Article

The biomechanical characteristics of the bone-periodontal ligament-cementum complex

Division of Biomaterials and Bioengineering, Department of Preventive and Restorative Dental Sciences, University of California San Francisco, San Francisco, CA 94143, USA.
Biomaterials (Impact Factor: 8.56). 09/2010; 31(25):6635-46. DOI: 10.1016/j.biomaterials.2010.05.024
Source: PubMed

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.

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    • "Mechanical strains created by mastication and through tooth contact influence the complex in various ways. PDL, which is a vascularized ligament unlike that the in musculoskeletal system, gets blood supplied through the physical continuum it maintains with alveolar bone (Ho et al., 2010). Therefore, blood flow under function can be an effective means of delivering chemokines for cell migration, differentiation and proliferation (Park et al., 2004). "
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    ABSTRACT: In this qualitative study, the presence of various types of molecules prompting cell behavior at the periodontal ligament (PDL)-bone and PDL-cementum attachment sites (AS) has been documented using three-week-and three-month-old scleraxis-green fluorescent protein (GFP) transgenic mouse line. Strain-dominant regions were identified by overlapping both angular distributions of GFP-expressing PDL cells and phalloidin-stained actin filaments of the cytoskeleton along the direction of collagen fibers of the coronal and apical extracellular matrix (ECM) in both age groups, except in the apical region of three-week-old animals. Differences in biomolecular expression with age were indicative of a dominance of passive pullout stretch in a developing molar of a three-week-old, compared to an active pullout stretch in a fully functional, cyclically loaded three-month-old dentoalveolar complex. In general, presence of CD146+ cells around capillaries were CD31+ and were detected in the PDL, dental pulp, endosteal space and bone marrow 50 microns (µm) from the ligament-bone AS. In three-week-old mice, NG2+ cells were along the PDL-cementum AS and concentrated at the root apex, an active site for developing root through growth of secondary cementum. The three-month-old mice showed increased NG2 expression in their apical region and alveolar crest, which are active biomechanical sites during tooth function. The NG2+ cells were not associated with blood vessels. Osx-positive cells—a marker for precursors to osteoblasts and cementoblasts—were identified directly at the respective AS. Bone sialoprotein was distributed evenly in coronal regions with a rich expression in cement lines of apical bone in three-week-old mice, which contrasted with that of three-month-old animals—a result that indicates active remodeling during tooth eruption. Results of this study show overlapping but unique location of putative progenitor cells, which may be related to their regenerative capacity necessary for tooth eruption and function. Conceivably, the cells and matrix molecules can form respective interfaces from the original PDL-bone and PDL-cementum AS in a load-bearing dentoalveolar complex.
    Full-text · Chapter · Jan 2016
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    • "It was also shown that the less-stiff region (enthesis) and the CDJ are bordered by the soft PDL ( $ 5 kPa–9 MPa) on one side and the stiffer (14– 17 GPa) cementum on the other, thus forming a mechanically optimized graded interface that was proposed to facilitate tooth attachment and provide improved load bearing ability to the tooth complex. In a subsequent study, biglycan, fibromodulin and decorin were found in the PDL–bone and PDL–cementum interfaces, also contributing for the mechanical properties of the resulting mechanically graded resulting interface (Ho et al., 2010). More recently, a similar approach to that adopted by Xu et al. (1998) was utilized (Chiu et al., 2012). "
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    ABSTRACT: It has been widely shown that proteoglycans (PG) and their glycosaminoglycan (GAG) side-chains form supramolecular aggregates that interconnect the collagenous network in connective tissues and play a significant role in regulating the mechanical behavior of the extracellular matrix, particularly in soft tissues. However, collective evidence of the mechanical participation of PGs and GAGs in mineralized tissues remains poorly explored in the literature. Here, we address this knowledge gap and discuss the participation of PGs on the biomechanics of mineralized tissues including dentine, cementum and bone. We review evidence suggesting that, on a microscale, PGs regulate the hydrostatic and osmotic pressure, as well as the poroelastic behavior of dentine and bone. On the nanoscale, we review the so-called sliding filament theory and intramolecular stretching of GAGs. We also discuss recent interpretations whereby folding and unfolding of the PG protein core, potentially in association with SIBLING proteins, may be a contributing factor to the mechanical behavior of mineralized tissues. Finally, we review in vitro and in vivo studies of mineralized tissues with targeted disruption or digestion of specific PG family members, which provide further insights into their relevance to the mechanical properties of load bearing hard tissues. In summary, this review brings forth collective evidence suggesting that PGs and GAGs, although less than 5% of the tissue matrix, may play a role in the mechanical behavior and durability of mineralized tissues.
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    • "Bone-tendon Ex vivo X-ray Moriggl et al. (2003) Bone-tendon Dual energy CT Johnson et al. (2007), Deng et al. (2009), Sun et al. (2008) Bone-cartilage Ex vivo Phase-contrast X-ray Ismail et al. (2010) Others Bone-cartilage Ex vivo AFM Campbell et al. (2012) Cementum-peridontal ligament Ex vivo AFM Ho et al. (2010), Lin et al. (2012) Biotechnol Lett produces images at a single focal plane allowing a sharper image and z-stacks to be produced to a depth of a few hundred microns depending on the sample properties (Pawley 2006). But it will provide limited information on hard tissues with only topological information being provided through reflectance imaging . "
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    ABSTRACT: Interfaces between different tissues play an essential role in the biomechanics of native tissues and their recapitulation is now recognized as critical to function. As a consequence, imaging the hard/soft tissue interface has become increasingly important in the area of tissue engineering. Particularly as several biotechnology based products have made it onto the market or are close to human trials and an understanding of their function and development is essential. A range of imaging modalities have been developed that allow a wealth of information on the morphological and physical properties of samples to be obtained non-destructively in vivo or via destructive means. This review summarizes the use of a selection of imaging modalities on interfaces to date considering the strengths and weaknesses of each. We will also consider techniques which have not yet been utilized to their full potential or are likely to play a role in future work in the area.
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