Effectiveness of acupuncture for temporomandibular disorders and associated symptoms

BACKGROUND AND OBJECTIVES: Temporomandibular disorder is defined as a set of clinical problems involving masticatory muscles, temporomandibular joint and associated structures. For having multifactorial etiology, several treatments are proposed and successfully used. However, most recommended therapies are those reversible and noninvasive, which should be the first choice to treat temporomandibular disorders. This study aimed at discussing acupuncture to treat temporomandibular disorders and associated symptoms. CONTENTS: This is a review of 34 articles published between 1983 and 2015. Since acupuncture aims at returning balance to body and harmony between physical and psychical parts by stimulating specific points, it may be considered therapy of choice to treat temporomandibular disorders. In TMD patients, evidences have shown efficacy in increasing temporomandibular joint movement amplitude, accelerating serotonin, encephalin and endorphin release, thus favoring masticatory muscles relaxation and pain relief. According to recent articles, most commonly used points for this purpose are ST6, ST7, SJ21, SJ17, SI18, Taiyaing and Yintang (face and head) and LI4 (extrafacial). CONCLUSION: Acupuncture is as effective to control facial pain as conventional Western therapies. It is considered useful, of low cost and provides better quality of life to patients treated with this technique.


INTRODUCTION
According to the American Academy of Orofacial Pain (AAOP) 1 , temporomandibular disorder (TMD) is a set of clinical signs and symptoms involving masticatory muscles, temporomandibular joint (TMJ) and associated structures.Currently, TMD are basically divided in two major groups, which are joint disorders and masticatory muscles disorders 2 .Most frequently reported symptoms by patients are muscle fatigue, pain on face, TMJ and/or masticatory muscles, headache and earache and jaw movements limitation and/ or shifts 2 .It has multifactorial etiology basically summarized as high psychological stress and pain amplification states, together with a wide range of specific risk factors 3 .Literature data have shown high incidence of TMD in general population, varying from 21.5 to 51.8%.It affects all age groups, although its highest incidence is between 20 and 45 years of age.From 15 to 30 years of age, most frequent causes are of muscle origin and, as from 40 years of age of joint origin.Females are more affected than males, in a proportion of five females for each male [4][5][6][7][8][9] .Approximately 3.6 to 7% of the population have sufficiently severe TMD to look for medical assistence 1 .Reversible and noninvasive therapies are the most recommended to treat TMD and should be the first choice 10 .Among these techniques, one should stress acupuncture [10][11][12][13][14][15][16][17] .Due to its recent use in dentistry, its noninvasive character and effective results, it has been successfully used for this purpose 14,16,[18][19][20][21][22][23][24] .Acupuncture is a millenary technique of Traditional Chinese Medicine (TCM) which has been justified and structured on philosophical, rather than scientific basis 25 .The word has Latin etymology (acus = needle and puncture = prick) and means needles insertion on specific skin points, called acupoints or acupuncture points, aiming at healing and preventing diseases [26][27][28] .Acupuncture aims at developing body balance by intervening in the physical body to help reestablishing lost harmony between physical and psychic parts 25 .Literature suggests that, in TMD patients, acupuncture speeds serotonin, encephalin and endorphin release, being effective to increase jaw movement amplitude and oral function, decreasing muscle hyperactivity, favoring masticatory muscles relaxation, thus decreasing pain 24 .Acupuncture is no longer considered an alternative method, but rather it started to be a treatment alternative without major adverse effects for using own body substances to control pain 14 .In face of the topicality of the subject, we propose a literature review on acupuncture indications, action mechanism and possible side-effects, when used to treat TMD and associated symptoms.

CONTENTS
An exploratory search was carried out in Pubmed, Scielo and LILACS databases.Several books and articles were selected, published between 1983 and 2015, on the efficacy of acupuncture for TMD.Descriptors were "acupuncture analgesia", "temporomandibular joint dysfunction syndrome" and "facial pain", in addition to their equivalent in Portuguese, "analgesia por acupunctura", "transtornos da articulação temporomandibular" and "dor facial".In total, 34 articles were selected for matching the objectives of our study, being these narrative reviews and systematic reviews, case reports and clinical trials.Acupuncture uses individuals' bioenergetic balance, promoting sensation of wellbeing (endogenous opioids release) and dramatically decreasing muscle tension points and/or trigger-points, frequent in TMD patients 29 .So, it is important tool to manage patients with joint 16 and muscle 24 disorders, with good clinical results 24,30,31 .According to the principles of the technique, needle entrance in skin causes micro-inflammation which moves natural serotonin, encephalin and endorphin production.The release of these neurotransmitters blocks painful stimuli propagation, impairing its perception by the brain.So, body response is faster, decreasing symptoms intensity, often making them disappear.Acupuncture stimulates blood circulation dynamics due to regional microdilation and relaxation; it releases hormones, such as cortisol and endorphins; increases host resistance by means of stimulating hypothalamus, hypophysis and other important glands for systemic recovery; it normalizes body functions and stimulates metabolism of different organs 24,28 .So, it is characterized as potent analgesic, sedative and relaxant, which is the basis for its application in dental treatments 32 .It may be indicated as first treatment option when patients are allergic or suffer severe adverse effects induced by drugs, in cases of liver or kidney function failure, history of gastric bleeding when using anti-inflammatory drugs, or for the elderly needing many drugs 29,32 .For having few adverse effects, it provides further safety for hypertensive, diabetic, cardiac and hemophilic patients, children, pregnant women and those affected by human immunodeficiency virus (HIV) 29 .It is an effective and economic method, causes few clinically relevant adverse effects and may promote decreased salivation, nausea and postoperative pain, by regulating homeostasis and immunodefensive and antiinflammatory responses 32 .Acupuncture adverse effects are minimal, being in general associated to dizziness, nausea and, in some cases, transient erythema or increased pain in the first hours 26 .In dentistry, acupuncture is effective to treat orofacial pains, such as idiopathic trigeminal neuralgias, herpes-zoster, maxillary sinusitis, toothache, TMJ arthritis, as well as in patients with dry mouth, bruxism and TMD 29 .It may be indicated for pre-treatment of anxious, stressed or hypertensive patients or with systemic diseases, and to improve assistance quality since it is able to induce analgesia in Endodontics, Periodontics and Surgical procedures 33 .Acupuncture has been indicated to treat chronic facial pain resistant to conventional treatments (occlusal splint or physical jaw exercises), especially in cases of muscle pain.Some selected studies have compared the efficacy of occlusal splint and acupuncture.Both therapies resulted in significant improvement of subjective symptoms and clinical signs in the stomatognatic system, with significant pain decrease in all evaluation variables, during 12 months of study 11,13,33 .Another study has shown that, for patients under anti-inflammatory drugs to control orofacial pain, TCM was effective to decrease drug use 34 .Most studies involving acupuncture as therapeutic method were carried out with female samples, due to the high prevalence of TMD in this gender 16,33,35,36 .With samples in mean age group between 20 and 40 years, results have shown that treatment efficacy is not influenced by age, but rather by pain intensity and number of sessions to be performed 17 .However, it is important to stress that different studies based on TCM principles, have not evaluated TMD alone, but rather the body as a whole, posture and general health among other aspects, before determining the adequate therapy.Different protocols regarding acupuncture points used for TMD, type of stimulation, number of sessions and intervals between them are described in the literature.Since application sites and number of sessions change from individual to individual and depend on the origin of the problem, it is difficult to compare protocols and results of different studies.However, some authors 14,15 mention average of 6-8 sessions lasting 30 minutes each to obtain effective results of TMD treatment by acupuncture and, although there are reports of improvement in the first session, pain relief is seen in the medium term with consequent jaw function improvement 16,17 .Treatment duration may vary in a case-by-case basis and for the same disease, because one has to take into account whether it is acute or chronic disease and even different individual responses to treatment with acupuncture.In chronic conditions, during acupuncture treatment, symptoms are expected to improve as from the fourth session although each individual responds differently.In acute processes, results are fast with few applications, but in chronic processes they may require months of treatment.In cases of extreme pain, improvement might be immediate, being that as from the second session treatment may be once a week in a total of six sessions and may continue for three months until symptoms remission 17 .Some more recent studies evaluating the effects of acupuncture in TMD 16,[22][23][24]31,34,35,38 , and published in the last five years, are described in table 1. There is nostandard clinical protocol to select points used in each treatment.Differently from Western therapies, acupuncture is applied based on biopsychosocial data collected by TCM during patients' anamnesis, that is, all protocols should be tailored according to each patient's needs.However, this is not possible in most clinical trials, as shown by the literature 24 .As shown in table 1, some studies use special protocols and others use fixed protocols.According to recent studies, most commonly used points in protocols to treat TMD-induced facial pain and associated symptoms are ST6, ST7, SJ21, SJ17, SI18, Taiyaing and Yintang (face and head) and LI4 (extrafacial) (Table 2, Figure 1) 16,[22][23][24]31,34,35,38 .Notwithstanding promising acupuncture results, a systematic review has shown that there are still controversies and limitations to the effectiveness of acupuncture to treat TMD 38 , which suggests that studies in the area shall continue for the definition of better treatment protocols and to measure the real efficacy of the technique as compared to most traditional modalities to treat TMD.

CONCLUSION
Acupuncture has been shown to be effective to control facial pain, especially pain of muscular origin.For having low incidence of side effects, its use may be continuous, being an excellent option to control or treat pain and TMD.

Figure 1 .
Figure1.Location of commonly used acupoints to treat temporomandibular disorders37

Table 1 .
Summary of more recent studies (last five years) on temporomandibular disorder treatment with acupuncture

Table 2 .
Location and function of most commonly used acupoints to treat temporomandibular disorder 37 border, anterior masseter muscle border Relieves pain, calms the mind, treats facial pain and facial nerve spasm.Taiyang Between lateral eyebrow edge and lateral eyes epicanthus Calms pain, treats facial muscle spasm Yintang Face midline between eyebrows Interrupts pain, calms the mind, treats headache LI4 Between metacarpi I and II in muscle bulge Treats headaches, facial pains, trismus, head and neck anesthesia TMJ = temporomandibular joint.