Cellular turnover in epithelial rests of Malassez in the periodontal ligament of the mouse molar

Kyoko Oka, Masakazu Morokuma, Kyoko Imanaka-Yoshida, Yoshihiko Sawa, Keitaro Isokawa, Masaki J. Honda

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14 Citations (Scopus)


Fragments of Hertwig's epithelial root sheath persist in the periodontal ligament (PDL) in small clusters known as epithelial rests of Malassez (ERM). It is generally agreed that ERM are maintained as a quiescent and exclusively dental epithelial cluster in PDL. However, we speculate that homeostasis and cellular turnover underlies cluster maintenance. We also hypothesize that the fate of ERM clusters - diminishing or remaining - might be regulated via the presence or absence of epithelial stem cells therein. Histological analysis of aging mouse molar PDL showed that ERM clusters gradually increase in size with increasing age. Immunocytochemistry and cell culture revealed that ERM clusters contained Ki67-positive cells and were able to expand when brought in culture. The TdT-mediated biotin-dUTP nick-end labeling (TUNEL) procedure also detected signs of apoptosis. Finally, we identified putative epithelial stem cells in the clusters by 5-bromo-2′-deoxyuridine (BrdU) pulse-chase experiments and immunohistochemistry, using the stem-cell marker leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5). The results suggest that ERM clusters are maintained in the PDL, via cellular turnover, throughout life.

Original languageEnglish
Pages (from-to)484-494
Number of pages11
JournalEuropean Journal of Oral Sciences
Issue number6
Publication statusPublished - Dec 2012
Externally publishedYes


  • Apoptosis
  • Epithelial rests of Malassez
  • Periodontal ligament
  • Stem cell

ASJC Scopus subject areas

  • Dentistry(all)


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