Masticatory Muscles

ObjectivesThe purpose of this study was to evaluate the prognostic relevance of temporal muscle thickness (TMT) in melanoma patients with newly diagnosed brain metastases.MethodsTMT was retrospectively assessed in 146 melanoma patients with newly diagnosed brain metastases on cranial magnetic resonance images. Chart review was used to retrieve clinical parameters, including disease-specific graded prognostic assessment (DS-GPA) and survival times.ResultsPatients with a TMT > median showed a statistically significant increase in survival time (13 months) compared to patients with a TMT ConclusionTMT is an independent predictor of survival in melanoma patients with brain metastases. This parameter may aid in patient selection for clinical trials or to the choice of different treatment options based on the determination of frail patient populations.

Masticatory muscle thickness provides objective measurements of the oral motor function, which may change in patients with oral myofascial pain. In this study, we aimed to establish a reliable ultrasound (US) protocol for imaging the superficial and deep masticatory muscles and to identify the potential influencers of the measurements. Forty-eight healthy participants without orofacial pain were enrolled. The intra-and inter-rater reliabilities of US measurements for masseter, temporalis, and lateral pterygoid muscles were assessed. Intraclass correlation coefficients for all muscles were greater than 0.6. The generalised estimating equation was used to analyse the impact of age, gender, laterality, and body mass index on the measurements, whereby age and body mass index were likely to be associated with an increase in masticatory muscle thickness. The thickness tended to be lesser in females. Laterality seemed to exert minimal influence on masticatory muscle thickness. Our study shows acceptable reliability of US in the evaluation of superficial and deep masticatory muscle thickness. Future studies are warranted to validate the usefulness of US imaging in patients with oral myofascial pain syndrome.

The masticatory system is a complex and highly organized group of structures, including craniofacial bones (maxillae and mandible), muscles, teeth, joints, and neurovascular elements. While the musculoskeletal structures of the head and neck are known to have a different embryonic origin, morphology, biomechanical demands, and biochemical characteristics than the trunk and limbs, their particular molecular basis and cell biology have been much less explored. In the last decade, the concept of muscle-bone crosstalk has emerged, comprising both the loads generated during muscle contraction and a biochemical component through soluble molecules. Bone cells embedded in the mineralized tissue respond to the biomechanical input by releasing molecular factors that impact the homeostasis of the attaching skeletal muscle. In the same way, muscle-derived factors act as soluble signals that modulate the remodeling process of the underlying bones. This concept of muscle-bone crosstalk at a molecular level is particularly interesting in the mandible, due to its tight anatomical relationship with one of the biggest and strongest masticatory muscles, the masseter. However, despite the close physical and physiological interaction of both tissues for proper functioning, this topic has been poorly addressed. Here we present one of the most detailed reviews of the literature to date regarding the biomechanical and biochemical interaction between muscles and bones of the masticatory system, both during development and in physiological or pathological remodeling processes. Evidence related to how masticatory function shapes the craniofacial bones is discussed, and a proposal presented that the masticatory muscles and craniofacial bones serve as secretory tissues. We furthermore discuss our current findings of myokines-release from masseter muscle in physiological conditions, during functional adaptation or pathology, and their putative role as bone-modulators in the craniofacial system. Finally, we address the physiological implications of the crosstalk between muscles and bones in the masticatory system, analyzing pathologies or clinical procedures in which the alteration of one of them affects the homeostasis of the other. Unveiling the mechanisms of muscle-bone crosstalk in the masticatory system opens broad possibilities for understanding and treating temporomandibular disorders, which severely impair the quality of life, with a high cost for diagnosis and management.

BackgroundAtrophy of the masseter muscle can result in an aged facial appearance and diminished chewing function. Electrical stimulation (ES) is known for its ability to facilitate tissue healing and functional recovery, but its precise role in the repair of atrophic masseter muscles remains incompletely understood.MethodsWe induced masseter muscle atrophy in rats through botulinum toxin (BTX) injection and subsequently treated the animals with or without ES. Single-nucleus sequencing (sn-RNA seq) was conducted to analyse the changes in macrophages of masseter muscles between control, BTX and BTX + ES groups. The role and mechanism of macrophage phenotypic transformation in the process of ES promoting the recovery of atrophied masseter muscles were both verified through in vivo and in vitro experiments.ResultsOur results indicate that ES treatment within defined current parameters significantly ameliorated muscle condition by reducing atrophy-related gene expression (MuRF1: BTX: 10.15 ± 1.69; BTX + ES: 1.05 ± 0.06; Fbxo32: BTX: 8.62 ± 1.19, BTX + ES: 1.19 ± 0.07, p + cell number, BTX: 30 ± 2; BTX + ES: 6 ± 2, p +cell, BTX: 10 ± 3; BTX + ES: 33 ± 8, p ConclusionsOur findings suggest that ES can enhance masseter muscle tissue repair by modulating macrophage polarisation, offering valuable insights into the potential of ES in noninvasive tissue regeneration strategies for treating masseter muscle atrophy.