title: The biomechanical characteristics of the bone-periodontal ligament-cementum complex.
abstract: The relative motion between the tooth and alveolar bone is facilitated by the soft-hard tissue interfaces which include periodontal ligament-bone (PDL-bone) and periodontal ligament-cementum (PDL-cementum). The soft-hard tissue interfaces are responsible for attachment and are critical to the overall biomechanical efficiency of the bone-tooth complex. In this study, the PDL-bone and PDL-cementum attachment sites in human molars were investigated to identify the structural orientation and integration of the PDL with bone and cementum. These attachment sites were characterized from a combined materials and mechanics perspective and were related to macro-scale function. High resolution complimentary imaging techniques including atomic force microscopy, scanning electron microscopy and micro-scale X-ray computed tomography (Micro XCT) illustrated two distinct orientations of PDL; circumferential-PDL (cir-PDL) and radial-PDL (rad-PDL). Within the PDL-space, the primary orientation of the ligament was radial (rad-PDL) as is well known. Interestingly, circumferential orientation of PDL continuous with rad-PDL was observed adjacent to alveolar bone and cementum. The integration of the cir-PDL was identified by 1-2 microm diameter PDL-inserts or Sharpey's fibers in alveolar bone and cementum. Chemically and biochemically the cir-PDL adjacent to bone and cementum was identified by relatively higher carbon and lower calcium including the localization of small leucine rich proteins responsible for maintaining soft-hard tissue cohesion, stiffness and hygroscopic nature of PDL-bone and PDL-cementum attachment sites. The combined structural and chemical properties provided graded stiffness characteristics of PDL-bone (E(r) range for PDL: 10-50 MPa; bone: 0.2-9.6 GPa) and PDL-cementum (E(r) range for cementum: 1.1-8.3 GPa), which was related to the macro-scale function of the bone-tooth complex.
authors.affiliation: Division of Biomaterials and Bioengineering, Department of Preventive and Restorative Dental Sciences, University of California San Francisco, San Francisco, CA 94143, USA. sunita.ho@ucsf.edu
authors.forename: Sunita P
authors.initials: SP
authors.lastname: Ho
authors.forename: Michael P
authors.initials: MP
authors.lastname: Kurylo
authors.forename: Tiffany K
authors.initials: TK
authors.lastname: Fong
authors.forename: Stephen S J
authors.initials: SS
authors.lastname: Lee
authors.forename: Hanoch D
authors.initials: HD
authors.lastname: Wagner
authors.forename: Mark I
authors.initials: MI
authors.lastname: Ryder
authors.forename: Grayson W
authors.initials: GW
authors.lastname: Marshall
mesh_terms: D000539:Alveolar Process / Q000737:chemistry / Q000648:ultrastructure*; D001696:Biomechanical Phenomena; D003739:Dental Cementum / Q000648:ultrastructure*; D006801:Humans; D010513:Periodontal Ligament / Q000737:chemistry / Q000648:ultrastructure*; D014070:Tooth / Q000737:chemistry / Q000648:ultrastructure