title: Strain-guided mineralization in the bone-PDL-cementum complex of a rat periodontium.
abstract: OBJECTIVE
  The objective of this study was to investigate the effect of mechanical strain by mapping physicochemical properties at periodontal ligament (PDL)-bone and PDL-cementum attachment sites and within the tissuesper se.
  
  
  METHODS
  Accentuated mechanical strain was induced by applying a unidirectional force of 0.06N for 14 days on molars in a rat model. The associated changes in functional space between tooth and bone, mineral formation and resorbing events at the PDL-bone and PDL-cementum attachment sites were identified by using micro-X-ray computed tomography (micro-XCT), atomic force microscopy (AFM), dynamic histomorphometry, Raman microspectroscopy, AFM-based nanoindentation technique, and were correlated with histochemical stains specific to low and high molecular weight GAGs, including biglycan, and osteoclast distribution through tartrate-resistant acid phosphatase (TRAP) staining.
  
  
  RESULTS
  Unique chemical and mechanical qualities including heterogenous bony fingers with hygroscopic Sharpey's fibers contributing to a higher organic (amide III - 1240 cm-1) to inorganic (phosphate - 960 cm-1) ratio, with lower average elastic modulus of 8 GPa versus 12 GPa in unadapted regions were identified. Furthermore, an increased presence of elemental Zn in cement lines and mineralizing fronts of PDL-bone was observed. Adapted regions containing bony fingers exhibited woven bone-like architecture and these regions rich in biglycan (BGN) and bone sialoprotein (BSP) also contained high-molecular weight polysaccharides predominantly at the site of polarized bone growth.
  
  
  CONCLUSIONS
  From a fundamental science perspective the shift in local properties due to strain amplification at the soft-hard tissue attachment sites is governed by semiautonomous cellular events at the PDL-bone and PDL-cementum sites. Over time, these strain-mediated events can alter the physicochemical properties of tissuesper se, and consequently the overall biomechanics of the bone-PDL-tooth complex. From a clinical perspective, the shifts in magnitude and duration of forces on the periodontal ligament can prompt a shift in physiologic mineral apposition in cementum and alveolar bone albeit of an adapted quality owing to the rapid mechanical translation of the tooth.
authors.affiliation: Divisions of Orthodontics, University of California San Francisco, San Francisco, CA.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Grandfield
authors.affiliation: Divisions of Orthodontics, University of California San Francisco, San Francisco, CA.
authors.forename: Ralf Peter
authors.initials: RP
authors.lastname: Herber
authors.affiliation: Divisions of Orthodontics, University of California San Francisco, San Francisco, CA.
authors.forename: Ling
authors.initials: L
authors.lastname: Chen
authors.affiliation: Divisions of Orthodontics, University of California San Francisco, San Francisco, CA.
authors.forename: Sabra
authors.initials: S
authors.lastname: Djomehri
authors.affiliation: Divisions of Orthodontics, University of California San Francisco, San Francisco, CA.
authors.forename: Caleb
authors.initials: C
authors.lastname: Tam
authors.affiliation: Divisions of Orthodontics, University of California San Francisco, San Francisco, CA.
authors.forename: Ji-Hyun
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Divisions of Orthodontics, University of California San Francisco, San Francisco, CA.
authors.forename: Evan
authors.initials: E
authors.lastname: Brown
authors.affiliation: Divisions of Orthodontics, University of California San Francisco, San Francisco, CA.
authors.forename: Wood R
authors.initials: WR
authors.lastname: Woolwine
authors.affiliation: Divisions of Orthodontics, University of California San Francisco, San Francisco, CA.
authors.forename: Don
authors.initials: D
authors.lastname: Curtis
authors.affiliation: Division of Periodontics, Department of Orofacial Sciences, University of California San Francisco, San Francisco, CA.
authors.forename: Mark
authors.initials: M
authors.lastname: Ryder
authors.affiliation: Materials Science Division, The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA.
authors.forename: Jim
authors.initials: J
authors.lastname: Schuck
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA.
authors.forename: Samuel
authors.initials: S
authors.lastname: Webb
authors.affiliation: Department of Polymer Science, The University of Akron, OH 44325.
authors.forename: William
authors.initials: W
authors.lastname: Landis
authors.affiliation: Divisions of Orthodontics, University of California San Francisco, San Francisco, CA.
authors.forename: Sunita
authors.initials: S
authors.lastname: Ho
keywords: adaptations; attachment sites; bone-periodontal ligament-tooth complex; interfaces; mechanical strain; mineralization