|Year : 2014 | Volume
| Issue : 2 | Page : 47-52
Root resorption: Focus on signs and symptoms of importance for avoiding root resorption during orthodontic treatment
Department of Odontology, Orthodontics Section, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen N, Denmark
|Date of Web Publication||2-Jun-2014|
Department of Odontology, Orthodontics Section, Faculty of Health and Medical Sciences, University of Copenhagen, 20 Nørre Allé, DK-2200 Copenhagen N
Source of Support: None, Conflict of Interest: None
Introduction: This paper summarizes the different conditions, which have a well-known influence on the resorption of tooth roots, exemplified by trauma and orthodontic treatment. The concept of the paper is to summarize and explain symptoms and signs of importance for avoiding resorption during orthodontic treatment. The Hypothesis: The hypothesis in this paper is that three different tissue layers covering the root in the so-called periroot sheet can explain signs and symptoms of importance for avoiding root resorption during orthodontic treatment. These different tissue layers are; outermost - an ectodermal tissue layer (Malassez's epithelium), a middle layer - composed by the collagen-mesodermal tissue layer, and an innermost root-close innervation layer. Abnormalities in one of these tissue layers are thought to cause inflammatory processes in the periodontal membrane comparable to inflammatory processes provoked by trauma and orthodontic pressure. Inflammatory reactions are followed by resorptive processes in the periroot sheet and along the root surface. Evaluation of the Hypothesis: Different morphologies in the dentition are signs of abnormal epithelium or an abnormal mesodermal layer. It has formerly been demonstrated how demyelinization of the myelin sheaths in the peripheral nerves close to the root provoke resorption. Accordingly, conditions affecting these tissue layers can be associated not only with different morphologies but also with general symptoms and diseases (e.g., ectodermal dysplasia and hypophosphatasia).
Keywords: Orthodontics, root resorption, innervation, ectoderm, periodontal membrane
|How to cite this article:|
Kjaer I. Root resorption: Focus on signs and symptoms of importance for avoiding root resorption during orthodontic treatment. Dent Hypotheses 2014;5:47-52
| Introduction|| |
Orthodontists know that root resorption can be provoked by orthodontic forces.  They also know that susceptibility to resorption varies from person to person.  Besides orthodontic forces, there are several other factors that can provoke resorption processes on the root surface.  The histochemical process on the root surface resulting in resorption of root cementum and root dentine has been elucidated in several publications.  Even then, this process and what initiates this process is not fully understood. One question recently posed within the field is why different factors and diseases can lead to root resorption.  In order to answer this question, a more detailed understanding of the root surface and types of tissue covering the root surface is necessary. This paper highlights this tissue covering and explains how the different tissue types hypothetically explain root resorption.
Periroot sheet cover
Three main tissue types form the periroot sheet, which can be compared to a periosteum covering the bone. The tissue components recently described  are demonstrated and shown in [Figure 1].
|Figure 1: The schematic overview of the tissue types in the root-close periodontal membrane. The tissue types within the blue circle marked is root dentine (light grey), cementum (dark grey), innervation layer close to the cementum (yellow dots), and covering the innervation layer is a fiber layer (green crosses). Outermost in the root-close membrane are oblong ectodermal tissue components, Malassez's epithelium (dark red). Light red contours indicate surrounding vessels. The parallel lines to the left indicate the loose periodontal tissue layer|
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Different immunohistochemical examinations of tissues/cells close to the roots revealed that particularly nerves (close to the root), ectomesenchyme (dense fiber layer), and epithelium of Malassez (farthest from the root) comprise the periroot sheet layer. 
After this short introduction to tissue components on the root surface, focus can be redirected to the etiology behind root resorption. Distinction will be made between the processes of disease causing resorption and why/how this disease process can activate resorption.
What causes root resorption?
The known etiologies behind root resorption are presented in an overview article by Gunraj.  One of these is external resorption after trauma. In such cases, resorption is caused by inflammation of the pulp and/or in the periodontal tissue [Figure 2]. Permanent tooth roots can also be affected by resorption caused by pressure in the periodontal ligament, as seen in connection with tooth eruption, orthodontic tooth movement, or tumors [Figure 3]. It is presumed that pressure changes create an inflammatory condition in the periodontal membrane that is followed by a root resorption process as illustrated in [Figure 2] and [Figure 3].
|Figure 2: Drawings illustrating tissue reaction after tooth root trauma. The root-close tissue layers are explained in Figure 1. The root trauma is indicated by a black S-shaped line. (a) Demonstrates the root-close tissue immediately after the fracture. (b) The purple color shows the bleeding or lymph secretion that follows the trauma and (c) suggests how inflammation at the trauma area are followed by resorption processes (blue-purple shadow)|
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|Figure 3: Drawings illustrating tissue reaction due to pressure from orthodontic appliance indicated by black arrows. The root-close tissue layers are explained in Figure 1. (a) Shows the tissue layers before reaction due to appliance. (b) Illustrates the compression of the tissue layers due to force from the orthodontic appliance. (c) Shows the bleeding or lymph secretion after pressure and (d) suggests how inflammation due to the pressure is followed by resorption processes (blue-purple shadow)|
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The history of root resorption is often obscure and referred to as idiopathic.  General diseases can also cause root resorption, but information in the literature is extremely sparse. A recent study  suggests how root resorption can be explained in general diseases. These are ectodermal dysplasia, tuberous sclerosis caused by ectodermal abnormalities, and osteogenesis imperfecta caused by abnormal mesoderm, and finally, viral diseases disrupting the innermost neuroepithelial layer close to the root. This hypothesis is demonstrated in [Figure 4] and will be further clarified.
|Figure 4: An overview of the root-close periodontal membrane in different conditions or diseases affecting the ectoderm (ecto), mesoderm (meso), and neuroectoderm (neuro). The root-close tissue layers are explained in Figure 1 and marked in figure (a). (b) Illustrates that general changes in the ectoderm (e.g., ectodermal dysplasia) affect the root-close tissue layer, which hypothetically appear as thin red lines. (c) Illustrates that general changes in the mesoderm or ectomesenchymal (e.g., osteogenesis imperfect) affect the root-close tissue layer illustrated by sparse green lines. (d) Illustrates that general changes in the neuroectoderm (e.g. meningitis spreading to peripheral nerves) affect the root-close tissue layer which appear with very few yellow dots|
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| The Hypothesis|| |
The hypothesis behind the most recent resorption studies  is that different types of idiopathic resorption can be explained by the composition of the periroot sheet. This hypothesis is illustrated in [Figure 4] and shows the different conditions affecting the ectoderm, mesoderm, and neuroectoderm that are thought to lead to inflammation. This inflammatory process is believed to initiate root resorption and is comparable to the inflammatory process provoked by trauma and orthodontic forces. The hypothesis is based specifically on the ectodermal, mesodermal, and neuroectodermal influences on root morphology and resorption processes.
The ectodermal tissue layer in the periroot sheet is formed by the epithelial cells of Malassez. These are the red cell groups in [Figure 5]. The ectodermal tissue layer affects both the tooth morphology and the occurrence of idiopathic resorptions in ectodermal diseases.
|Figure 5: An overview of the mucosal epithelium influence on tooth formation. Drawing (a) illustrates an early primary tooth bud. The epithelium is colored red, mucous is colored green, and neuroepithelium is yellow. Note that the epithelial protrusion from the stem, that will form the permanent tooth bud, is formed from the same epithelium. (b) Shows the tooth crown with a half-formed root. The colors indicate the same tissues as in (a). Note that the follicle covering the crown is in its inner aspect formed by epithelium. Along the root appears Malassez's epithelium. (c) Represents an unstained section of an extracted root. The immunohistochemical reaction (in brown) indicates Malassez's epithelium covering the outer area of the root-close periodontal membrane. (d) An orthopantomogram from a mixed dentition. The red contours indicate the areas influenced by ectoderm|
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It is well-known that the ectoderm - or the oral mucosa- forms the early tooth bud. It later composes the inner layer in the dental follicle and the cells of Malassez along the root surface [Figure 5]a and b. This ectodermal layer influences the tooth morphology. The orthopantomogram in [Figure 5]c illustrates red contours expressing the structures influenced by the ectoderm.
Different morphologies of incisors and molars from dentitions susceptible to root resorption are shown in [Figure 6]. The figures are reprinted from a national study  involving pretreatment panoramic and profile radiographs from 107 patients who had developed excessive root resorption during the orthodontic treatment (more than one-third of one or more roots had been resorbed). This study identified two characteristic phenotypes of dentitions in 102 of the patients. Before the treatment was initiated, approximately 90 of the patients had more than three of the following morphological signs: Invaginations, short roots, deviant root morphology, collum resorption, crown malformations, ectopia, and agenesis.
|Figure 6: An overview of the mucosal epithelium influence on root morphology and root resorption. Drawings on the left illustrate abnormal root resorption in the primary dentition (upper), abnormal root morphology in the permanent dentition (middle), and deviant crown and root morphology in the permanent incisors (lower). These drawings indicate factors, which in combination predict root resorption in connection with orthodontic appliance. Similar conditions are illustrated in the corresponding radiographs. The right column contains a photo and two radiographs from a patient with tuberous sclerosis with skin afflictions (upper) and cervical root resorptions (middle and lower)|
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Ectodermal dysplasia is a condition in which root resorption occurs.  Other diseases such as tuberous sclerosis with skin afflictions are also prone to root resorption  [Figure 6].
Tuberous sclerosis is a dominant hereditary disease that affects chromosome 9q34 or 16p13. In this general disease, cervical resorption occurs as a first symptom.
Mesodermal or ectomesenchymal tissues
The mesodermal and ectomesenchymal tissue layer affects both the tooth morphology and the occurrence of idiopathic resorptions in diseases.
In the drawing of an early tooth bud formation [Figure 5]a and b, the green areas are the mesodermal or ectomesenchymal areas, which later compose the pulpal tissue and the middle layer of the periroot sheet. If this layer is malformed or disrupted, the morphology of the teeth has a characteristic appearance: Short plumby roots and obliterations in the pulp chambers [Figure 7]. Collum resorptions and a vertical open bite can be characteristic symptoms as well. In the national study mentioned,  12 patients showed plumb roots combined with resorptive changes in the condyle and with open bite. Open bite has formerly been associated with root resorption. 
|Figure 7: An overview of the ectomesenchymal influence on craniofacial and dental morphology. Upper left: Profile radiograph of a patient with skeletal open bite. The four dental radiograph images to the right illustrating cervical root resorption, plump root morphology, and short incisor root, which are all conditions predisposing root resorption during orthodontic treatment. Lower: Three radiographs illustrating abnormal root morphology and cervical root resorption in Paget's disease|
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One general disease with root resorption as a known complication is osteitis deformans (Paget's disease in bone).  In this condition, root resorption begins at the collum and plumb roots are observed [Figure 7]. Osteogenesis imperfecta, hypophosphatemia, and hypocalcemia are also examples of mesodermal diseases where root resorption occurs.
The neuroectodermal layer is the innermost layer of the periodontal periroot sheet. How this layer or the peripheral nerves influence the tooth morphology is not known. This jaw innervation has been mapped in several studies , and is illustrated in [Figure 8].
|Figure 8: An overview of the neuroectodermal-derived peripheral nerves and the nervous influence on root resorption. The upper image illustrates a panoramic radiograph of an adult female. The different colors illustrate the different innervation paths to different jaw fields (red - incisors, green canine - premolars, and blue - molars). Demyelinization of the right nasopalatine nerve (red) due to the meningitis virus attack at the age of 10 is depicted in the lower left part of the figure. The drawing on the skin indicates areas with change in sensitivity. The lower figures demonstrate how cervical resorption, first in the central incisor and then in the lateral incisor, also occur as a consequence of the demyelinization. The resorption is limited to the frontonasal field. The lower right radiographic images show abnormal cervical resorption due to whooping cough at the age of 6. All teeth in the left part of the maxilla and in the incisor field of the mandible were extracted due to aggressive resorption|
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Disruption of the peripheral nerves
A recent study of two cases  has demonstrated that also peripheral nerves play a role in root resorption. These resorptions were first categorized as idiopathic. After follow-up and treatment over a course of 6 years, the one case [Figure 8] revealed a whole new explanation for innervation-induced resorption limited to four jaw fields where innervation changes occurred after whooping cough. Another case [Figure 8] was a patient diagnosed with aggressive/idiopathic resorption in a frontonasal incisor field. In that case, the resorption was caused by meningitis virus. The virus attack had disturbed the peripheral nerves and the incisors were affected by resorption.
With these two examples of collum resorptions the idiopathic classification of these conditions was changed. In both cases, the resorption types were innervation-induced and occurred in limited fields defined by the innervation of different branches of the peripheral nerves. It is supposed that the virus disturbs the myelin sheaths along the peripheral nerves and that demyelinization provokes inflammation and later resorption along the tooth root.
| Evaluation of the Hypothesis|| |
A summary of the information given in this paper appears in [Figure 9].
|Figure 9: Demonstration of the tissue layers in the human close-root periroot sheet cover. Shown and explained in Figure 1. The arrows from the three main tissue components indicate which tissue layer is affected in the different diseases named to the right. This figure illustrates hypothetically how different changes/diseases in the different tissue layers could explain various conditions in the periroot sheet layer leading to inflammation and root resorption|
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It seems logical that a disruption of the innervation by virus attack can provoke an inflammatory condition in the periodontal layer close to the root. Similarly, it can be presumed that changes in congenital diseases that involve the ectodermal-Malassez layer can create an imbalance in this layer and provoke resorption. Particularly, the Malassez layer has been in focus in order to understand the etiology behind resorption, and the process behind orthodontic tooth movement.  Furthermore, the mesodermal intermediate fiber layer seems to be responsible for the changes in osteitis deformans and for the plumb roots and the open bite.
In a recent study, it was demonstrated that transplantation of a premolar has a poor prognosis when the tooth is transplanted to a region where a primary molar has been arrested in eruption.  This shows how the eruption process, the alveolar bone growth, and the resorption process depend on a healthy and functioning periroot-sheet layer. It seems to be exactly these three cell/tissue layers in the membrane that are decisive for a successful transplantation of a tooth from one site in the mouth to another.
A distinction between dentitions affected by root resorption with known and unknown etiology is important for a number of reasons, especially when evaluating whether resorption is orthodontically provoked or not. If an orthodontic appliance is inserted in a dentition with milder signs of idiopathic root resorption, severe progression of the resorption process can be expected. Therefore, careful diagnostics of the dentition is important before inserting the orthodontic appliance. Another argument for a distinction between idiopathic and orthodontically-induced resorption is evident in cases of complaints.
There are still several types of idiopathic root resorption which are not understood, but it is believed that the periroot sheet could be a key in the future diagnostics and in understanding the etiology behind root resorption.
Avoiding root resorption in orthodontics
Symptoms and signs of importance for avoiding resorption during orthodontic treatment (demonstrated in [Figure 10]) are the following:
- Diagnose abnormal resorption patterns in the primary dentition. Such dentitions are often predisposed to resorption in the permanent dentition. ,
- Several morphological characteristics demonstrated are warning sign for orthodontists who are planning treatment with fixed appliance. 
- General diseases exemplified by ectodermal deviations in hair, skin, and teeth should be diagnosed before applying orthodontic treatment. These are warning signs for resorption.
|Figure 10: Symptoms and signs of importance for avoiding resorption during orthodontic treatment. (a and b) exemplify that it is important to diagnose abnormal resorption patterns in the primary dentition, often leading to resorption in the permanent dentition. Radiographs (c and d) demonstrate how the first molar with normal root length (c) can change to a short distal root (d) without previous orthodontic treatment. A condition like this and conditions shown in Figure 6 are morphological characteristics that should be a warning sign for orthodontists, who are planning treatment with fixed appliance. The three figures to the right are shown with permission from orthodontist, Izabella Vest Hansen. The figures demonstrate a patient with ectodermal signs in hair, skin, and molars, which should be diagnosed before applying orthodontic treatment. The maxillary first molar roots have nearly completely resorbed without orthodontic treatment. The mandibular first molar is secondarily retained, indicating an abnormal functioning of the periodontal membrane|
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| References|| |
|1.||Kjær I. Morphological characteristics of dentitions developing excessive root resorption during orthodontic treatment. Eur J Orthod 1995;17:25-34. |
|2.||Gunraj MN. Dental root resorption. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;88:647-53. |
|3.||Talic NF, Evans CA, Daniel JC, Zaki AE. Proliferation of epithelial rests of Malassez during experimental tooth movement. Am J Orthod Dentofacial Orthop 2003;123:527-33. |
|4.||Kjær I. External root resorption: Different etiologies explained from the composition of the human root-close periodontal membrane. Dent Hypotheses 2013;4:75-9. |
|5.||Kjær I, Nolting D. The human periodontal membrane: focusing on the spatial interrelation between the epithelial layer of Malassez, fibers, and innervation. Acta Odontol Scand 2009;67:134-8. |
|6.||Kjær I. New diagnostics of the dentition on panoramic radiographs-focusing on the peripheral nervous system as an important aetiological factor behind dental anomalies. Orthod Waves 2012;71:1-16. |
|7.||Kjær I, Nielsen MH, Skovgaard LT. Can persistence of primary molars be predicted in subjects with multiple tooth agenesis? Eur J Orthod 2008;30:249-53. |
|8.||Smith NH. Monostotic Paget's disease of the mandible presenting with progressive resorption of the teeth. Oral Surg Oral Med Oral Pathol 1978;46:246-53. |
|9.||Bille ML, Nolting D, Kjær I. Immunohistochemical studies of the periodontal membrane in primary teeth. Acta Odontol Scand 2009;67:382-7. |
|10.||Kjær I, Strøm C, Worsaae N. Regional aggressive root resorption caused by neuronal virusinfection. Case Rep Dent 2012;2012:693240. |
|11.||Brice GL, Sampson WJ, Sims MR. An ultrastructural evaluation of the relationship between epithelial rests of Malassez and orthodontic root resorption and repair in man. Aust Orthod J 1991;12:90-4. |
|12.||Bokelund M, Andreasen JO, Christensen SS, Kjær I. Autotransplantation of maxillary second premolars to mandibular recipient sites where the primary second molars were impacted, predisposes for complications. Acta Odontol Scand 2013;71:1464-8. |
|13.||Bille ML, Kventy MJ, Kjaer I. A possible association between early apical resorption of primary teeth and ectodermal characteristics of the permanent dentition. Eur J Orthod 2008;30:346-51. |
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]