia - have high heritability and, in a less severe form, could be also found in non-syndromic children suffering from POSA. As genetic factors play a role in both POSA and craniofacial dysmorphisms, we hypothesize that some genes associated with specific craniofacial features that are involved in the development of the orofacial area may be also considered candidate genes for POSA. The genetic background of POSA in children is less explored than in adults; so far, only one genome-wide association study for POSA has been conducted; however, children with craniofacial disorders were excluded from that study. In this narrative review, we discuss syndromes that are commonly associated with severe craniofacial dysmorphisms and a high prevalence of sleep-related breathing disorders (SRBD), including POSA. We also summarized information about their genetic background and based on this, proposed 30 candidate genes for POSA affecting craniofacial development that may play a role in children with syndromes, and identified seven of these genes that were previously associated with craniofacial features risky for POSA development in non-syndromic children. The evidence-based approach supports the proposition that variants of these candidate genes could lead to POSA phenotype even in these children, and, thus, should be considered in future research in the general pediatric population.

Craniofacial characteristics in Crouzon's syndrome: A systematic review and meta-analysis

The purpose of this meta-analysis was to strengthen the credibility of primary research results by combining open-source scientific material, namely a comparison of craniofacial features (Cfc) between Crouzon's syndrome (CS) patients and non-CS populations. All articles published up to October 7, 2021, were included in the search of PubMed, Google Scholar, Scopus, Medline, and Web of Science. The PRISMA guidelines were followed to conduct this study. PECO framework was applied in the following ways: Those who have CS are denoted by the letter P, those who have been diagnosed with CS via clinical or genetic means by the letter E, those who do not have CS by the letter C, and those who have a Cfc of CS by the letter O. Independent reviewers collected the data and ranked the publications based on their adherence to the Newcastle-Ottawa Quality Assessment Scale. A total of six case-control studies were reviewed for this meta-analysis. Due to the large variation in cephalometric measures, only those published in at least two previous studies were included. This analysis found that CS patients had a smaller skull and mandible volumes than those without CS.in terms of SNA° (MD = -2.33, p = <0.001, I2 = 83.6%) and ANB°(MD = -1.89, p = <0.005, I2 = 93.1%)), as well as ANS (MD = -1.87, p = 0.001, I2 = 96.5%)) and SN/PP (MD = -1.99, p = 0.036, I2 = 77.3%)). In comparison to the general population, people with CS tend to have shorter and flatter cranial bases, smaller orbital volumes, and cleft palates. They differ from the general population in having a shorter skull base and more V-shaped maxillary arches.

Crouzon syndrome in a fraternal twin: A case report and review of the literature

BACKGROUND

Crouzon syndrome (CS; OMIM 123500) is an autosomal dominant inherited craniofacial disorder caused by mutations in the fibroblast growth factor receptor 2 (FGFR2) gene. CS is characterized by craniofacial dysostosis, exophthalmos, and facial anomalies with hypoplastic maxilla and relative mandibular prognathism.

CASE SUMMARY

Our report involves a 6-year-old fraternal twin boy with many caries in the oral cavity who presented with characteristic features of CS based on clinical and radiographic examinations along with Sanger sequencing. The fraternal girl did not show any abnormalities indicating CS. Carious teeth and poor oral hygiene were managed promptly through administering appropriate behavior guidance, orthodontic treatment was planned, and preventive procedures were described.

CONCLUSION

CS could occur in a fraternal twin caused by a de novo mutation of the FGFR2 gene. Oral hygiene instruction, preventive programs on oral hygiene, orthodontic treatment, and maxillary osteotomy were required for treatment.

Meckel's Cartilage in Mandibular Development and Dysmorphogenesis

The Fgfr2c^C342Y/+ Crouzon syndrome mouse model carries a cysteine to tyrosine substitution at amino acid position 342 (Cys342Tyr; C342Y) in the fibroblast growth factor receptor 2 (Fgfr2) gene equivalent to a FGFR2 mutation commonly associated with Crouzon and Pfeiffer syndromes in humans. The Fgfr2c C342Y mutation results in constitutive activation of the receptor and is associated with upregulation of osteogenic differentiation. Fgfr2c^C342Y/+ Crouzon syndrome mice show premature closure of the coronal suture and other craniofacial anomalies including malocclusion of teeth, most likely due to abnormal craniofacial form. Malformation of the mandible can precipitate a plethora of complications including disrupting development of the upper jaw and palate, impediment of the airway, and alteration of occlusion necessary for proper mastication. The current paradigm of mandibular development assumes that Meckel’s cartilage (MC) serves as a support or model for mandibular bone formation and as a template for the later forming mandible. If valid, this implies a functional relationship between MC and the forming mandible, so mandibular dysmorphogenesis might be discerned in MC affecting the relationship between MC and mandibular bone. Here we investigate the relationship of MC to mandible development from the early mineralization of the mandible (E13.5) through the initiation of MC degradation at E17.7 using Fgfr2c^C342Y/+ Crouzon syndrome embryos and their unaffected littermates (Fgfr2c^+/+). Differences between genotypes in both MC and mandibular bone are subtle, however MC of Fgfr2c^C342Y/+ embryos is generally longer relative to unaffected littermates at E15.5 with specific aspects remaining relatively large at E17.5. In contrast, mandibular bone is smaller overall in Fgfr2c^C342Y/+ embryos relative to their unaffected littermates at E15.5 with the posterior aspect remaining relatively small at E17.5. At a cellular level, differences are identified between genotypes early (E13.5) followed by reduced proliferation in MC (E15.5) and in the forming mandible (E17.5) in Fgfr2c^C342Y/+ embryos. Activation of the ERK pathways is reduced in the perichondrium of MC in Fgfr2c^C342Y/+ embryos and increased in bone related cells at E15.5. These data reveal that the Fgfr2c C342Y mutation differentially affects cells by type, location, and developmental age indicating a complex set of changes in the cells that make up the lower jaw.

Craniofacial Phenomics: Three-Dimensional Assessment of the Size and Shape of Cranial and Dentofacial Structures

Craniofacial phenomics has opened up numerous opportunities to correlate genetic and epigenetic factors to craniofacial phenotypes in order to improve our understanding of growth and development in health and disease. Three-dimensional (3D) imaging has played a key role in advancing craniofacial phenomics by facilitating highly sensitive and specific characterizations of craniofacial and dental morphology. Here we describe the use of micro-computed tomography (micro-CT) to image the murine craniofacial complex, followed by surface reconstruction for traditional morphometric analyses. We also describe the application of geometric morphometrics, based on Generalized Procrustes Analysis, for use in human premolars. These principles are interchangeable between various vertebrate species, and between various surface imaging techniques (including micro-CT and 3D surface scanners), offering a high level of versatility and precision for extensive phenotyping of the entire craniofacial complex.

Rare Genetic Syndromes and Oral Anomalies: A Review of the Literature and Case Series with a New Classification Proposal

Rare genetic syndromes, conditions with a global average prevalence of 40 cases/100,000 people, are associated with anatomical, physiological, and neurological anomalies that may affect different body districts, including the oral district. So far, no classification of oral abnormalities in rare genetic syndromes is present in the literature. The aim of this narrative review is to analyze literature on rare genetic syndromes affecting dento-oro-maxillofacial structures (teeth, maxillary bones, oral soft tissues, or mixed) and to propose a classification according to the detected oral abnormalities. In addition, five significant cases of rare genetic syndromes are presented. The Scale for the Assessment of Narrative Review Articles (SANRA) was followed for this review. From 674 papers obtained through PubMed search, 351 were selected. Sixty-two rare genetic syndromes involving oral manifestations were found and classified. The proposed classification aims to help the clinician to easily understand which dento-oro-maxillofacial findings might be expected in the presence of each rare genetic syndrome. This immediate framework may both help in the diagnosis of dento-oro-maxillofacial anomalies related to the underlying pathology as well as facilitate the drafting of treatment plans with the involvement of a multidisciplinary team.

Dental phenotype in Crouzon syndrome: A controlled radiographic study in 22 patients

OBJECTIVE

This retrospective radiographic controlled study investigates the dental phenotype in patients with Crouzon syndrome to determine if differences are observed as suggested by the FGFR2^C342Y/+ Crouzon mouse models, and whether these models could be of interest to study the role of this mutation in tooth development.

DESIGN

We assessed dental phenotype using dedicated linear measurements in 22 children with Crouzon syndrome and compared tooth morphology in both primary and permanent dentitions to an age-matched control group. Descriptive statistics were performed with "Sex" and "Age" as covariates for the permanent tooth models and "Sex" only for the primary tooth models, to take into account potential confounding factors.

RESULTS

We showed that permanent but not primary tooth dimensions were globally reduced in Crouzon syndrome, without microdontia. In permanent dentition, crown height, mesiodistal and faciolingual cervical diameters were reduced by 6.3%, 5.7% and 5.5% respectively (p < 0.05).

CONCLUSION

Our results underline the implication of Fibroblast Growth Factor Receptor 2 (FGFR2) in dental development of humans and contribute to support FGFR2^C342Y/+ Crouzon mouse models as partial replicas of this condition, including in the oral region.

Early mandibular morphological differences in patients with FGFR2 and FGFR3-related syndromic craniosynostoses: A 3D comparative study

Syndromic craniosynostoses are defined by the premature fusion of one or more cranial and facial sutures, leading to skull vault deformation, and midfacial retrusion. More recently, mandibular shape modifications have been described in FGFR-related craniosynostoses, which represent almost 75% of the syndromic craniosynostoses. Here, further characterisation of the mandibular phenotype in FGFR-related craniosynostoses is provided in order to confirm mandibular shape modifications, as this could contribute to a better understanding of the involvement of the FGFR pathway in craniofacial development. The aim of our study was to analyse early mandibular morphology in a cohort of patients with FGFR2- (Crouzon and Apert) and FGFR3- (Muenke and Crouzonodermoskeletal) related syndromic craniosynostoses. We used a comparative geometric morphometric approach based on 3D imaging. Thirty-one anatomical landmarks and eleven curves with sliding semi-landmarks were defined to model the shape of the mandible. In total, 40 patients (12 with Crouzon, 12 with Apert, 12 with Muenke and 4 with Crouzonodermoskeletal syndromes) and 40 age and sex-matched controls were included (mean age: 13.7 months ±11.9). Mandibular shape differed significantly between controls and each patient group based on geometric morphometrics. Mandibular shape in FGFR2-craniosynostoses was characterized by open gonial angle, short ramus height, and high and prominent symphysis. Short ramus height appeared more pronounced in Apert than in Crouzon syndrome. Additionally, narrow inter-condylar and inter-gonial distances were observed in Crouzon syndrome. Mandibular shape in FGFR3-craniosynostoses was characterized by high and prominent symphysis and narrow inter-gonial distance. In addition, narrow condylar processes affected patients with Crouzonodermoskeletal syndrome. Statistical analysis of variance showed significant clustering of Apert and Crouzon, Crouzon and Muenke, and Apert and Muenke patients (p < 0.05). Our results confirm distinct mandibular shapes at early ages in FGFR2- (Crouzon and Apert syndromes) and FGFR3-related syndromic craniosynostoses (Muenke and Crouzonodermoskeletal syndromes) and reinforce the hypothesis of genotype-phenotype correspondence concerning mandibular morphology.

Ten Years of Micro-CT in Dentistry and Maxillofacial Surgery: A Literature Overview

Micro-computed tomography (micro-CT) is a consolidated imaging technology allowing non-destructive three-dimensional (3D) qualitative and quantitative analysis by the observation of microstructures with high resolution. This paper aims at delivering a structured overview of literature about studies performed using micro-CT in dentistry and maxillofacial surgery (MFS) by analyzing the entire set of articles to portray the state of the art of the last ten years of scientific publications on the topic. It draws the scenario focusing on biomaterials, in vitro and in/ex vivo applications, bone structure analysis, and tissue engineering. It confirms the relevance of the micro-CT analysis for traditional research applications and mainly in dentistry with respect to MFS. Possible developments are discussed in relation to the use of the micro-CT combined with other, traditional, and not, techniques and technologies, as the elaboration of 3D models based on micro-CT images and emerging numerical methods. Micro-CT results contribute effectively with whose ones obtained from other techniques in an integrated multimethod approach and for multidisciplinary studies, opening new possibilities and potential opportunities for the next decades of developments.

Titania nanotube-based protein delivery system to inhibit cranial bone regeneration in Crouzon model of craniosynostosis

BACKGROUND

Craniosynostosis is a developmental disorder characterized by the premature fusion of skull sutures, necessitating repetitive, high-risk neurosurgical interventions throughout infancy. This study used protein-releasing Titania nanotubular implant (TNT/Ti) loaded with glypican 3 (GPC3) in the cranial critical-sized defects (CSDs) in Crouzon murine model (Fgfr2c342y/+ knock-in mutation) to address a key challenge of delaying post-operative bone regeneration in craniosynostosis.

MATERIALS AND METHODS

A 3 mm wide circular CSD was created in two murine models of Crouzon syndrome: (i) surgical control (CSDs without TNT/Ti or any protein, n=6) and (ii) experimental groups with TNT/Ti loaded with GPC3, further subdivided into the presence or absence of chitosan coating (on nanotubes) (n=12 in each group). The bone volume percentage in CSDs was assessed 90 days post-implantation using micro-computed tomography (micro-CT) and histological analysis.

RESULTS

Nano-implants retrieved after 90 days post-operatively depicted well-adhered, hexagonally arranged, and densely packed nanotubes with average diameter of 120±10 nm. The nanotubular architecture was generally well-preserved. Compared with the control bone volume percentage data (without GPC3), GPC3-loaded TNT/Ti without chitosan coating displayed a significantly lower volume percent in cranial CSDs (P<0.001). Histological assessment showed relatively less bone regeneration (healing) in GPC3-loaded CSDs than control CSDs.

CONCLUSION

The finding of inhibition of cranial bone regeneration by GPC3-loaded TNT/Ti in vivo is an important advance in the novel field of minimally-invasive craniosynostosis therapy and holds the prospect of altering the whole paradigm of treatment for affected children. Future animal studies on a larger sample are indicated to refine the dosage and duration of drug delivery across different ages and both sexes with the view to undertake human clinical trials.

Dentinal dysplasia type 1: A 3D micro-computed tomographic study of enamel, dentine and root canal morphology

Dentine dysplasia type 1 is a rare and complex dental anomaly. Our aim was to conduct a morphometric assessment of a dentinal dysplasia type 1c (DD1c) caries-free mandibular second molar, extracted due to symptomatic apical periodontitis. Controls consisted of five intact mandibular second molars. Micro-computed tomography analysis showed that the DD1c volume % for enamel, dentine/cementum and pulp chamber fell in the 0.36th, 99.97th and 0.09th percentiles of the control teeth (P < 0.01). It also revealed an extremely complicated root canal system in the DD1c tooth with a varying degree of dentine mineralisation and aberrant dentine deposition in the pulp chamber. A crack extending from the external tooth surface to the pulp chamber was identified as a potential site for microbial invasion. Clinical implications include preventive measures and early intervention in reversible pulpitis. Conclusion: Micro-CT imaging can be useful in establishing post-extraction diagnosis of cracks and phenomic characterisation of tooth anomalies.

Mandibular dysmorphology due to abnormal embryonic osteogenesis in FGFR2-related craniosynostosis mice

One diagnostic feature of craniosynostosis syndromes is mandibular dysgenesis. Using three mouse models of Apert, Crouzon and Pfeiffer craniosynostosis syndromes, we investigated how embryonic development of the mandible is affected by fibroblast growth factor receptor 2 (Fgfr2) mutations. Quantitative analysis of skeletal form at birth revealed differences in mandibular morphology between mice carrying Fgfr2 mutations and their littermates that do not carry the mutations. Murine embryos with the mutations associated with Apert syndrome in humans (Fgfr2^+/S252W and Fgfr2^+/P253R) showed an increase in the size of the osteogenic anlagen and Meckel's cartilage (MC). Changes in the microarchitecture and mineralization of the developing mandible were visualized using histological staining. The mechanism for mandibular dysgenesis in the Apert Fgfr2^+/S252W mouse resulting in the most severe phenotypic effects was further analyzed in detail and found to occur to a lesser degree in the other craniosynostosis mouse models. Laser capture microdissection and RNA-seq analysis revealed transcriptomic changes in mandibular bone at embryonic day 16.5 (E16.5), highlighting increased expression of genes related to osteoclast differentiation and dysregulated genes active in bone mineralization. Increased osteoclastic activity was corroborated by TRAP assay and in situ hybridization of Csf1r and Itgb3. Upregulated expression of Enpp1 and Ank was validated in the mandible of Fgfr2^+/S252W embryos, and found to result in elevated inorganic pyrophosphate concentration. Increased proliferation of osteoblasts in the mandible and chondrocytes forming MC was identified in Fgfr2^+/S252W embryos at E12.5. These findings provide evidence that FGFR2 gain-of-function mutations differentially affect cartilage formation and intramembranous ossification of dermal bone, contributing to mandibular dysmorphogenesis in craniosynostosis syndromes.

This article has an associated First Person interview with the joint first authors of the paper.

Summary: FGFR2 gain-of-function mutations differentially affect cartilage formation and intramembranous ossification of dermal bone, resulting in abnormal embryonic osteogenesis of the mandible.