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Alterations in the stomatognathic system due to amyotrophic lateral sclerosis

Abstract Objectives: To compare the molar bite force, electromyographic activity, chewing efficiency and thickness of the masseter and temporalis muscles in individuals with amyotrophic lateral sclerosis (ALS) and healthy individuals. Material and Methods: Thirty individuals enrolled in the study were divided into the study group (with ALS, n=15) and control group (healthy individuals, n=15). Data regarding molar bite force (right and left), electromyographic activity (mandibular rest, right and left laterality, protrusion, and maximum voluntary contraction), chewing efficiency (habitual and non-habitual), and masticatory muscle thickness (rest and maximum voluntary contraction) were tabulated and subjected to statistical analysis (Student’s t-test, p≤0.05). Results: Comparisons between the groups demonstrated a statistically significant increase in the electromyographic activity of the right masseter (p=0.03) and left masseter (p=0.03) muscles during mandibular rest; left masseter (p=0.00), right temporalis (p=0.00), and left temporalis (p=0.03) muscles during protrusion; and right masseter (p=0.00), left masseter (p=0.00), and left temporalis (p=0.00) muscles during left laterality, in individuals with ALS as compared with healthy individuals. A statistically significant decrease was observed in the habitual chewing efficiency of the right masseter (p=0.00) and right temporalis (p=0.04) muscles in individuals with ALS. No statistically significant difference between the groups was found the masticatory muscle thickness and maximal molar bite force. Conclusions: ALS may lead to modifications in the activities of the stomatognathic system, including muscular hyperactivity and reduction in chewing efficiency; however, no change has been observed in the masticatory muscle thickness and molar bite force.


Introduction
Amyotrophic lateral sclerosis (ALS) is a chronic, progressive, complex, age-associated syndrome that affects the functions of the superior and inferior neuromotor system through sclerosis and destruction of cells and nerves, leading to the patient's weakness, causing progressive paralysis, and eventually resulting in death 20 . ALS may be classified as sporadic, which is the most common form globally, and familial, which affects individuals by autosomal dominant inheritance 2 . In the literature, few studies on the effect of ALS on masticatory muscles can be found, but there is a possibility of disease interference in mandibular mobility and orofacial pain 25 .
Muscular degeneration begins at the body extremities. It is usually asymmetrical and presents bilateral progression, thereby resulting in the individual's inability to perform voluntary movements during breathing, swallowing, and phonation; it does not alter the sensory and intellectual functioning 9 .
The global incidence proportion of ALS is 1.9 to 4.5/100,000 persons per year 1 . As age is an important predisposing factor, its prevalence increases to 6/100,000 people, among individuals between 58-60 years 29 .
Individuals with ALS present with a compromised skeletal muscle system led research groups to assess the consequences of the disease in the human body 13,15 . ASL promotes functional changes in the stomatognathic system, such as dysphonia, dysarthria, dysphagia, salivation and pattern of force and tongue activity 27 . However, gaps still exist in our knowledge of the impact of ALS on the stomatognathic system, especially regarding masseter and temporal, which are important muscles for mastication. Therefore, the objective of this clinical research was to demonstrate possible changes in the activity of the stomatognathic system in individuals with ALS by assessing the maximal molar bite force, electromyographic activity, chewing efficiency, and thickness of the masseter and temporalis muscles.

Electromyographic analysis
Electromyograph MyoSystem-BrI (DataHominis, Uberlândia, Minas Gerais, Brazil) was used to analyze the electromyographic activity of the right and left masseter, and right and left temporalis muscles.

Muscle thickness analysis
NanoMaxx Ultrasound System equipment (SonoSite, Inc., Bothell, Washington, USA) was used to analyze the thickness (centimeters) of the right and left masseter, and right and left temporalis muscles.

Digital palpation and linear transducer movement
confirmed the location of masticatory muscles 3 Table 1 shows the average age and anthropometric measures for the ALSG and CG. No statistically significant differences were found between the groups. data at each clinical condition for the ALSG and CG. Statistically significant differences (p≤0.05) were found in the electromyographic activity between the ALSG and CG during mandibular rest to right masseter (p=0.03) and left masseter (p=0.03) muscles; protrusion to left masseter (p=0.001), right temporal (p=0.001) and left temporal (p=0.03) muscles;

Results
and left laterality to right masseter (p=0.001), left masseter (p=0.001) and left temporal (p=0.002) muscles (Figures 1-5). Table 3 presents the averages of the habitual and non-habitual chewing efficiency for the ALSG and CG.
A statistically significant difference (p≤0.05) between the ALSG and CG regarding non-habitual chewing (right masseter and right temporalis muscles) was observed (Figures 6-8).      muscles during maximal voluntary contraction and mandibular rest for the ALSG and CG. No statistically significant differences were found between the groups (Figures 9, 10).
The average values of the maximal molar bite force (right and left sides) are presented in Table 5   In this study, electromyography was performed in    Similarly, muscle thickness can also interfere with the masticatory process, and normality patterns related to the thickness of the masticatory muscles are well delineated 4 . In this study, the thickness of the masseter and temporalis muscles during mandibular rest and dental clenching in maximum voluntary contraction were well defined, allowing precise measurements, without statistically significant differences in the averages for the analyzed muscles, between the ALSG and CG. Based on the results of the study by Arts, et al. 5 (2008), muscle thickness is lower in individuals with ALS; however, the muscles analyzed in their study were not the muscles of the stomatognathic system.
Our results led to some questions regarding the thickness of the masseter and temporalis muscles.
Can ALS occur without severe muscle impairment atrophying the skeletal striated musculature? Can the function of masticatory muscles be protected from the disease, in such a way that there is no change in muscle thickness? Further studies will be needed to answer these questions.
The evaluation of maximal molar bite force is fundamental to investigate the impairment of masticatory efficiency because of the pre-established theory that the better the system, the greater the force exerted 16,22 . Our results demonstrated that no To complement the results of this research, the non-correlation between age and sex and the results was statistically affirmed.
Although all the subjects were in the early stage of the disease, they did not present the same symptoms, thus this condition may be a limitation of our study.