1733 Poisson’s Ratio Measurements of the Porcine Temporomandibular Joint Disc
M.W. BEATTY1, K. EVANS2, A. HOYT3, A. JACOBSEN4, B. SIMETICH1, J.C. NICKEL1, and L.R. IWASAKI1, 1University of Nebraska Medical Center College of Dentistry, Lincoln, USA, 2University of Nebraska-Lincoln, USA, 3University of Nebraska Medical Center College of Medicine, Omaha, USA, 4University of Washington, Seattle, USA

Poisson's ratio values derived for cartilage may not apply to the TMJ disc, which exhibits a directional collagen network and is orthotropic in tension.  Objectives: To measure Poisson's ratio values in 3 dimensions and compare measurements at different extensions.  Methods: Porcine TMJ discs were sectioned into dumbbells with the tensile axis oriented in either the anteroposterior (AP) or mediolateral (ML) directions. Upper and lower marks were placed on the gauge length with India ink to measure strain occurring // and _|_ to the tensile axis.  Marks were placed on either width (AP, ML) or thickness (superior-inferior, SI) surfaces, in order to view strain occurring in one of two planes. Dumbbells were elongated at 1 N/s for ML, 5 N/s for AP, in order to generate linear elastic responses.  Mark separation was recorded with a digital video camera and stress-strain (SS) curves recorded.  The linear region was divided into three sections, and video frames for each section were used to measure distances between marks with Scion Image (Frederick, MD).  Four Poisson's ratio values were calculated (n=5): AP/ML, SI/ML, ML/AP, SI/AP.  For each trial, a mean value was calculated for each section of the SS curve and a “pooled” mean calculated for three sections combined.  Best and worst measurement groups were identified based on their deviation from the pooled mean.  Results: Mean ± s.e.m. for best group were AP/ML=1.2±0.19, SI/ML=1.1±0.15, ML/AP=2.3±0.38 and SI/AP=1.1±0.46, which differed from the worst group (p≤0.05).  Conclusions: The best values were obtained by measuring extension over a long region of linear elasticity.  AP/ML values were larger than expected, possibly because AP fibers were shortened during sectioning of ML dumbbells, resulting in excessive transverse strain.

Seq #166 - TMJ - Structure and Function I
9:00 AM-11:00 AM, Friday, 8 March 2002 San Diego Convention Center Room 16A (Mezzanine Level)

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