Dental Development in Children and Its Influences on Craniofacial Morphology

The relationship between dental development and facial morphology has been a point of interest for dental care professionals. In this thesis, we investigated the patterns of child’s dental development by analyzing the effects of genetic, endocrine and other dental determinants. Further, we explored the influence of dental determinants on craniofacial morphology in children. All studies published in this thesis were embedded in the Generation R Study, a population-based prospective cohort from fetal life until young adulthood. The rationale and findings of the studies published in this thesis are organized into three parts.
Part I elaborates on the mechanism of dental and facial development in the intrauterine and postnatal period, and the factors which are influencing these growth changes. We also specify the aims of this thesis. Part II of the thesis is focused on the characteristics and determinants of dental development. In Chapter 2, we report a 1.5 years advanced dental development in children born after the year 2000 compared to children born 40 years earlier; a result showing substantial secular changes of dental development in the Dutch population. These findings contradict previous studies which underline that dental development is a biologically stable process and independent of other environmental factors. Chapter 3 reflects on the genetic background of dental development. We confirmed 9 loci which were previously associated with the eruption of teeth, and also confirmed 3 new loci: IGF2BP3, IRX5, and PAX9. In Chapter 4 we expand the knowledge of the endocrine regulation of dental development by reporting and association between thyroid function and dental development. We observed that thyroid peroxidase antibody positivity in mothers during pregnancy as well as thyroid stimulating hormone at birth and during early childhood were inversely associated with dental development. These findings suggest that thyroid hormones might also regulate the function of tooth-forming cells. Concluding, in Chapter 5, we established a link between dental development and tooth agenesis, where we demonstrated that children with hypodontia had delayed dental development. Therefore, considering that tooth development is a polygenic trait, a potential underlying mechanism linking tooth agenesis and delayed dental development is the number of genetic variants present. For example, a smaller number of variants may cause delayed dental development, while a greater number of variants could cause tooth agenesis.
Part III describes the influence of hypodontia and dental development on the craniofacial morphology of 9-year-old children. In Chapter 6 we observed a strong association between hypodontia and retroclination of incisors. Furthermore, hypodontia in the upper jaw was associated with the tendency toward a (pseudo) Class III jaw relationship, while lower jaw hypodontia was associated with reduced vertical facial parameters in the posterior region. The underlying mechanisms explaining these associations were undeniably due to the compensational mechanism of the surrounding tissues towards the region of agenetic tooth. However, another underlying mechanism might be that genetic markers which are involved in tooth development also regulate facial growth. Chapter 7 describes the altered cephalometric growth pattern of children with delayed dental development. We observed that advanced dental development was associated with an increased sagittal and vertical facial growth. Further, we observed that above-average advanced dental development was associated with a tendency for Class II malocclusion, incisor, and lip protrusion. Therefore, we can conclude that dental development, either portrayed as the change of the rate of dental development or tooth agenesis, influences craniofacial characteristics of a child. These findings might be useful for an orthodontist in early diagnosis of malocclusion and when assessing the prognosis of applied treatment.
Chapter 8 provides an insight into the main findings of the studies from previous chapters and reviews methodological considerations, clinical implications, and future directions.