title: Effects of mechanical tension on matrix degradation by human periodontal ligament cells cultured in collagen gels.
abstract: BACKGROUND
  Periodontal ligament (PDL) cells are thought to play a crucial role in the remodelling of periodontal tissues during orthodontic tooth movement.
  
  
  OBJECTIVE
  The objective of this study was to analyse the effects of mechanical tension on matrix degradation by PDL cells cultured in collagen gels.
  
  
  METHODS
  The gels were prepared free-floating or attached to the culture wells and cultured for up to 22 d. In free-floating gels very little mechanical tension is generated within the matrix, whereas in attached gels tension is highly increased.
  
  
  RESULTS
  At d 8, free-floating gels had contracted to 2% of their original wet weight. Attached gels had contracted to only 40%, but by d 15 all gels had spontaneously detached from the wells and had contracted rapidly. The collagen content of free-floating gels had decreased to 30% of the initial value at d 22. Collagenase activity was detected in the culture media of the free-floating gels and the presence of matrix metalloproteinases (MMPs) 2 and 9 was shown by zymography. In addition, histological sections showed matrix degradation around the cells. This shows that ligament cells in free-floating gels are actively resorbing the collagen matrix. The collagen content of attached gels did not change during the first 8 d but, after detachment, it rapidly decreased to 2%. Therefore, mechanical tension seems to prevent degradation of the matrix. In contrast, relaxation of the tension enhances the resorptive activity.
  
  
  CONCLUSIONS
  The sensitivity of PDL cells to mechanical tension may be essential for the remodelling of periodontal tissues and their adaptation to physiological and orthodontic forces.
authors.affiliation: Department of Orthodontics and Oral Biology, College of Dental Science, University Medical Centre Nijmegen, Nijmegen, The Netherlands. h.vondenhoff@dent.umnc.nl
authors.forename: J W
authors.initials: JW
authors.lastname: Von den Hoff
mesh_terms: D000328:Adult; D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism; D017364:Collagenases / Q000378:metabolism*; D003799:Dental Stress Analysis; D005109:Extracellular Matrix / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D005782:Gels; D006025:Glycosaminoglycans / Q000378:metabolism; D006801:Humans; D010513:Periodontal Ligament / Q000166:cytology / Q000378:metabolism*; D013314:Stress, Mechanical
chemical_list: D024042:Collagen Type I; D005782:Gels; D006025:Glycosaminoglycans; D017364:Collagenases