Ydk01

TMJ articular disc porosity (water volume fraction) was determined using the buoyancy method^{37 (link)}. Immediately preceding electrical conductivity experiments, specimen weight was recorded in air (W_wet) and in phosphate buffered saline (W_PBS) using a density determination kit and analytical balance (Sartorius YDK01, Germany). Immediately following electrical conductivity measurements, specimens were lyophilized and specimen dry weight (W_dry) recorded. Porosity (ϕ^w) was calculated by:
$${\varphi }^{\mathrm{w}}=\frac{{\mathrm{W}}_{\text{wet}}-{\mathrm{W}}_{\text{dry}}}{{\mathrm{W}}_{\text{wet}}-{\mathrm{W}}_{\text{PBS}}}\frac{{\rho }_{\mathit{\text{PBS}}}}{{\rho }_w}$$ where ρ_PBS and ρ_w are the mass densities of the PBS solution and water, respectively. Lyophilized tissues were then assayed for GAG content by Blyscan Glycosaminoglycan Assay kit (Biocolor Ltd., Newtonabbey, Northern Ireland), and expressed as a ratio of dry weight (µg/mg dry weight) and wet weight (µg/mg wet weight).

To quantify 3D human TMJ muscle attachment morphometry, a previously developed co-registered 3D digitization and CBCT imaging-based method was utilized to generate the 3D muscle attachment surfaces (Figure 1B) through cadaveric dissection (She et al., 2018 (link)). Morphometric analysis using a 3D bounding box technique was performed on each reconstructed 3D muscle attachment surface with a defined skull-based coordinate system. The size (Length, Width, Thickness, Area), 3D centroid coordinates (x, y, z), and orientation relative to the sagittal (SA), frankfurt (FHA) and frontal (FA) anatomical planes were determined for the bilateral temporalis, masseter, lateral pterygoid and medial pterygoid muscles. Masticatory muscle volumes were determined using a density determination kit and analytical balance (Sartorius YDK01, Germany) (Wright et al., 2018 (link)).