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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 5

Exploration of the relationship between mandibular size and TMJ force with inverse dynamic musculoskeletal model.

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Exploration of the relationship between mandibular size and TMJ force wi...
(A) Construction of inverse dynamic musculoskeletal models derived from 16 specimens (8 female, 8 male) without TMJ disorders and driven by live kinematics, EMG data, and bite forces from reference participants (Supplemental Figure 4). 3 bite force levels (11 N, 30 N, and 60 N) simulate varying bite force scenarios, with magnitudes based on human bite forces during consumption of foods with diverse textures. (B) Analysis of morphological indicators, such as 3D and 2D mandibular lengths, ramus width, and height, shows a negative correlation with TMJ joint force across bite force levels of 11N, 30N, and 60N (n = 16, 8 males and 8 females). Specifically, participants with larger mandibles tend to have reduced joint forces at a given bite force level. This trend is statistically significant, as seen in the correlations for 3D mandibular length (11 N, 30 N, and 60 N: P = 0.001, R²=0.5340), 2D mandibular length (11 N, 30 N, 60 N: P = 0.014, R²=0.3627), ramus width (11 N, 30 N, 60 N: P = 0.005, R²=0.4382), and ramus height (11 N, 30 N, 60 N: P = 0.003, R²=0.4719). Solid lines represent curve fittings where the differences are statistically significant (P < 0.05). Further, the moment arm ratio, which dictates the relationship between muscle force and bite force, suggests nonproportional scaling in the human mandibular musculoskeletal system (see Supplemental Figure 5). Specifically, individuals with smaller mandibles have smaller muscle force and bite force moment arm ratios, leading to increased joint forces at a given bite force. This observation aligns with clinical findings that link smaller mandibular sizes in females and patients with class II dentofacial deformity to a higher risk of TMJ disorders due to elevated joint forces.

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