title: A qualitative investigation of RANKL, RANK and OPG in a rat model of transient ankylosis.
abstract: BACKGROUND
  Previous studies have found ankylosis occurs as a part of the inflammatory process of aseptic root resorption initiated in a rat model. The physiologic mechanisms behind the development of dentoalveolar ankylosis and healing response are still unclear. While receptor activator of nuclear factor-κβ ligand (RANKL), receptor activator of nuclear factor-κβ (RANK) and osteoprotegerin (OPG) have gained momentum in the understanding of resorption, no study to date has investigated their role in dentoalveolar ankylosis.
  
  
  OBJECTIVE
  The aims of this study were to investigate if, and when, ankylosis occurred in the rat PDL, whether the resolution of ankylosis occurred with time and, finally, to observe the expression of RANKL, RANK and OPG during the ankylotic process.
  
  
  METHODS
  Dry ice was applied for 20 minutes to the upper right first molar crown of 15 eight-week-old, male Sprague-Dawley rats. An additional three rats served as untreated external controls. Groups of three rats were sacrificed after the thermal insult on day 0, 4, 7, 14 and 28 respectively. Each maxilla was dissected out and processed for histological examination and RANKL, OPG and RANK immunohistochemistry.
  
  
  RESULTS
  By the use of light microscopy and H&E staining, no ankylosis was detected in the external control group and the experimental groups at days 0 and 4. On day 7, disruption within the periodontal ligament was observed in the interradicular region and the initial signs of ankylosis were seen in the form of finger-like projections extending from the alveolar bone towards the cementum. Fourteen days after the thermal insult, all animals exhibited extensive ankylosis that spanned the entire interradicular periodontal space. At 28 days, the development of ankylosis appeared to have ceased and repair was observed, together with an intact periodontal ligament in all but one rat. Positive staining results were obtained with RANKL, RANK and OPG antibodies. The expressions of RANKL, RANK and OPG were similar in the external control group, 0-, 4-, and 28-day experimental groups. In the 7- and 14-day experimental groups, RANKL, RANK and OPG were expressed in the blood vessels within the ankylotic regions.
  
  
  CONCLUSIONS
  During the development of ankylosis and its resolution, it was concluded from their simultaneous presence that there is a complex interaction between RANKL, RANK and OPG that requires further investigation.
authors.affiliation: Orthodontic Unit, The University of Adelaide, South Australia, Australia. Linda.curl@smartorthodontics.com.au
authors.forename: Linda
authors.initials: L
authors.lastname: Curl
authors.forename: Chien Wei
authors.initials: CW
authors.lastname: Tan
authors.forename: Craig W
authors.initials: CW
authors.lastname: Dreyer
authors.forename: Wayne
authors.initials: W
authors.lastname: Sampson
mesh_terms: D000539:Alveolar Process / Q000737:chemistry / Q000473:pathology; D000818:Animals; D003080:Cold Temperature / Q000009:adverse effects; D003739:Dental Cementum / Q000737:chemistry / Q000473:pathology; D004195:Disease Models, Animal; D007150:Immunohistochemistry; D008297:Male; D055806:Microvessels / Q000737:chemistry / Q000473:pathology; D008963:Molar / Q000293:injuries; D053244:Osteoprotegerin / Q000032:analysis*; D010513:Periodontal Ligament / Q000098:blood supply / Q000737:chemistry / Q000473:pathology; D053245:RANK Ligand / Q000032:analysis*; D011897:Random Allocation; D017207:Rats, Sprague-Dawley; D053246:Receptor Activator of Nuclear Factor-kappa B / Q000032:analysis*; D013997:Time Factors; D020254:Tooth Ankylosis / Q000378:metabolism* / Q000473:pathology; D019228:Tooth Crown / Q000293:injuries; D014092:Tooth Root / Q000737:chemistry / Q000473:pathology; D014945:Wound Healing / Q000502:physiology
chemical_list: D053244:Osteoprotegerin; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; C506032:Tnfrsf11b protein, rat