We proposed a novel jaw movement tracking method that can measure in six degrees of freedom. The magnetic field generated by a permanent magnet paired with a small, low-power-consumption Hall effect magnetic sensor is used to estimate the relative distance between two objects—in this instance, the lower and upper jaws. By installing a microelectromechanical system (MEMS) orientation sensor in the device, we developed a mouthpiece-type sensing device that can measure voluntary mandibular movements in three-dimensional orientation and position. An evaluation of individuals wearing this device demonstrated its ability to measure mandibular movement with an accuracy of approximately 3 mm. Using the movement recording feature with six degrees of freedom also enabled the evaluation of an individual’s jaw movements over time in three dimensions. In this method, all sensors are built onto the mouthpiece and the sensing is completed in the oral cavity. It does not require the fixation of a large-scale device to the head or of a jig to the teeth, unlike existing mandibular movement tracking devices. These novel features are expected to increase the accessibility of routine measurements of natural jaw movement, unrestricted by an individual’s physiological movement and posture.

[Purpose] Ultrasonography can be used to non-invasively analyze any cross-section of the human body and to measure tissue elasticity, thickness, and brightness. This study was performed to examine the quantitative and qualitative changes in the masseter muscle at rest and at maximal occlusion, and to evaluate the relationship between these changes and the general health of the individual. [Participants and Methods] The study cohort comprised 30 healthy adults. Correlations between basic participant information (sex, age, height, body weight, body mass index, body fat, maximum bite force, handgrip strength, and tongue pressure) and masseter muscle ultrasonographic data were examined. [Results] Masseter muscle thickness was significantly greater in males than in females. Body weight and body mass index correlated positively with masseter muscle thickness. Body mass index and body fat percentage correlated positively with masseter muscle brightness. Tongue pressure correlated positively with handgrip strength. [Conclusion] Our analyses of muscle thickness and brightness suggest that ultrasonography may be useful in evaluating masseter muscle quantity and quality, and that the condition of the masseter muscle may correlate with the overall health status of the individual.

Previous studies, the changes in tongue hardness with growth were scarcely ever described, but tongue pressure and morphology were the focus of them. Given that, we decided to use ultrasound to examine the changes in tongue hardness during growth. 60 paediatric patients (30 boys and 30 girls) aged 6 to 11 years (mean age, 8.5 ± 1.7 years) who visited the Department of Orthodontics, Showa University Dental Hospital were selected for the study. Tongue hardness was measured using real-time ultrasound tissue elastography. The measured values of tongue elasticity were subjected to the Shapiro – Wilk test, and QQ plot for checking the normality. Pearson’s correlation coefficient was used to confirm the significance of the relationship among the three measurements of tongue elasticity, age, sex, height, weight, BMI, body fat, tongue pressure, and hand strength. We confirmed that the use of ultrasound SWE and SE are valuable for the measurement of tongue elasticity. A negative correlation between age and tongue elasticity SE (extraoral) (r = −0.26, P < 0.05), body weight and tongue elasticity SE (extraoral) (r = −0.30, P =＜0.05). It was suggested that tongue hardness changes with changes with age. The balance between the tongue and perioral muscles is affected with the position of the teeth. Perioral muscle function is closely associated with malocclusion onset, particularly during childhood when maxillofacial growth and development are rapid. Therefore, the use of ultrasonography device can aid in the evaluation of treatments to improve perioral muscle function.

Mandibular asymmetry often requires orthognathic surgery, and postsurgical relapse remains a concern. The masseter muscle may influence stability, but most studies have emphasized volumetric rather than qualitative changes. This prospective study evaluated 24 patients with mandibular asymmetry using ultrasonography preoperatively and at 1, 3, and 6 months after surgery. The parameters measured were thickness, stiffness ratio, echo intensity, and blood flow. The results showed significant postoperative adaptations. Masseter echo intensity increased markedly at 1 month (p < 0.001), peaked at 3 months (p = 0.042), and decreased toward baseline at 6 months (p < 0.001). Blood flow increased significantly from T1 to T2 (p < 0.001). Bite force dropped transiently at 1 month (p < 0.001) but recovered by 6 months (p < 0.001). At baseline, BMI correlated with echo intensity (r = 0.724, p < 0.001) and grip strength correlated with bite force (r = 0.705, p < 0.001). The stiffness ratio difference (contraction–rest) correlated with bite force (right: r = 0.629; left: r = 0.690). Relapse occurred in 25% of patients and correlated only with preoperative deviation and not ultrasound indices. Conclusions: Ultrasonography revealed meaningful qualitative muscle changes during recovery, though these were not strong predictors of relapse. Ultrasound remains a reliable, noninvasive tool for monitoring postoperative adaptation.

The human mandible has been investigated from both clinical and evolutionary perspectives. Recent advances in genome science have identified the genetic regulation of human mandibular shape and size. Identification of genes that regulate mandibular shape and size would not only enhance our understanding of the mechanisms of mandibular growth and development but also help define a strategy to prevent mandibular dysplasia. This review provides a comprehensive summary of why and how the mandible was evaluated in the human mandible genome study. The variation in human mandibular shape and size has been progressively clarified, not only by focusing on the mandible alone but also by using extremely diverse approaches. The methods of data acquisition for evaluating human mandibular shape and size variation are well established. Furthermore, this review explains how to proceed with future research.