Review of the Genetic Basis of Jaw Malformations

Three-dimensional mandibular characteristics in skeletal malocclusion : A cross-sectional study

PURPOSE

We aimed to comprehensively analyse a possible correlation between skeletal malocclusions, gender and mandibular characteristics in all three dimensions in adults and to identify mandibular characteristics that are typical for extreme skeletal patterns.

METHODS

A 3D model of the skull was calculated in 111 adult patients (mean age = 27.0 ± 10.2 years; 49 women, 62 men) from available computed tomography or cone beam computed tomography scans of their heads. Based on the 3D models, the skeletal patterns were examined in (a) the transversal dimension regarding asymmetry according to menton deviation, (b) the sagittal dimension according to the Wits appraisal and (c) the vertical dimension according to the maxillomandibular plane angle. The mandibular characteristics assessed were linear (ramus height and width, body length), angular (ramus, gonial and body angle) and volumetric (ramus/mandibular volume, body/mandibular volume) parameters.

RESULTS

No correlation between transversal skeletal asymmetry and mandibular characteristics were found, while sagittal (F(16, 174) = 3.32, p < 0.001, η2 = 0.23) and vertical (F(16, 174) = 3.18, p < 0.001, η2 = 0.23) skeletal patterns were shown to have a significant effect on the mandible. Gender correlated with mandibular characteristics independently from the skeletal pattern. Discriminant analysis revealed that class II and III patients differed in ramus and body angle with class II patients showing higher angles (ramus angle: class II = 89.8 ± 3.9° vs. class III = 84.4 ± 4.8°; body angle: class II = 87.7 ± 4.8° vs. class III = 82.1 ± 5.2°). Hypo- and hyperdivergent patients were discriminated by gonial angle, body angle and body/mandibular volume with hyperdivergent patients having a greater gonial and body angle and body/mandibular volume (gonial angle: hypodivergent = 114 ± 9.3° vs. hyperdivergent = 126.4 ± 8.6°; body angle: hypodivergent = 82.9 ± 4.4° vs. hyperdivergent = 87.7 ± 6.5°; body/mandibular volume: hypodivergent = 72.4 ± 2.7% vs. hyperdivergent = 76.2 ± 2.6%).

CONCLUSION

When analysing 3D data for treatment planning of adult patients, the orthodontist should pay attention to angular and volumetric characteristics of the mandible to identify extreme skeletal sagittal or vertical malocclusions.

Treatment of Skeletal Class II Division 1 Using Twin Block Myofunctional Appliance

Myofunctional appliances are customarily used to treat Class II malocclusions in growing children to alter their growth. Functional appliances are widely accepted to enhance skeletal relationships in the short term efficiently. It utilizes muscular forces by muscles to make dental and skeleton modifications. The myofunctional appliance might be removable or fixed. The variation of mode and method of action depends on the design, but the forces created by the muscles' stretching provide their effect. According to research, the effectiveness of functional appliances as a therapy for Class II malocclusion might be influenced by mandibular growth patterns. Their low skeletal maturation influence outweighs the primary dentoalveolar impact of the twin block myofunctional orthodontic appliances. Class II malocclusions can benefit by using myofunctional appliances in specific clinical situations, such as when the patient is still developing. These devices make the fixed appliance phase easier to use, but their effectiveness depends heavily on the patient's compliance. In this case, an 11-year-old female expressed concern about the forward positioning of her upper front teeth when she visited the department of orthodontics. Twin block, a myofunctional appliance, was used to manage it, and then fixed orthodontic treatment was used to fine-tune the occlusion. This case report illustrates the design and treatment effects.

Skeletal Class III Malocclusion Is Associated with ADAMTS2 Variants and Reduced Expression in a Familial Case

Skeletal Class III malocclusion with maxillary deficiency is a severe maxillofacial disease with unclear pathogenic mechanisms. We recruited a Han Chinese family who was clinically diagnosed with skeletal Class III malocclusion and maxillary deficiency. Using whole exome sequencing, a missense variant in ADAMTS2 (NM_014244: c.3506G>T: p.G1169V) was identified and predicted as deleterious by in silico tools. We also found ADAMTS2 variants associated with deficient maxillary development in a cohort. ADAMTS2 expression in HEK293 cells showed significant decrease due to the variant, which was also consistent in dental pulp stem cells from the proband and a healthy control. In the adamts2-knockdown zebrafish model, the length and width of the ethmoid plate, as well as the length of the palatoquadrate became significantly shorter than the control group (p < 0.001), while there was no significant difference in the length and width of the mandible. The expression of Sox3, which was required in early embryonic craniofacial development, was significantly downregulated in the adamts2-knockdown zebrafish embryos. Bioinformatic and cellular studies showed that the decreased expression of ADAMTS2 may inhibit downstream ErbB signaling pathway transduction and restrain subsequent osteogenesis in human adult mesenchymal stromal cells. Collectively, these data showed that ADAMTS2 (c.3506G>T: p.G1169V) may confer susceptibility to risk of skeletal Class III malocclusion with maxillary deficiency.

Orofacial Cleft and Mandibular Prognathism-Human Genetics and Animal Models

Many complex molecular interactions are involved in the process of craniofacial development. Consequently, the network is sensitive to genetic mutations that may result in congenital malformations of varying severity. The most common birth anomalies within the head and neck are orofacial clefts (OFCs) and prognathism. Orofacial clefts are disorders with a range of phenotypes such as the cleft of the lip with or without cleft palate and isolated form of cleft palate with unilateral and bilateral variations. They may occur as an isolated abnormality (nonsyndromic-NSCLP) or coexist with syndromic disorders. Another cause of malformations, prognathism or skeletal class III malocclusion, is characterized by the disproportionate overgrowth of the mandible with or without the hypoplasia of maxilla. Both syndromes may be caused by the presence of environmental factors, but the majority of them are hereditary. Several mutations are linked to those phenotypes. In this review, we summarize the current knowledge regarding the genetics of those phenotypes and describe genotype-phenotype correlations. We then present the animal models used to study these defects.

Teratogenicity and toxicity of the new BPA alternative TMBPF, and BPA, BPS, and BPAF in chick embryonic development

Bisphenol A (BPA) is a widely known, yet controversial reproductive toxin, capable of inducing reproductive, developmental, and somatic growth defects across species. Due to scientific findings and public concern, companies have developed BPA alternatives remarkably similar to BPA. However, these alternatives have had much less testing and oversight, yet they are already being mass-produced and used across industries from plastics to food-contact coatings. The newest one, tetramethyl bisphenol F (TMBPF), is the least well-studied and has never been investigated in embryological models, however it continues to be mass produced and found in various products. Here, we used the chicken embryotoxicity screening test to compare the toxicities and potencies of several BPA analogs including TMBPF. We exposed developing chicken (Gallus gallus domesticus) embryos in ovo, from embryonic day 5 to 12 (E5-12), to increasing concentrations of BPA, bisphenol S (BPS), bisphenol AF (BPAF), and TMBPF, from 0.003 to 30 μM, and analyzed their developmental and toxic effects. The bisphenols significantly impaired development, growth, and survival in a dose-dependent manner, even at low, environmentally relevant concentrations of 3-30 nM. There was severely reduced growth and developmental delay, with exposed embryos averaging half the size and weight of control vehicle-treated embryos. The most common and severe dysmorphologies were craniofacial, eye, gastrointestinal, and body pigmentation abnormalities. The bisphenols caused dose-dependent toxicity with the lowest LC₅₀s (lethal concentration with 50% survival) ever demonstrated in chick embryos, at 0.83-2.92 μM. Notably, TMBPF was the second-most toxic and teratogenic of all chemicals tested (rank order of BPAF > TMBPF > BPS > BPA). These results underscore the adverse effects of BPA replacements on early embryo development and may have implications for reproductive health and disease across species, including pregnancy exposures in humans.

Mandibulofacial Dysostosis Attributed to a Recessive Mutation of CYP26C1 in Hereford Cattle

In spring 2020, six Hereford calves presented with congenital facial deformities attributed to a condition we termed mandibulofacial dysostosis (MD). Affected calves shared hallmark features of a variably shortened and/or asymmetric lower mandible and bilateral skin tags present 2–10 cm caudal to the commissure of the lips. Pedigree analysis revealed a single common ancestor shared by the sire and dam of each affected calf. Whole-genome sequencing (WGS) of 20 animals led to the discovery of a variant (Chr26 g. 14404993T>C) in Exon 3 of CYP26C1 associated with MD. This missense mutation (p.L188P), is located in an α helix of the protein, which the identified amino acid substitution is predicted to break. The implication of this mutation was further validated through genotyping 2 additional affected calves, 760 other Herefords, and by evaluation of available WGS data from over 2500 other individuals. Only the affected individuals were homozygous for the variant and all heterozygotes had at least one pedigree tie to the suspect founder. CYP26C1 plays a vital role in tissue-specific regulation of retinoic acid (RA) during embryonic development. Dysregulation of RA can result in teratogenesis by altering the endothelin-1 signaling pathway affecting the expression of Dlx genes, critical to mandibulofacial development. We postulate that this recessive missense mutation in CYP26C1 impacts the catalytic activity of the encoded enzyme, leading to excess RA resulting in the observed MD phenotype.

Etiology of Malocclusion and Dominant Orthodontic Problems in Mixed Dentition: A Cross-sectional Study in a Group of Thai Children Aged 8-9 Years

Background:

Etiology of malocclusion can be the cause of deviation in the skeleton, dental, and soft tissue development in children. Identifying etiology of malocclusion and dominant orthodontic problems as well as early detection could help in future effective treatment, management, and public health planning.

Materials and Methods:

A cross-sectional study was performed among 202 children. Consensus process was carried out between experienced orthodontic experts in etiology of malocclusion, dominant orthodontic problems, type of early treatment, and malocclusion severity. Fisher’s exact test and descriptive statistics were used to explain the study results.

Results:

Etiology of malocclusion was detected in both congenital and acquired etiology (64.3%), followed by acquired etiology only (29.7%). The top three dominant orthodontic problems were caries (22.5%), early loss of primary tooth (15.6%), and tendency of crowding in permanent dentition (14.6%). Nearly all the children needed restoration (86.4%) and interceptive orthodontic treatment (69.3%), whereas severe malocclusion level was found in one-fourth of the children (26.0%). Statistical significance was found between type of early treatment and malocclusion severity (P < 0.001).

Conclusion:

Acquired etiology was very high. Caries and early loss of primary teeth were dominant orthodontic problems. An early treatment, especially preventive orthodontic treatment, was needed in almost all children. Malocclusion severity higher than moderate level was found in more than half of the children.

Impaired ribosome biogenesis: mechanisms and relevance to cancer and aging

The biosynthesis of ribosomes is a complex process that requires the coordinated action of many factors and a huge energy investment from the cell. Ribosomes are essential for protein production, and thus for cellular survival, growth and proliferation. Ribosome biogenesis is initiated in the nucleolus and includes: the synthesis and processing of ribosomal RNAs, assembly of ribosomal proteins, transport to the cytoplasm and association of ribosomal subunits. The disruption of ribosome biogenesis at various steps, with either increased or decreased expression of different ribosomal components, can promote cell cycle arrest, senescence or apoptosis. Additionally, interference with ribosomal biogenesis is often associated with cancer, aging and age-related degenerative diseases. Here, we review current knowledge on impaired ribosome biogenesis, discuss the main factors involved in stress responses under such circumstances and focus on examples with clinical relevance.