Putative role of epithelial rests of Malassez in alleviation of traumatic occlusion

Background: Epithelial cell rests of Malassez (ERM) are odontogenic epithelial cells located throughout life within the periodontal matrix. It has long been thought to be a functionless remnant, though recent studies suggested their role in periodontium regeneration and homeostasis. Aim of study: The aim of the present study was to investigate the role of ERM in alleviating the deteriorating effect of an induced primary acute traumatic occlusion in rats. Material and methods: Twenty four, 7 month old male rats were used in this study. Animals were randomly divided into two equal groups, a control and traumatic occlusion groups. Rats in the latter group had the occlusal surfaces of their right maxillary first molars unilaterally raised 1e2 mm with our innovative 7/8 nickel chrome stainless steel crowns that had free distal surfaces. Three rats, from each group, were euthanized at 1, 3, 6, and 9 weeks. Half of their right mandibular first molar-specimens were processed for light microscope (LM) and the other for transmission electron microscope (TEM). Results: Rats in the control group revealed no difference in their normal ordinary periodontal ligaments (PDL) structure, by LM, at all times.Ultrastructurally, all samples revealed similarity in having closely approximated restingERMcells.Onthe other hand, after one and threeweeks of traumatic occlusion, thereweremild progressive PDL disorganization, cementum resorption togetherwith phagocytic and secretory ERM cells, respectively. Interestingly, at later stages on the 6th and 9th week, signs of repair and remodeling of PDL structure weremanifested alongwith the establishment of closely juxtaposed clusters ofERMwith apoptotic and secretory characters, respectively. Conclusion: ERM cells appeared to have an important role within the periodontal apparatus. Their diverse ultrastructural features during periodontal deterioration and regeneration would suggest their role in alleviating the injury resulted from induced traumatic occlusion.