Title: Sexual Dimorphisms in Human Temporomandibular Disc Mechano-Electro-Chemical Properties
Matthew Coombs (Presenter)
Medical University of South Carolina
Gregory Wright, Clemson University
Xingju Nie, Medical University of South Carolina
Thierry Bacro, Medical University of South Carolina
Michael Lecholop, Medical University of South Carolina
Michael Kern, Medical University of South Carolina
Xiaojing Chen, Central South University
Hai Yao, Medical University of South Carolina
Objectives: Temporomandibular joint disorders (TMJDs) disproportionately affect women (3-8 times), with approximately 30% of TMJDs including disc degeneration. TMJD etiology is currently unknown. The objective of this study was to investigate sexual dimorphisms in temporomandibular disc mechano-electro-chemical properties, which could result in a loading environment which predisposes women to TMJD development.
Methods: Intact human temporomandibular joints (TMJs) were excised and imaged using a preclinical 7T MR, and solid models of the temporomandibular disc were reconstructed for morphometric analysis. TMJ discs were extracted, and underwent an incremental stress-relaxation tensile testing protocol to determine disc viscoelasticity, and electro-chemical assays to determine disc extracellular matrix fixed charge density (FCD).
Results: Statistical modelling showed significant effects for donor sex for disc morphometry and FCD. When considering skull size and shape, female temporomandibular discs were proportionally larger than male discs in their anteroposterior length (p=0.0199), with no difference in their mediolateral width. Temporomandibular discs for male discs had higher FCD compared to females (p=0.007), with FCD twice as high for males compared to females in the disc posterior band. Human TMJ discs trended stiffer for females compared to males, with higher Young’s Modulus and Instantaneous Modulus, and relaxing proportionally less.
Conclusions: These findings establish important sexual dimorphisms in temporomandibular disc mechano-electro-chemical properties. Differences in disc size and shape between males and females is anticipated to alter stress and strain patterns. Coupled with their increased stiffness and decreased viscoelastic response, the TMJ disc could experience higher stresses in females compared to males. Additionally, FCD is an important regulator of disc compressive modulus through osmotic swelling pressure, and could be an important contributor to tissue viscoelasticity. In conclusion, these findings build on our understanding of the structure-function relationships within the TMJ disc, and provide potential insights into etiological mechanisms behind the increased prevalence of TMJDs among women.