Temporomandibular joint disorder (TMJ disorder, TMD) is a disease due to an impaired jaw joint caused by a problem with the masticatory muscle, ligament, and other surrounding structures. Pain, restricted mouth opening, and joint crepitation are the main symptoms, and occlusion abnormality, restriction or asymmetry of mandibular movement, joint hypertonia, and headache may also appear. Additionally, ear symptoms, including tinnitus, hearing loss, dizziness, ear pain, muffled hearing, and dysphagia, can occur [1]. In the Korean National Health and Nutritional Examination Survey of 7,830 people aged ≥ 19 years conducted in 2009, 3.1% of the respondents had TMD, and 10.5% had TMD symptoms [2]. In TMD therapy, Western medicine uses behavioral, pharmacologic, physical, and occlusal appliance therapies [3]. Korean medicine uses acupuncture, laser acupuncture, pharmacoacupuncture, chuna manual therapy (MT), herbal medicine, exercise therapy, and Korean medicine physiotherapy. Particularly, acupuncture treatment showed an excellent level of evidence in single and parallel treatments [4]. Various clinical studies on acupuncture for TMD, including randomized-controlled trials (RCTs), are being conducted in Korea and worldwide. These studies have also been reported in systematic reviews and meta-analyses [5-20]. However, an additional review study was needed because these review studies were either not included in the China National Knowledge Infrastructure (CNKI) during the search [5,7,10,11], focused on the effectiveness of other treatments [6,19,20], utilized other treatments [8,9], or needed to be updated because they have been published several years ago [12-18]. The previous review studies investigated RCTs published until 2017 and reported that acupuncture was significantly effective for TMD [5,8]. Therefore, we decided to include RCTs published between January 2018 and January 2023 to avoid overlapping with existing review studies.

The present systematic review and meta-analysis utilized data from RCTs recently published, specifically within 5 years ago, in Korean (OASIS, Koreantk, KISS, NDSL, RISS, KMBASE, and KoreaMed) and international databases (PubMed, Cochrane, Embase, and CNKI) to confirm the effectiveness of acupuncture and electroacupuncture treatment for TMD.

1. Search strategy

In this study, we searched 11 online databases, including CNKI, PubMed, Cochrane Library, EMBASE, and Korean databases (OASIS, Koreantk, KISS, Scienceon [NDSL], RISS, KMBASE, and KoreaMed). Based on the “Medical Subject Headings (MeSH),” the search term related to TMD (“Temporomandibular Joint Disorder,” “Temporomandibular Joint Syndrome,” “Temporomandibular Joint Dysfunction,” “Craniomandibular Disorders,” “Temporomandibular Arthritis,” and “Costen’s Syndrome”) and acupuncture (“Acupuncture,” “Acupuncture Therapy,” “Acupuncture Points,” “Dry Needling,” “Needle,” and “Electroacupuncture”) were combined. Searching was performed by translating into the language of the corresponding country according to each database. The search strategy details are described in Appendix 1.

2. Eligibility criteria

This study targeted RCTs on acupuncture and electroacupuncture treatment for patients with TMD published in Korea and overseas and selected studies published between January 2018 and January 2023. Studies utilizing acupuncture for the treatment or control group, studies using acupuncture combined with the treatment received by the control group for the treatment group, and studies using acupuncture for the treatment group and using sham acupuncture for the control group were selected. The patients’ age, sex, and disease duration were not restricted, nor were the acupuncture treatment sites or acupoint sites.

The present review study aimed to confirm the effectiveness of acupuncture treatment and electroacupuncture on TMD. Studies only using acupuncture needling or electroacupuncture treatment, excluding other acupuncture techniques, such as warm acupuncture, acupotomy, and auricular acupuncture, were included. Moreover, studies utilizing 2 or more combined treatments, including acupuncture in the treatment group, were excluded, and studies performing acupuncture treatment in both treatment and control groups were also excluded. Studies without full-text accessibility, articles, clinical trials, case studies, literature review, systematic reviews, and non-human participant research were also excluded.

3. Selecting article and data extraction

Studies were selected based on the above inclusion and exclusion criteria. After excluding duplicate studies, an eligible study was selected by checking the title and abstract. Then, through the full text, information about the participants, treatment plan of the treatment and control groups, outcome measurement, and treatment results were extracted. Furthermore, according to the standards for reporting interventions in clinical trials of acupuncture (STRICTA) guidelines [21], data on the period and frequency of treatment, acupoints, needling time retention, needling details, and needle types were extracted.

4. Risk of bias assessment

Cochrane’s risk of bias (RoB) tool [22] was used to evaluate the RoB in the included studies. Each item was rated as high, low, or unclear according to the RoB degree. A discussion with a third researcher was held if there was a difference of opinion.

5. Data synthesis and analysis

After summarizing the outcome measures capable of quantitative analysis from the included studies, a meta-analysis was performed using the meta package of the R Foundation for Statistical Computing (R version 4.1.1). Mean difference or standardized mean difference was used for continuous data, and risk ratio was used for dichotomous data. Higgin’s I-squared (I²) statistic was performed to confirm the heterogeneity between studies. If I² statistic was 0–40%, heterogeneity between studies would be considered as low, 30–60% as moderate, 50–90% as substantial, and 75–100% as high [23]. The random-effects model of a 95% confidence interval (CI) was used, and the forest plot was adopted as the resulting model.

1. Study selection

Altogether, 718 studies were searched across 11 Korean and international online databases, including 83 in PubMed, 120 in the Cochrane Library, 137 in EMBASE, 136 in CNKI, and 242 in 7 Korean online databases. Moreover, 19 studies were added from previous systematic studies. After excluding 217 duplicate studies from the search, the titles and abstracts of 520 studies were checked, and 229 studies were excluded, including 50 studies not relevant to acupuncture treatment for TMD, 12 studies not utilizing a human model, 136 studies using improper treatment, and 31 studies that were not clinical studies. The full texts of the remaining 291 studies were checked, and 273 studies were excluded, including 46 without full texts, 74 case studies, 33 systematic reviews, 27 literature reviews, 37 articles, 2 protocol studies, and 54 studies not meeting the criteria. Of the 18 studies [24-41] that matched the criteria, 14 were used to conduct a meta-analysis. A Preferred Reporting Item for Systematic Reviews and Meta-Analyses (PRISMA) flow chart was used to schematize the process of selecting studies and data extraction (Fig. 1). The characteristics of the selected studies are summarized in Table 1.

Table 1 . Characteristics of included studies.

First author (y)	Sample size (TG/CG) (included→analyzed)	TG/CG sex and mean age (mean ± SD)	TG/CG disease duration (mean ± SD)	Treatment intervention	Control intervention	Outcome measure	Result summary	Adverse event
Sū (2022) [24]	72 (36/36)→70 (35/35)	M/F = 16/19 32.00 (P25: 23.00–P75: 39.00, SD not reported) M/F = 13/22 29.00 (P25: 22.00–P75: 39.00, SD not reported)	1.40 (P25: 0.80–P75: 5.43) (mo) 2.20 (P25: 0.37–P75: 12.20) (mo)	ATx + CT	PT + MT	1) Effective rate 2) Recurrence rate 3) VAS 4) Fricton index (DI, PI, and CMI) 5) sEMG (RMS, MF)	1)–5) TG > CG (p < 0.05)	None
Yang (2021) [25]	63 (32/31)→60 (30/30)	M/F = 12/18 (34.50 ± 7.36) M/F = 13/17 (31.37 ± 7.18)	4.63 ± 1.07 (mo) 4.77 ± 1.01 (mo)	ATx + CT	Exercise therapy	1) VAS 2) Helkimo score 3) Effective rate	1) TG > CG (p = 0.042) 2) TG > CG (p = 0.036) 3) TG > CG (p = 0.006)	NR
Wú (2021) [26]	66 (33/33)→63 (32/31)	M/F = 6/26 (32.47 ± 12.57) M/F = 7/24 (34.45 ± 15.41)	24.66 ± 12.92 (d) 26.81 ± 11.93 (d)	Atx + CT	PT + MT	1) Effective rate (TMD dysfunction, anxiety, and depression) 2) VAS 3) Fricton index (DI, PI, CMI, MM, JN, and JP) 4) SAS, SDS	1)–4) TG > CG (p < 0.05)	NR
Wāng (2021) [27]	60 (30/30)→58 (29/29)	M/F = 5/24 (39.24 ± 12.97) M/F = 6/23 (43.91 ± 16.34)	8.48 ± 5.88 (d) 8.28 ± 6.84 (d)	E-ATx	W-med (ointment)	1) Fricton index (MM, JN, JP, MP, DI, PI, and CMI) 2) Effective rate	1) TG > CG (p < 0.05) 2) TG > CG (p < 0.05)	NR
Xuē (2020) [28]	68 (34/34)→64 (33/31)	M/F = 12/21 (34.00 ± 8.88) M/F = 10/21 (31.77 ± 9.78)	25.09 ± 12.75 (d) 26.26 ± 9.57 (d)	ATx + CT	MT	1) Effective rate 2) VAS 3) Fricton index (DI, PI, CMI, MM, JN, and JP)	1) TG > CG (p < 0.05) 2) TG > CG (p < 0.05) 3) TG > CG (p < 0.05)	NR
Wang (2020) [29]	60 (30/30)→60 (30/30)	M/F = 17/13 (29.62 ± 13.67) M/F = 14/16 (33.03 ± 18.05)	3.59 ± 1.82 (mo) 3.25 ± 1.46 (mo)	ATx + CT	W-med (ibuprofen)	1) MMO 2) VAS 3) Recurrence rate 4) Effective rate	1)–4) TG > CG (p < 0.05)	NR
Chén (2019) [30]	48 (24/24)→48 (24/24)	M/F = 16/8 (34.41 ± 2.22) M/F = 10/14 (34.35 ± 2.27)	6.93 ± 1.04 (mo) 6.84 ± 1.07 (mo)	ATx + CT	W-med (ibuprofen)	1) VAS 2) MMO 3) Effective rate	1) TG > CG (p < 0.05) 2) TG > CG (p < 0.05) 3) TG > CG (p = 0.001)	NR
Dīng (2019) [31]	118 (82 [42 + 40]/36)→ 112 (80 [42 + 38]/32)	TG1: M/F = 14/28 (35.24 ± 9.54) TG2: M/F = 18/20 (36.18 ± 10.15) CG: M/F = 12/20 (36.81 ± 7.58)	3.55 ± 0.80 (wk) 3.61 ± 0.68 (wk) 3.72 ± 0.58 (wk)	1) ATx + CT 2) ATx	MT	1) VAS 2) Clicking level of joint 3) MMO 4) Fricton index (DI, PI, and CMI) 5) Effective rate	1) TG1, TG2 > CG (p < 0.01), TG1 = TG2 (p > 0.05) 2) TG1, CG > TG2 (p < 0.01), TG1 = CG (p > 0.05) 3) TG = TG2 = CG (p > 0.05) 4) Fricton index (DI): TG1, CG > TG2 (p < 0.01), TG = CG (p > 0.05) Fricton index (PI): TG1, TG2 > CG (p < 0.01), TG1 = TG2 (p > 0.05) Fricton index (CMI): TG1 > TG2 (p < 0.01), TG1 > CG (p < 0.05), TG2 = CG (p > 0.05) 5) TG1 > CG > TG2	NR
Yè (2019) [32]	40 (20/20)→40 (20/20)	M/F = 9/11 (44.05 ± 12.40) M/F = 10/10 (42.05 ± 10.88)	3.50 ± 1.70 (wk) 3.55 ± 1.76 (wk)	E-ATx + CT	PT	1) VAS 2) Painless mouth opening range	1) TG > CG (p < 0.01) 2) TG > CG (p < 0.01)	NR
Chén (2018) [33]	56 (28/28)→56 (28/28)	M/F = 13/15 (33.23 ± 9.23) M/F = 12/16 (32.57 ± 10.81)	37.43 ± 25.78 (d) 34.55 ± 28.59 (d)	PT	ATx	1) VAS 2) Fricton index (DI, PI, and CMI)	1) TG > CG (p < 0.05) 2) TG > CG (p < 0.05)	NR
Hú (2018) [34]	69 (35/34)→69 (35/34)	M/F = 13/22, min: 15–max: 65 (mean & SD not reported) M/F = 15/19, min: 16–max: 64 (mean & SD not reported)	Min: 1 wk–max: 4 y (mean & SD not reported) Min: 10 d–max: 3.5 y (mean & SD not reported)	E-ATx + CT	PT	1) Effective rate 2) Recurrence rate	1) TG > CG (p < 0.05) 2) TG > CG (p < 0.05)	NR
Dib-Zakkour (2022) [35]	36 (18/18)→36 (18/18)	Min: 18–max: 40 (sex and mean & SD of age not reported, not divided between TG & CG)	NR	ATx	Sham Atx	1) EMG activity (muscle activity value of the masseter muscle) 2) Mouth opening value 3) Symmetry of opening and closing mouth 4) Time needed to achieve maximum force 5) Posterior disclusion time 6) Articular and facial pain 7) Articular sound	TG > CG	NR
Peixoto (2021) [36]	81 (18/63 [20 + 19 + 24])→60 (15/45 [15 + 15 + 15])	Min: 18–max: 65 (sex and mean & SD of age not reported, not divided between TG & CG)	NR	ATx (scalp ATx)	1) OS 2) PT + MT 3) Counseling	1) TMD diagnoses 2) VAS 3) PSQI 4) WHOQOL-Bref	1) TG, CG1, CG2 > CG3 2) TG, CG1, CG2 > CG3 3) CG1, CG2 > TG, CG3 4) CG1, CG2 > TG, CG3	NR
Aksu (2019) [37]	63 (42 [20 + 22]/21)→63 (42 [20 + 22]/21)	M/F = 10/53 (39.4 ± 41.9), min: 18–max: 65 (not divided between TG & CG)	NR	1) ATx + CT 2) TrP injection + CT	Exercise + protection training	1) VAS 2) Mouth opening level 3) Functional limitation 4) Facial pain 5) Tender points of facial and neck muscle (palpation, algometry method)	TG1 = TG2 = CG	NR
Lopez-Martos (2018) [38]	60 (40 [20 + 20]/20)→60 (40 [20 + 20]/20)	TG1: M/F = 5/15; 38.5 (18–57, SD not reported) TG2: M/F = 2/18; 36 (19–58, SD not reported) CG: M/F = 1/19; 42 (25–62, SD not reported)	NR	1) PNE 2) ATx	Sham ATx	1) VAS (pain at rest, pain on mastication) 2) MMO 3) TMJ functionality test (100 point test) 4) Tolerance to treatment and subjective evaluation (5 point test)	TG1, TG2 > CG TG1 > TG2	Self-limiting hematoma (one patient in the PNE group)
Özden (2020) [39]	60 (40 [20 + 20]/20)→60 (40 [20 + 20]/20)	Min: 18–max: 65 (age was not reported) TG1: M/F = 9/11 TG2: M/F = 7/13 CG: M/F = 13/7	NR	1) Superficial ATx 2) Deep ATx	None	1) PPT 2) VAS 3) MMO	1) TG1, TG2 > CG 2) TG1, TG2 > CG TG1 > TG2 3) TG1 = TG2 = CG	None
Dalewski (2019) [40]	90 (60 [30 + 30]/30)→90 (60 [30 + 30]/30)	TG1: M/F = 6/24; 31.2 (min: 18–max: 56, SD not reported) TG2: M/F = 7/23; 31.3 (min: 21–max: 65, SD not reported) CG: M/F = 5/25; 28.7 (min: 18–max: 52, SD not reported)	NR	1) NSAID (nimesulide) + CT 2) ATx + CT	OS	1) VAS 2) SPAQ	TG1 > CG TG2 = CG	NR
Kütük (2019) [41]	40 (20/20)→40 (20/20)	M/F = 5/15 (34.6 ± 9.3) M/F = 6/14 (33.0 ± 6.8)	NR	ATx	Injection (abobotulinum toxin-A)	1) VAS (pain at rest, pain during chewing) 2) Crepitation 3) MMO 4) Functional limitation 5) Jaw strength 6) Muscle spasm 7) Protrusion angle	1) VAS (pain at rest): TG > CG (p = 0.048) VAS (pain during che wing): TG = CG (p = 0.708) 2) TG = CG (p = 1.000) 3) TG = CG (p = 0.436) 4) TG = CG (p = 0.632) 5) TG = CG (p = 0.625) 6) TG = CG (p = 0.054) 7) Protrusion angle: TG = CG (p = 0.177) Protrusion angle (right): TG > CG (p = 0.009) Protrusion angle (left): TG > CG (p = 0.002)	NR

M, male; F, female; TG, treatment group; SD, standard deviation; CG, control group; CT, control treatment; PT, physical therapy; W-med, Western medicine; MT, manual therapy; VAS, visual analog scale; DI, dysfunction index; PI, palpation index; CMI, craniomandibular index; sEMG, surface electromyography; NSAID, nonsteroidal anti-inflammatory drug; RMS, root mean square; MF, median frequency; MM, mandibular movement; JN, joint noise; JP, joint palpation; SAS, self-rating anxiety scale; SDS, self-rating depression scale; NR, not reported; MP, muscle palpation; MMO, maximum mouth opening; OS, occlusal splint; EMG, electromyography; PSQI, Pittsburgh sleep quality index; WHOQOL-Bref, World Health Organization quality of life; PPT, pressure pain threshold; PNE, percutaneous needle electrolysis; SPAQ, sleep and pain activity questionnaire; TrP, trigger point; ATx, acupuncture treatment; E-ATx, electroacupuncture treatment..

Figure 1. A flow diagram of study selection and data extraction according to the Preferred Reporting Item for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. TMD, temporomandibular joint disorder.

2. Characteristics of the selected studies

Four of the 18 studies were published in 2018, 6 in 2019, 2 in 2020, 4 in 2021, and 2 in 2022. Eleven studies were conducted in China, 3 in Turkey, and 1 each in Lithuania, Brazil, Spain, and Poland. Eleven studies were written in Chinese, and 7 were written in English.

Altogether, 1,150 patients participated in the RCTs, of which 611 and 498 were allocated to the treatment and control groups, respectively, and evaluated. Of the 7 studies, 41 patients were dropped. The study’s sample size ranged from a minimum of 36 to a maximum of 112 participants. 4 studies had < 50 participants, 13 had 50–100 participants, and 1 had > 100 participants. The sample size of the treatment group was distributed from 15 to 80, and the control group was distributed from 18 to 45. The participating patients included 349 males and 664 females, excluding 96 who participated in 2 studies that did not report sex data.

The participants’ age was measured in 14 of 18 studies, and the average and standard deviation of the age were calculated in 11 of these studies. The treatment group’s age ranged from 29.62 ± 13.67 to 44.05 ± 12.40 years, whereas the control group’s age ranged from 28.7 to 43.91 ± 16.34 years. For the duration of disease, 10 studies calculated for the average and standard deviation values. The treatment group’s disease duration ranged from 8.48 ± 5.8 (days) to 6.93 ± 1.04 (months), whereas the control group’s disease duration ranged from 8.28 ± 6.84 (days) to 6.84 ± 1.07 (months).

Regarding the treatment groups, 11 were parallel treatment groups, including the treatment of the control group, and 7 were single treatment groups. 3 groups received electroacupuncture treatment, 1 received scalp acupuncture, and 14 received acupuncture utilizing acupoints and trigger points (TrP).

In the control groups, 4 received MT or exercise therapy, which was the most frequent treatment. 3 received physical therapy (PT), 3 received MT combined with PT, 2 received Western medicine, 2 received occlusal splints, 2 received sham acupuncture, 1 received Western ointment, 1 received a botulinum toxin injection, 1 received counseling, and 1 received no treatment.

Of the 18 studies, 5 were 3-arm parallel trials with 1 control and 2 treatment groups, 1 was a 4-arm parallel trial with 1 treatment and 3 control groups, and the other 12 were 2-arm parallel trials.

Furthermore, Chen et al.’s [33] study was conducted with PT for the treatment group and acupuncture for the control group.

At least 2 to 7 evaluation indexes were used per study. Among them, the visual analog scale (VAS) was the most common evaluation index used (16 out of 18 studies), followed by 9 studies utilizing the efficacy rate, 6 using Fricton index, 6 using maximum mouth opening, 3 utilizing recurrence rate, 2 using electromyography, and 2 using functional limitation. The other evaluation indexes were used once in the study.

In 18 studies, the treatment effects of 43 patient groups, including the treatment and control groups, were analyzed.

In the 11 studies with parallel treatment groups receiving acupuncture (ATx) or electroacupuncture (E-ATx) combined with the treatment for the control groups, 8 studies reported that the evaluation index of the treatment and control groups was improved compared to that before treatment, and the improvement in the treatment group was statistically significant compared to that of the control group [24-26,28-30,32,34].

Ding [31] reported that the parallel treatment, single acupuncture treatment, and control groups had improved evaluation index after treatment as compared to that before treatment. Regarding VAS, a statistically significant difference was observed after treatment between the parallel treatment and single treatment groups and control group, and no statistically significant difference was observed between the 2 treatment groups. Regarding the joint’s clicking level, a statistically significant difference was observed after treatment between the parallel treatment and control groups and the single treatment group, and no statistically significant difference was observed between the 2 treatment groups. In terms of maximum mouth opening, no statistically significant difference was observed among all treatment groups. In the dysfunction index of the Fricton index, a statistically significant difference was observed after treatment between the parallel treatment and control groups and single treatment group, and no statistically significant difference was observed between the 2 treatment groups. In the palpation index of the Fricton index, a statistically significant difference was observed after treatment between the parallel treatment and single treatment groups and the control group, and no statistically significant difference was observed between the 2 treatment groups. In the craniomandibular index of the Fricton index, a statistically significant difference was observed after treatment between the parallel treatment group and single treatment and control groups. The treatment’s efficacy rate was in the following order: parallel treatment group > control group > single treatment group.

Aksu et al. [37] reported that the evaluation index of pain and functional limitation of the treatment and control groups were improved after treatment as compared to that before treatment. However, no significant difference was observed between the 2 groups. Furthermore, exercise and protection training performed by both groups were more effective as compared to the invasive methods.

Dalewski et al. [40] showed that the parallel treatment group receiving nonsteroidal anti-inflammatory drugs (NSAIDs) and occlusal appliances showed statistically significant effects than the control group receiving occlusal appliances only. Moreover, the parallel treatment group receiving acupuncture and occlusal appliance and the control group showed no statistically significant difference in the evaluation index of pain and quality of life.

In the 7 studies with single treatment groups receiving ATx or E-ATx, 1 study reported that the evaluation index of the treatment and control groups improved as compared to that before treatment, and the improvement in the treatment group was statistically significantly different as compared to that of the control group [27]. In 1 study with the control group receiving ATx, the treatment group showed statistically significant improvement than the control group [33].

Dib-Zakkour et al. [35] reported that acupuncture treatment significantly reduced facial pain and muscle activity tension, and changes in the static position and trajectory of the jaw joint movement were observed via a digital occlusion analysis. Additionally, the asymmetry of the jaw joint arch was reduced during mouth opening and closing, and maximum mouth opening was increased.

Peixoto et al. [36] reported that scalp acupuncture reduced short-term pain intensity for the treatment group; however, it had no effect in improving the quality of life and sleep (PSQI, WHOQOL-Bref), as compared to the control group receiving an occlusal splint as well as MT and PT.

Lopez-Martos et al. [38] demonstrated that the acupuncture and percutaneous needle electrolysis (PNE) treatment groups statistically significantly differ in pain relief and maximum interincisal opening than the sham acupuncture group. Additionally, the PNE group experienced treatment effects more quickly than the ATx group.

Özden et al. [39] showed that the evaluation index of VAS and pressure pain threshold (PPT) scores at 3 and 6 weeks of superficial dry needling (SDN) and deep dry needling (DDN) was significantly improved as compared to that before treatment . However, the evaluation index at 3 and 6 weeks after treatment showed no significant difference between the 2 treatment groups. For maximum mouth opening, no significant difference was observed at 3 and 6 weeks after treatment. SDN significantly reduced pain as compared to DDN when the pain VAS scores were compared.

Kütük et al. [41] showed that when comparing the evaluation index at 6 weeks after treatment between the treatment groups injected with botulinum toxin and acupuncture, statistically significant differences were observed in VAS (pain at rest) score, but the lateral protrusion angle in the acupuncture group and other evaluation indexes showed no significant differences.

Lopez-Martos et al. [38] showed that 1 patient in the PNE group had a self-limiting hematoma, and 2 studies reported that no adverse events were observed. Other 15 studies did not report adverse events.

3. Details of acupuncture interventions

Details of acupuncture interventions are described in Table 2.

Table 2 . Details of acupuncture and electroacupuncture interventions.

First author (y)	Treatment period	Treatment frequency	Number of needle insertion	Name of acupoints used	Depth of insertion	Response sought	Needle stimulation	Retention time	Needle type
Sū (2022) [24]	3 wk	3×/wk	8 sites	ST7 (Bi), SI19 (Uni, P), GB3 (Uni, P), ST6 (Uni, P), TE17 (Uni, P), and ST36 (Bi)	0.3–0.5 cun (ST6, ST7) 0.5–1.0 cun (SI19, GB3, TE17) 1.0–1.2 cun (ST36)	De qi	Manual (10 min, “even reinforcing-reducing method”)	20 min	0.30 × 40 mm
Yang (2021) [25]	4 wk	6×/wk	NR	TrP (masseter, temporalis, platysma, medial pterygoid, and sternocleidomastoid muscles)	NR	Muscle twitch response	NR	NR	0.25 × 25 mm
Wú (2021) [26]	3 wk	3×/wk	6 sites	ST7 (Bi), GB3 (Uni, P), ST6 (Uni, P), SI19 (Uni, P), and TE17 (Uni, P)	0.5–1.0 cun	De qi	Manual (10 min, “even reinforcing-reducing method”)	20 min	0.30 × 40 mm
Wāng (2021) [27]	2 wk	5×/wk	4 sites	ST7 (Uni, P), ST6 (Uni, P), SI19 (Uni, P), LI4 (Uni, P), and Ashi-point	0.5–1.0 cun	Soreness and distension	Manual, electrical (“even reinforcing-reducing method,” electro-stimulate ST7 and ST6)	20 min	0.30 × 40 mm
Xuē (2020) [28]	4 wk	3×/wk	2 sites	ST7 (Bi)	1.0 cun	Soreness, tingling, distension, and heavy feeling	Manual (5 min, “even reinforcing-reducing method”)	20 min	0.30 × 40 mm
Wang (2020) [29]	2 wk	7×/wk	8 sites	ST6 (Uni, P), ST7 (Uni, P), GB2 (Uni, P), TE17 (Uni, P), EX-HN5 (Uni, P), SI18 (Uni, P), LI20 (Uni, O), and LI4 (Uni, O)	NR	De qi	Manual (“even reinforcing-reducing method,” “reducing twirling method,” Simultaneously, open and close the patient mouth during acupuncture)	30 min	1.5 cun
Chén (2019) [30]	2 wk	6×/wk	7 sites	ST7 (Uni, P), ST6 (Uni, P), TE17 (Uni, P), GB2 (Uni, P), EX-HN5 (Uni, P), SI18 (Uni, P), and LI4 (Uni, O)	NR	De qi	Manual (“even reinforcing-reducing method,” “reducing twirling method,” simultaneously, open and close the patient mouth during acupuncture)	30 min	1.5 cun
Dīng (2019) [31]	2–4 wk	3×/wk	7 sites	GB3 (Uni, P), ST6 (Uni, P), ST7 (Uni, P), SI18 (Uni, P), SI19 (Uni, P), TE17 (Uni, P), and LI4 (Uni, P)	20 mm	De qi	Manual (10 min, “lifting–thrusting method,” “twirling method,” “even reinforcing-reducing method”)	30 min	0.30 × 40 mm
Yè (2019) [32]	2 wk	5×/wk	5 sites	SI19 (Uni, P), ST7 (Uni, P), ST6 (Uni, P), LI4 (Uni, P), ST36 (Uni, P) (if liver and kidney deficiency, plus KI3, and BL18)	NR	De qi	Electrical (electro-stimulate ST7 and ST6)	30 min	0.25 × 25 mm
Chén (2018) [33]	4 wk	3×/wk	3 sites	SI19 (Uni, P), ST7 (Uni, P), ST6 (Uni, P)	NR	De qi	Manual (“even reinforcing-reducing method”)	30 min	1.5 cun, 40 mm
Hú (2018) [34]	2 wk	7×/wk	8 sites	SI19 (Uni, P), TE17 (Uni, P), ST7 (Uni, P), ST6 (Uni, P), LI4 (Bi), GB34 (Bi), Ashi-point	NR	De qi	Manual, Electrical (“lifting–thrusting method,” “reinforcing twirling method,” “reducing twirling method,” “even reinforcing-reducing method,” Electro-stimulate [9 V, 1.5 mA, 1.45 Hz] ST7 and SI19)	30 min	0.25 × 25 mm, 0.25 × 40 mm
Dib-Zakkour (2022) [35]	NR	NR	NR	TrP (masseter muscle)	NR	Local spasm response	NR	10 min	0.30 × 30 mm
Peixoto (2021) [36]	4 wk	2×/wk	8 sites	GV20 (Uni), GV21 (Uni), GV22 (Uni), GV24 (Uni), The lower 2/5 of the motor and sensory area (Bi)	NR	NR	Manual (rotational movements while the patient performed 6 cycles of diaphragmatic breathing)	30 min	0.25 × 30 mm
Aksu (2019) [37]	3 wk	2×/wk	NR	TrP (masseter and lateral pterygoid muscles)	NR	NR	Manual (needle was turned around itself once in 5 min)	20 min	NR
Lopez-Martos (2018) [38]	3 wk	1×/wk	NR	TrP (lateral pterygoid muscle)	NR	Local twitch response	NR	NR	0.25 × 40 mm
Özden (2020) [39]	3 wk	1×/wk	NR	TrP (masseter muscle)	5 mm (SDN) 10 mm (DDN)	NR	Manual (immediately after immersion, the needle was rotated clockwise, and after 10 min, rotated again)	20 min	0.25 × 25 mm
Dalewski (2019) [40]	2 wk	1×/wk	5 sites	TrP (similar acupuncture points: SI19, ST7, ST6, ST5, and SI18)	NR	NR	NR	30 min	0.6 × 13 mm
Kütük (2019) [41]	6 wk	NR	NR	TrP	NR	NR	Manual (the needle was inserted into the muscle, and the same point was needled rapidly 8 to 10 times)	NR	38 mm long needle

Bi, bilateral; Uni, unilateral; P, painful site; O, opposite site; NR, not reported; TrP, trigger point; SDN, superficial dry needling; DDN, deep dry needling..

For acupuncture therapy, the most common duration of therapy was 2 weeks in 6 studies, 3 weeks in 5 studies, 4 weeks in 4 studies, 6 weeks in 1 study, and 2–4 weeks in 1 study. 1 research study also failed to provide information on treatment duration.

In 5 studies, treatment was frequently conducted 3 times per week; 4 studies, once per week; 2 studies, 7 times per week (every day); 2 studies, 5 times per week; 2 studies, 6 times per week; and 1 study, twice per week. 2 studies did not report the frequency of treatment.

The most commonly used acupoint for TMD was ST7 in 10 studies, ST6 in 9 studies, SI19 in 7 studies, LI4 in 6 studies, TE17 in 6 studies, SI18 and GB3 in 3 studies, and ST36, GB2, and EX-HN5 in 2 studies. LI20, KI3, BL18, and GB34 were also used once in each study. 2 studies reported using Ashi points during the treatment. GV20, GV21, GV22, and GV24 of the Governor Vessel, lower 2/5 of the motor area, and Jiao Shunfa sensory area were used as treatment acupoints in Peixoto et al.’s [36] study using scalp acupuncture. 7 studies reported that acupuncture was performed on the muscle TrP.

4 studies inserted needles into a depth of 0.5–1.0 cun, 1 study into a depth of 20 mm, and 1 study into a depth of 5 mm for SDN and 10 mm for DDN.

8 studies inserted a needle for acupuncture until “de qi” was felt, 3 inserted needles into TrP until the muscle twitch response was observed, and 2 inserted needles until the patient reported soreness, tingling, distension, and heavy feeling. Peixoto et al. [36] reported that a needle was inserted into the scalp until resistance was felt.

For manual stimulation of acupuncture, 9 studies used the even reinforcing-reducing method, 4 used the twirling method, 2 used the lifting–thrusting method, 3 used a rotating needle for stimulation, and 1 used rapidly needling for stimulation.

Among the 3 electroacupuncture studies, 2 connected electrodes to ST6–ST7 and 1 connected to ST7–SI19. For the voltage, current, and frequency of the electroacupuncture, 3 studies reported that it was performed with 9 V, 1.5 mA, 1.45 Hz, a longitudinal wave, and a continuous wave of low frequency, respectively.

The acupuncture retention time was 30 minutes in 8 studies, 20 minutes in 6 studies, and 10 minutes in 1 study. 3 studies did not report the retention time.

In studies involving acupuncture needles, 5 studies used 0.30 × 40 mm needles, 4 used 0.25 × 25 mm needles, 3 used 1.5 cun length needles, 2 utilized 0.25 × 40 mm needles, and 0.25 × 30 mm, 0.30 × 30 mm, 0.6 × 13 mm, 38 mm without diameter described were used once for each study. One study did not report the type of acupuncture needle.

4. Risk of bias assessment

The RoB was evaluated using Cochrane’s RoB tool for the 18 selected RCT studies. The graph and summary of the RoB details are shown in Figs. 2 and 3.

Figure 2. Risk of bias graph of the included studies.

Figure 3. Risk of bias summary of the included studies. +, low risk of bias; −, high risk of bias; ?, unclear bias.

Eleven studies were assessed as having a “low risk,” 6 of which used software to generate random numbers, and 5 studies used random number tables. Two studies were classified as having a “high risk” because they used the treatment order or arrival order as the randomization method. The other 5 studies utilized random allocation; however, the specific method was not reported. These studies were classified as having an “unclear risk.”

Six studies using software to generate random numbers were rated as having a “low risk” because the allocation order was concealed. Seven studies, 5 of which used random number tables, and 2 of which used the treatment order or arrival order as the randomization method, were rated as having a “high risk” because the allocation order was not concealed. The allocation concealment in the other 5 studies was not reported and was assessed as having an “unclear risk.”

In 2 studies, a double-blind trial was performed for the researcher and participants; therefore, they were considered as having a “low risk.” In the remaining 16 studies, blinding of the researcher and participants was not mentioned. Furthermore, blinding the researcher and participants was difficult due to the characteristic of acupuncture treatment, as it is considered a “high risk” procedure.

Among the 4 studies, 2 reported that the researcher was blinded when analyzing the results, whereas the other 2 studies reported that a double-blind trial was conducted for both the researcher and participants, resulting in a “low risk” assessment. In the remaining 14 studies, the researcher was not blinded when evaluating the results; therefore, they were considered as having an “unclear risk.”

Among the 12 studies, 4 studies reporting the causes of missing values and 8 studies without missing values were assessed as having a “low risk.” Of the 5 studies, 3 studies not reporting the reasons for missing values and 2 studies failing to report missing values were classified as having an “unclear risk.” In Peixoto et al.’s [36] study, 21 of the 81 studies at the beginning of the study were excluded, resulting in a missing value of > 20%; therefore, they were assessed as having a “high risk.”

The RoB in all 18 studies was classified as having a “low risk” because all the expected results were reported without omission when comparing the protocols prepared in advance.

The RoB was assessed as having an “unclear risk” despite the potential of increased risk in all 18 studies due to a lack of data to evaluate other biases.

5. Meta-analysis

The mean, standard deviation, and treatment efficacy rate of 14 out of the 18 studies were used in the meta-analysis. VAS, Fricton index (dysfunction, palpation, and craniomandibular indexes), maximum mouth opening, and effective rate were adopted as evaluation indexes for performing a meta-analysis. The details of the meta-analysis are shown in Figs. 4–9.

Figure 4. Forest plot of the visual analog scale score: acupuncture and electroacupuncture treatment groups versus the control group. MD, mean difference; SD, standard deviation; CI, confidence interval; ATx, acupuncture treatment; MT, manual therapy; W-med, Western medicine; E-ATx, electroacupuncture treatment; PT, physical therapy.

The evaluation index was analyzed for 2 RCTs comparing the treatment group, which combined the acupuncture treatment with PT and MT, and the control group, which only received PT and MT.

For VAS (Fig. 4), the pain score was reduced in the treatment group as compared to the control group; however, this difference was not statistically significant (mean difference [MD], −1.26; 95% CI, −1.75 to −0.78; p = 0.73), and low heterogeneity existed between studies (I² = 0%).

For the dysfunction index (Fig. 5), the evaluation index was reduced in the treatment group as compared to the control group; however, this difference was not statistically significant (MD, −0.05; 95% CI, −0.10 to 0.00; p = 0.12), and a moderate heterogeneity existed between studies (I² = 58%).

Figure 5. Forest plot of Fricton index (dysfunction index) score: acupuncture and electroacupuncture treatment groups versus the control group. SD, standard deviation; MD, mean difference; CI, confidence interval; ATx, acupuncture treatment; E-ATx, electroacupuncture treatment; MT, manual therapy; PT, physical therapy.

Regarding the palpation index (Fig. 6), the evaluation index was reduced in the treatment group as compared to the control group; however, this difference was not statistically significant (MD, −0.06; 95% CI, −0.09 to −0.02; p = 0.42), and low heterogeneity existed between studies (I² = 0%).

Figure 6. Forest plot of Fricton index (palpation index) score: acupuncture and electroacupuncture treatment groups versus the control group. SD, standard deviation; MD, mean difference; CI, confidence interval; ATx, acupuncture treatment; E-ATx, electroacupuncture treatment; MT, manual therapy; PT, physical therapy.

For the craniomandibular index (Fig. 7), the evaluation index was reduced in the treatment group as compared to the control group; however, this difference was not statistically significant (MD, −0.05; 95% CI, −0.10 to 0.00; p = 0.14), and a moderate heterogeneity existed between studies (I² = 54%).

Figure 7. Forest plot of Fricton index (craniomandibular index) score: acupuncture and electroacupuncture treatment groups versus the control group. SD, standard deviation; MD, mean difference; CI, confidence interval; ATx, acupuncture treatment; E-ATx, electroacupuncture treatment; MT, manual therapy; PT, physical therapy.

For the efficacy rate (Fig. 9), the rate was improved in the treatment group as compared to the control group; however, this difference was not statistically significant (risk ratio [RR], 1.09; 95% CI, 0.97–1.22; p = 0.85), and low heterogeneity existed between studies (I² = 0%).

Figure 9. Forest plot of the efficacy rate: acupuncture and electroacupuncture treatment groups versus the control group. RR; risk ratio, CI, confidence interval; ATx, acupuncture treatment; E-ATx, electroacupuncture treatment; MT, manual therapy; PT, physical therapy; W-med, Western medicine.

The evaluation index of the efficacy rate and VAS was analyzed for 3 RCTs comparing the treatment group, receiving acupuncture treatment with MT, and the control group, receiving only MT.

For VAS (Fig. 4), the pain scale was reduced in the treatment group as compared to the control group and showed a statistically significant difference (MD, −1.15; 95% CI, −2.09 to −0.21; p < 0.01) and high heterogeneity among studies (I² = 92%).

For the efficacy rate (Fig. 9), it was improved in the treatment group as compared to the control group; however, this difference was not statistically significant (RR, 1.18; 95% CI, 0.95–1.47; p = 0.07), and a substantial heterogeneity existed among studies (I² = 63%).

The Fricton index was analyzed for 2 RCT studies that compared the treatment group receiving combined acupuncture treatment with MT, with the control group receiving only performed MT.

For the dysfunction index (Fig. 5), the index was reduced in the treatment group as compared to the control group and showed a statistically significant difference (MD, −0.03; 95% CI, −0.07 to 0.01; p = 0.01) and high heterogeneity among studies (I² = 85%).

Regarding the palpation index (Fig. 6), the index was reduced in the treatment group as compared to the control group; however, this difference was not statistically significant (MD, −0.06; 95% CI, −0.09 to −0.03; p = 1.00), and low heterogeneity existed among studies (I² = 0%).

For the craniomandibular index (Fig. 7), the evaluation index was reduced in the treatment group as compared to the control group; however, this difference was not statistically significant (MD, −0.04; 95% CI, −0.07 to −0.01; p = 0.10), and a substantial heterogeneity existed among studies (I² = 62%).

The evaluation index was analyzed for 2 RCTs comparing the treatment group, receiving combined acupuncture treatment with Western medicine, with the control group receiving only Western medicine treatment.

For VAS (Fig. 4), the pain score was reduced in the treatment group as compared to the control group; however, this difference was not statistically significant (MD, −0.92; 95% CI, −0.98 to −0.86; p = 1.00), and low heterogeneity existed among studies (I² = 0%).

For maximum mouth opening (Fig. 8), the evaluation index was reduced in the treatment group as compared to the control group and showed a statistically significant difference (MD, 3.37; 95% CI, 1.41–5.32; p = 0.02) and high heterogeneity was observed among studies (I² = 81%).

Figure 8. Forest plot of maximum mouth opening: acupuncture and electroacupuncture treatment groups versus the control group. MD, mean difference; SD, standard deviation; CI, confidence interval; ATx, acupuncture treatment; MT, manual therapy; W-med, Western medicine.

For the efficacy rate (Fig. 9), it was improved in the treatment group as compared to the control group; however, this difference was not statistically significant (RR, 1.29; 95% CI, 1.05–1.58; p = 0.18), and a moderate heterogeneity existed among studies (I² = 44%).

The present study evaluated the efficacy of acupuncture and electroacupuncture in patients with TMD and provided evidence for clinical use by conducting a systematic review and meta-analysis of RCT studies on acupuncture for TMD between 2018 and 2023 using Korean and international databases. Altogether, 18 RCT studies and 1,109 patient data were included in the present study.

Most of the studied patients were female (349 males and 664 females). The patients’ age ranged from 29 to 44 years, and the disease duration ranged from 8 days to 7 months in both groups. This result is consistent with the previously reported prevalence and duration of TMD [42].

Among 9 studies, 8 had parallel treatment groups, and 1 study had a single treatment group; the comparison of the efficacy rate between the interventions showed that both groups showed improvement after treatment, and the improvement was statistically significantly different between the treatment and control groups. A previous study using PT for the treatment group and acupuncture as the only treatment for the control group showed that the treatment group showed significant improvement, as compared to the control group. In the other 8 studies, statistically significant differences were observed in various evaluation indexes among 6 studies, including 1 with a parallel treatment group and 5 with single treatment groups [31,38,41], and the treatment group showed partial improvement as compared to the control group [35,36,39]. 2 studies with parallel treatment groups reported no statistically significant differences between the 2 groups [37,40].

The acupoint frequency in treatment intervention based on STRICTA guidelines was in the order of ST7, ST6, SI19, LI4, and TE17. Adjacent acupoints of the TMJ were mainly selected as therapeutic acupoints. Acupoints SI18, GB3, ST36, GB2, EX-HN5, LI20, KI3, BL18, GB34, GV20, GV21, GV22, and GV24 were also selected as therapeutic acupoints in 1 to 3 times of included studies. Furthermore, besides the World Health Organization standard acupuncture points, the Ashi-point, lower 2/5 of the motor and sensory areas of Jiao Shunfa, and TrP of the muscle were also selected.

The use of RoB assessment has limitations. First, “high risk” studies were identified after random sequence generation and allocation concealment, which is because studies using the treatment order or arrival order for randomization were included, and studies using random number table did not report information of concealment. Further studies will have to adopt a randomization method with a low RoB, and concealment information must be reported when using a random number table. Second, most studies showed a “high risk” of blinding the study participants and researchers. Given that blinding to general acupuncture treatment is challenging, further studies using treatments capable of blinding, such as sham acupuncture, to control groups will be needed.

Following a meta-analysis of 14 studies with parallel treatment groups, the dysfunction index and VAS were statistically significant for the parallel treatment groups receiving acupuncture combined with MT, and maximum mouth opening was statistically significant for the parallel treatment groups receiving acupuncture combined with Western medicine. However, the evaluation index of effectiveness was low in the meta-analysis, and the heterogeneity among studies was high. According to these results, the interventions in the treatment and control groups are widely used in clinics and have sufficient evidence. These interventions were identified when various studies comparing their efficacy were applied to the meta-analysis.

The results of this systematic review and meta-analysis involving 18 studies demonstrated that acupuncture and electroacupuncture were beneficial in relieving pain and alleviating restriction of mouth opening, and there was a reason for clinical use. However, this study had several limitations. First, this study conducted a systematic review of RCTs on acupuncture for TMD from Korean research databases; however, the identified studies focused on adjacent, distal, or a combination of acupuncture used to treat TMD [43], studies of chuna used to treat TMD [44], and these studies utilized acupuncture in both the treatment and control groups, so they do not meet the criteria. Second, the treatment interventions used in these studies were acupuncture, electroacupuncture, MT, and PT, and each intervention has strong clinical evidence and effectiveness. However, further studies using more effective treatment interventions are necessary because it is difficult to determine which treatment is more effective owing to the diverse types of interventions used. Finally, as we only included RCTs published within the last 5 years, the number of included studies was limited (18), and 11 of them were locally biased as studies were searched from the CNKI Chinese database. Further studies are required in the future to compensate for these limitations.

The present systematic review and meta-analysis analyzed 18 RCT studies and 1,109 patients with TMD were evaluated. Among the included studies, 9 reported that the treatment and control groups showed improvement after treatment, which was statistically significantly different between the 2 groups; the other 6 studies reported that the treatment group showed a partial improvement compared to the control group and a statistically significant difference was observed in some evaluation indexes. After performing a meta-analysis, the evaluation index of VAS and dysfunction index were statistically significantly different between the parallel treatment group receiving acupuncture with MT and the control group receiving only MT. Moreover, the parallel treatment group receiving acupuncture combined with Western medicine showed statistically significant evaluation index of maximum mouth opening than the control group receiving only Western medicine. However, this study included only 18 studies, which is a small sample size. The included studies showed regional bias, and the RoB assessment revealed high risks for randomization, concealment, and researcher and participant blinding. Further studies are needed to compensate for these limitations.

Conceptualization: JHK, JSY. Data curation: JSY, JN, SA. Formal analysis: JSY, YGS. Funding acquisition: JHK. Investigation: JSY, JN, SA. Methodology: JSY, YGS. Project administration: JSY, HWC. Supervision: JHK, JUS. Visualization: JSY, SJK. Writing – original draft: JSY. Writing – review & editing: JSY, JHK, JUS.

The authors have no conflicts of interest to declare.

This research was supported by the Dongshin University research grants.

This research did not involve any human or animal experiment.