Treatment of Temporomandibular Joint Disorders by Ultrashort Wave and Extracorporeal Shock Wave: A Comparative Study

Abstract

Background

This study was carried out to compare the therapeutic efficacy of extracorporeal shock wave (ESW) and ultrashort wave (UW) for temporomandibular joint disorder (TMD).

Material/Methods

A total of 80 patients with myofascial pain and TMD were enrolled in this study. The subjects were randomized to receive ESW or UW treatments. Patients in the ESW group received 1 ESW treatment for 4 weeks and patients in the US group were given US treatment once a day for 5 days per week for 4 weeks. The pain was measured using visual analog scale (VAS) and mouth opening was determined as pain-free maximum mouth opening (MMO) before and 4 weeks after the treatments. Other parameters assessed included functional indexes of temporomandibular joint such as mandibular movement (MM), joint noise (JN), joint press (JP), and disability index (DI).

Results

After therapy, VAS, MMO, MM, JN, JP, and DI in ESW group, and VAS in UW group were significantly improved (P<0.05) as compared to before therapy. VAS, MMO, and the functional indexes of temporomandibular joint in the ESW group were significantly better than those in the UW group (1.79 vs. 2.00, 3.23 vs. 2.03, 1.79 vs. 2.41, 1.45 vs. 2.27, 1.55 vs. 2.59, and 3.30 vs. 4.79, respectively. P<0.05).

Conclusions

ESW significantly reduces pain and improves the functional indexes of temporomandibular joint and mouth opening limit for TMD patients as compared with UW therapy.

Background

Temporomandibular disorders (TMDs) are clinical conditions that affect the masticatory musculature, temporomandibular joint (TMJ), and associated structures [1]. The common symptoms of TMD include clicking of the joint, limited mouth opening, and muscle with joint pain, which is the most significant clinical symptom. The pain can be myogenic, arthrogenic, or mixed types [2]. A number of studies have examined the efficacy of physical therapies for the dysfunction of TMJ and pain, such as electrotherapy, massage, and physical and exercise therapy [3,4]. Among them, UW therapy is demonstrated to be able to reduce pain and inflammation, and improve the functions of the mouth [4,5]. However, this treatment is relatively slow in relieving pain [6].

Extracorporeal shock wave (ESW) has been widely recognized as a biological modulator that results in differentiation of mesenchymal stem cells, neovascularization, and release of angiogenetic factors [7,8]. Previous studies have shown that ESW is beneficial for musculoskeletal disorders, with a success rate between 65% and 91%, with few and negligible complications [9]. Some preliminary studies showed that ESW is effective in treating TMJ disorders [10]. However, a better understanding of the therapeutic effects of the physical therapy interventions is still required for rational use of this therapy for TMD treatment. In this study, we investigated the therapeutic effects of UW and ESW on reliving pain and increasing pain-free maximum mouth opening (MMO) in patients with myogenic or mixed TMD. Our results may help improve therapeutic management of the disease.

Material and Methods

Subjects

A total of 80 TMD patients treated at our hospital between July 2013 and September 2018 were included. Participants were included if they were older than 18 years and had diagnosed myofascial pain with or without mouth opening limitation based on the Research Diagnostic Criteria for TMD (RDC/TMD) [11]. They were also included if they had unilateral or bilateral joint impairment or disc displacement associated with myofascial pain. Those criteria are shown to have excellent intraclass correlation coefficient with TMD, especially for myofascial pain diagnosis [12]. Subjects were excluded if they had polyarthritis, acute trauma, joint infection, surgical treatment (physiotherapy, splint therapy, and acupuncture) within the 3 months prior to the study, depression, and other mental problems. Patients were asked not to take pain-relief medication or muscle relaxants at least 24 hours prior to the evaluations or during the treatment period. This study was approved by the Research Ethics Committee of Shanxi Medical University. Written informed consent was obtained from every patient before treatment.

Patient data and interventions

After detailed physical examinations, a specially-designed evaluation form was filled out for each patient. Demographic data such as age, sex, duration of pain, and other clinical data were collected (Table 1).

Table 1.

Baseline characteristics of patients.

Characteristics	Extracorporeal shock wave	Ultrashort wave	P
Patients (n)	40	40
Age (years)	25.8±7.7	35.0±8.0	0.59
Pain duration (days)	24.3±6.7	25.8±7.7	0.51
Affected side (right/left)	6/14	10/10	0.36
Sex (Male/Female)	7/13	6/14	0.45
VAS	3.40±1.93	3.10±2.02	0.63
MMO	1.73±0.38	1.61±0.53	0.42
MM	5.56±0.60	5.55±0.55	0.94
JN	3.10±0.63	3.11±0.68	0.92
JP	3.88±0.83	3.93±0.87	0.40
DI	8.81±0.80	8.80±0.72	0.98

To compare the effectiveness of UW and ESW, patients were randomly assigned (using a simple randomization table) into 2 groups. Patients in the UW group received UW at an intensity of 45 W and wavelength of 6 meters using an ultra-short-wave emitter (Hannover, Germany). UW was applied by placing the electrodes 2 to 3 cm to the mandibular joint, and each treatment lasted 15 min once a day for 5 in a week for 4 weeks. Patients in the ESW group were given 1000 to 1500 shocks at 8 Hz frequency using a radial extracorporeal shock wave device (EMS, Swiss). The device was connected to a 15-mm diameter applicator according to the producer’s recommendations, and patients were treated once a week for 4 weeks.

Outcome assessment

Before and 4 weeks after the therapies, patients were assessed for pain using the visual analog scale (VAS), which uses a 10-cm ruler with left and right sides corresponding to no pain (0) and unbearable pain [13], respectively. The assessing physicians were blinded to the patients. The participants were asked to move the marker to indicate their pain level. Pain-free MMO was measured using an analog vernier caliper with a 0.05 mm precision, as previously described [14]. Participants were seated and asked to open their mouths as far as possible without pain. At the limit of mouth opening that was pain-free, the distance between the upper and lower central incisors (not considering the overbite) was determined. The temporomandibular index were assessed as described elsewhere [15,16], including mandibular movement (MM), joint noise (JN), joint press (JP), and disability index (DI).

Statistical analysis

Data are expressed as mean±standard derivation and analyzed using the Statistical Package for the Social Sciences (SPSS Inc., Chicago, IL, USA). The Wilcoxon rank test was used to compare intra-group differences for pain between before and 4 weeks after treatment, and the Mann-Whitney rank test was conducted for comparing the intergroup difference. Within-group comparisons for pain-free MMO were performed using the paired-sample t test. The independent-samples t test was used for intergroup pain comparisons between pre-treatment and 4 weeks post-treatment. A value of p<0.05 was considered statistically significant.

Results

Baseline data

Initially, 86 consecutive patients visiting the Physical and Rehabilitation Outpatient Clinic were selected for this study. Six patients refused to participate and the remaining 80 patients were randomized to receive UW or ESW treatments. No participants dropped out during the study. Basic characteristics of the patients are summarized in Table 1, and there was no difference in those characteristics between the 2 groups, including sex, age, duration of disease, VAS, MMO, MM, JN, JP, and DI.

VAS and MMO

Before the therapies, there was no difference in VAS and MMO between the 2 groups (p>0.05). Four weeks after the therapies, VAS and MMO were better than before the therapies (p=0.004 and 0.012, respectively, Table 2). In addition, the improvements were greater in the ESW group than in the UW group (p=0.014 and 0.013, respectively, Table 2) after the treatments.

Table 2.

Visual analog scale score and maximum month opening before and after.

Variables		Extracorporeal shock wave	Ultrashort wave	P
VAS	Before	3.40±1.93	3.10±2.02	0.63
	After	2.00±1.08	0.95±1.15	0.004
P		0.007	0.0001
MMO (cm)	Before	1.73±0.38	1.61±0.53	0.427
	After	2.03±0.33	3.23±0.37	0.012
P		0.011	0.013

Fricton index

Before the therapies, the Fricton indexes measured as MM, JN, JP, and DI were similar between the 2 groups (p=0.012, 0.015, 0.012, and 0.021, respectively, Table 3). After the treatments, these parameters were better than before the treatments (p<0.05, Table 3). Furthermore, these indexes were better in the ESW than in the UW group (Table 3) after the treatments.

Table 3.

Fricton indexes before and after therapy.

Variables		Extracorporeal shock wave (n=40)	Ultrashort wave (n=40)	P
MM	Before	5.56±0.60	5.55±0.55	0.94
	After	2.41±0.52	1.79±0.46	0.012
P		0.013	0.023
JN	Before	3.10±0.63	3.11±0.68	0.92
	After	2.27±0.71	1.45±0.59	0.015
P		0.034	0.012
JP	Before	3.88±0.83	3.93±0.87	0.40
	After	2.59±0.59	1.55±0.73	0.012
P		0.032	0.018
DI	Before	8.81±0.80	8.80±0.72	0.98
	After	4.79±0.67	3.30±0.51	0.021
P		0.023	0.021

Discussion

TMD is a collective term for clinical disorders in the masticatory musculature, TMJs, and associated structures [17]. This dysfunction leads to impairments in chewing, swallowing, and speaking. The main signs include pain, joint noises, reduced range of motion, and mandibular deviation. Therefore, TMD patients should be treated from multiple perspectives, including pharmacological and physical treatment [18,19]. Although a number of methods are available [20], proper selection of treatment method is very important for better treatment of the disease [6,19]. The patients in our study had relatively long TMD duration, and were slow in response to UW therapy, which requires longer treatment time and often results in poor patient compliance.

Recently, ESW has become increasingly popular as a physical treatment for a number of disorders. Our comparison showed that ESW is more effective than UW in treating TMD, leading to better VAS, MMO, and Fricton indexes after treatment. ESW is a mechanical (acoustic) wave with a low-frequency pressure that propagates rapidly in space [21,22]. It is non-invasive and results in rapid patient response. Earlier studies showed that during the occurrence and development of TMD, cytokines such as IL-1, IL-6, and TNF-α are involved in inflammation of the synovium, leading to destruction of articular cartilage and excessive apoptosis of chondrocytes in the soft tissue of bone and joints as a result of increased NO content and the imbalance of local metabolism in the joint [23–25]. ESW can reduce NO content in the articular fluid, reduce the apoptosis of chondrocytes, promote the proliferation of articular cartilage and the repair of cartilage defects, and inhibit the secretion of inflammatory cytokines [26,27].

We found that the VAS scores of both groups declined after therapy, and the extent of decrease was greater in the ESW group than in the UW group. Furthermore, the pain-free MMO in both groups was improved after therapy, and the improvement was larger in the ESW group than in the UW group, demonstrating that ESW is better than UW for TMD treatment. The beneficial effect of shock waves is associated with micro-destruction [28,29], which is likely to result in micro-tears of non-vascularized or scantily vascularized tissues, and thus stimulate the revascularization by the local release of growth factors and mobilization of stem cells, leading to increased blood supply to the tissue [28,30]. Previous studies have suggested that these mechanisms also play a role in reducing the muscle tone for spasticity [31]. In addition, ESW may generate an analgesic effect during the treatment that blocks the activation and transmission of pain signals by non-invasive stimulation of cell membranes and nerve endings [32–34], which may be related to reduced pain and increased MMO.

UW therapy also is effective in treating TMD, although not as effective as ESW in our study. It induces changeable intracellular pressure, which acts as an „internal tissue massage”, leading to changes in the nervous conductivity, raising the threshold of pain, and improving muscle relaxation. Biochemical studies showed that UW increased the enzymatic activity that accelerates metabolism and regenerative processes [35,36].

Although our study provides valuable information regarding ESW in treating TMD, there are limitations. It was a single-center study with a limited number of participants. Patients were not stratified for treatments and the follow-up time was relatively short. Further studies are needed to validate our results with more patients and stratification is needed to optimize the patient conditions for better treatment outcomes.

Conclusions

The results showed that the efficacy of both treatments is comparable and substantially decreased pain and increased MMO. ESW is more effective, with fewer treatment sessions and requiring less time and cost for patients.

Abbreviations

ESW

extracorporeal shock wave

UW

ultrashort wave

TMD

temporomandibular joint disorder

VAS

visual analog scale

MMO

maximum mouth opening

MM

mandibular movement

JN

joint noise

JP

joint press

DI

disability index