Dental Hypotheses

: 2014  |  Volume : 5  |  Issue : 2  |  Page : 47--52

Root resorption: Focus on signs and symptoms of importance for avoiding root resorption during orthodontic treatment

Inger Kjaer 
 Department of Odontology, Orthodontics Section, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen N, Denmark

Correspondence Address:
Inger Kjaer
Department of Odontology, Orthodontics Section, Faculty of Health and Medical Sciences, University of Copenhagen, 20 Nørre Allé, DK-2200 Copenhagen N


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«SQ»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).

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

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Kjaer I. Root resorption: Focus on signs and symptoms of importance for avoiding root resorption during orthodontic treatment. Dent Hypotheses [serial online] 2014 [cited 2022 May 28 ];5:47-52
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Orthodontists know that root resorption can be provoked by orthodontic forces. [1] They also know that susceptibility to resorption varies from person to person. [1] Besides orthodontic forces, there are several other factors that can provoke resorption processes on the root surface. [2] The histochemical process on the root surface resulting in resorption of root cementum and root dentine has been elucidated in several publications. [3] 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. [4] 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 [5] are demonstrated and shown in [Figure 1].{Figure 1}

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. [5]

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. [2] 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}{Figure 3}

The history of root resorption is often obscure and referred to as idiopathic. [2] General diseases can also cause root resorption, but information in the literature is extremely sparse. A recent study [4] 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}

 The Hypothesis

The hypothesis behind the most recent resorption studies [6] 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.

Ectodermal tissue

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}

Tooth morphology

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 [1] 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}


Ectodermal dysplasia is a condition in which root resorption occurs. [7] Other diseases such as tuberous sclerosis with skin afflictions are also prone to root resorption [4] [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, [1] 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. [2] {Figure 7}


One general disease with root resorption as a known complication is osteitis deformans (Paget's disease in bone). [8] 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 [5],[9] and is illustrated in [Figure 8].{Figure 8}

Disruption of the peripheral nerves

A recent study of two cases [10] 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}

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. [11] 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. [12] 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. [1],[13] Several morphological characteristics demonstrated are warning sign for orthodontists who are planning treatment with fixed appliance. [1] 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}


1Kjær I. Morphological characteristics of dentitions developing excessive root resorption during orthodontic treatment. Eur J Orthod 1995;17:25-34.
2Gunraj MN. Dental root resorption. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;88:647-53.
3Talic 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.
4Kjær I. External root resorption: Different etiologies explained from the composition of the human root-close periodontal membrane. Dent Hypotheses 2013;4:75-9.
5Kjær 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.
6Kjær 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.
7Kjær 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.
8Smith 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.
9Bille ML, Nolting D, Kjær I. Immunohistochemical studies of the periodontal membrane in primary teeth. Acta Odontol Scand 2009;67:382-7.
10Kjær I, Strøm C, Worsaae N. Regional aggressive root resorption caused by neuronal virusinfection. Case Rep Dent 2012;2012:693240.
11Brice 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.
12Bokelund 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.
13Bille 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.