Oral and craniofacial research in the Generation R study: an executive summary

OBJECTIVES

Oral conditions are of high prevalence and chronic character within the general population. Identifying the risk factors and determinants of oral disease is important, not only to reduce the burden of oral diseases, but also to improve (equal access to) oral health care systems, and to develop effective oral health promotion programs. Longitudinal population-based (birth-)cohort studies are very suitable to study risk factors on common oral diseases and have the potential to emphasize the importance of a healthy start for oral health. In this paper, we provide an overview of the comprehensive oral and craniofacial dataset that has been collected in the Generation R study: a population-based prospective birth cohort in the Netherlands that was designed to identify causes of health from fetal life until adulthood.

METHODS

Within the multidisciplinary context of the Generation R study, oral and craniofacial data has been collected from the age of 3 years onwards, and continued at the age of six, nine, and thirteen. Data collection is continuing in 17-year-old participants.

RESEARCH OUTCOMES

In total, the cohort population comprised 9749 children at birth, and 7405 eligible participants at the age of seventeen. Based on questionnaires, the dataset contains information on oral hygiene, dental visits, oral habits, oral health-related quality of life, orthodontic treatment, and obstructive sleep apnea. Based on direct measurements, the dataset contains information on dental caries, developmental defects of enamel, objective orthodontic treatment need, dental development, craniofacial characteristics, mandibular cortical thickness, and 3D facial measurements.

CONCLUSIONS

Several research lines have been set up using the oral and craniofacial data linked with the extensive data collection that exists within the Generation R study.

CLINICAL RELEVANCE

Being embedded in a multidisciplinary and longitudinal birth cohort study allows researchers to study several determinants of oral and craniofacial health, and to provide answers and insight into unknown etiologies and oral health problems in the general population.

Novel Genetic Determinants of Dental Maturation in Children

Dental occlusion requires harmonious development of teeth, jaws, and other elements of the craniofacial complex, which are regulated by environmental and genetic factors. We performed the first genome-wide association study (GWAS) on dental development (DD) using the Demirjian radiographic method. Radiographic assessments from participants of the Generation R Study (primary study population, N1 = 2,793; mean age of 9.8 y) were correlated with ~30 million genetic variants while adjusting for age, sex, and genomic principal components (proxy for population stratification). Variants associated with DD at genome-wide significant level (P < 5 × 10-8) mapped to 16q12.2 (IRX5) (lead variant rs3922616, B = 0.16; P = 2.2 × 10-8). We used Fisher's combined probability tests weighted by sample size to perform a meta-analysis (N = 14,805) combining radiographic DD at a mean age of 9.8 y from Generation R with data from a previous GWAS (N2 = 12,012) on number of teeth (NT) in infants used as proxy of DD at a mean age of 9.8 y (including the ALSPAC and NFBC1966). This GWAS meta-analysis revealed 3 novel loci mapping to 7p15.3 (IGF2BP3: P = 3.2 × 10-8), 14q13.3 (PAX9: P = 1.9 × 10-8), and 16q12.2 (IRX5: P = 1.2 × 10-9) and validated 8 previously reported NT loci. A polygenic allele score constructed from these 11 loci was associated with radiographic DD in an independent Generation R set of children (N = 703; B = 0.05, P = 0.004). Furthermore, profiling of the identified genes across an atlas of murine and human stem cells observed expression in the cells involved in the formation of bone and/or dental tissues (>0.3 frequency per kilobase of transcript per million mapped reads), likely reflecting functional specialization. Our findings provide biological insight into the polygenic architecture of the pediatric dental maturation process.

Effectiveness of the new mandatory mouthguard use and orodental injuries in Dutch field hockey

ObjectivesUp to 68% of field hockey players have experienced at least one orodental injury in their sport career. Therefore, the Royal Dutch Hockey Association (KNHB) made mouthguard use mandatory for field hockey players during competition and training from August 2015 onwards.This study evaluates the effects of the new regulations on mouthguard use and the occurrence of injuries in Dutch field hockey.MethodsA 35-item online questionnaire about mouthguard use and orodental injuries was sent to 13 field hockey clubs in the Netherlands. Absolute numbers and percentages of mouthguard ownership, mouthguard use, number and type of injuries were assessed. The results were related to comparable data before mandatory mouthguard use. Associations of gender and training frequency with the number of injuries were analysed with logistic regression.ResultsIn total, 1169 hockey players were included in the study and almost all owned a mouthguard (females:99.6%, males:93.7%), which significantly increased after implementation (p < 0.001). 90.6% of the respondents wore a mouthguard during matches and 70.1% during training. Of the 1169 players, 68(5.8%) experienced at least one orodental injury after the implementation with a total of 100 injuries. Injuries happened more often during matches (63.2%) than during training (36.8%). Lip cuts account for most of the injuries, the number of broken (p = 0.116) and knocked out teeth (p = 0.026) decreased.ConclusionAlthough mouthguard use already increased in recent years, the new regulations led to an additional increase and a successful change of attitude towards mouthguard use. Most importantly, the severity of orodental injuries decreased measurable.

Outcomes of dental implants in young patients with congenital versus non-congenital missing teeth

Objective

This cross-sectional study aims to investigate the effect of the cause of missing teeth on the survival and subjective success of dental implant treatment (DIT) in young patients with missing teeth due to non-congenital causes (tooth loss) in comparison to patients with missing teeth because of congenital causes (hypodontia and oligodontia).

Material and methods

All patients were asked 7 questions to extract information about the survival and subjective success of DIT. Implant survival function was designed using the Kaplan-Meier analysis. Differences in implant success outcomes were studied using binary logistic regression analysis.

Results

One hundred ten patients aged 18 to 40 years old were included, whereof 32 patients with tooth loss, 25 patients with hypodontia and 53 patients with oligodontia. In the tooth loss group, implant survival reached 96.9%; in the hypodontia group 96.0%; and in the oligodontia group 88.7%. Regarding subjective implant success, patient satisfaction was significantly higher (p < 0.040) among patients with congenital missing teeth in comparison to patients with tooth loss. Other implant success components showed no statistically significant difference (p > 0.050) between the groups.

Conclusion

The cause of missing teeth does not influence implant survival. However, the cause of missing teeth does have a significant impact on patient satisfaction (implant success), ascertaining young patients with congenital missing teeth as more satisfied of DIT than young patients with tooth loss.

Clinical relevance

Young patients with tooth agenesis and with an increased number of missing teeth are more content about the treatment with dental implants than patients with tooth loss. Furthermore, a consensus regarding the assessment of implant success is an essential concern for clarification.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40729-021-00362-7.

The association of maternal folic acid supplementation and prenatal folate and vitamin B12 concentrations with child dental development

OBJECTIVE

Low folic acid, folate and vitamin B12 might affect tooth formation and mineralization. The conversion of folic acid into folate is catalysed by the methylenetetrahydrofolate (MTHFR) enzyme which is encoded by the MTHFR gene. Among 3728 mothers and their 10-year-old children from the Generation R Study, we investigated associations of maternal folic acid supplementation and prenatal folate and vitamin B12 concentrations with child dental development. Secondly, we checked the modifying effect of MTHFR-C677T polymorphism.

METHODS

Information on folic acid supplementation was obtained by questionnaires. Concentrations of folate and vitamin B12 were measured from venous samples taken in early pregnancy. Developmental stages of teeth were defined by the Demirjian method at the age-10 assessment. In addition, dental age of the children was calculated using the Dutch standard. GLM and multivariate linear regression models were built to study the associations.

RESULTS

Folic acid supplementation started when pregnancy was known (β = -0.09; 95% CI: -0.17, -0.01) and folic acid supplementation started prior to known pregnancy (β = -0.12; 95% CI: -0.20, -0.04) were both associated with decelerated dental development by 1-2 months lower dental age of 10-year-old children. Folate (β = -0.02, 95% CI: -0.05, 0.02) and vitamin B12 (β = 0.03, 95% CI: -0.00, 0.06) were not associated with dental age. MTHFR-C677T did not modify the associations.

CONCLUSIONS

Maternal folic acid supplementation delays dental development of children by 1-2 months dental age, whereas maternal folate and vitamin B12 concentrations in early pregnancy do not affect the timing of child dental development.

Skeletal maturation in relation to ethnic background in children of school age: The Generation R Study

Ethnicity is a well-established determinant of pediatric maturity, but the underlying genetic and environmental contributions to these ethnic differences are poorly comprehended. We aimed to evaluate the influence of ethnicity on skeletal age (SA), an assessment of pediatric maturation widely used in clinical settings. We included children from the Generation R Study, a multiethnic population-based pregnancy cohort, assessed at a mean age of 9.78 (±0.33) years. SA was evaluated by a trained observer on hand DXA scans using the Greulich and Pyle method. Ethnic background was defined as geographic ancestry (questionnaire-based assessment) (N = 5325) and genetic ancestry (based on admixture analysis) (N = 3413). Associations between the ethnic background and SA were investigated separately in boys and girls, using linear regression models adjusted for age, height and BMI. Based on geographic ancestry, 84% of the children were classified as European, 6% as Asian and 10% as African. Children of European background had on average younger SA than those of Asian or African descent. Asian boys had 0.46 (95% CI 0.26-0.66, p-value < 0.0001) and African boys 0.36 years (95% CI 0.20-0.53, p-value < 0.0001) older SA as compared to European boys. Similarly, Asian girls showed 0.64 (95% CI 0.51-0.77, p-value < 0.0001) and African girls 0.38 years (95% CI 0.27-0.48, p-value < 0.0001) older SA as compared to European girls. A similar pattern was observed in the analysis with genetically-defined ancestry. Furthermore, an increase in the proportion of Asian or African component was associated with older SA in both boys (log[Non-European/European]proportion = 0.10, 95% CI 0.06-0.13, p-value < 0.0001) and girls (log[Non-European/European]proportion = 0.06, 95% CI 0.04-0.08, p-value < 0.0001). In summary, children of Asian and African backgrounds have on average older SA as compared to children of European descent, partially explained by a genetic component.

Dental development and craniofacial morphology in school-age children

INTRODUCTION

The growth of the craniofacial complex is important for establishing a balanced relationship among the teeth, jaws, and other facial structures. However, there is still a lack of information about craniofacial parameters that are affected by the rate of dental development. The aim of this study was to investigate the association between dental development and craniofacial morphology in school-age children.

METHODS

This study was embedded in the Generation R Study, Rotterdam, The Netherlands. In 3,896 children aged 8 to 11 years, dental development was assessed from panoramic radiographs and craniofacial morphology was assessed by combining cephalometric parameters into 9 uncorrelated principal components, each representing a distinct skeletal or dental craniofacial pattern. The statistical analysis was performed using linear and nonlinear regression model.

RESULTS

Dental development was positively associated with the bimaxillary growth (β = 0.04; 95% CI 0.01 to 0.08). Children with above-average dental development had a tendency toward Class II jaw relationship (β = -0.08; 95% CI -0.13 to -0.04). Regarding dental parameters, the proclination increased for incisors and lips with advanced dental development (β = 0.15 [95% CI 0.10 to 0.19] and β = 0.13 [95% CI 0.09 to 0.17], respectively), but the incisor proclination remained more pronounced in children that had above-average dental development.

CONCLUSIONS

The findings of this large population-based study show that dental development is associated with specific dental and skeletal cephalometric characteristics in school-age children. Further longitudinal studies are necessary to confirm the observed effects over time.

The role of accelerated dental development on the occurrence of aberrant dental traits that indicate malocclusion

BACKGROUND

Timing of dental development might help orthodontists to optimize initiation of treatment and to prevent and intercept dental misalignment. This study examines the association between timing of dental development and aberrant dental traits such as crowding, impaction, and hypodontia.

METHODS

This study was performed using 4446 ten-year-old children from a multiethnic birth cohort, the Generation R Study. Dental development was defined using the Demirjian method. Crowding, impaction, and hypodontia were ascertained from 2D and 3D pictures and radiographs. We built three series of logistic regression models to test the associations of dental age with crowding, impaction, and hypodontia. Similar models were built to investigate the associations of the developmental stages of each left mandibular tooth with crowding, impaction, and hypodontia.

RESULTS

Inverse associations were found between every 1-year increase in dental age and the presence of crowding [odds ratio (OR) = 0.84, 95% confidence interval (CI): 0.79, 0.89], impaction of teeth (OR = 0.66, 95% CI: 0.52, 0.84), and hypodontia (OR = 0.52, 95% CI: 0.47, 0.56). Lower developmental stages of the second premolar were associated with the presence of crowding (OR = 0.90, 95% CI: 0.83, 0.98). Lower developmental stages of the second premolar (OR = 0.88, 95% CI: 0.79, 0.98), first molar (OR = 0.76, 95% CI: 0.65, 0.90), and the second molar (OR = 0.83, 95% CI: 0.73, 0.94) were associated with the presence of tooth impaction. Lower developmental stages of all mandibular teeth except the central incisor were associated with hypodontia (P < 0.05).

CONCLUSION

Accelerated dental development is associated with lower occurrence of crowding, impaction, and hypodontia.

The Associations of Maternal and Neonatal Vitamin D with Dental Development in Childhood

BACKGROUND

Vitamin D influences the formation and mineralization of teeth.

OBJECTIVE

To investigate the association of maternal and neonatal vitamin D concentrations with the dental development of 10-y-old children, in a population-based prospective cohort study among 3,770 mothers and children in the Netherlands.

METHODS

Maternal venous blood samples were collected in the second trimester (median 20.4 weeks of gestation; range: 18.5-23.2 wk) whereas umbilical cord blood samples were collected immediately after delivery (median 40.1 weeks of gestation; range 35.9-42.3 wk). Dental development was defined using the Demirjian method. Multivariate regression models were built to analyze the studied associations.

RESULTS

High concentrations of 25-hydroxyvitamin D [25(OH)D] during midpregnancy (β: -0.04; 95% CI: -0.08, -0.01) and at birth (β: -0.06; 95% CI: -0.10, -0.02) were associated with a lower dental age in children. The children of mothers with severe vitamin D deficiency [25(OH)D <25.0 nmol/L] during midpregnancy exhibited a higher dental age (β: 0.14; 95% CI: 0.03, 0.24) and higher developmental stages of the mandibular first premolar (β: 0.32; 95% CI: 0.04, 0.60) compared with the children of mothers with optimal values of 25(OH)D (≥75.0 nmol/L). Children with vitamin D deficiency [25(OH)D 25.0-49.9 nmol/L] at birth exhibited a higher dental age (β: 0.11; 95% CI: 0.01, 0.20), higher developmental stages of the mandibular second premolar (β: 0.27; 95% CI: 0.02, 0.51), and higher developmental stages of the mandibular second molar (β: 0.24; 95% CI: 0.00, 0.48) compared with children with sufficient-to-optimal values of 25(OH)D (≥50.0 nmol/L) at birth.

CONCLUSION

Higher maternal and neonatal 25(OH)D concentrations are associated with decelerated dental development in childhood. The lower the vitamin D level during midpregnancy or at birth, the higher the dental age of children, and the higher the developmental stages of the mandibular teeth.

Does dental caries affect dental development in children and adolescents?

Although a link between dietary changes, caries, and dental development has been observed, the literature provides little insight about this relationship. The aim of our study was to investigate the association between dental caries and dental development in a clinical sample of Albanian children and adolescents. In total, 118 children and adolescents, born between 1995 and 2004 and aged 6-15 years, were included. Dental caries in the deciduous dentition was assessed using the Decayed, Filled Teeth (dft) index and dental caries in the permanent dentition was assessed using the Decayed, Missing, Filled Teeth (DMFT) index. Dental development during the permanent dentition was determined using the Demirjian method. Linear and ordinal regression models were applied to analyze the associations of dental caries with dental age and developmental stages of each left mandibular tooth. Dental caries in the deciduous dentition, estimated as a median dft of 2.0 (90% range, 0.0-9.1), was significantly associated with lower dental age (β = -0.21; 90% CI: -0.29, -0.12) and with delayed development of the canine, both premolars, and the second molar. Untreated dental caries (dt) was associated with lower dental age (β = -0.19; 90% CI: -0.28, -0.10). Dental caries in the permanent dentition, estimated as a median DMFT of 1.0 (90% range, 0.0-8.0), was not significantly associated with dental age (β = 0.05; 90% CI: -0.04, 0.14). However, the DMFT was associated with the advanced stages of development of both premolars and the second molar. The untreated dental caries in the deciduous dentition delays the development of permanent teeth.

Rare and Common Variants Conferring Risk of Tooth Agenesis

We present association results from a large genome-wide association study of tooth agenesis (TA) as well as selective TA, including 1,944 subjects with congenitally missing teeth, excluding third molars, and 338,554 controls, all of European ancestry. We also tested the association of previously identified risk variants, for timing of tooth eruption and orofacial clefts, with TA. We report associations between TA and 9 novel risk variants. Five of these variants associate with selective TA, including a variant conferring risk of orofacial clefts. These results contribute to a deeper understanding of the genetic architecture of tooth development and disease. The few variants previously associated with TA were uncovered through candidate gene studies guided by mouse knockouts. Knowing the etiology and clinical features of TA is important for planning oral rehabilitation that often involves an interdisciplinary approach.

Ancestry and dental development: A geographic and genetic perspective

OBJECTIVE

In this study, we investigated the influence of ancestry on dental development in the Generation R Study.

METHODS

Information on geographic ancestry was available in 3,600 children (1,810 boys and 1,790 girls, mean age 9.81 ± 0.35 years) and information about genetic ancestry was available in 2,786 children (1,387 boys and 1,399 girls, mean age 9.82 ± 0.34 years). Dental development was assessed in all children using the Demirjian method. The associations of geographic ancestry (Cape Verdean, Moroccan, Turkish, Dutch Antillean, Surinamese Creole and Surinamese Hindustani vs Dutch as the reference group) and genetic content of ancestry (European, African or Asian) with dental development was analyzed using linear regression models.

RESULTS

In a geographic perspective of ancestry, Moroccan (β = 0.18; 95% CI: 0.07, 0.28), Turkish (β = 0.22; 95% CI: 0.12, 0.32), Dutch Antillean (β = 0.27; 95% CI: 0.12, 0.41), and Surinamese Creole (β = 0.16; 95% CI: 0.03, 0.30) preceded Dutch children in dental development. Moreover, in a genetic perspective of ancestry, a higher proportion of European ancestry was associated with decelerated dental development (β = -0.32; 95% CI: -.44, -.20). In contrast, a higher proportion of African ancestry (β = 0.29; 95% CI: 0.16, 0.43) and a higher proportion of Asian ancestry (β = 0.28; 95% CI: 0.09, 0.48) were associated with accelerated dental development. When investigating only European children, these effect estimates increased to twice as large in absolute value.

CONCLUSION

Based on a geographic and genetic perspective, differences in dental development exist in a population of heterogeneous ancestry and should be considered when describing the physiological growth in children.

Thyroid Function during Early Life and Dental Development

Children with low levels of thyroid hormones (hypothyroidism) have delayed tooth eruption, enamel hypoplasia, micrognathia, and anterior open bite, whereas children with hyperthyroidism may suffer from accelerated tooth eruption, maxillary, and mandibular osteoporosis. However, it is still unknown whether thyroid function variations within the normal or subclinical range also have an impact on hard dental tissues in healthy children. The objective of this study was, therefore, to investigate the association between thyroid function from the fetal period until early childhood and dental development at school age. This study is embedded in the Generation R Study, a population-based cohort study established in Rotterdam, the Netherlands. Maternal thyroid function (thyroid-stimulating hormone [TSH], free thyroxine [FT4], and thyroid peroxidase antibody [TPOAb] concentrations) was measured during early pregnancy, and thyroid function of the offspring (TSH and FT4) was measured in cord blood at birth and in early childhood (6 y). Dental development was assessed from panoramic radiographs of children of school-going age (9 y). In total, 2,387 to 2,706 subjects were available for the multivariable linear regression analysis, depending on the point in time of thyroid function measurement. There was an inverse association between cord blood and early childhood TSH concentrations with dental development, with a -0.06 lower standard deviation (SD) per 1 mU/L of TSH (95% confidence interval [CI], -0.11 to -0.01) and a -0.06 lower SD per 1 mU/L of TSH (95% CI, -0.11 to 0.00), respectively. There was no association between the maternal thyroid function during pregnancy and the dental development score of the child. However, TPOAb-positive mothers had children with a -0.20 SD (adjusted 95% CI, -0.35 to -0.04) lower dental development score compared with TPOAb-negative mothers. The findings of this study suggest that the thyroid hormone is involved in the maturation of teeth from the early stages of life onward.

The association between hypodontia and dental development

OBJECTIVES

In this cross-sectional study, we aimed to investigate the pattern of hypodontia in the Dutch population and determine the association between hypodontia and dental development in children with and without hypodontia, applying three different standards, Dutch, French Canadian, and Belgian, to estimate dental age.

METHODS

We used dental panoramic radiographs (DPRs) of 1488 children (773 boys and 715 girls), with a mean age of 9.76 years (SD = 0.24) participating in a population-based cohort study in Rotterdam, the Netherlands, born in 2002-2004, and 452 children (219 boys and 233 girls) with a mean age of 9.83 years (SD = 1.09) participating in a mixed-longitudinal, interdisciplinary population-based cohort study in Nijmegen, the Netherlands born in 1960-1968.

RESULTS

The prevalence of hypodontia in the Generation R Study was 5.6 % (N = 84) and 5.1 % (N = 23) in the Nijmegen Growth Study. Linear regression analysis showed that children with hypodontia had a 0.37 [95 % CI (-0.53,-0.21)] to 0.52 [95 % CI (-0.76,-0.38)] years lower dental age than children without hypodontia. The ordinal regression analysis showed a delay in development of mandibular second premolars [1.68 years; 95 %CI (-1.90,-1.46)], mandibular first premolars [0.57 years; 95 % CI (-0.94,-0.20)], and mandibular second molars [0.47 years; 95 % CI (-0.84,-0.11)].

CONCLUSION

These findings suggest that children with hypodontia have a delayed dental development.

CLINICAL RELEVANCE

The delay of dental development in children with hypodontia should be taken into consideration and therefore orthodontists should recognize that a later start of treatment in these patients may be necessary.

The impact of malocclusions on oral health-related quality of life in children-a systematic review and meta-analysis

Introduction

A limited amount of systematic literature reviews on the association between malocclusions and oral health-related quality of life (OHRQOL) summarize inconclusive results. Therefore, we conduct a systematic review and meta-analysis on the association of malocclusions with OHRQOL in children.

Methods

Relevant studies were identified in Pubmed, Embase, Cochrane, Google Scholar and other databases. All studies with data on malocclusions or orthodontic treatment need and OHRQOL in children were included. Methodological quality of the studies was assessed with the Newcastle-Ottawa Scale (NOS). Random effects models were used to estimate summary effect measures for the association between malocclusion and OHRQOL in a continuous and a categorical data analysis. Tests for heterogeneity, publication bias and sensitivity of results were performed.

Results

In total, 40 cross-sectional studies were included in the meta-analyses. Summary measures of the continuous data show that OHRQOL was significantly lowered in children with malocclusions (standardized mean difference (95 % CI] = 0.29 (0.19–0.38)). The summary odds ratio for having an impact on OHRQOL was 1.74 times higher in children with malocclusion than in children without malocclusions. Heterogeneity among studies was partly explained by malocclusion assessment, age of the children and country of study conduction.

Conclusion

Our results provide evidence for a clear inverse association of malocclusion with OHRQOL. We also showed that the strength of the association differed depending on the age of the children and their cultural environment.

Clinical relevance

Dentists benefit from understanding the patient differences regarding the impact of malocclusions.

Electronic supplementary material

The online version of this article (doi:10.1007/s00784-015-1681-3) contains supplementary material, which is available to authorized users.