Epithelial rests of Malassez in experimental animals at different ages.

Epithelial rests of Malassez (ERMs) are fragments of Hertwig's sheath in the periodontal ligament. There is extensive knowledge of their role in the etiology ofpathological processes and current evidence links them to maintenance of periodontal homeostasis. The aim of this study was to assess the behavior of ERMs with relation to the changes in periodontal tissues during growth in an experimental model with Wistar rats. Mesiodistal sections were made of the first lower molars from Wistar rats aged 1 month (n=7), 3 months (n=7) and 5 months (n=6). Sections were stained with H&E to evaluate number of ERMs/ mm, size/area of ERMs (pm2), height of periodontal ligament (PL.h) (pm), area of cement in the furcation zone (C.Ar) (pm2) and bone area related to the ERM zone (BAr/TAr)(%). Posthoc Bonferroni and ANOVA were applied for statistical analysis of results. Number of ERMs/mm declined significantly with age (1m: 4.34±1.51, 3m: 1.48±0.89, 5m: 0.27± 0.50, p<0.05), and there was great variability in size. There was significant increase in C.Ar (1m: 3418.96 ± 905.88, 3m: 19365.76 ± 5500.52, 5m: 32182.76 ± 7114.51, p< 0.05) and interradicular (BAr/TAr) (1m: 25.26 ± 2.37, 3m: 44.70 ± 3.95, 5m: 46.81 ± 7.80, p< 0.05: 1 vs 3, 1 vs 5). There was significant decline in PLh at 5 months (1m: 141.42 ± 29.25, 3m: 162.06 ± 28.21, 5m: 124.72 ± 18.67, p< 0.05: 1 vs. 3, 3 vs. 5). The decline in number of ERMs as animal age increases may be related to the significant increase in C.Ar and reduction in PL.h. It remains to ascertain its relationship with the increase observed in BAr/ TAr. Further studies are needed to learn more about the role of ERMs and their relationship with periodontal tissues when confronted with different normal and pathological stimuli.