Evaluation of Oral Soft Tissues in a Rat Model Using a Custom-Built Shear Modulus Instrument: An Unique Method

The biomechanical properties of soft tissues, in particular those of the oral cavity, could provide valuable information to clinicians.  One property, the shear modulus, could provide such information about gingival, buccal, and lingual soft tissues, and aid in the understanding of soft tissue grafting and pathologies.   Changes at the cellular and molecular level eventually manifest themselves at the gross anatomical level, either visually or texturally.  While current assessment of such changes is either visually or histologically, the mechanical properties should also be evaluated. However, there is a dearth of information regarding an acceptable method or instrument for measuring the shear moduli of such tissue.   We have developed a device that can provide such biomechanical information, allowing clinicians to objectively evaluate the soft tissue of the oral cavity.

The shear modulus is obtained by applying a force to an elastic material, and then measuring the displacement of the material in a parallel direction.  The force divided by the displacement yields the shear modulus; a value that is constant for a given material.  Our device has been developed to measure the surface deformation of oral soft tissues using alternating negative and positive pressures.   Vacuum pump and air compressor lines feed into a main nozzle that when placed on the soft tissue provides a seal with a concomitant force. In the rear of the nozzle is a camera that allows real time viewing of the deformation.

Six recently deceased Sprague-Hawley rats will be used for our study.  They have been provided to us by the Loma Linda University Animal Care facility; their previous use will not effect our evaluation and results.  Each animal is placed in the supine position, and the device is placed on six sites in the oral cavity:  anterior mandible, one side of the posterior mandible, anterior maxilla, one side of the posterior maxilla, one side of the buccal mucosa, and one side of the tongue.  For each soft tissue site, the shear modulus was studied using an adjustable pressure at the tip that induced local mechanostimulation of each site.  This value was then used with the finite element modeling software (COMSOL) to calculate the dimensional changes to the varying pressures. 

Utilizing the values obtained from the COMSOL program, we will be able to determine the shear modulus of the oral soft tissues.  Our results will demonstrate that biomechanical properties vary from region to region within the oral cavity, which can provide clinicians with additional information regarding soft tissue grafting, and subsequent integration of those grafts.  There is little information in the literature regarding the biomechanical properties of intact oral soft tissues, in particular the oral & maxillofacial region.  It is our hope that this device can be the starting point for developing technology that could provide valuable information on assessing the biomechanical properties of oral soft tissues.

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2.  Gotkas S, Dmytruk JJ, McFetridge PS.  Biomechanical behavior of oral soft tissues.  J Periodontol  82:1178-1186, 2011.