Botulinum toxin type A and acupuncture for masticatory myofascial pain: a randomized clinical trial

Abstract BoNT-A has been widely used for TMD therapy. However, the potential benefits compared to dry needling techniques are not clear. Objective this study aimed to compare the immediate effects of botulinum toxin type A (BoNT-A) injections and Acupuncture in myofascial temporomandibular disorders (TMD) patients. Methodology 54 women were divided into three groups (n=18). AC patients received four sessions of traditional acupuncture, being one session/week during 20-min. BoNT-A patients were bilaterally injected with 30U and 10U in masseter and anterior temporal muscles, respectively. Moreover, a control group received saline solution (SS) in the same muscles. Self-perceived pain was assessed by visual analog scale, while pressure pain threshold (PPT) was verified by a digital algometer. Electromyographic evaluations (EMG) of anterior temporal and masseter muscles were also measured. All variables were assessed before and 1-month after therapies. The mixed-design two-way repeated measures ANOVA and Tukey’s post-hoc tests were used for analysis, considering a=0.05. Results Self-perceived pain decreased in all groups after one month of therapy (P<.001). BoNT-A was not better than AC in pain reduction (P=0.05), but both therapies were more effective in reducing pain than SS (P<0.05). BoNT-A was the only treatment able to improve PPT values (P<0.05); however, a severe decrease of EMG activity was also found in this group, which is considered an adverse effect. Conclusion after one month of follow-up, all therapies reduced the self-perceived pain in myofascial TMD patients, but only BoNT-A enhanced PPT yet decreased EMG.


Introduction
Myofascial pain (MFP) is a disorder characterized by localized muscle tenderness, regional pain, and limited range of motion. 1 It is the most typical cause of persistent regional pain, such as back and shoulder pain, tension-type headaches, and facial pain. 2 Furthermore, it is a common condition in dentistry with prevalence from 10% to 68% among subjects with temporomandibular disorders (TMD). 3 Masticatory myofascial pain (MMFP) has a complex pathogenesis expressed by a multifactorial etiology, which led to the proposal of numerous conservatives, reversible, and minimally invasive therapies to treat this condition. 4 The needling technique is a minimally invasive therapy widely used for MMFP and it can be classified as an injection technique (IT), often referred to as "wet needling," and dry needling (DN). While the IT deliver pharmacological agents, e.g., anesthetics, botulinum toxins or other agents, with needles, 5 the DN consists in the insertion of thin monofilament needles, as the ones used for acupuncture practice, without any injectate. 6 Acupuncture is a therapeutic method of the traditional Chinese medicine which differs from conventional DN techniques since needles are not inserted just in the painful region. Its antinociceptive effects 7 include immediate reduction in local, referred, and widespread pain, 8 and reduction in peripheral and central sensitization. 5 Although a recent randomized clinical trial reported pain reduction of 84% after one month of treatment -concluding that acupuncture was effective for MMFP pain 9 , available systematic reviews did not find further advantages in the use of acupuncture for MMFP over other treatments such as oral appliances, behavioral therapy, and/or pharmacotherapies. 10,11 These controversies might be due to several methodological shortcomings, leading to inconclusive results, which expose the need for high quality studies comparing the efficacy of acupuncture with other treatments.
Botulinum toxin type A (BoNT-A) is an FDAapproved treatment for some pain disorders (as dystonia and migraine), becoming one of the most popular IT used to control MFP. 4 Animal studies have demonstrated that peripheral injections of BoNT-A have analgesic effects on pain stages by inhibiting the release of nociceptive mediators (peripherally and centrally), mechanism independent of its neuromotor effect. 12,13 Based on this data, BoNT-A has been used as an off-label treatment to control MMFP.
Moreover, a few well-designed clinical trials 14,15, control group. For this allocation, a software was used (https://random-allocation-software.software. informer. com/2.0/) and the sequence was sealed in an opaque envelope, which was operated by a researcher not involved in other procedures of this study. The investigator assessing the outcomes was masked to the treatment assignments.

Botulinum toxin type A (BoNT-A)
BoNT-A (100 U; Botox, Allergan, Irvine, California, CA, USA) was reconstituted using non-preserved sterile saline solution 0.9%. A single bilateral injection This injection technique consisted in inserting the needle into the soft tissue until reaching the bone; then, the needle was slightly moved to place the tip inside the muscle. Before injection, a careful aspiration was performed to avoid a possible intravascular administration.

Saline Solution (SS)
SS (NaCl 0.9%) was bilaterally injected into the same muscles and sites, following the same protocol and doses, as described for BoNT-A injections.
Injections of BoNT-A and SS were performed in a single appointment by the same trained clinician, who was blinded to the treatment assignment.

Self-perceived pain: Visual Analog Scale (VAS)
VAS is a 100 mm horizontal line, anchored by the words "no pain" at the left end, and "worst pain imaginable" at the right end. Participants were instructed to mark a line at any point, representing the level of current, worst, and average pain of the last month.

Pain sensitivity: Pressure Pain Threshold (PPT)
PPT was assessed by a digital algometer (Kratos DDK-20; São Paulo, Brazil) with 1 cm 2 circular flat rod, for the bilateral evaluation of the masseter and anterior temporal muscles. Patients were instructed to indicate the moment when the pressure became painful. They were sat in a chair with the Frankfurt plane parallel to the ground, and muscles should be relaxed. The circular flat rod was perpendicularly pressed to the surface skin at a 0.5 kg/cm² rate, following the sequence: right anterior temporal, right masseter, left masseter, and left anterior temporal muscles. After a five-minutes rest, the pressure was applied again, as follows: left anterior temporal, right anterior temporal, left masseter, and right masseter.

Electromyographic assessment
The bilateral EMG signals of the anterior temporal and the superficial masseter muscles were recorded by Before the recordings, the volunteers' skin was cleaned with cotton and 70% alcohol, and a function

Statistical analysis
All data for groups and periods were expressed as means ± standard deviation (SD) and were assessed for normal distribution with the Shapiro-Wilk test. A mixed-design repeated measures two-way ANOVA test was used to observe the difference among groups over time and within the group. The statistical analysis compared the results observed before the treatment (baseline) with those observed one month after the therapies. Moreover, the three groups were compared to verify a possible statistically significant difference among therapies. The ANOVA test was followed by post hoc Tukey's test. All analyses were performed using SPSS for Windows (release 21.0, SPSS Inc.), with a 5% significance level.

Electromyographic activity (EMG)
The EMG results for both masseter and anterior temporal muscles demonstrated that only volunteers in the BoNT-A group presented a significant reduction of the EMG activity one-month after the treatment (P<.001). Intergroup comparisons at the one-month follow-up showed a significant decrease in the masseter muscle activity in BoNT-A group compared to acupuncture (P =.020) and SS (P <.001), and these results were also found for the anterior temporal muscles (P <.001) (Figure 4).

Discussion
The main findings of this study were that -after four weeks -all treatment groups (acupuncture, BoNT-A, and SS) were able to significantly reduce the self-perceived pain, without differences between acupuncture and BoNT-A, while both treatments were superior to the SS group. Moreover, considering the PPT values for both masseter and anterior temporal muscles, only BoNT-A group lead to a significant increase in PPT. Likewise, only patients treated with BoNT-A showed a significant reduction of the EMG activity in both studied muscles.
Pain is considered one of the most common reasons for a TMD patient seek treatment. 26  Different uppercase letters represent significant differences among groups (P<0.05); different lowercase letters denote significant differences among assessment time points (P<0.05); PPT: Pressure pain threshold; kg/cm 2 =Kilogram per square centimeter. Table 1-Mean and standard deviation (SD) of pain pressure threshold (kg/cm -2 ) for each group, before and after treatments Botulinum toxin type A and acupuncture for masticatory myofascial pain: a randomized clinical trial Note that, in this study, BoNT-A improved all variables in a refractory MMFP population. These results reinforce that BoNT-A should not be the first option to MMFP treatment due to possible adverse effects, but it could be considered in patients that do not mitigate their pain with more conservative managements, fact that is corroborated by other studies. 14,15,39 The EMG results for the masseter and anterior temporal muscles demonstrated that only patients treated with BoNT-A presented a significant reduction of the EMG activity one month after treatment (P<.001).
Intergroup comparisons showed a significant decrease in muscle activity for both muscles in BoNT-A group when compared to acupuncture and SS groups. A reduction in EMG activity of masticatory muscles is expected after an intramuscular injection of BoNT-A once this toxin inhibits the release of acetylcholine at the neuromuscular junction of presynaptic motor neurons, reducing muscle activity. 39 In fact, a temporary regional weakness is one of the most common adverse effects related to the use of BoNT-A in TMD treatment. 19 A recent report also showed a The occurrence and the intensity of these adverse effects are directly related to higher doses and repeated injections. 19 In the present study, only a single injection of BoNT-A was used (30U in each masseter and 10U in each anterior temporal). Based on previous investigations, 15 this dosage is able to reduce pain in MMFP patients, but it also allows the full recovery of muscle activity, which returned to normal EMG values after three months. 15 Anyway, a reduction in the EMG activity of masticatory muscles is an adverse effect that must be considered; once acupuncture did not promote a significant change in EMG values, this could be considered an advantage of acupuncture over BoNT-A. Notably, the reduction of EMG values in BoNT-A groups is not responsible for decreasing subjective pain. Studies have demonstrated that BoNT-A presents an analgesic effect which is independent and precedes its neuromuscular effects.
The EMG results in the acupuncture and BoNT-A groups confirms the disconnection between muscle electrical activity and muscle pain. Besides EMG reduction, patients receiving BoNT-A injections also reported adverse effects like edema and pain during injection, being the last also reported by the SS group.
Conversely, self-reported adverse effects for the acupuncture group comprised itching and reddening of the skin, without pain symptoms nor edema.
These results suggest that all studied needling therapies (acupuncture, BoNT-A, and SS) are effective after one month of follow-up in reducing the selfperceived pain in patients with refractory MMFP; and, that BoNT-A seems to be superior due to the improvement in PPT values. Nevertheless, caution is necessary when judging these findings, since some limitations should be considered. Selecting only women as the study population hinder our results to be generalized to male patients. However, it was necessary once MMFP is more prevalent in this gender.
Even though the 1-month follow-up is a restricted time of evaluation, our main objective was to assess the immediate effects of the proposed treatments; however, studies considering longer periods of evaluation should be performed. Finally, the effects of the proposed therapies on the psychosocial status of myofascial TMD patients should be also evaluated, considering that psychosocial variables generally act as chronification factors for TMDs.

Conclusion
After one month of follow-up, all therapies reduced the self-perceived pain in patients with MMFP. BoNT-A was not superior to acupuncture in pain reduction, but both were superior to SS; moreover, BoNT-A was the only treatment able to improve PPT values.
However, only patients treated with BoNT-A reduced the EMG activity in the injected muscles which should be considered as an adverse effect.