title: Cyclic stretching force-induced early apoptosis in human periodontal ligament cells.
abstract: OBJECTIVE
  Human periodontal ligament (PDL) cells occur changes in morphology and express relative protein by stretching force. However, whether stretching force, especially excessive stretching force, induces PDL cell apoptosis is not yet clearly understood. In the present study we investigated the relationship between early apoptosis and stretching force in human PDL cells in vitro.
  
  
  METHODS
  The human PDL cells were obtained from healthy premolars. After three to five passages, the cells were stretched by strain 1%, 10% and 20% for 30 min, 1 h, 6 h and 12 h, then early apoptosis were detected through annexin fluorescein isothiocyanate (V-FITC) binding by flow cytometry and confocal laser scanning microscopy.
  
  
  RESULTS
  The experiments indicated that human PDL apoptotic cells in the early stage increased in a time- and force-dependent manner in response to stretching strain within 6 h, and then apoptosis decreased at 12 h. Human PDL cells which stretched inclined parallel to each other and aligned their long axis perpendicular to the stretching force vector, but in the centre of the disc, cells showed minimal deformation and unidirectional alignment of PDL cells.
  
  
  CONCLUSIONS
  The overall results suggested that stretching force not only influenced morphology but also induced early apoptosis in human PDL cells.
authors.affiliation: Department of Prosthodontics, School of Stomatology, Ninth People's Hospital, School of Medicine, Shanghai JiaoTong University, Shanghai, China.
authors.forename: W
authors.initials: W
authors.lastname: Zhong
authors.forename: C
authors.initials: C
authors.lastname: Xu
authors.forename: F
authors.initials: F
authors.lastname: Zhang
authors.forename: X
authors.initials: X
authors.lastname: Jiang
authors.forename: X
authors.initials: X
authors.lastname: Zhang
authors.forename: D
authors.initials: D
authors.lastname: Ye
mesh_terms: D000293:Adolescent; D017209:Apoptosis / Q000502:physiology*; D002478:Cells, Cultured; D019245:Compressive Strength; D003799:Dental Stress Analysis; D004548:Elasticity; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D008297:Male; D018613:Microscopy, Confocal; D008858:Microscopy, Phase-Contrast; D010513:Periodontal Ligament / Q000166:cytology* / Q000502:physiology*; D013718:Tensile Strength