Tooth dimensions in hypodontia with a known PAX9 mutation

Genetic and Morphological Variation in Hypodontia of Maxillary Lateral Incisors

(1) Background: Hypodontia has a multifactorial aetiology, in which genetic factors are a major component. Associated with this congenital absence, the formed teeth may show differences in size and shape, which may vary with the specific genetic variants and with the location of the missing teeth. The aims of the present study were to investigate a specific variant of MSX1, derive morphometric tooth measurements in a sample of patients with isolated maxillary lateral incisor agenesis and matched controls, and model the findings. (2) Methods: Genotyping of the MSX1 rs8670 genetic variant and morphometric measurements with a 2D image analysis method were performed for 26 hypodontia patients and 26 matched controls. (3) Results: The risk of upper lateral incisor agenesis was 6.9 times higher when the T allele was present. The morphometric parameters showed significant differences between hypodontia patients and controls and between the unilateral and bilateral agenesis cases. The most affected crown dimension in the hypodontia patients was the bucco-lingual dimension. In crown shape there was significant variation the Carabelli trait in upper first molars. (4) Conclusions: The MSX1 rs8670 variant was associated with variations in morphological outcomes. The new findings for compensatory interactions between the maxillary incisors indicate that epigenetic and environmental factors interact with this genetic variant. A single-level directional complex interactive network model incorporates the variations seen in this study.

Rethinking the Genetic Etiology of Nonsyndromic Tooth Agenesis

PURPOSE OF REVIEW

Genetic studies in humans and animal models have improved our understanding of the role of numerous genes in the etiology of nonsyndromic tooth agenesis (TA). The purpose of this review is to discuss recently identified genes potentially contributing to TA.

RECENT FINDINGS

Despite research progress, understanding the genetic factors underlying nonsyndromic TA has been challenging given the genetic heterogeneity, variable expressivity, and incomplete penetrance of putatively pathogenic variants often observed associated with the condition. Next-generation sequencing technologies have provided a platform for novel gene and variant discoveries and informed paradigm-shifting concepts in the etiology of TA. This review summarizes the current knowledge on genes and pathways related to nonsyndromic TA with a focus on recently identified genes/variants. Evidence suggesting possible multi-locus variation in TA is also presented.

The Human Genetics of Dental Anomalies

The development of tooth is a highly complex procedure and mastered by specific genetic programs. Genetic alterations, environmental factors, and developmental timing can disturb the execution of these programs, and result in various dental anomalies like hypodontia/oligodontia, and supernumerary teeth, which are commonly seen in our clinical practice. Advances in molecular research enabled the identification of various genes involved in the pathogenesis of dental anomalies. In the near future, it will help provide a more accurate diagnosis and biological-based treatment for these anomalies. In this article, we present the molecular phenomenon of tooth development and the genetics of various dental anomalies.

Folding Stability of Pax9 Intronic G-Quadruplex Correlates with Relative Molar Size in Eutherians

Eutherian dentition has been the focus of a great deal of studies in the areas of evolution, development, and genomics. The development of molar teeth is regulated by an antero-to-posterior cascade mechanism of activators and inhibitors molecules, where the relative sizes of the second (M2) and third (M3) molars are dependent of the inhibitory influence of the first molar (M1). Higher activator/inhibitor ratios will result in higher M2/M1 or M3/M1. Pax9 has been shown to play a key role in tooth development. We have previously shown that a G-quadruplex in the first intron of Pax9 can modulate the splicing efficiency. Using a sliding window approach with we analyzed the association of the folding energy (Mfe) of the Pax9 first intron with the relative molar sizes in 42 mammalian species, representing 9 orders. The Mfe of two regions located in the first intron of Pax9 were shown to be significantly associated with the M2/M1 and M3/M1 areas and mesiodistal lengths. The first region is located at the intron beginning and can fold into a stable G4 structure, whereas the second is downstream the G4 and 265 bp from intron start. Across species, the first intron of Pax9 varied in G-quadruplex structural stability. The correlations were further increased when the Mfe of the two sequences were added. Our results indicate that this region has a role in the evolution of the mammalian dental pattern by influencing the relative size of the molars.

Genetic variants in tooth agenesis-related genes might be also involved in tooth size variations

OBJECTIVE

The present study aimed to evaluate if genetic variants in PAX9, MSX1, TGFα, FGF3, FGF10, FGF13, GLI2 and GLI3 are involved in TS of permanent teeth.

MATERIALS AND METHODS

Pretreatment dental records from orthodontic patients were assessed prior to recruitment. Patients with tooth agenesis and congenital anomalies (including oral cleft) and/or syndromes were excluded. Dental casts were used to measure the maximum crown dimensions of all fully erupted permanent teeth except second and third molars in mesiodistal direction. Teeth with caries, occlusal wear, mesiodistal restorations, and obvious deformities were not evaluated. Genomic DNA samples were used for genotyping. The allelic discrimination of 13 genetic variants was performed. The associations between TS and genotype were analyzed by linear regression, adjusted by gender at a significance level of p ≤ 0.05.

RESULTS

Genetic polymorphisms in the tooth agenesis-related genes studied here were associated with increased and decreased TS, in both maxilla and mandible (p < 0.05).

CONCLUSION

This study reported associations of novel tooth agenesis-related gene variants with permanent tooth size variations.

CLINICAL RELEVANCE

The presence of some genetic variants could allow the prediction of permanent tooth size.

Maxillary incisor root morphology in patients with nonsyndromic tooth agenesis: A controlled cross-sectional pilot study

INTRODUCTION

This study aimed to investigate the association between root morphology of maxillary incisors and nonsyndromic tooth agenesis in patients compared with a control group without agenesis.

METHODS

This controlled cross-sectional pilot study (1:4) was performed with a random sample of 335 records from Brazilian applicants for orthodontic treatment, paired by sex and age. Panoramic and periapical radiographs were analyzed to diagnose tooth agenesis and to assess root morphology. The agenesis group (n = 67) included patients with nonsyndromic tooth agenesis, and the control group (n = 268) included patients without tooth agenesis. The statistical analysis included the Student t test and z test, conditional logistic regression, and odds ratio estimates.

RESULTS

Occurrence of root morphological changes was significantly higher among patients with agenesis (P <0.05). Significant morphological changes (short, blunt, apically bent, and pipette-shaped roots) were found in the roots of remaining teeth when comparing agenesis and control groups (P <0.05). Patients with agenesis were more likely to show root morphological changes (odds ratio, 74.23; 95% confidence interval, 16.93-325.46; P <0.001).

CONCLUSION

Patients with agenesis are more likely to present root morphological changes, which should be considered to minimize problems during orthodontic treatments.

Three-dimensional geometric morphometric analysis of tooth shape in hypodontia: II size variation

The study aimed to evaluate differences in tooth size between patients with hypodontia and those with normal complement of permanent teeth using three-dimensional geometric morphometric analysis. The number of anatomical landmarks was recorded on the clinical crown of the permanent teeth on three-dimensional scanned study models of hypodontia and in control subjects. The study sample comprised 120 patients with hypodontia (mild, moderate, severe) and 40 controls matched for age and sex. Tooth size differences were tested statistically using multivariate statistics. Size variation was for the most part found to be significant, especially when the control subjects were compared with the hypodontia groups. The explained variance among group membership was generally larger in the anterior and premolar region than in the molar region Sexual dimorphism was found less in the anterior region than in the posterior region; therefore, the sexes were pooled more often for teeth in the anterior region. Quantitative measurement of tooth size in patients with hypodontia may enhance the multidisciplinary management of these patients.

The Changing Landscape in the Genetic Etiology of Human Tooth Agenesis

Despite much progress in understanding the genetics of syndromic tooth agenesis (TA), the causes of the most common, isolated TA remain elusive. Recent studies have identified novel genes and variants contributing to the etiology of TA, and revealed new pathways in which tooth development genes belong. Further, the use of new research approaches including next-generation sequencing has provided increased evidence supporting an oligogenic inheritance model for TA, and may explain the phenotypic variability of the condition. In this review, we present current knowledge about the genetic mechanisms underlying syndromic and isolated TA in humans, and highlight the value of incorporating next-generation sequencing approaches to identify causative and/or modifier genes that contribute to the etiology of TA.

Mesiodistal and Buccolingual Dimensions in Croatian Orthodontic Hypodontia Patients' Teeth

OBJECTIVE

This study compared mesiodistal (MD) and buccolingual (BL) tooth dimensions of hypodontia patients with a control group with complete dentition. The null hypothesis was that there was no difference in tooth sizes between hypodontia patients and the controls.

METHODS

The sample comprised 76 patients with hypodontia (50 female and 26 male) aged between 11 and 18 years. The control group comprised 50 females and 26 males with the same age range as the study group. Mesiodistal (MD) and buccolingual (BL) dimensions were measured on pretreatment dental casts with a digital caliper to the nearest 0.01 mm. The data were analyzed using Statistica 7.1 (StatSoft Inc.) statistical package (descriptive statistics, test of distribution normality, parametric statistics).

RESULTS

The most common congenitally missing teeth were the lower second premolars (left 13.45% and right 13.90%) and upper lateral incisors (both left and right 12.56%), followed by upper second premolars (right 9.4o% and left 10.31%). The greatest differences between the study and control group were found in upper lateral incisors, 8.08% in MD and 6.40% in BL dimension. The smallest difference was found in BL dimension of lower lateral incisor (2.37%), MD dimension of lower second premolars and upper first molar (2.61%) and MD dimension of lower central incisor (2.26%).

CONCLUSION

The teeth are smaller in subjects with hypodontia than those of the controls on average 4.02% in MD dimension and 3.85% in BL dimension. The tooth that showed the greatest difference in tooth dimension was maxillary lateral incisor.

Tooth Size in Patients with Mild, Moderate and Severe Hypodontia and a Control Group

Objectives:

To compare tooth size between subjects with mild, moderate and severe hypodontia and a control group.

Material and Methods:

The study comprised 120 patients with hypodontia divided into three groups of 40 mild (≤2 teeth congenitally missing), 40 moderate (3-5 teeth congenitally missing) and 40 severe (≥6 teeth congenitally missing) hypodontia; and 40 age and sex matched controls. Tooth size was recorded by measuring the mesiodistal and buccolingual dimensions of all fully erupted teeth on study models using digital callipers and compared between all hypodontia and control groups using Two-way ANOVA and Post Hoc Tests of subgroup comparison.

Results:

Two-way ANOVA revealed patients with hypodontia had significantly smaller mesiodistal and buccolingual tooth dimensions compared with controls (p<0.05). Furthermore patients with more severe hypodontia demonstrated significantly smaller tooth dimensions than those in the mild and moderate hypodontia subgroups (p<0.05). The most affected tooth in terms of tooth size reduction was the maxillary lateral incisor and the least affected tooth was the mandibular first molar.

Conclusion:

Patients with hypodontia have smaller tooth dimensions than control. Tooth size appears to be affected by the degree of hypodontia, with severe hypodontia having a greater effect on tooth size reduction. The findings of this study may contribute to understanding the aetiology of hypodontia and aid the multidisciplinary management of this complex condition.

On the Etiology of Molar-Incisor Hypomineralization

Molar-incisor hypomineralization (MIH) is a condition that is defined based on its peculiar clinical presentation. Reports on the etiology of the condition and possible risk factors are inconclusive and the original suggestion that MIH is an idiopathic condition is often cited. Our group was the first to suggest MIH has a genetic component that involves genetic variation in genes expressed during dental enamel formation. In this report, we provide a rationale to explain the preferential affection of molars and incisors. We suggest that MIH is a genetic condition based on its prevalence, which varies depending on the geographic location, and the evidence that on occasion second primary molars, permanent canines, and premolars can show signs of hypomineralization of enamel when molars and incisors are affected.

The prevalence and distribution of hypodontia in a sample of Qatari patients

OBJECTIVE

The aims of this study were to determine the prevalence of hypodontia in the permanent dentition in a sample of Qatari patients attending a dental center and to compare the results with the reported findings of other populations.

MATERIALS AND METHODS

Orthodontic files including orthopantomographs of 1000 patients (655 females and 345 males, 11-36-year-old) were examined and inspected for evidence of hypodontia.

RESULTS

The prevalence of hypodontia in the present Qatari sample was 7.8%; 6.9% was in males and 8.2% in females. Hypodontia was found more frequently in the maxilla than in the mandible. The distribution of missing teeth was noticed in the left side more than the right side. The most frequently missing teeth were the maxillary lateral incisors followed by the mandibular second premolars, maxillary second premolars, and mandibular left lateral incisor. The majority of patients with hypodontia had one or two teeth missing, but rarely more than four teeth were missing in the same patient. Bilateral missing teeth in the current study was commonly seen in the maxillary lateral incisor (14.1%) followed by mandibular second premolar (12.8%) and maxillary second premolar (6.4%).

CONCLUSIONS

The prevalence of hypodontia in a sample of Qatari individuals was within the range reported in the literature for other populations. The incidence of hypodontia in the anterior segment requires multidisciplinary team approach (orthodontic and prosthodontic) to restore the esthetic and function and improve patient self-esteem.

Prevalence of hypodontia and associated factors: a systematic review and meta-analysis

OBJECTIVES

To determine the prevalence and factors associated with hypotonia.

DESIGN

Systematic review and meta-analysis.

DATA SOURCE

A search strategy was developed along with inclusion criteria and run in MEDLINE and EMBASE (published from 2002 to August 2012) databases to reveal all studies on the prevalence of hypodontia or associated factors. A hand search of reference lists and a Google search aimed to improve the sensitivity of the literature search.

SELECTION CRITERIA

All studies on the prevalence of hypodontia or associated factors published from 2002 onwards were included. Abstracts of non-English papers were also analyzed.

DATA SELECTION AND EXTRACTION

All potential articles were checked against the inclusion criteria independently, and in duplicate by two investigators. A checklist was used to assess the quality of selected studies.

MAIN OUTCOME

Prevalence of hypodontia, excluding third molars.

RESULTS

The overall prevalence of hypodontia was found to be 6.4% (95% CI: 5.7, 7.2). There was a statistically significant difference in the prevalence of hypodontia by continent (Q = 34.18, P<0.001). Prevalence of hypodontia was the highest in Africa: 13.4% (95% CI: 9.7, 18.0), followed by Europe (7% CI: 6.0-8.0%), Asia (6.3% CI: 4.4, 9.1) and Australia (6.3% CI: 5.3, 7.4) with a lower prevalence in North America (5.0% CI: 4.1-5.9) and Latin America and Caribbean (4.4% CI: 3.2-6.1). Females were found to have a higher prevalence than males (combined OR 1.22; 95% CI: 1.14, 1.30). The most commonly affected teeth were mandibular second premolars followed by maxillary lateral incisors and maxillary second premolars. The prevalence of mild, moderate and severe hypodontia was found to be 81.6, 14.3 and 3.1% respectively.

CONCLUSIONS

There was a high variation in the prevalence of hypodontia between the studies. African populations were found to have a higher risk for tooth agenesis and there was an increased risk for females to have hypodontia than males.

Maxillary lateral incisor agenesis and its relationship to overall tooth size

STATEMENT OF PROBLEM

Agenesis of the maxillary lateral incisor has been linked to differences in the size of the remaining teeth. Thus, the mesiodistal space required for definitive esthetic restoration in patients with missing maxillary lateral incisors may be reduced.

PURPOSE

The purpose of this study was to determine whether a tooth size discrepancy exists in orthodontic patients with agenesis of one or both maxillary lateral incisors.

MATERIAL AND METHODS

Forty sets of dental casts from orthodontic patients (19 men and 21 women; mean 15.9 years of age; all of European origin) were collected. All casts had agenesis of one or both maxillary lateral incisors. Teeth were measured with a digital caliper at their greatest mesiodistal width and then compared with those of a control group matched for ethnicity, age, and sex. Four-factor ANOVA with repeated measures of 2 factors was used for statistical analysis (α=.05).

RESULTS

Orthodontic patients with agenesis of one or both maxillary lateral incisors exhibited smaller than normal tooth size compared with the control group. The maxillary arch had a larger tooth size difference between the control and test groups than the mandibular arch (there was a significant Jaw × Group interaction [F=4.78, P=.032]).

CONCLUSIONS

Agenesis of one or both maxillary lateral incisors is significantly associated with tooth size discrepancy, which may affect the space remaining for restoration of the remaining teeth.

Infraocclusion: Dental development and associated dental variations in singletons and twins

OBJECTIVE

The aim of this study was to investigate the prevalence of selected dental variations in association with infraocclusion, as well as determining the effects of infraocclusion on dental development and tooth size, in singletons and twins.

DESIGN

Two samples were analysed. The first sample comprised 1454 panoramic radiographs of singleton boys and girls aged 8-11 years. The second sample comprised dental models of 202 pairs of monozygotic and dizygotic twins aged 8-11 years. Adobe Photoshop CS5 was used to construct reference lines and measure the extent of infraocclusion (in mm) of primary molars on the panoramic radiographs and on 2D images obtained from the dental models. The panoramic radiographs were examined for the presence of selected dental variations and to assess dental development following the Demirjian and Willems systems. The twins' dental models were measured to assess mesiodistal crown widths.

RESULTS

In the singleton sample there was a significant association of canines in an altered position during eruption and the lateral incisor complex (agenesis and/or small tooth size) with infraocclusion (P<0.001), but there was no significant association between infraocclusion and agenesis of premolars. Dental age assessment revealed that dental development was delayed in individuals with infraocclusion compared to controls. The primary mandibular canines were significantly smaller in size in the infraoccluded group (P<0.05).

CONCLUSION

The presence of other dental variations in association with infraocclusion, as well as delayed dental development and reduced tooth size, suggests the presence of a pleiotropic effect. The underlying aetiological factors may be genetic and/or epigenetic.

Is there a relationship between increased tooth number and increased tooth size? A case report

A unifying theory has been proposed that links anomalies of tooth size and number. Application of this theory suggests that anomalies of tooth size and number may share a common aetiology but could also be predicted. This article highlights an association between macrodontia and hyperdontia as demonstrated by two clinical cases. These cases demonstrate a localized association and effect on the dentition and highlight the possible predictive application of this theory.

CLINICAL RELEVANCE

Clinicians should be made aware of the possibility of supernumeraries associated with macrodont teeth.

Evaluation of tooth size in patients with congenitally-missing teeth

Background and aims

Hypodontia is a common developmental abnormality of dentition. This study aimed to determine tooth width in patients affected with mild hypodontia and compare the results with a control group without tooth agenesis.

Materials and methods

The orthodontic records of 25 patients with congenital missing of one or two teeth (hypodontia group), and 25 subjects with full dentition (control group) were selected. The greatest mesiodistal width of each tooth was measured on the study models by a digital caliper. Tooth width measurements were compared between the groups using a student t-test at p < 0.05 of significance.

Results

Patients with hypodontia showed narrower teeth than the control subjects. The differences in tooth size between the two groups were statistically significant for the first and second premolars and first molar in the maxillary right and for the second premolar in the maxillary left quadrants (p < 0.05). In the lower arch, the first and second premolars and also first molar in both sides of hypodontia patients demonstrated significant reduction in tooth size compared to the control group (p < 0.05).

Conclusion

These findings suggest that patients with mild hypodontia have narrower teeth than normal subjects especially in posterior segments, which may have clinical implications during the orthodontic treatment process.

Recessive oligodontia linked to a homozygous loss-of-function mutation in the SMOC2 gene

OBJECTIVE

Recently, several genes have been reported with mutations or variants that underlie a number of syndromic and non-syndromic forms of oligodontia including MSX1, PAX9, AXIN2, EDA and WNT10A. This study aimed to identify the causal mutations in a consanguineous Pakistan family with oligodontia and microdontia.

DESIGN

Exome sequencing was performed in two of affected members of the Pakistan family.

RESULTS

The exome sequencing data revealed that the affected individuals were homozygous with a novel mutation in exon 8 of the SMOC2 gene, c.681T>A (p.C227X).

CONCLUSIONS

This is the second report describing SMOC2 mutations with oligodontia and microdontia underlining the key role for this signalling molecule in tooth development.

Mesio-Distal and Buccal-Lingual Tooth Dimensions are Part of the Cleft Spectrum: A Pilot for Future Genetic Studies

Objective : Considering that oral clefts and tooth dimensions may be part of the same phenotypic spectrum, the aim of this study was to investigate tooth dimensions in permanent dentition and dental malformations, including tooth size discrepancies, of subjects born with clefts compared with individuals without clefts. Design : Cross-sectional study. Participants : The cleft group was composed of 66 subjects, and the noncleft group consisted of 66 healthy unrelated subjects. Main Outcome Measures : The mesio-distal and buccal-lingual crown diameter of fully erupted permanent teeth outside the cleft area was measured using a digital caliber. Clinical records and radiographs were used to evaluate the type of clefts and dental anomalies. Results : The lower second premolar was significantly reduced in the CLP and CP groups. The upper lateral incisor was found to be significantly smaller in the CP group, only for mesio-distal dimensions (P < .05). Dental agenesis was found in eight (12%) cleft subjects and supernumerary teeth in two (3%). Conclusions : Subjects born with oral clefts presented size reduction in specific dental groups.

Multilevel complex interactions between genetic, epigenetic and environmental factors in the aetiology of anomalies of dental development

Dental anomalies are caused by complex interactions between genetic, epigenetic and environmental factors during the long process of dental development. This process is multifactorial, multilevel, multidimensional and progressive over time. In this paper the evidence from animal models and from human studies is integrated to outline the current position and to construct and evaluate models, as a basis for future work. Dental development is multilevel entailing molecular and cellular interactions which have macroscopic outcomes. It is multidimensional, requiring developments in the three spatial dimensions and the fourth dimension of time. It is progressive, occurring over a long period, yet with critical stages. The series of interactions involving multiple genetic signalling pathways are also influenced by extracellular factors. Interactions, gradients and spatial field effects of multiple genes, epigenetic and environmental factors all influence the development of individual teeth, groups of teeth and the dentition as a whole. The macroscopic, clinically visible result in humans is a complex unit of four different tooth types formed in morphogenetic fields, in which teeth within each field form directionally and erupt at different times, reflecting the spatio-temporal control of development. Even when a specific mutation of a single gene or one major environmental insult has been identified in a patient with a dental anomaly, detailed investigation of the phenotype often reveals variation between affected individuals in the same family, between dentitions in the same individual and even between different teeth in the same dentition. The same, or closely similar phenotypes, whether anomalies of tooth number or structure, may arise from different aetiologies: not only mutations in different genes but also environmental factors may result in similar phenotypes. Related to the action of a number of the developmental regulatory genes active in odontogenesis, in different tissues, mutations can result in syndromes of which dental anomalies are part. Disruption of the antagonistic balance between developmental regulatory genes, acting as activators or inhibitors can result in dental anomalies. There are critical stages in the development of the individual tooth germs and, if progression fails, the germ will not develop further or undergoes apoptosis. The reiterative signalling patterns over time during the sequential process of initiation and morphogenesis are reflected in the clinical association of anomalies of number, size and form and the proposed models. An initial step in future studies is to combine the genetic investigations with accurate recording and measurement of the phenotype. They also need to collate findings at each level and exploit the accurate definition of both human and murine phenotypes now possible.