Effect of a centric stabilization splint on masticatory muscles in patients with temporomandibular disorders: An electromyographic study

Abstract

Aim:

Occlusal splint treatment is commonly used to treat a variety of temporomandibular disorders (TMDs), with efficacy ranging between 70% and 90%. Centric splints are effective in relieving muscular soreness in individuals with TMD. Electromyography (EMG) quantifies muscle activity and can be used as an accessory diagnostic tool to evaluate the efficiency of the splint on the masticatory complex. Electromyography is used for assessing patients with TMD and observing muscle electromyography. TMD patients have altered electromyographic (EMG) masticatory muscle activity because of its change in electrical activity index or because of the compensatory mechanism for the disorder. Therefore, this study serves to evaluate the efficacy of the centric stabilization splint on TMD using EMG.

Settings and Design:

This cross-sectional study enrolled Ten TMD Patients with TMD, who underwent treatment with centric stabilization splint.

Materials and Methods:

The study involved ten young adults with TMD aged 18–45 years who were recruited without regard to sex, religion, caste, or socioeconomic background. The participants were randomized to receive a flat-contact upper stabilization splint and pregelled EMG electrodes to assess the immediate impact of centric splints on TMDs. After 3 months of follow-up, muscle activity and muscle symmetrical activity were measured to assess improvement in the symptoms of TMD.

Statistical Analysis Used:

The Shapiro–Wilk test was used to assess the normality of the variables' distribution using SPSS 26.0. Symmetrical activity and treatment response were investigated using the Wilcoxon signed-rank test.

Results:

It showed an improvement in the temporalis, masseter, and sternocleidomastoid muscles' resting EMG activity. A statistically significant improvement was seen in the EMG activity of the bilateral temporalis, right masseter, right sternocleidomastoid, and left digastric muscles while clenching. The masseter, sternocleidomastoid, and digastric muscles all displayed significantly enhanced symmetrical activity (P < 0.05).

Conclusions:

This research concludes that a centric stabilizing splint assists in relieving TMD symptoms. There was enhanced masticatory muscle activity both at rest and during function. Furthermore, there was an improvement in symmetrical activity of the masticatory muscles, which improved balance and enhanced the effective functioning of the masticatory complex.

INTRODUCTION

A wide range of clinical complications affecting the stomatognathic system, specifically the masticatory muscles, temporomandibular joint (TMJ), and surrounding tissues, are linked to temporomandibular disorders (TMDs).[1,2] Mandibular movement abnormalities, joint sounds, and muscle and joint discomfort or pain are the primary symptoms and indicators of TMDs. The pain linked to TMJ dysfunction is characterized by its chronic, recurring, or persistent nature. It extends beyond the TMJ and masticatory muscles to potentially affect adjacent tissues, including the teeth, ears, neck, temples, forehead, and back muscles. Effective management of stomatognathic system TMD necessitates a holistic and methodical strategy. TMDs constitute over 30 conditions that affect the masticatory muscles and jaw joint, causing discomfort and dysfunction.[3] Although symptoms may manifest at any stage of life, the highest incidence rate is observed among adults aged 20–40 years. There are numerous factors that can contribute to TMDs, such as jaw injury, bruxism, arthritis, malocclusion, and stress.[2] Patients with TMDs that are linked to stomatognathic system problems may benefit from behavioral modifications, medication, physiotherapy, patient education, and removable appliances such as a centric occlusal splint. Based on the material, there are numerous varieties of splints, e.g., hard and soft splints. Occlusal splint therapy is a tried-and-true method of treating TMDs.[4] Centric splints can effectively treat symptoms of TMJ pain and muscle myalgia.[4] Centric stabilization splint reinstates the condyle-disk relationship, hence reducing muscle hyperactivity. The splint therapy can control tooth interference and mandibular movement. This will modify the muscle hyperactivity and balance the masticatory muscles. The depressor muscles (masseter, temporalis, and medial pterygoid) become overactive as a result of tooth interferences, which activate excursive movements resulting in mandibular deviation.[5] Occlusal splint therapy reduces pain severity, increases mouth opening, and also increases synchronization between depressors and elevators of the mandible in patients with TMDs. To access this synchronization, EMG is used. Muscle electromyography (EMG) quantifies the electrical activity of muscles.[5] It measures the electrical activity in muscles using the nerve impulse firing potential. It is used to measure the muscle activity at rest and at function. It also evaluates the synchronicity of the right and left masticatory muscles. Therefore, EMG can be used to assess the improvement of bilateral muscle activity both at rest and at function in TMD patients after centric splint intervention.

As far as the authors are aware, there is a lack of EMG studies that simultaneously evaluate muscle synchronization and activity during rest and function in patients with TMD.[6] Therefore, the objective of this investigation is to evaluate the masticatory muscular electrical activity in TMD patients before and after centric splint intervention using electromyography. The authors hypothesized the following: (i) patients with TMD would show abnormal masticatory muscle activity at rest and at function (pretreatment), (ii) the altered muscle activity would normalize posttreatment, and (iii) the synchronicity of the right and left masticatory muscles would improve posttreatment.

MATERIALS AND METHODS

This cross-sectional study was conducted in the department of prosthodontics and the study received approval from the institutional ethics committee, and each patient's informed permission was obtained being MAIDS/Ethical Committee/2016/3273.

Study procedure

Inclusion criteria

The research comprised patients with ages ranging from 18 to 45 years (both included). Without regard to sex, religion, caste, or socioeconomic background, patients were recruited. Selection criteria included the Research Diagnostic Criteria TMD (RDC/TMD) categorization with Axis 1 who were completely dentate or at least had adequate occlusal stops.

Exclusion criteria

Patients with limited mouth openings or those who had previously received occlusal appliances as therapy and orthodontics were also disqualified from the research.

Sample size calculation

The sample size was maintained in line with Al Quran and Kamal's 2013[7] study, which used EMG to assess the immediate impact of centric splints on TMDs. Using formulas of comparison of two independent means with 0.05 and 0.2 as the initial values, the sample size was determined to be 10 patients or more, at the very least.

Centric splint fabrication

Ten young adults with TMD between the ages of 18 and 45 years volunteered to participate in this research. A flat-contact upper stabilization splint comprised heat-cured, strong acrylic resin. Jaw registration was done in centric relation, and the anterior teeth were kept apart by 2 mm. To provide broad and flat occlusal contact with the mandible in the central position, the hard splint was inserted, and occlusion correction was done accordingly to give flat contacts on splint.

EMG measurement (pretreatment)

Pregelled, sticky metal foil EMG electrodes were stuck on muscle to measure EMG. An earth electrode was placed on the left shoulder in the back region.

• For masseter, the most conspicuous region was positioned along a line connecting the angle of the mandible with the outer canthus of the eye [Figure 1]

• The electrodes for the temporalis muscle were positioned on the right side, slightly behind the hairline and near the muscle's anterior border

• The electrodes for the sternocleidomastoid muscle were stuck at the angle of the clavicle, near where the muscle attaches

• For the digastric muscle, they were attached to the anterior belly of the muscle, close to where the muscle inserts into the hyoid bone.

Figure 1.

Electrodes placed at masseter muscle

Using EMG electrodes, records of maximal clenching and rest were recorded for each muscle [Figure 2]. To measure synchronization, the balance between the right and left muscles was recorded and stored in BioJVA™ software [Figure 3].

Figure 2.

EMG (BioJVA^™) machine

Figure 3.

Data recorded in BioJVA™ software

To prevent muscular tiredness, the participants were given a 5-min break between each session of recordings. Each participant was instructed to perform a maximal clenching at the start until the maximum was obviously attained.

Follow-up and EMG measurement (posttreatment)

After 3 months of follow-up, the balance parameter, resting and maximal clenching muscle activity, and TMD symptom alleviation were assessed once more.

Statistical evaluation

To determine whether the variables followed a normal distribution, the Shapiro–Wilk test was done using SPSS 26.0 (IBM Corp. Released 2019. IBM SPSS Statistics for Windows, version 26.0. Armonk, NY, USA: IBM Corp) software. By determining the significance of variations in the EMG activity of all muscles and the balance of the following right and left muscles, the Wilcoxon signed-rank test was used to analyze symmetrical activity and treatment response.

RESULTS

Based on our research protocol, 10 participants were selected and given centric stabilization splints. The data were collected and analyzed using SPSS 26.0 (IBM Corp. Released 2019. IBM SPSS Statistics for Windows, version 26.0. Armonk, NY, USA: IBM Corp) software. The Shapiro–Wilk test was employed to determine the distribution's normality, and the box-plot graph was utilized to depict this normality, illustrated in Figure 4.

Figure 4.

Box-plot chart after evaluating the distribution's normality using the Shapiro–Wilk test with a 95% confidence limit. X-axis: Group of masticatory muscle. Y-axix: EMG amplitude at rest. X-axis: 1-Right temporalis muscle; 2-Left temporalis muscle; 3-Right masseter; 4-Left masseter; 5-Left sternocleidomastoid; 6-Right sternocleidomastoid; 7-Right digastric; 8-Left digastric

The muscle activity at rest was measured for all the patients before and after intervention with splint therapy. The electrical activity of muscles at rest improved after the treatment. This effect of the centric splint on the electrical activity of masticatory muscles at rest has been analyzed using the Mann–Whitney test in Table 1. On analysis, it was observed that the temporalis, masseter, and sternocleidomastoid Muscles' activity at rest showed a statistically significant improvement (P < 0.05).

Table 1.

Mann–Whitney U-test showing intra-group comparison of electrical activity of masticatory muscles at rest

Intra-group comparison of electrical activity of masticatory muscles at rest
	Paired differences of mean	95% CI of the difference		P
		Lower	Upper
RT - RT_S	−0.220	−0.467	0.027	0.075
LT - LT_S	−0.390	−0.582	−0.198	0.001
RM - RM_S	0.590	0.404	0.776	0.001
LM - LM_S	−0.030	−0.165	0.105	0.627
RSCM - RSCM_S	−0.240	−0.388	−0.092	0.005
LSCM - LSCM_S	−0.010	−0.305	0.285	0.941
RD - RD_S	−0.040	−0.332	0.252	0.764
LD - LD_S	0.180	−0.019	0.379	0.071

P<0.01 highly significant, P<0.05 significant, P>0.05 no significant. RT: Right temporalis, LT: Left temporalis, RM: Right masseter, LM: Left masseter, RSCM: Right sternocleidomastoid, LSCM: Left sternocleidomastoid, RD: Right digastric, LD: Left digastric, CI: Confidence interval, S_: Patient wearing splint

The maximum volumetric clenching was measured using EMG for all the subjects before and after the splint therapy. It was observed that a significant improvement was pragmatic in all the muscles. The statistical evaluation was done using the Mann–Whitney test which is illustrated in Table 2. The analysis showed that the temporalis, right masseter, right sternocleidomastoid, and left digastric muscles' electrical activity during clenching showed a statistically significant improvement (P < 0.05).

Table 2.

Mann–Whitney U-test showing intra-group comparison of electrical activity of masticatory muscles during clenching

Intra-group comparison of electrical activity of masticatory muscles during clenching
	Paired differences of mean	95% CI of the difference		P
		Lower	Upper
RT_CLENCH - RT_CLENCH_S	11.530	10.067	12.993	0.002
LT_CLENCH - LT_CLENCH_S	10.020	7.115	12.925	0.003
RM_CLENCH - RM_CLENCH_S	11.720	10.455	12.985	0.002
LM_CLENCH - LM_CLENCH_S	−1.840	−4.083	0.403	0.096
RSCM_CLENCH - RSCM_CLENCH_S	−0.460	−0.932	0.012	0.050
LSCM_CLENCH - LSC_CLENCH_S	−0.160	−0.897	0.577	0.635
RD_CLENCH - RD_CLENCH_S	2.760	−3.146	8.666	0.318
LD_CLENCH - LD_CLENCH_S	−0.810	−1.120	−0.500	0.001

P<0.01 highly significant, P<0.05 significant, P>0.05 no significant. RT: Right temporalis, LT: Left temporalis, RM: Right masseter, LM: Left masseter, RSCM: Right sternocleidomastoid, LSCM: Left sternocleidomastoid, RD: Right digastric, LD: Left digastric, CLENCH: Muscles during clenching

The synchronization of bilateral masticatory muscle is crucial. It was observed that the synchronization between the muscles was improved when evaluated through EMG. The comparison of this synchronization was assessed and analyzed statistically using the Mann–Whitney test in Table 3. The balance between the right and left masseter, sternocleidomastoid, and digastric muscles improved significantly (P < 0.05).

Table 3.

Mann–Whitney U-test showing comparison of symmetrical activity of masticatory muscles

Comparison of symmetrical activity of masticatory muscles
	Paired differences of mean	95% confidence limits		P
		Lower	Upper
TEMP_PRE - TEMP _POST	6.107	−12.756	14.876	0.866
MAS_PRE - MAS_POST	2.316	−12.140	−1.660	0.005
SCM_PRE - SCM_POST	2.565	−34.502	−22.898	0.002
DIG_PRE - DIG_POST	3.054	1.891	15.709	0.018

P<0.01 highly significant, P<0.05 significant, P>0.05 no significant. TEMP: Temporalis muscle, DIG: Digastric muscle, SCM: Sternocleidomastoid muscle, MAS: Masseter muscle, _PRE: Before wearing splint, _POST: After wearing splint

DISCUSSION

The TMJ system encompasses the neuromuscular system around the TMJ and accompanying masticatory musculature. TMDs are divided generally as myogenous and arthrogenous.[8] Pain in TMD may radiate to TMJ Area, facial ragion and behind the ears. It is accompanied by clicking joints, limited jaw opening, and disbalance in masticatory muscles, which may appear as severe muscular myalgia.[9] A complete diagnostic evaluation utilizing RDC/TMD is needed for the most effective treatment of TMJ disorders.[10] The noninvasive treatments for TMD include medication, physical therapy, occlusal splints, and cognitive-behavioral therapies.[11] The best technique to cure TMD is to reinstate the proper disc-condyle interface. We normally employ a central stabilizing splint for this.[12] The centric splint reduces myogenic pain and reverses symptoms of TMD. Electromyography (EMG) was performed to examine the electrical activity of muscles. The benefit of electromyography is that it is noninvasive, as it employs surface electrodes that are put over a respectable muscle on the surface of the skin.

EMG examination of masticatory muscles is of utmost importance for understanding the neuromuscular pathophysiology of TMD conditions.[13,14,15] A full EMG examination should only be done using standardized (normalized) results.[16,17,18] For early raw result processing, normalization is important to allow effective statistical analysis.[19] By comparing the muscle electrical potentials to the reference values, the muscular electrical potentials were standardized. Of the techniques studied, maximum voluntary gripping on these cotton rolls was proven to have the most consistent values and was hence used to measure EMG during clenching.[20,21,22]

In this research, we compared patients before and after the splint therapy, through EMG. The findings demonstrate that before treatment, patients exhibited reduced resting and functional electrical activity of the masseter, sternocleidomastoid, and temporalis muscles. A previous study revealed that TMD patients' masticatory muscles were less effective and had decreased EMG activity which may reflect a reduction in muscular efficacy.[14,15,16,17] TMD patients have lowered electrical potential; our results imply that a lower bite force is to be predicted. This electrical activity got improved with time. After follow-up of 3 months, There was Improvement in EMG Activity of the muscles.

Chaves et al.[21] applied Axis I RDC/TMD to examine changes in TMD patients. Both at rest and during maximum clenching, raw and normalized EMG data were noted down. Contrary to our investigation, Chaves et al. observed no anomalies in TMD patients.

In our analysis, we identified an increase in synchronization of muscle activity in masseter, sternocleidomastoid, and digastric muscles (P < 0.05). This result was confluent with other studies.[23,24,25] Berni et al.[26] found that myogenous TMD patients had substantially decreased electrical activity in the masseter, temporalis, and suprahyoid muscles at rest, and that this activity was much more pronounced during maximum volumetric clenching recorded on parafilm in these patients. Similar to those results, Rodrigues et al.[27] revealed that TMD patients displayed reduced masseter and temporalis EMG values at rest and volumetric clenching postures.

The current study's drawback, which is consistent with other investigations, was a lack of data on the precise assessment of the lateral pterygoid muscle activity.[7] We did not, however, investigate every malocclusion-related factor that may possibly contribute to TMD. Another potential drawback of the research is that pain-related TMD may have both arthrogenous and myogenous etiologies, and EMG muscle activity may vary between the two groups. As a result, additional investigation is essential to validate the aforementioned statement.

CONCLUSIONS

The following results may be obtained from this clinical study:

1. A centric stabilizing splint assists in relieving TMD symptoms

2. The masticatory muscles' activity is markedly improved by the centric splint in TMD patients. In our study, it was found that the central stabilization splint improved rest and functional electrical activity, particularly in the temporalis, sternocleidomastoid, and masseter muscles

3. After treatment with the centric splint, there was an improvement in the synchronization of the masticatory muscles, which results in effective functioning of the masticatory complex.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.