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Technical Briefs

Load Response of Periodontal Ligament: Assessment of Fluid Flow, Compressibility, and Effect of Pore Pressure

[+] Author and Article Information
Marzio Bergomi

Laboratoire de Mécanique Appliquée et D’Analyse de Fiabilité, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015, Switzerlandmarzio.bergomi@epfl.ch

H. W. Anselm Wiskott1

Biomaterials Laboratory, Faculty of Medicine, University of Geneva, Geneva 1205, Switzerlandanselm@wiskott.com

John Botsis, Aïssa Mellal

Laboratoire de Mécanique Appliquée et D’Analyse de Fiabilité, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015, Switzerland

Urs C. Belser

Division of Fixed Prosthodontics, Faculty of Medicine, University of Geneva, Geneva 1205, Switzerland

1

Corresponding author.

J Biomech Eng 132(1), 014504 (Dec 09, 2009) (5 pages) doi:10.1115/1.4000154 History: Received January 16, 2009; Revised June 17, 2009; Posted September 03, 2009; Published December 09, 2009; Online December 09, 2009

The periodontal ligament (PDL) functions both in tension and in compression. The presence of an extensive vascular network inside the tissue suggests a significant contribution of the fluid phase to the mechanical response. This study examined the load response of bovine PDL under different pore pressure levels. A custom-made pressure chamber was constructed. Rod-shaped specimens comprising portions of dentine, bone, and intervening layer of PDL were extracted from bovine mandibular molars. The dentine ends of the specimens were secured to the actuator while the bone ends were affixed to the load cell. The entire assemblage was surrounded by the pressure chamber, which was then filled with saline. Specimens loaded at 1.0 Hz sinusoidal displacement were subjected to four different environmental fluid pressures (i.e., pressures of 0.0–1.0 MPa). The video images recorded during the tests were analyzed to determine whether or not fluid exchange between the PDL and the surrounding medium took place during mechanical loading. A value for the tissue’s apparent Poisson ratio was also determined. The following observations were made: (1) fluid was squeezed out and pumped into the ligament during the compressive and tensile loading phases, (2) the PDL was highly compressible, and (3) the pore pressure had no influence on the mechanical response of the PDL. The present tests emphasized the biphasic structure of PDL tissue, which should be considered as a porous solid matrix through which fluid can freely flow.

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Figure 3

(a) Parameters used in the determination of the apparent Poisson ratio (d0 sample diameter, Δd change in diameter, ⟨w0⟩ average PDL width at rest, and Δw axial displacement) and (b) axial (εaxial) and transverse (εtrans) strains. The computed instant (ν) and averaged (over three loading cycles) apparent Poisson ratio (ν¯) are also plotted. In the present sample, the apparent Poisson ratio was 0.11±0.07

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Figure 4

Effect of pore pressure on load response of five samples (S1–S5): Note the absence of any notable effect of a variation in pore pressure

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Figure 1

Typical load-displacement curve of a tension-compression test on periodontal ligament: The tissue responds elastically on tensile loading (i.e., no energy dissipation) and as a viscous solid on compression; features common to other soft tissue’s mechanical response are the extended zone of no response on both sides of the zero position (i.e., the origin), the toe, and the linear portions of the tensile path

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Figure 2

(a) Dimensional specifications of the cylindrical specimen and (b) pressure chamber (see text for details)

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