DOI: 10.1051/odfen/2018129 J Dentofacial Anom Orthod 2017;20:402 © The author Tooth eruption disorders associated with systemic and genetic diseases: clinical guide C. Choukroune Qualified specialist in Dentofacial Orthopedics, former Hospital Resident, private practice in Boulogne-Billancourt SUMMARY Tooth eruption is defined as the movement of the dental root and the tooth from its original devel- opment site in the alveolar process to its functional position in the oral cavity. Despite vast amounts of research, the exact mechanism of tooth eruption remains unknown. The authors have shown that the dental crown is not necessary for tooth eruption, whereas the dental follicle seems to be essential for the process. The formation of an eruption pathway by bone resorption allows the root to breach the oral cavity, at the same time, bone formation occurs at the basal level of the dental root. Multiples genetic and molecular structures coordinate these events. Sometimes it is by studying pathological conditions that we discover the essential interactions that occur during tooth eruption. Frequently, a delayed tooth eruption (DTE) is the first, if not the only, expression of a local or general pathology. A DTE can affect directly the diagnosis, the treatment planning, or the timing of the orthodontic treatment. Therefore, it is essential for the orthodontist to identify the cause of a DTE for implementing the correct treatment. KEY WORDS Tooth eruption, genetic disease inborn, systemic disease, delayed tooth eruption INTRODUCTION Dental eruption is a unique physiolog- between osteoblasts, osteoclasts, and the ical event; the tooth is the only organ to dental follicle (DF), involving many genet- appear a few months or years after birth. ic factors. These studies have opened the This complex and finely regulated process way for the discovery of multiple genetic, influences the normal development of the molecular, and tissue interactions that oc- craniofacial region. cur during dental eruption. In the 1980s, many teams looked at the The study of genetic or acquired disorders mechanisms behind dental eruption; their has made it possible, among other things, work has highlighted complex interactions to understand the mechanisms involved in Address for correspondence: Chloé Choukroune 150, rue Gallieni – 92100 Boulogne- Billancourt – France Article received: 20-04-2017. Email: [email protected] Accepted for publication: 18-05-2017. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1 Article available at https://www.jdao-journal.org or https://doi.org/10.1051/odfen/2018129 C. CHOUKROUNE dental eruption and has shown how Although the development of the these interactions are essential for craniofacial region is of interest to or- the smooth running of the process. A thodontists, the clinical signs of sys- disruption of the eruption process can temic and genetic disorders responsi- occur in the context of systemic or ge- ble for eruptive disorders are still not netic disorders; the clinical picture can fully understood by practitioners. This range from a simple delay to a com- article summarizes the clinical signs plete agenisis. Often, changes in the of the main disorders presenting as eruption process are the first, if not eruption disorders after reviewing the the only, manifestation of a systemic mechanisms which affect eruption. or genetic pathology. The precise iden- This is to improve management and tification of the cause of a disruption of diagnosis so that treatments can be the eruption process helps refine the better adapted to meet the needs of diagnosis, define the overall treatment patients and their families. plan, and the orthodontic treatment schedule. ERUPTION STAGES Eruption is defined as the movement Pre-eruptive phase of the tooth germ from its site of devel- opment in the alveolar processes to its Long before eruption, the tooth germ functional position in the oral cavity22. will undergo intra-alveolar movements Before teeth achieve their functional during its development, which do not placement on the arch, they undergo affect the direction of eruption6,7,45. many movements. According to Ten Because of the rapid development of Cate, these complex movements can the deciduous teeth (DT), their germs be organized into three phases25: will overlap at a given moment within the maxillae. Maxillary growth will force – Pre-eruptive movements: undergone the roots of the second deciduous mo- by deciduous and permanent teeth lars to move backward the roots of the within the tissues before the onset front teeth to move forward to prevent of eruption; cluttering. – Eruptive movements: when the tooth The permanent teeth (PT) germs are moves from its intraosseous position initially in the same bony crypt as the to its functional position on the arch. deciduous teeth but are located on This phase can be divided into intra-al- their lingual slope25. veolar and supra-alveolar eruption; After DT eruption, PT occupy their own – Posteruptive movements: the tooth crypts. They will move considerably dur- remains in its functional position and ing growth, for example from a lingual adapts to the growth of the jaw and position for premolar germs to a more proximal and occlusal wear. 2 Choukroune C. Tooth eruption disorders associated with systemic and genetic diseases: clinical guide Tooth eruption disorders associated with systemic AND Genetic diseases: CLINICAL GUIDE Figure 1 Panoramic view of a 9-year-old boy showing mandibular premolar germs located between the roots of deciduous molars. Note the mesial inclination of the second man- dibular permanent molar (ODF service, Pitié-Salpêtrière Hospital). Figure 2 Panoramic view of a 9-year-old child showing bone resorption that occurs over 37/47 germs and the formation of an “eruption path” across the bone (ODF service, Pitié-Salpêtrière Hospital). vestibular position between the roots of before initiating the eruptive move- the deciduous molars (Figure 1). ment. They result from the combination These pre-eruptive movements aim of two factors: on the one hand, the to position the germ in its final position movements made by the germ itself, J Dentofacial Anom Orthod 2017;20:402 3 C. CHOUKROUNE and on the other hand, the “passive” The supraosseous phase is the pro- movements of the germ because of cess by which the tooth emerges into maxillary growth25. A lack of maxillary the oral cavity. When the deciduous growth can disrupt these movements. tooth falls out, the bone that surrounds Few things are known about these the root is reabsorbed. With the erup- pre-eruptive mechanisms and it is tion of the permanent tooth, the alveo- difficult to know if they are predeter- lar bone is reconstructed thanks to the mined or if they represent an adaptive osteogenic activity of the periodontal response. They are used to correctly ligament. Then, the gingival defect is position the germ and its bone crypt repaired progressively, and the alveolar before the actual eruption begins6. process is built44. When teeth appear in the oral cavity, Eruptive phase they are subject to environmental fac- tors such as the muscular pressures of The eruptive phase can itself be di- the cheeks, tongue, and lips, as well as vided into three stages: intraosse- the eruptive forces of adjacent teeth,25 ous phase, supraosseous phase, and which will continue until the teeth posteruptive phase. reach their final position on the dental Intraosseous eruption begins as soon arch. The displacement of the teeth to as crown formation is complete7. It cor- the occlusal plane is ensured by root responds to the entire germ eruption elongation and bone formation at the phase through bone and occurs with apical level and at the level of the in- mainly axial movements6 (Fig. 2). ter-radicular septa22. It is similar for both teeth. Numerous Finally, the posteruptive phase includes other events accompany the intraosse- all movements made after the teeth have ous eruption of the germ: root elonga- reached the occlusal plane. They include tion is initiated as well as the develop- adaptive growth movements of the jaw ment of the periodontal ligament and as well as compensatory movements the gingival junction. caused by occlusal and proximal wear. PHYSIOLOGY OF ERUPTION For over 70 years, multiple theories The authors examined the proposed have been proposed to explain the eruption mechanisms and tested mul- eruptive phenomenon. It must be said tiple hypotheses: that despite numerous studies and publications on the subject, the pre- – Collagen contraction of the periodon- cise mechanism of the eruption is still tal ligament has been proposed to unknown. explain the eruptive phenomenon. Eruption could be attributed to many However, no cause-effect relationship factors that have been studied, ap- was found between the eruption rate proved, and then disapproved over and collagen turnover rate43. Many time. experiments have been performed in 4 Choukroune C. Tooth eruption disorders associated with systemic and genetic diseases: clinical guide Tooth eruption disorders associated with systemic AND Genetic diseases: CLINICAL GUIDE This indicates that the root is not the motor of dental eruption (Fig. 3). Role of the dental crown Another hypothesis was that eruption depended on the dental organ itself, and particularly on the crown. A series of excellent experiments conducted by Marks and Cahill in the 1980s focused on showing the role of the crown and DF during eruption. In one of their experiments, they Figure 3 show that DF is essential to the erup- Tooth 45 having erupted in the absence of root elongation (ODF service, Pit- tion, whereas the crown is not. Indeed, ié-Salpêtrière Hospital). by replacing a premolar crown in dogs with a metal object, but leaving DF in the presence of a collagen inhibitor place, the metal object still erupted.