Gas1 Regulates Patterning of the Murine and Human Dentitions through Sonic Hedgehog.

The mammalian dentition is a serially homogeneous structure that exhibits wide numerical and morphological variation among multiple different species. Patterning of the dentition is achieved through complex reiterative molecular signaling interactions that occur throughout the process of odontogenesis. The secreted signaling molecule Sonic hedgehog (Shh) plays a key role in this process, and the Shh coreceptor growth arrest-specific 1 (Gas1) is expressed in odontogenic mesenchyme and epithelium during multiple stages of tooth development. We show that mice engineered with Gas1 loss-of-function mutation have variation in number, morphology, and size of teeth within their molar dentition. Specifically, supernumerary teeth with variable morphology are present mesial to the first molar with high penetrance, while molar teeth are characterized by the presence of both additional and absent cusps, combined with reduced dimensions and exacerbated by the presence of a supernumerary tooth. We demonstrate that the supernumerary tooth in Gas1 mutant mice arises through proliferation and survival of vestigial tooth germs and that Gas1 function in cranial neural crest cells is essential for the regulation of tooth number, acting to restrict Wnt and downstream FGF signaling in odontogenic epithelium through facilitation of Shh signal transduction. Moreover, regulation of tooth number is independent of the additional Hedgehog coreceptors Cdon and Boc, which are also expressed in multiple regions of the developing tooth germ. Interestingly, further reduction of Hedgehog pathway activity in Shhtm6Amc hypomorphic mice leads to fusion of the molar field and reduced prevalence of supernumerary teeth in a Gas1 mutant background. Finally, we demonstrate defective coronal morphology and reduced coronal dimensions in the molar dentition of human subjects identified with pathogenic mutations in GAS1 and SHH/GAS1, suggesting that regulation of Hedgehog signaling through GAS1 is also essential for normal patterning of the human dentition.

Information for oral and maxillofacial patients: can it be improved?

The aim and objective of this study was to evaluate the quality and readability of leaflet and online Oral and Maxillofacial Surgery patient information leaflets (PILs). The quality, readability and grade level of each PIL was assessed using the DISCERN, Flesch Reading Ease and Flesh-Kincaid Grade Level instruments respectively. In total, 140 patient information leaflets were assessed. For both leaflet and online PILs, many items of the DISCERN instrument were deemed of low quality and poorly reported. The median overall quality score was 30.2. Variation in the quality and readability scores between leaflet and online PILs and those produced by various societies was evident. Overall, PILs were deemed to be of moderate quality. Online PILs were of lower quality, more difficult to read and aimed at a higher reading age level.

WNT10A mutation results in severe tooth agenesis in a family of three sisters.

OBJECTIVES: To identify the genetic basis of severe tooth agenesis in a family of three affected sisters. PATIENTS AND METHODS: A family of three sisters with severe tooth agenesis was recruited for whole-exome sequencing to identify potential genetic variation responsible for this penetrant phenotype. The unaffected father was tested for specific mutations using Sanger sequencing. Gene discovery was supplemented with in situ hybridization to localize gene expression during human tooth development. RESULTS: We report a nonsense heterozygous mutation in exon 2 of WNT10A c.321C>A[p.Cys107*] likely to be responsible for the severe tooth agenesis identified in this family through the creation of a premature stop codon, resulting in truncation of the amino acid sequence and therefore loss of protein function. In situ hybridization showed expression of WNT10A in odontogenic epithelium during the early and late stages of human primary tooth development. CONCLUSIONS: WNT10A has previously been associated with both syndromic and non-syndromic forms of tooth agenesis, and this report further expands our knowledge of genetic variation underlying non-syndromic forms of this condition. We also demonstrate expression of WNT10A in the epithelial compartment of human tooth germs during development.

National clinical guidelines for the management of unerupted maxillary incisors in children.

This article summarises recently updated guidelines produced by the Clinical Governance Directorate of the British Orthodontic Society through the Clinical Standards Committee of the Faculty of Dental Surgery, Royal College of Surgeons of England (FDSRCS) on the management of unerupted maxillary incisor teeth in children. The maxillary incisor teeth usually erupt in the early mixed dentition but eruption disturbances can occur and are often attributable to local factors. A failure of eruption will affect the developing occlusion and potentially influence psychological development of the child. The general principles of management for delayed eruption or impaction of these teeth is to ensure that adequate space exists in the dental arch and to remove any obstruction to eruption. Consideration should also be given to further promoting eruption through surgical exposure of the incisor, with or without subsequent orthodontic traction. A number of factors influence the decision-making process, including patient age, medical history, potential compliance, aetiology and position of the unerupted incisor. Treatment planning should be complemented by careful clinical assessment and the use of appropriate special investigations. To optimise the treatment outcome a multidisciplinary specialist approach is recommended.

Vax1 Plays an Indirect Role in the Etiology of Murine Cleft Palate.

Cleft lip with or without palate (CLP) and isolated cleft palate (CP) are common human developmental malformations with a complex etiology that reflects a failure of normal facial development. VAX1 encodes a homeobox-containing transcription factor identified as a candidate gene for CLP in human populations, with targeted deletion in mice associated with multiple anomalies, including disruption of the visual apparatus and basal forebrain, lobar holoprosencephaly, and CP. We have investigated Vax1 function during murine palatogenesis but found no evidence for a direct role in this process. Vax1 is not expressed in the developing palate and mutant palatal shelves elevate above the tongue, demonstrating morphology and proliferation indices indistinguishable from wild type. However, mutant mice did have a large midline cavity originating from the embryonic forebrain situated beneath the floor of the hypothalamus and extending through the nasal cavity to expand this region and prevent approximation of the palatal shelves. Interestingly, despite strong expression of Vax1 in ectoderm of the medial nasal processes, the upper lip remained intact in mutant mice. We found further evidence of disrupted craniofacial morphology in Vax1 mutants, including truncation of the midface associated with reduced cell proliferation in forebrain neuroectoderm and frontonasal mesenchyme. Sonic hedgehog (Shh) signal transduction was downregulated in the mutant forebrain, consistent with a role for Vax1 in mediating transduction of this pathway. However, Shh was also reduced in this region, suggestive of a Shh-Vax1 feedback loop during early development of the forebrain and a likely mechanism for the underlying lobar holoprosencephaly. Despite significant associations between VAX1 and human forms of CLP, we find no evidence of a direct role for this transcription factor in development of this region in a mutant mouse model.

Impact of Obesity on Orthodontic Tooth Movement in Adolescents: A Prospective Clinical Cohort Study.

Obesity is a widespread chronic inflammatory disorder characterized by an increased overall disease burden and significant association with periodontitis. The aim of this prospective clinical cohort study was to investigate the effect of obesity on orthodontic tooth movement. Fifty-five adolescent patients (27 males, 28 females) with a mean (SD) age of 15.1 (1.7) years and mean (SD) body mass index (BMI) of 30.2 (3.5) kg/m2 in obese and 19.4 (2.2) kg/m2 in normal-weight groups were followed from start of treatment to completion of tooth alignment with fixed orthodontic appliances. Primary outcome was time taken to complete tooth alignment, while secondary outcomes included rate of tooth movement and change in clinical parameters (plaque/gingival indices, unstimulated whole-mouth salivary flow rate, gingival crevicular fluid biomarkers). Data collection took place at baseline (start of treatment: appliance placement), 1 h and 1 wk following appliance placement, and completion of alignment. Results were analyzed by descriptive statistics followed by generalized estimating equation regression modeling. There were no significant differences between groups in time taken to achieve tooth alignment (mean [SD] 158.7 [75.3] d; P = 0.486). However, at 1 wk, initial tooth displacement was significantly increased in the obese group ( P < 0.001), and after adjusting for confounders, obese patients had a significantly higher rate of tooth movement compared with normal-weight patients (+0.017 mm/d; 95% confidence interval, 0.008-0.025; P < 0.001) over the period of alignment. Explorative analyses indicated that levels of the adipokines leptin and resistin, the inflammatory marker myeloperoxidase (MPO), and the cytokine receptor for nuclear factor kappa-B ligand (RANKL) were significantly different between obese- and normal-weight patients and associated with observed rates of tooth movement. This represents the first prospective data demonstrating a different response in obese patients compared with normal-weight patients during early orthodontic treatment. These differences in the response of periodontal tissues to orthodontic force in the presence of obesity have potential short- and long-term clinical implications.

Non-syndromic severe hypodontia caused by a novel frameshift insertion mutation in the homeobox of the MSX1 gene.

OBJECTIVE: Inherited congenital anomalies in tooth number, particularly hypodontia are relatively common. Although substantial progress has been made that permits a better understanding of the causes of tooth agenesis, overall knowledge of the phenotype:genotype correlations in this anomaly are still lacking. The aim in this study was to identify the causal gene mutation(s) in a family of two sisters with severe hypodontia (oligodontia) including 2nd premolars and 1st and 3rd molars, using whole exome sequencing (WES). METHODS: WES was performed using in-solution hybridization, followed by massively parallel sequencing. RESULTS: A frameshift insertion of 7 basepairs (GCAAGTT) in the homebox of MSX1 gene located in the exon 2 in heterozygous state has been identified in both sisters (NM_002448:exon2:c.572_573ins GCAAGTT: p.F191fs). CONCLUSION: We conclude that this frameshift mutation in the homeodomain (which plays an essential role in DNA binding) of MSX1 gene is responsible for tooth agenesis in this family. This expands the phenotype-genotype correlation associated with MSX1 mutations.

Supplemental vibrational force during orthodontic alignment: a randomized trial.

This prospective 3-arm parallel-group randomized clinical trial investigated the effect of supplemental vibrational force on rate of orthodontic tooth alignment with fixed appliances. Eighty-one subjects (40 males, 41 females; mean age, 14.1 y) undergoing first premolar extraction-based fixed appliance treatment were randomly allocated to treatment supplemented with daily use (20 min) of a removable intraoral vibrational device (AcceleDent; OrthoAccel Technologies Inc.; n = 29), an identical nonfunctional (sham) device (n = 25), or fixed appliances only (n = 27). Mandibular study casts were taken at baseline (treatment start: placement of 0.014-in. nickel-titanium arch wire), initial alignment (0.018-in. nickel-titanium arch wire), and final alignment (0.019 x 0.025-in. stainless steel arch wire). Overall mean irregularity index in the mandibular arch at baseline was 8.5 ± 3.8 mm (95% CI, 7.6 to 9.3) with no significant difference between groups (P = 0.73). For the total sample, mean irregularity index at initial alignment was 2.7 ± 2.8 mm (95% CI, 2.2 to 3.4) with no significant difference between groups (P = 0.40). Mean time from baseline to initial alignment was 59 ± 25 d (95% CI, 54.5 to 65.6); from initial to final alignment, 150 ± 62.5 d (95% CI, 136 to 165); and baseline to final alignment, 209 ± 65 d (95% CI, 195 to 224). Kaplan-Meier analysis demonstrated that patterns of alignment were not significantly different among the 3 groups (P = 0.66). Multivariate linear regression for initial and overall alignment rates using initial irregularity index as the covariate showed no significant differences among groups. The most important influence on both initial and overall rates of alignment was initial irregularity (P = 0.1 × 10(-4)). This prospective randomized clinical trial found no evidence that supplemental vibrational force can significantly increase the rate of initial tooth movement or reduce the amount of time required to achieve final alignment when used in conjunction with a preadjusted edgewise fixed appliance (ClinicalTrials.gov NCT02314975).

The use of functional appliances in contemporary orthodontic practice.

Functional appliances have been used for over 100 years in orthodontics to correct Class II malocclusion. During this time numerous different systems have been developed often accompanied by claims of modification and enhancement of growth. Recent clinical evidence has questioned whether they really have a lasting influence on facial growth, their skeletal effects appearing to be short term. However, despite these findings, the clinical effectiveness of these appliances is acknowledged and they can be very useful in the correction of sagittal arch discrepancies. This article will discuss the clinical use of functional appliances, the underlying evidence for their use and their limitations.

National clinical guidelines for the extraction of first permanent molars in children.

This article summarises recently updated guidelines produced by the Clinical Governance Directorate of the British Orthodontic Society through the Clinical Standards Committee of the Faculty of Dental Surgery, Royal College of Surgeons of England (FDSRCS) on the extraction of first permanent molars in children. The first permanent molar is susceptible to chronological enamel defects, molar-incisor hypomineralisation and caries, which may necessitate enforced extraction in the developing dentition. In the right circumstances, the extraction of these teeth can be followed by successful eruption of the second permanent molar and ultimately, third molar eruption to complete the molar dentition. For this reason, elective extraction of first permanent molars with a questionable long-term prognosis should be considered when planning enforced extractions. However, a number of factors can influence the decision-making process, including the necessity for a general anaesthetic to allow extraction, potential cooperation with restorative or orthodontic treatment and likely future preventative practice within the family. Moreover, the presence of any underlying malocclusion also needs to be evaluated within the context of extraction planning. The current available evidence has been evaluated and awarded a grade based upon those recommended by the Scottish Intercollegiate Guidelines Network.

Assessing the influence of chin prominence on perceived attractiveness in the orthognathic patient, clinician and layperson.

The purpose of this investigation was to undertake an objective and quantitative evaluation of how the degree of chin prominence influences perceived attractiveness. The chin prominence of an idealized profile image was altered in 2 mm increments from -24 to 12 mm, in order to represent retrusion and protrusion of the chin, respectively. These images were rated on a 7-point Likert scale by a pre-selected group of pre-treatment orthognathic patients, clinicians and laypeople. In treatment planning to alter the sagittal prominence of the chin in an individual with an otherwise normal soft tissue facial profile, an 'ideal' sagittal position with soft tissue pogonion on or just behind a true vertical line through subnasale may be used. Chin retrusion or protrusion up to 4mm is essentially unnoticeable. Surgery is desired for chin protrusions greater than 6mm and retrusions greater than 10mm. The overall direction of aesthetic opinion appears to be the same for all the observer groups; the greater the retrusion or prominence of the chin, the less the rating of the perceived attractiveness and the greater the desire for surgical correction.

Does the Eastman correction over- or under-adjust ANB for positional changes of N?

Cephalometric analyses are useful for planning and provision of orthodontic treatment. A and B points are used to resemble the anterior part of maxilla and mandible and N represents the anterior part of the cranial base. The position of N may influence measurements of SNA, SNB, and ANB and changes of N in the antero-posterior plane are thought to have a larger influence on the above measurements than vertical ones. Several methods have been proposed to address this issue, such as the Wits appraisal, the 'Individualized ANB', and the 'Eastman correction'; the latter is mainly used in the UK. This study used a geometrical model of a lateral cephalogram with standard Caucasian average values for SN length, position of A and B points for male and female patients. Linear and angular measurements were digitized using Dolphin™ Imaging software. N was moved in antero-posterior and vertical planes and subsequent changes of SNA, SNB, and ANB were measured and the Eastman correction applied. The correction overestimated the SNA and ANB values in the opposite direction to the directly measured SNA and ANB when N moved posteriorly towards S: The directly measured values tended to show a Class II relationship but the correction indicated a Class III skeletal base. As N moved anteriorly, the Eastman correction overestimated the measured Class III skeletal relationship; SNA did not fall below 81 for correction in the opposite direction. Vertical positional changes had little impact on the underlying ANB and correction was not indicated clinically.

Revisiting the supernumerary: the epidemiological and molecular basis of extra teeth.

Supernumerary teeth are a common clinical and radiographic finding and may produce occlusal and dental problems. The aetiological basis of extra teeth is poorly understood in human populations; however, the mouse provides a useful model system to investigate the complex genetics of tooth development. This article describes recent advances in our understanding of the genetic basis of supernumerary teeth. We have reviewed biological evidence that provides insight into why supernumerary tooth formation may occur. Indeed, many of the molecular signalling pathways known to be involved in normal development of the tooth germ can also give rise to additional teeth if inappropriately regulated. These include components of the Hedgehog, FGF, Wnt, TNF and BMP families, which provide a useful resource of candidate genes that may potentially play a role in human supernumerary tooth formation.

Psychological characteristics of women who require orthognathic surgery: comparison with untreated controls.

Improvement in appearance is an important motivation for orthodontic treatment and orthognathic surgery, and two possible underlying causes are objective physical abnormalities, or the patient's personality type that leads them to concentrate on their appearance and request unnecessary interventions. Questionnaires that measure personality traits were given to 30 women who required orthognathic operations, and a control group of 30 other women. Traits measured were: satisfaction with the appearance of the face, head, and body; tendency to compare their appearance with that of others; the extent to which they are aware of their appearance and how they thought they should look; sense of self identity; depression; anxiety; and self-esteem. The only difference between patients and controls was that patients were more dissatisfied with their facial appearance than the others. Orthognathic patients were psychologically normal except that they had more dissatisfaction with their facial appearance. As this was the only difference, it is likely that their desire for operation was caused by a genuine physical abnormality rather than a perceived exaggerated aesthetic problem. It seems, therefore, that any patient who seeks orthognathic treatment because they have a personality that causes them to dwell on their appearance (which may lead them to hold unrealistic expectations of intervention) are screened out of the process before they begin treatment.

The influence of craniofacial to standing height proportion on perceived attractiveness.

An idealised male image, based on Vitruvian Man, was created. The craniofacial height was altered from a proportion of 1/6 to 1/10 of standing height, creating 10 images shown in random order to 89 observers (74 lay people; 15 clinicians), who ranked the images from the most to the least attractive. The main outcome was the preference ranks of image attractiveness given by the observers. Linear regressions were used to assess what influences the choice for the most and the least attractive images, followed by a multivariate rank ordinal logistic regression to test the influence of age, gender, ethnicity and professional status of the observer. A craniofacial height to standing height proportion of 1/7.5 was perceived as the most attractive (36%), followed by a proportion of 1/8 (26%). The images chosen as most attractive by more than 10% of observers had a mean proportion of 1/7.8(min=1/7; max=1/8.5). The images perceived as most unattractive had a proportion of 1/6 and 1/10. The choice of images was not influenced by the age, gender, ethnicity or professional status of the observers. The ideal craniofacial height to standing height proportion is in the range 1/7 to 1/8.5. This finding should be considered when planning treatment to alter craniofacial or facial height.

Regenerative approaches in the craniofacial region: manipulating cellular progenitors for oro-facial repair.

This review aims to highlight the potential for regeneration that resides within the bony tissues of the craniofacial region. We examine the five main cues which determine osteogenic differentiation: heritage of the cell, mechanical cues, the influence of the matrix, growth factor stimulation and cell-to-cell contact. We review how successful clinical procedures, such as guided tissue regeneration and distraction osteogenesis exploit this resident ability. We explore the developmental origins of the flat bones of the skull to see how such programmes of differentiation may inform new therapies or regenerative techniques. Finally we compare and contrast existing approaches of hard tissue reconstruction with future approaches inspired by the regenerative medicine philosophy, with particular emphasis on the potential for using chondrocyte-inspired factors and replaceable scaffolds.

Familial human hypodontia--is it all in the genes?

The congenital absence of teeth is one of the commonest developmental abnormalities seen in human populations. Familial hypodontia or oligodontia represents an absence of varying numbers of primary and/or secondary teeth as an isolated trait. While much progress has been made in understanding the developmental basis of tooth formation, knowledge of the aetiological basis of inherited tooth loss remains poor. The study of mouse genetics has uncovered a large number of candidate genes for this condition, but mutations in only three have been identified in human pedigrees with familial hypodontia or oligodontia: MSX1, PAX9 and AXIN2. This suggests that these conditions may represent a more complex multifactorial trait, influenced by a combination of gene function, environmental interaction and developmental timing. Completion of the human genome project has made available the DNA sequence of the collected human chromosomes, allowing the localisation of all human genes and, ultimately, determination of their function. Therefore it is likely that our understanding of this complex developmental process will continue to improve, not only during normal development but also when things go wrong.

Analysis of the morbidity of submerged deciduous molars: the use of imaging techniques.

A case is presented of a 13-year-old patient who had a class I occlusion on a class I skeletal base but with a retained and submerged deciduous molar causing impaction of the second premolar. Diagnostic imaging illustrates the potential challenges of the removal of the retained deciduous molar. Magnetic resonance imaging used to identify the path of the inferior alveolar neurovascular bundle clearly delineates its intimate association with the impacted teeth and underscores the risk of trauma during extraction. This is discussed with regard to other cases of submerged molars, and a strategy is outlined.

Sonic hedgehog regulates epithelial proliferation and cell survival in the developing tooth germ.

Shh expression is highly restricted to the future sites of tooth development during the initiation of odontogenesis. This suggests a role for Shh as a proliferative factor, as localized epithelial thickenings invaginate to form a tooth bud. We have investigated this role by blocking Shh signaling between E10.5 and E12.5 in murine mandibular processes using a 5E1 blocking antibody and the PKA activator Forskolin. This results in down-regulation of Ptc, a principle target of Shh signaling. The effects of inhibition varied with developmental time. At E10.5, tooth development was arrested as epithelial thickenings and the numbers of teeth developing were considerably reduced. Inhibition at E12.5 produced localized apoptosis in the epithelium at the tip of the tooth buds, although some teeth were able to develop. Thus, Shh has dual roles in early odontogenesis, first in bud formation by stimulating epithelial proliferation, and second in the development of cap-stage tooth germs by increasing epithelial cell survival.

Construction for the modern head: current concepts in craniofacial development.

The vertebrate head is a highly complex composite structure whose morphological characteristics are controlled at the level of the gene. There is now increasing evidence for the role of gene families that encode transcription factors in determining the embryonic plan of the developing craniofacial complex. These genes act as regulators of gene transcription being intimately involved with the control of complex interactions between multiple downstream genes. Combinatorial expression of the Hox genes (a family of highly conserved master regulatory genes related to the homeotic genes of the fruitfly Drosophila) have been shown to play a definitive role in patterning distinct regions of the craniofacial complex. In the vertebrate, Hox genes pattern the hindbrain and branchial regions of the developing head up to and including structures derived from the second branchial arch. The first branchial arch and more rostral regions of the head are patterned by groups of homeobox genes more diverged from the original Hox clusters. Transgenic mice, with targeted disruptions in many of these genes, are now providing insights into the molecular mechanisms that lie behind a number of craniofacial defects seen in man.