Apoptosis in the early developing periodontium of rat molars

Development of the periodontium involves a series of complex steps that res ult in the formation of root dentine, cementum, bone and fibres of the liga ment. These precisely controlled and timed events require the participation of the enamel organ derived epithelial cells of Hertwig's (HRS) and ectome senchymal cells of the dental follicle. These events involve rapid turnover of the tissues and cells, including disappearance of epithelial cells of H RS, Thus, it seemed likely to us that programmed cell death (apoptosis) may play a role in the development of the periodontium. Fragments of first molars, obtained from 14- and 29-day-old rats, were fixe d in glutaraldehyde-formaldehyde and processed for light and electron micro scopy. For the TUNEL method for detection of apoptosis, specimens were fixe d in 4% formaldehyde and embedded in paraffin. Results confirmed that epithelial cells of HRS maintain a close relationshi p with the forming dentine root, and that they may become trapped in the de ntino-cemental junction. Some of the epithelial cells exhibited ultrastruct ural features which are consistent with the interpretation that they were u ndergoing programmed cell death, i.e. apoptosis. Periodontal fibroblast-lik e cells showed typical images of apoptosis and engulfed apoptotic bodies; T UNEL positive structures were present in all corresponding regions. It seem s therefore that apoptosis of epithelial cells of HRS and fibroblast-like c ells of the periodontal Ligament constitutes an integral part of the develo pmental process of the tissues of the periodontium. Anat Rec 258:136-144, 2 000. (C) 2000 Wiley-Liss, Inc.