Temporomandibular disorder is one of the main reasons for the pain and damage to the function in the head, jaws and neck (1,2) term is somewhat misleading because it includes two types of pain, one originates from the temporomandibular joint , and another originates mainly from the muscles of mastication - Myofacial pain (MFP). The last is the one we seek to explore the etiology of this pain is explained using a biological-psychological model, which reflects the complex interaction between physical factors, behavioral, social and emotional influences (3). The pain may last from weeks to many months; it is usually more severe on one side of the face, especially at pre-auricular area (front ear). Intensity of the pain is usually moderate; it has a squeezing, dull nature. It worsens during mouth opening and often causes opening restriction (5, 4). One can find trigger points where the pain is harsh and radiates to remote areas. Treatment is often integrated, multi-systemic and comprehensive (7, 6): physical therapy, behavioral therapy, night splints, Trigger point injection, and the use of drugs from different families are used to manage and treat MVP. Among the drugs that we use routinely are: Amitriptyline and nortriptyline from the family of tricyclic antidepressants (TAC's). These drugs were originally intended to treat depression and now days there primary use is to treat chronic pain from muscle origin, the use is in low doses of 10-35 mg /d, with no connection to the anti-depressive effect (8,9,10,11). . Gabapentin is gaba-amino buyic acid (GABA) analogue originally developed as an anti-epileptic (12). This drug is also used as a first treatment in neuropathic pain (13). A study published in 2007 by Kimos et al (14) suggested that using gabapentin at higher doses up to 4200 mg per day is a therapeutic option for myofacial pain. The authors prospectively examined the use of gabapentin versus placebo in myofacial pain over 12 weeks in 50 patients, of whom 36 completed the study, the results demonstrated improvement in any parameter. Another study conducted in our department and accepted for publication in journal of orafacail pain \& headache examined retrospectively gabapentin Vs amitriptyline with better results for gabapentin in more complex and widely spread disorder. To gabapentin side effect drug interactions profile better than amitriptyline (16). Moreover, gabapentin has no anticholinergic which usually limits the use of amitriptyline. Therefore, gabapentin may be an attractive alternative for the treatment of MFP. Our clinic use gabapentin routinely as second option after lack of response to amitriptyline. The aim of this study is to compare prospectively the efficacy amitriptyline in low doses up to 20 mg to gabapentin at low doses up to 900mg.

Patients over the age of 18 that will come to orofacial pain clinic in the department of Oral medicine, and which will be diagnosed as suffering from facial pain originating from chewing muscles (MVP) for at least three months, will be invited to participate in the study. The examination is the one we use routinely and includes: patient demographics: age, sex, marital status, occupation, and medical history. Pain characteristics includes : Location, duration, intensity (subjective), the nature of the pain, whether pain is prolonged or not, frequency and duration of attacks, disruption of sleep, quality of life and everyday functioning (work, company), whether the pain is accompanied by autonomic of systemic signs and whether the patient suffers from pain in the body outside the region head and neck. Patient will receive a questionnaire examining the accompanying emotional distress (AXIS II). Masticatory muscle involvement will be examined by palpation, load testing, restriction or non-limitation of mouth opening. All of which are routinely use in our department.

Patients will receive an explanation of the nature of the disease and possible treatments. Patients that would like to participate in the study, will sign a consent form, receive a pain questionnaire and start medication treatment which is acceptable in cases of myofacial pain. The drugs that will be used are: amitriptyline up to 20 mg and Gabapentin up to 900 mg. Patients with any side effects will call to receive instructions. After one month, patients will be invited to our clinic. A clinical examination, similar to one mention above will be performed with re-filling of the questionnaires. First medication treatment will discontinue and after two weeks will be replaced with the equivalent drug. Meaning patients that will begin with amitriptyline will continue with gabapentin (after two weeks break) and vice versa (cross over design). After another month patients will be invited to the clinic for further similar clinical examination and questionnaires fulfilling, then, if necessary patients will continue their preferred treatment. . All patients will give their consent to participate in the study.

Criteria for improvement include: 1. Intensity of pain according to VAS scale. 2. The frequency of the attacks. 3. The frequency of use of other drugs (for the treatment of chronic or acute pain). 4. Improving function - open mouth, free jaw movement. 5. Quality Health Index (AXIS II).