title: Physical properties of root cementum: Part 18. The extent of root resorption after the application of light and heavy controlled rotational orthodontic forces for 4 weeks: a microcomputed tomography study.
abstract: BACKGROUND
  The aim of this prospective randomized clinical trial was to quantitatively measure and compare the locations, dimensions, and volume of root resorption craters in human premolars after the application of controlled light and heavy rotational orthodontic forces over a 28-day (4-week) period.
  
  
  METHODS
  Fifteen patients requiring bilateral extraction of maxillary first premolars as part of their orthodontic treatment were recruited for this study. Each patient received a heavy (225 g) rotational force on 1 premolar and a light (25 g) rotational force on the contralateral premolar. Orthodontic rotational forces were applied over 28 days with buccal and palatal cantilever springs; 0.016-inch beta-titanium molybdenum alloys were used to apply the light force and 0.018-inch stainless steel was used for the heavy force. After the 28-day experimental period, the upper first premolars were extracted under stringent protocols to prevent root surface damage. The samples were then scanned using a microcomputed tomography (micro-CT) scan x-ray system (SkyScan 1072, Skyscan, Aartselaar, Belgium), and analyzed using convex hull algorithm (CHULL2D; University of Sydney, Sydney, Australia) software to obtain direct volumetric measurements.
  
  
  RESULTS
  The mean volume of resorption craters was 0.42 in the light force group and 0.51 in the heavy force group (P = 0.013). When separated at the root level, the difference in volume of root resorption craters between the 2 groups was significantly different only at the midlevel (P = 0.001). Root resorption craters were consistently detected at the boundaries between the buccal and distal surfaces and the mesial and lingual surfaces. The result supports our hypothesis that positive areas develop significantly more root resorption craters at all 3 levels, as compared with minimal areas (paired t test <0.001).
  
  
  CONCLUSIONS
  Heavy rotational forces caused more root resorption than light rotational forces and compression areas (buccal-distal and lingual-mesial surfaces in this study) showed significantly higher root resorption than other areas at all levels of the root.
authors.affiliation: Discipline of Orthodontics, Faculty of Dentistry, University of Sydney, Australia.
authors.forename: Andy T J
authors.initials: AT
authors.lastname: Wu
authors.forename: Tamer
authors.initials: T
authors.lastname: Turk
authors.forename: Canan
authors.initials: C
authors.lastname: Colak
authors.forename: Selma
authors.initials: S
authors.lastname: Elekdağ-Turk
authors.forename: Allan S
authors.initials: AS
authors.lastname: Jones
authors.forename: Peter
authors.initials: P
authors.lastname: Petocz
authors.forename: M Ali
authors.initials: MA
authors.lastname: Darendeliler
mesh_terms: D000293:Adolescent; D000497:Alloys / Q000737:chemistry; D001641:Bicuspid / Q000473:pathology; D001696:Biomechanical Phenomena; D055598:Chemical Phenomena; D003722:Dental Alloys / Q000737:chemistry; D003739:Dental Cementum / Q000473:pathology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D011446:Prospective Studies; D012391:Root Resorption / Q000145:classification / Q000209:etiology* / Q000473:pathology; D012399:Rotation; D013193:Stainless Steel / Q000737:chemistry; D013314:Stress, Mechanical; D013997:Time Factors; D014087:Tooth Movement Techniques / Q000295:instrumentation / Q000379:methods*; D014092:Tooth Root / Q000473:pathology*; D055114:X-Ray Microtomography / Q000379:methods
chemical_list: D000497:Alloys; D003722:Dental Alloys; C525450:titanium molybdenum alloy; D013193:Stainless Steel