Small vertical changes in jaw relation affect motor unit recruitment in the masseter

Is Muscle Pain in Temporomandibular Disorder a Hyperactivity Problem? A Clinical, Thermographic, and Electromyographic Analysis

ABSTRACT

This study aimed to report clinical data on muscle pain in temporomandibular disorders using thermography, algometry, and surface electromyography (EMG). This was done to support or rule out the hypothesis that painful muscles are always related to muscular hyperactivity. This cross-sectional, analytical study included 50 participants who underwent clinical examination and evaluation of anterior temporal muscles and bilateral masseters using thermography, algometry, and EMG. The muscles with greater pain symptoms had hyporadiation and a lower temperature compared with both contralateral muscles and muscles in the asymptomatic group. There was no muscle hyperactivity at rest on EMG analysis; however, there was a greater capacity for muscle recruitment of these symptomatic muscles after a joint decompression test with cotton rolls, suggesting hypoactivity of the affected muscles in the symptomatic patient group. Muscle pain may be related to hypoactivity of the musculature when there is neurological inhibition of the recruitment of muscle fibers, and treatment must consider these neurophysiological alterations.

LEVEL OF EVIDENCE

Level IV.

Effects of 8-week oral splint usage on body flexibility and muscle strength-endurance performance in Pilates practitioners

Purpose

We investigated the acute and chronic effects of oral splint on muscle strength-endurance performance and body flexibility.

Methods

Twelve Pilates practitioners (age 49.5 ± 5.8 years; mass 58.6 ± 6.5 kg) were evaluated with (OS) and without (CTRL) oral splint. Before (PRE) and after (POST) 8 weeks of oral splint usage during Pilates activity, muscle strength-endurance and body flexibility were evaluated through a frontal plank exercise and a Toe-touch test in OS and CTRL. Before each test, the highest electrical activation (EMG) of masseter and temporal muscles during maximal occlusion was determined. During frontal plank, the time-to-exhaustion, the maximum voluntary activation of masticatory muscles and the time of muscles activation have been determined.

Results

No OS vs CTRL and PRE vs POST differences were found in the maximum voluntary activation of temporal and masseter muscles. The time-to-exhaustion in OS was longer than CTRL in both PRE (P = 0.049) and POST sessions (P = 0.043). Time of masticatory muscles activation during plank was moderately greater in OS at PRE (P = 0.020) and POST (P = 0.022), while no difference between PRE and POST emerged in both conditions. Higher muscular activation was found in OS than CTRL at PRE (P = 0.031) and POST (P = 0.031), whereas no difference between PRE and POST appeared. No effect on flexibility emerged neither acutely nor chronically.

Conclusion

Acute and chronic oral splint usage improved strength-endurance performance but not body flexibility. These findings suggest biomechanical and neural mechanisms influencing the muscle length and the concurrent activation potentiation, but not muscle tone and stiffness.

Masseter response to long-term experimentally induced anterior crossbite in Sprague-Dawley rats

OBJECTIVE

To detect the long-term response to unilateral anterior crossbite (UAC) in masticatory muscles and in molecular biomarkers of peripheral blood leukocytes.

DESIGN

Fifty-six six-week-old Sprague-Dawley rats were used. The gene-fold changes in peripheral blood leukocytes were detected by the microarray analysis to compare the rats that received 20-week UAC treatment with age-matched controls (n = 4). Muscle atrophy-related gene Fbxo32 was selected based on the data of the microarray analysis verified by using real-time PCR. The remaining 36 rats were randomly separated in the UAC and control groups at 12 and 20 weeks (n = 12). The protein expression of Fbxo32 and the muscle injury and myogenesis-related markers, αB-crystallin and desmin, were detected in the masseter and lateral pterygoid muscles by western blot assay.

RESULTS

In the 20-week UAC group, the masseter muscle weight was lower than that in the age-matched control group, and the expression level of Fbxo32 gene in peripheral blood leukocytes was increased according to the microarray analysis confirmed by real-time PCR detection. The increased protein expression levels of Fbxo32 were detected in the masseter in the 20-week UAC group, and the protein expression levels of desmin and αB-crystallin were decreased at this time point. No similar changes were detected in the lateral pterygoid muscle.

CONCLUSIONS

Masseter atrophy is induced by long-term stimulation of UAC. The increased expression of the Fbxo32 gene in peripheral blood leukocytes may be a candidate biological marker of masseter atrophy.

Effects of Two Different Self-Adapted Occlusal Splints on Electromyographic and Force Parameters During Elbow Flexors Isometric Contraction

Limonta, E, Arienti, C, Rampichini, S, Venturelli, M, Cè, E, Veicsteinas, A, and Esposito, F. Effects of two different self-adapted occlusal splints on electromyographic and force parameters during elbow flexors isometric contraction. J Strength Cond Res 32(1): 230-236, 2018-The study was aimed at determining the acute effects of 2 types of occlusal splints on maximum isometric strength and fatigue of the elbow flexors muscles. The hypothesis was that splint-induced masticatory muscle repositioning might improve primary muscles recruitment by stretching masticatory muscles especially with the thicker splint. On 9 physically active volunteers with no temporomandibular joint and masticatory muscles disorders, we assessed maximum voluntary contraction (MVC) of the elbow flexors with diurnal (OSD, 1-mm thick) and sport (OSSP, 3-mm thick) splints, and without splint (control, Ctrl). On different days, participants performed 60 seconds of isometric contraction at 100% MVC (100%60s) and 80% MVC contraction until exhaustion (80%exh) under OSD, OSSP, and Ctrl in random order. Time of force output within target (t-target), force distance from target (ΔF), and force coefficient of variation were calculated. Percentage of force decay (ΔFi-Fe) was determined during 100%60s. From the electromyographic (EMG) signal, root mean square (EMG RMS) and mean frequency (EMG MF) were determined. Neuromuscular efficiency (NE) was calculated as the ratio between force and EMG RMS. MVC contraction and NE were significantly higher in OSSP and OSD than in Ctrl. During MVC, EMG MF was significantly lower in both splint conditions, and EMG RMS showed a nonstatistical tendency to lower values under both splint conditions. During 80%exh, t-target was longer in OSD and OSSP (+7.8% and +5.2%, respectively) than in Ctrl. ΔFi-Fe was lower in OSSP than in Ctrl and OSD. These results support the hypothesis of a NE improvement of the elbow flexors possibly induced by acute, splint-induced masticatory muscles repositioning.