Introduction
The main symptoms of temporomandibular disorder (TMD) are temporomandibular joint clicking, pain in the temporomandibular joint and muscles of mastication, mouth opening problems, and jaw movement abnormalities [
1‐
8]. The causes of TMD are multifactorial, and anatomical abnormalities and associated functional, structural, and psychological factors have been identified [
1‐
8]. Conservative therapies in the early stages of treatment, rather than irreversible treatments such as aggressive surgery or occlusal adjustment, have recently been recommended in patients with TMD [
1‐
8]. These conservative therapies include pharmacotherapy and physical therapy; laser therapy is included within the broader category of physical therapy and is often administered in conjunction with muscle-stretching exercises [
1,
2,
6,
8,
9].
Muscle massage therapy is reported to improve blood flow and lymphatic flow, and muscle stretch therapy is reported to be effective in increasing the range of motion of the jaw [
8,
9]. Mouth opening training, such as muscle massage therapy and muscle-stretching therapy, are sometimes performed alone [
8,
9] or are often used in combination with other treatments such as dry needling [
8‐
10] or laser therapy [
6,
10‐
18].
Photobiomodulation therapy (PBMT) is a conservative type of therapy, and the irradiation delivered via PBMT is believed to have photobiomodulatory effects [
3,
6,
10,
12,
19]. It reportedly has pain-relieving effects on conditions that involve chronic pain such as TMD and dentin hypersensitivity [
1‐
3,
10‐
21]. Semiconductor lasers [
6,
10‐
21] and carbon dioxide (CO
2) lasers [
22‐
33] have both been used to elicit such effects. Among them, the CO
2 laser is used not only for surgical procedures [
23‐
25], such as incision and transpiration of tissue, but also as necessary application for tooth-extraction wounds [
26,
27] and promotion of healing of aphthous stomatitis treatment [
28‐
31]. CO
2 laser has a long wavelength and is absorbed by water, so it is considered to only have a reaction on tissue surface [
6,
22‐
30]. Furthermore, recent modalities such as the non-thermal, non-ablative CO
2 laser therapy (NACLT) or non-thermal, CO
2 laser therapy (NTCLT) have been reported to have pain relief effects on mucosal diseases such as Pemphigus vulgaris and Behcet’s disease [
31‐
33].
While almost all previously reported studies investigating PBMT for TMD have used semiconductor lasers [
1‐
3,
6,
10‐
21], very few have used CO
2 lasers [
22].
Thus, comparatively little is known about the effects of CO
2 laser–based therapy for TMD. However, there are reports that irradiation with a CO
2 laser reduces pain [
23‐
25,
28,
29,
31‐
33] and increases blood flow [
22]. Therefore, after CO
2 laser irradiation, additional muscle massage or muscle-stretching therapy may be performed [
8,
9], and the temporomandibular joint symptoms may be effectively eliminated [
3]. In addition, a method involving irradiating a laser to a trigger point has also been often used, which has been reported to have a therapeutic effect [
3,
6,
10,
11,
17].
We have been treating temporomandibular joints based on this hypothesis in Fukuoka Dental Office, and in this article, we study the effects retrospectively.
In the present study, physical therapy with a main focus on CO2 laser PBMT and mouth opening training was administered to patients with TMD symptoms, and the efficacy of the treatment was investigated.
Discussion
In TMD, wrong timing when introducing physiotherapy muscle massage therapy or muscle-stretching therapy may worsen symptoms [
8]. Furthermore, using a semiconductor laser for irradiation in patients may yield different results in patients depending on whether they are in the acute or chronic phase, and differences also exist on the maximum mouth opening capacity increase that could be achieved when comparing acute and chronic patients [
14]. Therefore, we started pharmacotherapy first with Amfenac sodium to avoid starting treatment in the acute phase.
Sprinting treatment has been reported to be effective in preventing clenching and protecting teeth and temporomandibular joints; however, the effects are not constant according to the literature [
1,
2,
8], and changes in occlusion such as open bite are feared [
2]. Therefore, sprinting treatment was not administered as part of the initial treatment. In this study, only 4 patients whose symptoms did not improve with laser treatment and mouth opening training received sprinting treatment, and the symptoms improved after the sprint was attached. Considering these cases, factors such as clenching and tooth contacting habit (TCH) are significant, and splint therapy may be effective if clenching or TCH does not improve even after patient education.
For muscle massage therapy and muscle-stretching therapy, there is a method involving extraoral and intraoral application [
8,
9]. However, in this study, as it is difficult for patients to maintain mouths opened, a method involving extraoral application was used. Considering that the CO
2 laser was of the tissue surface absorption type, irradiation was hindered in cases where hair was present, for example, when there was a trigger point in the temporal muscle. Therefore, laser irradiation was not performed on the temporal muscle, and only muscle massage therapy was performed.
Multiple clinical studies have investigated the use of tissue-penetrating semiconductor lasers [
10‐
17], and they have also been the subject of basic research reports [
18]. Clinical studies using semiconductor lasers in patients with TMD have reportedly yielded pain-relieving effects [
10‐
17], increased maximum mouth opening [
10,
14‐
17], anatomical changes including altered facial heights [
15], and increased range of motion in left and right temporomandibular joints [
16].
Peimani et al. [
18] used a rat TMD model to investigate the effects of semiconductor lasers histologically in an irradiated group and a control group. They reported that although there was a significant increase in the number of inflammatory cells 3 days after treatment initiation, after 7 days of treatment initiation, there was a significant reduction of inflammatory cells. Furthermore, arthritis had improved in the irradiated group compared with the control group. The authors concluded that the treatment had exerted anti-inflammatory effects.
There are few published reports on the effects of tissue surface absorption CO
2 lasers in patients with TMD. In the present study, we observed both pain reduction and an increase in maximum mouth opening capacity, as has been reported after semiconductor laser treatments [
11‐
17]. Makihara et al. [
22] used a Doppler flowmeter to measure vascular diameter and blood flow before and after irradiation of the temporomandibular joint with CO
2 PBMT. They reported increased vascular diameter and blood flow on the irradiated side 10 min after irradiation compared with before irradiation. They also reported an increase in blood flow compared with the contralateral side. There may have been changes in blood flow in the maxillofacial area due to the CO
2 PBMT, with muscle tension relief and pain relief effects achieved in the early stage of PBMT. These may have facilitated smooth muscle movement and efficient mouth opening training. Therefore, we believe that CO
2 PBMT and mouth opening training play a role as a conservative treatment option for TMD.
Regarding the pain relief effect of lasers, there are many and very few reports of semiconductor [
23‐
25,
28,
29] and CO
2 laser, respectively. As a CO
2 laser is mostly absorbed on the tissue surface [
22‐
33], it is not considered to cause a direct pain-relieving effect but rather to have a secondary effect, such as increased blood flow [
22]. Nevertheless, the irradiation method called NACLT or NTCLT, which also use CO
2 lasers, has been reported to have a pain-relieving effect [
31‐
33], so the possibility of analgesic relief for temporomandibular disorders cannot be ruled out.
Prior to this study, the authors exacerbated the pain of a few patients with peak pain in the acute phase when they were CO
2 laser–treated without drug administration. It was considered that this was due to hypersensitivity and increased blood flow at the time of inflammation [
6], and the nerves were pressed because the increased blood flow was promoted [
22]. For that purpose, all patients were given pharmacotherapy during the acute phase.
Moreover, the semiconductor laser can irradiate the temporal muscle region even with hair present [
23‐
25,
28,
29], but it is difficult to irradiate the same region with a CO
2 laser [
22‐
33]. This is a drawback of tissue absorption lasers such as CO
2 lasers.
In this study, there is one treatment arm which received a combination of three treatment modalities, including pharmacotherapy, stretching therapy, and laser therapy. The combination of all treatment modalities into one treatment arm precludes us from differentiating the individual effect of each [
19‐
21,
37,
38]. Moreover, we cannot rule out the placebo effect. As this study did not divide the participants into four groups (placebo [no treatment], opening training only, PBMT only, and PBMT and opening training), it was not possible to clarify the effect of each of PBMT and opening training [
3,
19‐
21,
37,
38]. Further research is needed in the future.
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