Skeletal malocclusion: a developmental disorder with a life-long morbidity

Orthodontic Treatment for Borderline Class III Malocclusion in Adults: Nonextraction Treatment with Anterior Bite Turbo: A Case Report

Retrusive upper lips, retroclined upper incisors, a shorter midface, and a larger maxillary-mandibular difference are the characteristics of borderline Class III malocclusion. Individuals with borderline Class III malocclusion frequently exhibit certain morphologic, dental, and skeletal traits, which should aid in the diagnosis of the condition. To report the case of a 22-year-old Vietnamese woman who complained of having tense front teeth and lacking confidence when smiling. Medical history did not find anything strange, there was root canal treatment of the first premolar on the left of the upper jaw, asymmetrical concave chin, and right deviation. Orthodontic camouflage treatment using anterior bite turbos in combination with early light short Class III elastics and box elastics was proposed since the patient declined to have orthognathic surgery. In just 10 months of treatment, a Class I molar and canine relationship was created, an anterior crossbite was corrected via mandibular retraction, and severe skeletal malocclusions were successfully treated without orthognathic surgery. Smiling currently showcases the patient's maxillary incisors more prominently, and her lower lip fullness has diminished, giving her a more attractive smile and a significant improvement to her facial profile.

Morphological integration in inferior alveolar canal and mandibular shapes

OBJECTIVE

During embryogenesis of mandible, the initial ossification centre begins at the bifurcation of the inferior alveolar (IA) and the mental nerves. Additionally, in congenital anomalies like craniofacial microsomia (CFM), the IA canal is completely absent on the microsomic side. These observations led us to hypothesise that there may be a morphological integration between these structures - the IA nerve and the mandibular shapes. Therefore, the primary objective of this study was to test for morphological integration between these structures and the secondary objective was to determine if there were shape variations in these structures among skeletal Classes I, II and III subjects.

SETTING AND SAMPLE POPULATION

The sample size of the study is 80 full-head cone-beam computed tomography (CBCT) scans (age 16-56 years).

METHODS

We retrieved CBCT scans from our archived database using specific inclusion/exclusion criteria. In the de-identified CBCT scans, traditional coordinate landmarks and sliding semi-landmarks were placed on the mandible and the IA canal (proxy for IA nerve). Using geometric morphometric analyses, we tested integration between the IA canal and the mandibular shapes. We used Procrustes ANOVA to test for overall shape variations among the three skeletal classes (Classes I, II and III).

RESULTS

The IA canal and posterior/inferior border of mandible showed strong integration (r-PLS = .845, P = .001). Similar strong integration was also observed between the IA canal and the overall shape of the mandible (r-PLS = .866, P = .001). Additionally, there was a statistically significant variation in overall shape between skeletal Class I and Class II (P = .008) and Class II and Class III (P = .001).

CONCLUSIONS

The strong integration between two structures suggests that the IA nerve may play a role in establishing mandibular shape early in development. We posit this may be important in driving mandibular defects seen in CFM, which warrants further investigation.

Association between Taql polymorphism of vitamin D receptor gene and vertical growth of the mandible: A cross-sectional study

Objective

To determine whether the gonial angle on digital panoramic radiographs is associated with vitamin D receptor (VDR) Taql polymorphism.

Methods

Genomic DNA samples were collected from the buccal mucosa of patients aged 26-43 years. TaqMan assay for single nucleotide polymorphism genotyping was used to detect the genotype of Taql polymorphism. The gonial angle was measured bilaterally on panoramic radiography. The normal gonial angle was fixed as 121.8°, and it represented the cutoff value for the high gonial angle (HGA) and low gonial angle (LGA) groups. Various genetic models were analyzed, namely dominant (homozygous [AA] vs. heterozygous [AG] + polymorphic [GG]), recessive (AA + AG vs. GG), and additive (AA + GG vs. AG), using the chi-squared test.

Results

The reliability of the gonial angle measurement was analyzed using a random sample (26%) of the tests, with the intra-examiner correlation showing an intra-class correlation coefficient of 0.99. The frequencies of the AA, AG, and GG genotypes of rs731236 polymorphism were 40.5%, 41.9%, and 17.6% in the HGA group and 21.8%, 51.0%, and 27.2% in the LGA group, respectively (P = 0.042). A statistically significant difference was observed in the allele frequencies between the two groups (P = 0.011). Moreover, a significant correlation was observed in the dominant genetic model.

Conclusions

Taql polymorphism in the VDR gene plays a critical role in the vertical growth of the mandible and decreased gonial angle.

Mechanical Characterization and Structural Analysis of Latex-Containing and Latex-Free Intermaxillary Orthodontic Elastics

Class II malocclusion is one of the most common dental anomalies and the use of intermaxillary elastomers is the standard method in its treatment. However, orthodontic elastics cannot exert continuous force over a period of time due to force degradation. Our goal was to mechanically characterize the different types of elastomers during static and cyclic loads, based on uniform methodology and examine the morphological changes after loading. Ten types of latex-containing and four latex-free intermaxillary elastics were examined from six different manufacturers. To determine the mechanical characteristics of the elastomers, tensile tests, cyclical tensile fatigue tests and 24 h relaxation tests were performed, and the elastics were also subjected to scanning electron microscopy (SEM) and Raman spectroscopy. Regardless of the manufacturer, the latex-containing elastomers did not show significant differences in the percentage of elongation at break during the tensile test. Only one type of latex-containing elastomer did not tear during the 24 h cyclical fatigue test. Fatigue was confirmed by electron microscopy images, and the pulling force reduced significantly. During the force relaxation test, only one latex-free ligature was torn; the force degradation was between 7.8% and 20.3% for latex ligatures and between 29.6% and 40.1% for latex-free elastomers. The results showed that dynamic loading was more damaging to ligatures than static loading, latex-containing elastomers were more resistant than latex-free elastics, and which observation could have clinical consequences or a potential effect on patient outcome.

TWIST1 interacts with β/δ-catenins during neural tube development and regulates fate transition in cranial neural crest cells

Cell fate determination is a necessary and tightly regulated process for producing different cell types and structures during development. Cranial neural crest cells (CNCCs) are unique to vertebrate embryos and emerge from the neural plate borders into multiple cell lineages that differentiate into bone, cartilage, neurons and glial cells. We have previously reported that Irf6 genetically interacts with Twist1 during CNCC-derived tissue formation. Here, we have investigated the mechanistic role of Twist1 and Irf6 at early stages of craniofacial development. Our data indicate that TWIST1 is expressed in endocytic vesicles at the apical surface and interacts with β/δ-catenins during neural tube closure, and Irf6 is involved in defining neural fold borders by restricting AP2α expression. Twist1 suppresses Irf6 and other epithelial genes in CNCCs during the epithelial-to-mesenchymal transition (EMT) process and cell migration. Conversely, a loss of Twist1 leads to a sustained expression of epithelial and cell adhesion markers in migratory CNCCs. Disruption of TWIST1 phosphorylation in vivo leads to epidermal blebbing, edema, neural tube defects and CNCC-derived structural abnormalities. Altogether, this study describes a previously uncharacterized function of mammalian Twist1 and Irf6 in the neural tube and CNCCs, and provides new target genes for Twist1 that are involved in cytoskeletal remodeling.

DNA methylation differences during development distinguish sympatric morphs of Arctic charr (Salvelinus alpinus)

Changes in DNA methylation in specific coding or non-coding regions can influence development and potentially divergence in traits within species and groups. While the impact of epigenetic variation on developmental pathways associated with evolutionary divergence is the focus of intense investigation, few studies have looked at recently diverged systems. Phenotypic diversity between closely related populations of Arctic charr (Salvelinus alpinus), which diverged within the last 10 000 years, offers an interesting ecological model to address such effects. Using bisulfite sequencing, we studied general DNA methylation patterns during development in the four sympatric morphs of Arctic charr from Lake Thingvallavatn. The data revealed strong differences between developmental timepoints and between morphs (mainly along the benthic - limnetic axis), both at single CpG sites and in 1,000bp-regions. Genes located close to differentially methylated CpG sites were involved in nucleosome assembly, regulation of osteoclast differentiation, and cell-matrix adhesion. Differentially methylated regions were enriched in tRNA and rRNA sequences, and half of them were located close to transcription start sites. The expression of 14 genes showing methylation differences over time or between morphs was further investigated by qPCR and nine of these were found to be differentially expressed between morphs. Four genes (ARHGEF37-like, H3-like, MPP3 and MEGF9) showed a correlation between methylation and expression. Lastly, histone gene clusters displayed interesting methylation differences between timepoints and morphs, as well as intragenic methylation variation. The results presented here provide a motivation for further studies on the contribution of epigenetic traits, such as DNA methylation, to phenotypic diversity and developmental mechanisms.

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.

Orofacial Muscle Weakening in Facioscapulohumeral Muscular Dystrophy (FSHD) Patients

Background: Facioscapulohumeral muscular dystrophy is the third most commonly found type of muscular dystrophy. The aim of this study was to correlate the D4Z4 repeat array fragment size to the orofacial muscle weakening exhibited in a group of patients with a genetically supported diagnosis of FSHD. Methods: Molecular genetic analysis was performed for 52 patients (27 female and 25 male) from a group that consisted of 36 patients with autosomal dominant pedigrees and 16 patients with either sporadic or unknown family status. The patients were tested with the southern blotting technique, using EcoRI/Avrll double digestion, and fragments were detected by a p13E-11 telomeric probe. Spearman’s correlation was used to compare the fragment size with the degree of muscle weakening found in the forehead, periocular and perioral muscles. Results: A positive non-significant correlation between the DNA fragment size and severity of muscle weakness was found for the forehead (r = 0.27; p = 0187), the periocular (r = 0.24; p = 0.232) and the left and right perioral (r = 0.29; p = 0.122), (r = 0.32; p = 0.085) muscles. Conclusions: Although FSHD patients exhibited a decrease in muscular activity related to the forehead, perioral, and periocular muscles the genotype–phenotype associations confirmed a weak to moderate non-significant correlation between repeat size and the severity of muscle weakness. Orofacial muscle weakening and its association with a D4Z4 contraction alone may not have the significance to serve as a prognostic biomarker, due to the weak to moderate association. Further studies with larger sample sizes are needed to determine the degree of genetic involvement in the facial growth in FSHD patients.

Changes in health-related quality of life after orthognathic surgery: a multicenter study

Objective

To evaluate changes in general and oral health-related quality of life (HRQoL) in patients with dentofacial deformity undergoing orthognathic surgery, and whether these changes vary according to type of deformity.

Material and methods

This is a prospective longitudinal multicenter study of patients with dentofacial deformities (n = 90). The Orthognathic Quality of Life Questionnaire (OQLQ), Oral Health Impact Profile (OHIP-14), and Short-Form Health Survey version2 (SF-36v2) were self-completed by patients before surgery, 3 and 6 months after orthognathic surgery. Change was tested using paired t-test, and compared between Class II and Class III of dentofacial deformity by unpaired t-test. The magnitude of change was examined estimating the standardized response mean (SRM).

Results

The OQLQ and OHIP-14 showed statistically significant improvements 6 months after surgery, compared with the pre-surgical evaluation, but the SF-36v2 only in the physical component summary. The SRM was large in OQLQ oral function (-1.11) and dentofacial facial aesthetics (-0.76) dimensions, and moderate in most of OHIP-14 dimensions. Differences in mean change between Class II and III were statistically significant for global scores of OQLQ (-10.08 vs -20.30, p = 0.0271) and OHIP-14 (-3.79 vs -10.56, p = 0.0144).

Conclusions

A significant improvement was observed in oral HRQoL and in the physical component of general health in patients with dentofacial deformities Class II and III after orthognathic surgery. Improvement was greater among Class III than in Class II patients.

Clinical relevance

These results provide patients, oral health care professionals, and planners with valuable information to make evidence-based decisions and facilitate shared clinical decision-making, taking into account the patients’ perspective.

Changes in Tongue Area, Pharyngeal Area, and Pharyngeal Airway Velocity after Correction of Mandibular Prognathism

This study aimed to investigate the correlation between the amount of mandibular setback, and the related changes of the tongue area, pharyngeal area, and pharyngeal airflow velocity. Twenty-five patients treated for mandibular prognathism, and serial cephalograms were obtained (T1: preoperation, T2: more than one year postoperation). The postoperative area of the tongue, pharyngeal airway space, and pharyngeal airflow velocity were investigated. Statistical analysis was performed with the Student t-test and Pearson correlation. The amount of mandible setback was significant after surgery (12.8 mm; p < 0.001). The pharyngeal area was significantly reduced 115.5 mm² (p = 0.046). There was a slight reduction of the tongue area (43.2 mm²; p = 0.305) and an increase of pharyngeal airflow velocity (0.3 m/s; p = 0.133). The Pearson correlation coefficient test showed no statistical significance among the amount of horizontal setback and vertical movement of the mandible, such as the reductions in the tongue area, the pharyngeal airway space, and the increase in pharyngeal airflow velocity. Larger amounts of mandibular setback caused a significant reduction of pharyngeal airway area, but without significant changes of the tongue area and pharyngeal airflow velocity.

Parathyroid Hormone Gene and Genes Involved in the Maintenance of Vitamin D Levels Association with Mandibular Retrognathism

In this study we evaluated whether single nucleotide polymorphisms (SNPs) in the genes encoding PTH, VDR, CYP24A1, and CYP27B1 were associated with mandibular retrognathism (MR). Samples from biologically-unrelated Brazilian patients receiving orthodontic treatment were included in this study. Pre-orthodontic lateral cephalograms were used to determine the phenotype. Patients with a retrognathic mandible were selected as cases and those with an orthognathic mandible were selected as controls. Genomic DNA was used for genotyping analysis of SNPs in PTH (rs694, rs6256, and rs307247), VDR (rs7975232), CYP24A1 (rs464653), and CYP27B1 (rs927650). Chi-squared or Fisher’s tests were used to compare genotype and allele distribution among groups. Haplotype analysis was performed for the SNPs in PTH. The established alpha was p < 0.05. Multifactor dimensionality reduction (MDR) was used to identify SNP–SNP interactions. A total of 48 (22 males and 26 females) MR and 43 (17 males and 26 females) controls were included. The linear mandibular and the angular measurements were statistically different between MR and controls (p < 0.05). In the genotype and allele distribution analysis, the SNPs rs694, rs307247, and rs464653 were associated with MR (p < 0.05). MDR analyses predicted the best interaction model for MR was rs694–rs927650, followed by rs307247–rs464653–rs927650. Some haplotypes in the PTH gene presented statistical significance. Our results suggest that SNPs in PTH, VDR, CYP24A1, and CYP27B1 genes are associated with the presence of mandibular retrognathism.

The correlation between back posture and sagittal jaw position in adult orthodontic patients

Objective

A debate remains in evidence-based medicine about the reciprocal interchange between dental occlusion and body postural therapy. Back posture deformity has been found to be related to trunk asymmetry as one characteristic of scoliosis that is commonly reported in occlusal development issue. This study aims to determine the correlation between back posture and sagittal jaw position in adult orthodontic patients treated at the dental hospital of Universitas Sumatera Utara.

Methods

This observational study was conducted on orthodontic patients who had routine orthodontic control between October 2019 and February 2020. The sagittal jaw relationship on pre-treatment cephalometry lateral-based on Steiner analysis was done with OrthoVision software. The back posture that related to cervical, thoracic, and lumbar measurement was performed using scoliometer plastic economy (Baseline®).

Results

From 128 patients, aged between 18 and 30 years, we found 72 patients with Class I, 41 patients with Class II, and 15 patients with Class III skeletal malocclusion. There were no significant differences of trunk asymmetry based on sagittal jaw relationship (p = 0.651). Additionally, there was no significant correlation between back posture and sagittal jaw position in Class II and Class III patients (r = 0.112, p > 0.05).

Conclusion

In this study, the sagittal jaw relationship had poor correlation to back posture in orthodontic adult patients due to a compensatory mechanism. The presence of temporomandibular dysfunction, sella-nasion-B point, and head posture are specific variables in a particular dento-skeletal type that should be considered in further studies.

Prevalence of malocclusion and orthodontic treatment needs among young adults in Jeddah city

OBJECTIVE

To assess the prevalence of malocclusion and orthodontic treatment needs in a Saudi sample of Jeddah city.

MATERIALS AND METHODS

A cross-sectional (descriptive) study was performed in 2017 among 3016 subjects (1507 females and 1509 males) selected according to stratified random sampling design. The inclusion criteria were Saudi students aged between 14-18 years with no craniofacial deformities or syndromes and no orthodontic treatment carried out. Malocclusion was assessed using the modified Bjork et al. system, and Angle's classification and orthodontic treatment need to be evaluated by using the IOTN (DHC). Descriptive, associations and gender differences were assessed by one-way ANOVA, Chi-square, and Fisher exact tests. Data was analyzed using STATA version 13.0 (StataCorp, College Station, Texas, USA). Statistical significance was set at P < 0.05.

RESULTS

Approximately 12% of the participants had normal occlusion, 57% had Class I malocclusion, 17% had Class II malocclusion, and 14% had Class III malocclusion. The highest prevalence of malocclusion traits was for displacement, followed by a crossbite. The IOTN results revealed slight need for orthodontic treatment in (n = 795-26%) moderate/borderline in (n = 1166-39%), and great need in (n = 1055-35%). Class II and III malocclusion, OJ, reverse overjet, scissor bite, open bite, midline discrepancies, and crowding were significantly higher in males than females (P < 0.05).

CONCLUSION

Overall, there was a high prevalence of malocclusion and high orthodontic treatment need. The most common malocclusion was Class I. The most common orthodontic treatment need was moderate to borderline.

Oral health-related quality of life in Loeys-Dietz syndrome, a rare connective tissue disorder: an observational cohort study

BACKGROUND

Loeys-Dietz syndrome (LDS) is a rare connective tissue disorder whose oral manifestations and dental phenotypes have not been well-characterized. The aim of this study was to explore the influence of oral manifestations on oral health-related quality of life (OHRQoL) in LDS patients.

MATERIAL AND METHODS

LDS subjects were assessed by the craniofacial team at the National Institutes of Health Clinical Center Dental Clinic between June 2015 and January 2018. Oral Health Impact Profile (OHIP-14) questionnaire, oral health self-care behavior questionnaire and a comprehensive dental examination were completed for each subject. OHRQoL was assessed using the OHIP-14 questionnaire with higher scores corresponding to worse OHRQoL. Regression models were used to determine the relationship between each oral manifestation and the OHIP-14 scores using a level of significance of p ≤ 0.05.

RESULTS

A total of 33 LDS subjects (51.5% female) aged 3-57 years (19.6 ± 15.1 years) were included in the study. The OHIP-14 scores (n = 33) were significantly higher in LDS subjects (6.30 [SD 6.37]) when compared to unaffected family member subjects (1.50 [SD 2.28], p < 0.01), and higher than the previously reported scores of the general U.S. population (2.81 [SD 0.12]). Regarding oral health self-care behavior (n = 32), the majority of LDS subjects reported receiving regular dental care (81%) and maintaining good-to-excellent daily oral hygiene (75%). Using a crude regression model, worse OHRQoL was found to be associated with dental hypersensitivity (β = 5.24; p < 0.05), temporomandibular joints (TMJ) abnormalities (β = 5.92; p < 0.01), self-reported poor-to-fair oral health status (β = 6.77; p < 0.01), and cumulation of four or more oral manifestations (β = 7.23; p < 0.001). Finally, using a parsimonious model, self-reported poor-to-fair oral health status (β = 5.87; p < 0.01) and TMJ abnormalities (β = 4.95; p < 0.01) remained significant.

CONCLUSIONS

The dental hypersensitivity, TMJ abnormalities, self-reported poor-to-fair oral health status and cumulation of four-or-more oral manifestations had significant influence on worse OHRQoL. Specific dental treatment guidelines are necessary to ensure optimal quality of life in patients diagnosed with LDS.

Facial Contouring by Using Dermal Fillers and Botulinum Toxin A: A Practical Approach

BACKGROUND

The perception of an attractive face is largely subjective. The purpose of this paper is to provide an insight and a practical approach to facial contouring management with hyaluronic acid (HA) implants and botulinum toxin A.

METHODS

This study is presenting the clinical experience of the authors regarding facial contouring. After a careful medical history, patients underwent an exhaustive aesthetic assessment that includes photographs and videos. Realistic treatment goals were discussed and agreed with the patient. Comprehensive treatment strategies for facial contouring, including HA implants and/or botulinum toxin A injections, were selected according to the patient needs.

RESULTS

Based on the MD codes^®, developed by Mauricio de Maio, these treatment strategies have been adapted to six different basic categories of facial shapes, namely round, square, triangular, inverted triangle, rectangle, oval and oblong faces. The incidence of complications was low and, in all the cases, was mild (edema, erythema and local ecchymosis), of limited duration, and was resolved without sequela.

CONCLUSIONS

The current article presented the personal experiences of the authors on a specific subject, and this fact should be considered when interpreting data from this paper. As other aesthetic treatments, facial contouring should be focused on the patient needs and to select a specific aesthetic approach according to different facial shapes. Finally, it is essential to have a good understanding of the potential associated complications, because it will help the specialist to take the necessary precautions to prevent them, and if they ever arise, to be able to deal with them effectively.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

The accuracy and stability of the maxillary position after orthognathic surgery using a novel computer-aided surgical simulation system

Background

Many reports have been published on orthognathic surgery (OGS) using computer-aided surgical simulation (CASS). The purpose of this study was to evaluate the accuracy of the maxillary repositioning and the stability of the maxilla in patients who underwent OGS using a newly developed CASS program, a customized osteotomy guide, and a customized miniplate.

Methods

Thirteen patients who underwent OGS from 2015 to 2017 were included. All patients underwent a bimaxillary operation. First, a skull-dentition hybrid 3D image was rendered by merging the cone beam computed tomography (CBCT) images with the dentition scan file. After virtual surgery (VS) using the FaceGide® program, patient-customized osteotomy guides and miniplates were then fabricated and used in the actual operation. To compare the VS with the actual surgery and postoperative skeletal changes, each reference point marked on the image was compared before the operation (T0) and three days (T1), four months (T2), and a year (T3) after the operation, and with the VS (Tv). The differences between ΔTv (Tv-T0) and ΔT1 (T1-T0) were statistically compared using tooth-based reference points. The superimposed images of Tv and T1 were also investigated at eight bone-based reference points. The differences between the reference points of the bone surface were examined to evaluate the stability of the miniplate on the maxilla over time.

Results

None of the patients experienced complications. There were no significant differences between the reference points based on the cusp tip between ΔTv and ΔT1 (p > 0.01). Additionally, there were no significant differences between the Tv and T1 values of the bone surface (p > 0.01). The mean difference in the bone surface between Tv and T1 was 1.01 ± 0.3 mm. Regarding the stability of the miniplate, there were no significant differences between the groups. The difference in the bone surface between T1 and T3 was − 0.37 ± 0.29 mm.

Conclusions

VS was performed using the FaceGide® program, and customized materials produced based on the VS were applied in actual OGS. The maxilla was repositioned in almost the same manner as in the VSP plan, and the maxillary position remained stable for a year.

Dental malocclusions are not just about small and weak bones: assessing the morphology of the mandible with cross-section analysis and geometric morphometrics

OBJECTIVES

Dental malocclusions in modern populations would be the result of small and weak jaws developing under low masticatory loads. We assess the validity of this by characterising the external and internal morphology of mandibles affected by class II and III malocclusions and comparing them with those from individuals with different masticatory load patterns.

MATERIALS AND METHODS

CTs from up to 118 individuals exerting intensive, medium and low masticatory loads with harmonic occlusion, and from class II and III individuals, were used to compare their external shape using geometric morphometrics, as well as their internal amount and distribution of cortical bone.

RESULTS

The low-load groups (harmonic, class II and III occlusion) are externally more gracile than the intense and medium load groups. But more relevant in shape variation is a marked allometric pattern, which differentiates class II (small) and III (large) mandibles. Despite gracility, the relative amount of cortical bone in the low-load groups is larger than in the remaining groups.

CONCLUSIONS

There is no evidence that the modern mandible, including class II and III individuals, is intrinsically small and weak. Instead, there is a rather large degree of morphological variation, which could be linked to a lack of constraints derived from low masticatory loads. Thus, the effect of other factors such as genetics, but also basal metabolism, should be looked in more depth.

CLINICAL RELEVANCE

Dental malocclusions are a common disorder whose aetiology has not been unravelled, and several to be considered in the prevention and therapy of malocclusion.

Mandible protraction alters Type I collagen, osteocalcin and osteonectin gene expression in adult mice condyle

Mandible condyle remodeling is a great challenge on craniofacial growth studies. The great majority of the reports deals with growing period. However, there is a great necessity to clarify the importance of functional stimulation on adult mandible condyle remodeling. By using an adult mouse model, we investigated the influence of mandible forwarding on condyle remodeling and gene expression by bone forming cells. Tomographic and scintigraphic evaluations showed sagittal growth and cell activity enhancement. RT-PCR showed that Type I collagen, osteocalcin and osteonectin expression level can be altered. We showed that functional stimulation is necessary to maintain the regular gene expression by condyle bone forming cells in adult mice. It opens new frame for further investigations aiming new clinical approaches to temporomandibular joint problems treatment, as well as mandible retrusion treatment.

Intercellular Genetic Interaction Between Irf6 and Twist1 during Craniofacial Development

Interferon Regulatory Factor 6 (IRF6) and TWIST1 are transcription factors necessary for craniofacial development. Human genetic studies showed that mutations in IRF6 lead to cleft lip and palate and mandibular abnormalities. In the mouse, we found that loss of Irf6 causes craniosynostosis and mandibular hypoplasia. Similarly, mutations in TWIST1 cause craniosynostosis, mandibular hypoplasia and cleft palate. Based on this phenotypic overlap, we asked if Irf6 and Twist1 interact genetically during craniofacial formation. While single heterozygous mice are normal, double heterozygous embryos (Irf6^+/−; Twist1^+/−) can have severe mandibular hypoplasia that leads to agnathia and cleft palate at birth. Analysis of spatiotemporal expression showed that Irf6 and Twist1 are found in different cell types. Consistent with the intercellular interaction, we found reduced expression of Endothelin1 (EDN1) in mandible and transcription factors that are critical for mandibular patterning including DLX5, DLX6 and HAND2, were also reduced in mesenchymal cells. Treatment of mandibular explants with exogenous EDN1 peptides partially rescued abnormalities in Meckel’s cartilage. In addition, partial rescue was observed when double heterozygous embryos also carried a null allele of p53. Considering that variants in IRF6 and TWIST1 contribute to human craniofacial defects, this gene-gene interaction may have implications on craniofacial disorders.

[Precision stomatology: current status and challenges]

The completion of human genome project and the progress in medical practice have inevitably lead to the development of precision medicine, which is a medical model that proposes the customization of medical care including medical decisions, practices, and/or medical products with patient's genetic background, environmental factors and life behavior being taken into account. The current work proposed precision stomatology for the first time, and by integrating data reported in recent literature, we described the current practice of precision stomatology in multiple disciplines in modem dentistry. The clinical significance of precision stomatology and its future challenges have also been discussed.