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Explainable deep learning and biomechanical modeling for TMJ disorder morphological risk factors
Shuchun Sun, Pei Xu, Nathan Buchweitz, Cherice N. Hill, Farhad Ahmadi, Marshall B. Wilson, Angela Mei, Xin She, Benedikt Sagl, Elizabeth H. Slate, Janice S. Lee, Yongren Wu, Hai Yao
Shuchun Sun, Pei Xu, Nathan Buchweitz, Cherice N. Hill, Farhad Ahmadi, Marshall B. Wilson, Angela Mei, Xin She, Benedikt Sagl, Elizabeth H. Slate, Janice S. Lee, Yongren Wu, Hai Yao
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Research Article Bone biology Metabolism

Explainable deep learning and biomechanical modeling for TMJ disorder morphological risk factors

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Abstract

Clarifying multifactorial musculoskeletal disorder etiologies supports risk analysis, development of targeted prevention, and treatment modalities. Deep learning enables comprehensive risk factor identification through systematic analyses of disease data sets but does not provide sufficient context for mechanistic understanding, limiting clinical applicability for etiological investigations. Conversely, multiscale biomechanical modeling can evaluate mechanistic etiology within the relevant biomechanical and physiological context. We propose a hybrid approach combining 3D explainable deep learning and multiscale biomechanical modeling; we applied this approach to investigate temporomandibular joint (TMJ) disorder etiology by systematically identifying risk factors and elucidating mechanistic relationships between risk factors and TMJ biomechanics and mechanobiology. Our 3D convolutional neural network recognized TMJ disorder patients through participant-specific morphological features in condylar, ramus, and chin. Driven by deep learning model outputs, biomechanical modeling revealed that small mandibular size and flat condylar shape were associated with increased TMJ disorder risk through increased joint force, decreased tissue nutrient availability and cell ATP production, and increased TMJ disc strain energy density. Combining explainable deep learning and multiscale biomechanical modeling addresses the “mechanism unknown” limitation undermining translational confidence in clinical applications of deep learning and increases methodological accessibility for smaller clinical data sets by providing the crucial biomechanical context.

Authors

Shuchun Sun, Pei Xu, Nathan Buchweitz, Cherice N. Hill, Farhad Ahmadi, Marshall B. Wilson, Angela Mei, Xin She, Benedikt Sagl, Elizabeth H. Slate, Janice S. Lee, Yongren Wu, Hai Yao

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Figure 7

Evaluation of contact behavior and tissue response in the TMJ using finite element mechanics models.

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Evaluation of contact behavior and tissue response in the TMJ using fini...
(A) The models encompass the TMJ condyle, fossa, and disc and provide insights into strain energy density, the energy deposited in the TMJ disc that can lead to tissue fatigue and damage. To assess contact behavior independent of joint force, constant joint force loads of 30 N and 60 N were applied. A fixed boundary condition was set for the fossa, with the joint force exerted on the condyle. The resulting TMJ disc strain energy density and contact area are depicted. (B) Analysis suggests a mild influence of condyle shape on determining energy density and contact area (n = 16, 8 males and 8 females). Average strain energy density versus condyle area (30 N: P = 0.816, R² = 0.0040; 60 N: P = 0.671, R² = 0.0133). Average strain energy density versus flatness ratio (30 N: P = 0.192, R² = 0.1182; 60 N: P = 0.041, R² = 0.2668). Contact area versus condyle area (30 N: P = 0.753, R² = 0.0073; 60 N: P = 0.615, R² = 0.0186). Contact area versus flatness ratio (30N: P = 0.048, R² = 0.2509; 60N: P = 0.101, R² = 0.1800). Solid lines represent curve fittings where the differences are statistically significant (P < 0.05) and dashed lines represent curve fittings where the differences are not statistically significant (P ≥ 0.05). While condyle size dictates the potential contact area capacity, actual contact is influenced more by shape. Even under a large joint force (60 N), less than half of the condyle area engaged in contact. A steeper condylar shape ensured improved joint congruency, distributing the load across a broader area. Interestingly, the shape of the TMJ condyle was found to be independent of mandibular size (r < 0.1), indicating that both mandibular size and condylar shape function as distinct morphological risk factors for TMJ disorders.

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ISSN 2379-3708

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