Periodontol Role of the epithelial cell rests of Malassez in the development, maintenance and regeneration of periodontal ligament tissues. Periodontitis is a highly prevalent inflammatory disease that results in damage to the tooth-supporting tissues, potentially leading to tooth loss. Periodontal tissue regeneration is a complex process that involves the collaboration of two hard tissues cementum and alveolar bone and two soft tissues gingiva and periodontal ligament. To date, no periodontal-regenerative procedures provide predictable clinical outcomes. To understand the rational basis of regenerative procedures, a better understanding of the events associated with the formation of periodontal components will help to establish reliable strategies for clinical practice.
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Figure 3 Scheme showing the conformation of ERM in longitudinal slice. Subsequently, ERM were considered as lymphatic channels coated by epithelium and filled with lymph 8. In subsequent research, Black 8 started to understand them as glandular tissue, 8 , 9 findings that have been proven wrong by recent histological studies.
Regarding the location, the ERM often occurs in the periodontal ligament, 11 , 12 with a predilection for the apex region, especially in the furca and cervical area of the tooth, in ascending order of frequency. Three morphological variations were observed: small, proliferative and differentiated. ERM incidence decreased with increasing age. Reeve and Wentz 16 determined the frequency of epithelial rests in patients aged years, classifying different ERM types and locations on the periodontal ligament.
The results showed that the ERM were present in all 31 specimens analyzed regardless of age , but the incidence decreased with increasing age. As for the most frequent types of REM, small and differentiated ones decrease with age, while proliferative ones increase with age.
Among young patients, most ERM were located in the cervical area and accumulated at the apex with increasing age. The authors suggested that ERM were persistent vestigial structures in the periodontal ligament with a potential role in the development of periodontal disease. According to the authors, the ERM were not isolated structures, forming a structure similar to a fishing net around tooth roots Fig 1 , giving ERM a role in maintaining the periodontal space and preventing alveolodental ankylosis.
Through scanning electron microscopy and immunohistochemistry, Ten Cate 18 reported lower metabolic activity in cells of remaining epithelial components, suggesting a possible role of ERM should be disregarded in adult patients. However, later Trowbridge and Shibata 19 identified mitotic activity in epithelium rests in experimental studies with animal models.
Such evidence created possibilities for further investigations. Using staining and electron microscopy to distinguish ERM in the surrounding region, Valderhaug and Zander 20 noted the presence of numerous blood vessels between the REM and dental cementum, with a larger number of ERM close to the cementoenamel junction, without, however, touching the cementum. This result suggests the participation of ERM in the regeneration and repair of cementum.
Although some functions have been assigned to ERM by several authors, none has been supported by solid scientific evidence. The papers published to date only described its morphological characteristics. However, Ten Cate 21 stated that ERM had a role in the formation of dental cysts, because the remaining epithelial cells from ERM behave the same way as other epithelial cells when the local tissue is changed.
With support from deep periodontal ligament tissue, inflammation can proliferate within such tissue, giving rise to dental cysts.
The ultrastructural characteristics of these cells provided evidence that they could be involved in mediating cementogenesis in the root resorption process, opening precedence for further research in this direction. The latter also promote release of bone matrix proteins, BMP-2, osteopontin, osteoprotegerin and sialoprotein, proteins that aid in the repair and periodontal regeneration phase, aside from contributing to the repair of cementum itself.
The modulation of enamel protein expression by epithelial remnants in the ERM thus suggests inherent regenerative ability, through directed and controlled strategies. These molecules have proven potential for bone remodelling throughout life. Orthodontic treatment, in turn, is essentially a periodontal event that involves an acute inflammatory response during its initial phase.
Furthermore, prostaglandins are important mediators of inflammation that play a key role in orthodontic movement, being synthesized by cyclooxygenases COX.
Prostaglandins stimulate bone resorption by increasing the number and activity of osteoclasts. Thus, prostaglandins have a major influence on the speed of orthodontic movement. The tooth movement induced by EGF causes an increase in periodontal tissue proliferation, which in turn is mediated by the continuous release induced by ERM. EGF plays an important role in the prevention of ankylosis and osteoclastogenesis and cementogenesis processes. These resistant structures are extremely important for maintaining homeostasis.
ERM are able to promote the maintenance and regeneration of the periodontal ligament space. The regeneration of periodontal tissue occurs through assistance in the renewal of cells that suffered some sort of damage.
Damage to periodontal tissue is directly associated with orthodontic movement, where hyalinizing outbreaks have been recorded on the pressure side in the periodontal ligament, mainly during the first hours after the application of force.
Unlike bone cells, cementoblasts do not have receptors for remodelling mediators, requiring the beginning of a cascade of events that causes the pH to normalize.
This promotes the inclusion of new collagen fibres at the damaged cementoblastic surface, induced by ERM, allowing the root surface to regenerate and return to its normal state.
After the application of force, the change in the levels of periodontal capillary pressure can trigger blood supply dysfunction until its collapse, according to the force applied. This process can result in cementoblast degradation and cementoid tissue layer formation. In this procedure, epithelial cells associated with ERM modify their distribution and express BMP-2, osteopontin and ameloblastin. Cementoblasts are involved in the process of remodelling and repair of the root surface.
The actions of these mediators result in bone remodelling, which involves resorption or bone deposition on opposite side of the periodontal ligament. ERM keep the bone away from the root surface through the release of mediators such as EGF, which induces osteoclasia. In cases of trauma, where the ERM are damaged, leading to necrosis, mediators that promote osteoclasia may not be present in the required concentration, which, as a result, may lead to alveolodental ankylosis.
When properly executed, the orthodontic movement is able to stimulate the secretory power of these cells, which prevents the recurrence of ankylosis. The growth in size of ERM during tooth movement indicates the level of the response to mechanical stimulation and its possible role in tooth remodelling.
ERM have been associated with the induction of this process from latent collagenase secretion in the extracellular matrix, allowing for the transformation of active collagenase enzymatic cleavage, resulting in the synthesis of collagen fibres. During the early inflammatory events that compose the induced movement process, the constriction of the microvasculature of the periodontal ligament results in focal areas of necrosis, with histological features of hyalinization.
The capacity to repair periodontium and to prevent cementum damages were connected with this process. Moreover, an increase in ankylosis events related to the processes and the hyalinization of periodontal tissue after the application of mechanical forces during the aging process can be associated to the potential of ERM.
Otherwise, more studies are necessary to clarify these functions and consequences in daily orthodontics practice. Dental Press J Orthod. Keinan D, Cohen RE. The significance of epithelial rests of Malassez in the periodontal ligament.
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Epithelial cell rests of Malassez
The epithelial cell rests of Malassez are part of the periodontal ligament cells around a tooth. These cell rests proliferate to form epithelial lining of various odontogenic cysts such as radicular cyst under the influence of various stimuli. They are named after Louis-Charles Malassez — who described them. Some rests become calcified in the periodontal ligament cementicles The epithelial cell rests of Malassez ERM are formed by persisting fragments of epithelial sheath Hertwig shaeth that participates in the tooth root development. ERM are found within the periodontal ligament. They undergo intensive age-related involution and are traditionally described as small clusters of functionally inactive cells.
epithelial cell rests of Malassez
Epithelial rests of Malassez: from latent cells to active participation in orthodontic movement.