Temporomandibular disorders (TMDs) are diseases that affect the temporomandibular joint (TMJ) and supporting structures1. The goal of treatment for TMDs is elimination or reduction of pain and joint sounds and a return to normal TMJ function. Such treatment involves a diet of soft foods, behavior modification, pharmacotherapy, inter-occlusal splints, intra-articular injections, physical therapy, arthrocentesis, arthroscopy, or open joint surgery. In recent years, low-level laser therapy (LLLT) has been introduced as a non-invasive physical treatment for TMDs and myofascial pain23. Because the pathogenic pathways cannot be clearly defined, reversible treatment, minimally invasive treatment, or no treatment is generally preferred. If conservative treatment fails, surgical treatment is then considered. The purpose of this article is to review the mechanisms, outcomes, and protocols of the main treatment methods for TMDs: pharmacotherapy, physical therapy, inter-occlusal splints, hyaluronic acid (HA) joint injection, botulinum toxin (BTX) type A injection, arthrocentesis, and arthroscopic treatment.

Occlusal splints are removable artificial occlusal surfaces that affect the relationship of the mandible to the maxilla and are used for diagnosis or therapy333435. The mechanisms of action as a treatment involve restoring the vertical dimension of occlusion, occlusal disengagement, joint unloading, masticatory muscle relaxation, or TMJ repositioning. Occlusal appliances are fabricated of either hard or soft acrylic resin. Hard acrylic resin occlusal appliances have several advantages over the soft appliances: the hardness of the resin enables quick and easy adjustments and easy repairs; the fit of the hard acrylic resin is more accurate, and methods of fabrication are more reliable; the hard resin also offers greater longevity, more color stability, less food debris accumulation, and more durability than the soft resin. The Acheson classification of occlusal appliances includes muscle relaxation appliances or stabilization appliances used to reduce muscle activity; anterior repositioning and orthopedic repositioning appliances; anterior bite plane and pivoting appliances; and soft or resilient appliances. The flat plane stabilization appliance (Michigan splint) is fabricated for the maxillary arch, but because it interferes with speech and aesthetics, it is often placed on the mandibular arch instead. This splint is supposed to protect teeth, relax the elevator muscles, provide stabilization, redistribute occlusal forces, and inhibit bruxism. The stabilization splint (SS), also known as the Tanner appliance, Fox appliance, Michigan splint, or the centric relation appliance, is a hard acrylic splint that provides temporary and removable ideal occlusion (ideal contact between the teeth for the muscles and the TMJs). Providing ideal occlusion through splint therapy reduces abnormal muscle activity and produces neuromuscular balance. Normally, patients wear the splint only at night. Over several visits, the splint needs to be adjusted by grinding some of its surface points because the lower jaw will adopt a new position as a result of wearing the splint. Eventually, the masticatory muscles relax into a consistent jaw relationship. The patients should then be reviewed at regular intervals. After a period of successful splint therapy (normally between two to three months), patients can be weaned off the splint. SS therapy can be beneficial for reducing depression and pain severity at rest and on palpation compared to no treatment24. In a 2004 Cochrane Review, Al-Ani et al.36 found insufficient evidence to support the use of splint therapy for the treatment of TMDs. Qvintus et al.37 further evaluated the long-term effects of splint therapy; after 1 year, 27.6% of TMD patients who received splint treatment and 37.5% of TMD patients who received counseling and instructions for masticatory muscle exercises reported ‘very good’ treatment effects.

OA is a common TMD. Patients with this disorder tend to exhibit a reduction in intra-articular HA concentration due to depolymerization by reactive oxygen species and production of acid molecules with a lower molecular weight than normal38. Consequently, lubrication is reduced, and joint mechanical stress is increased, resulting in clinical and radiographic progression of the disease. HA provides a longterm lubricating effect, reducing the actions of inflammatory mediators and increasing joint mobility. Results from studies with an active control group suggest that arthrocentesis plus HA injection is superior to arthrocentesis alone in patients with closed lock39. A protocol of two HA injections at weekly intervals is more effective than placebo injections of saline23, and joint catabolite levels decreased significantly with a supplemental HA injection4041. All studies reported a decrease in pain levels; other positive outcomes considered were condylar mobility42, kinesiographic43 and electromyographic recordings44, and a reduction in the Helkimo clinical dysfunction index40. Range of motion improved in the majority of studies, but a couple of papers4546 reported the absence of significant changes in mouth opening.

BTX is a strong biological exotoxin produced by Clostridium botulinum , a Gram-positive anaerobic bacterium. There are seven types of BTX, specified by the letters A to G, among which the strongest organic toxin is BTX-A. The mechanism of action is related to blocking the release of acetylcholine from a presynaptic neuromuscular synapse and, in the autonomous nervous system, blocking its release from postganglionic cholinergic neurons. BTX-A is used to treat bruxism, myofascial pain, disorders associated with TMJ disc displacement, and habitual dislocation of the mandible. The neurotoxin paralyzes the skeletal muscles by blocking calcium-dependent acetylcholine from nerve endings, causing functional denervation. The local paralysis is reversible; neuron regrowth occurs after 2 to 4 months4748. In experimental studies4950, a dose of 12.5 to 200 units per muscle was used. In three experimental studies495051, a single injection was administered; in another study52, 17% of patients received a second injection. Generally in these studies, the effects of the single dose lasted until the end of the follow-up period. In all investigated cases, the first dose yielded relatively favorable outcomes, and doses repeated after 2 to 6 months were performed to strengthen the effect of the previous injection. Treatment with BTX is contraindicated in women during pregnancy and lactation, in patients with known hypersensitivity to any component of the drug (for example, human albumin), during an infection or inflammation of the area to be injected, and in patients treated with aminoglycoside antibiotics, cyclosporine, D-penicillamine, tuba curare, succinylcholine, chloroquine, or hydroxyl chloroquine. BTX has immunogenic properties that can lead to the stimulation of antibody production. Antibodies can be either neutralizing (interfere with the activity of the drug and reduce the effectiveness of the treatment) or non-neutralizing (do not affect the drug) and are formed in response to repeated exposure to the neurotoxin protein complex. To minimize resistance to the BTX resulting from the production of autoantibodies, the lowest effective dose should be applied, with at least three-month intervals between treatments. Booster injections are not recommended. To treat masticatory muscle disorders, the injections are performed with a 12 mm needle and a force of 30 g, strictly intramuscularly after careful aspiration, and the muscle must be relaxed50. While the neurotoxin is being injected, the patient should sit in the dental chair; after the injection, the patient must remain in an upright position for four hours to reduce diffusion to the throat muscles, which carries risk of reflux53. BTX injections reduced the maxillofacial muscle pain associated with TMJ dysfunction52. Electromyography was used during injection in muscles that were difficult to access, including the lateral pterygoid muscle (8 out of 41 patients). Accordingly, localized pain occurred in 80% of patients and remained in about half of the patients for 3 months after injection52. Researchers noted adverse effects such as muscle paralysis and dysphagia in a number of patients54 but described those effects as temporary. They also pointed out that, four weeks after beginning the treatment, about 91% of patients reported improvement in facial pain54. Song et al.55 investigated the effects of BTX on the treatment of TMDs. They collected and defined an algorithm for treating TMD patients and determined that conservative treatments such as warm compresses, behavioral therapy, oral appliances, and drugs (anti-inflammatory drugs and muscle relaxants) should be used prior to BTX-A injection55. Emara et al.49 assessed the effects of BTX in the lateral pterygoid muscle for the treatment of joint click in 6 patients (11 joints). They observed that toxin injection eliminated the click sound in 10 joints during the first week and in one joint after one week. During the following three to four months, recurrence of the click sound was reported in only one joint49. A recent systematic review of BTX-A in the treatment of TMDs included five relevant trials involving 117 participants. Two trials revealed a significant between-group difference in myofascial pain reduction. A trial that compared BTX with fascial manipulation showed equal efficacy of pain relief from TMDs, and the other two trials showed no significant difference between the BTX and placebo groups.

Arthrocentesis occurs in three steps: forcing apart the joint constituents, washing away inflammation and degradable products, and eliminating intra-articular effusion to decrease intra-articular pressure, control pain, and improve function. High success rates have been reported for internal derangements (ID) and closed lock56. If arthrocentesis does not bring pain relief, the patient has a pathologic condition unresponsive to lavage, such as fibrous adhesions or osteophytes, which requires surgical correction. The effectiveness of arthrocentesis is temporary; also, it does not rehabilitate the micro-architecture of the TMJ. Injecting some biological or non-biological agent with tissue regeneration capacity into the TMJ might help stimulate regeneration processes, especially because intra-articular injections can stimulate regeneration and inhibit degenerative changes in the cartilage57. Different intra-articular injection agents, such as HA, corticosteroids, diclofenac sodium, and platelet-rich plasma, have been used to treat TMJ OA. The puncture site is performed 10 mm away and 2 mm below the canthus tragus line. The syringe has to be directed in a 45° angle from posterior to anterior and from downward to upward until the edge of the temporalis fossa is about 15 mm from the skin. An anterior puncture 20 mm away and 7 mm below the canthus tragus line is used for drainage. Instillation of 250 to 300 cm³ of Ringer solution is recommended for the entire procedure.

Surgical arthroscopy was introduced for anterior release of the joint capsule or the pterygoid muscle to allow for posterior repositioning of the disc and electrocautery of the posterior ligament. Good results were obtained by Davis et al.58. For the single puncture technique, the patient is prepared and draped in the standard fashion for arthroscopy. Approximately 2 mL of lactated Ringer solution is injected into the superior joint space with a 22-gauge needle. Next, an incision measuring approximately 0.5 cm is made along the pre-tragal skin crease. A 1.9-mm sharp trocar with a cannula is then inserted using a standard inferolateral technique. Once inside the joint, the sharp trocar is removed, and a 30° arthroscope is inserted. Next, an 18-gauge needle is placed as an outflow tract. Diagnostic arthroscopy is then performed in a standard fashion. Once the examination is complete, the arthroscope is removed. While the cannula is maintained in place, a switch stick is inserted to allow removal of the standard cannula and its replacement with a cannula with a laser portal (400 µm). Once the specialized cannula is inserted, a laser fiber (200 µm) can be inserted through the portal, and surgical maneuvers can be performed with a holmium:YAG laser. It is important to back the laser fiber slightly out of the joint while manipulating the cannula to a new position to avoid breaking the tip of the laser fiber. Once all the procedures have been performed, the laser fiber is removed, and arthrocentesis is performed with 400 mL of lactated Ringer solution. The joint space is injected with a Kenalog (Bristol-Myers Squibb, New York, NY, USA)/0.5% plain Marcaine (Hospira, Lake Forest, IL, USA) mixture, followed by hyaluronan. The incision is then closed with the single-cannula technique introduced by Stringer and Park59 for operative arthroscopy. This technique allows visualization of the TMJ, but once the examination is complete, the endoscope is removed, and the laser is inserted through the cannula, leaving the surgeon to perform the surgical maneuvers without visualization.

The OSCA technique provides the ability to perform three operations through one system: one-track arthrocentesis, standard arthrocentesis with diagnostic visualization, and visually guided surgery. This technique is relatively simple and includes a single working cannula without the need for a second puncture. Moreover, OSCA seems to be as effective as the traditional TMJ arthroscopy technique in regard to pain relief and mouth opening improvements. In addition, operative time is quite short, especially as the surgeon becomes familiar with the technique. The 55% decrease in pain level and 34% increase in maximum mouth opening following the OSCA procedure are within the ranges reported for standard techniques6061. Arthroscopic lysis and lavage is a standardized procedure for the treatment of chronic closed lock of the TMJ. The effect of arthroscopic lysis and lavage lies mostly in the irrigation of the joint cavity, washout of inflammatory cytokines, mobilization of the articular disc, stretching of the capsule, and lysis of intra-articular adhesions62. Machoň et al.63 evaluated the efficacy of arthroscopic lysis and lavage in treating patients with chronic closed lock and found that patients with a shorter duration of symptoms benefited more than those with a longer duration. Indresano62 hypothesized that lysis and lavage can reverse the problem when it is caught early, and that operative arthroscopy is required for prolonged, advanced stages of the disease. Patients in the early to intermediate stage had excellent results in 94% of cases. Smolka and Iizuka64 and Smolka et al.65 found similar results. Complications after arthroscopy of the TMJ usually present in the immediate postoperative phase and are mostly associated with fluid collection and vascular injury. Other rare complications include Horner syndrome, extravasation of fluid from the articular capsule, upper airway compression, variant petrotympanic fissure, infection of the infratemporal space, pseudoaneurysm, and arteriovenous fistula. Arthroscopic lysis and lavage was found to be effective in increasing mouth opening in patients suffering from intermediate/late stage ID and in decreasing and even eliminating the intermittent locking episodes and transient pain that characterize patients with early/intermediate stage ID. Several studies demonstrating the efficacy of TMJ arthroscopy have been published. In a multicenter study by McCain et al.66 involving 6 years and 4,831 joints, patients responded very well to TMJ arthroscopy for various forms of ID. TMJ arthroscopic lysis and lavage was specifically successful in intermediate and intermediate/late progression of ID (Wilkes stages III and IV), as reported by Murakami et al.67, who showed an average 90% success rate with arthroscopic lysis and lavage in a 5-year follow-up study.

Patient examination and discussion and magnetic resonance imaging (because most cases involve disc displacement) are followed by impression collection for splint construction (mostly maxillary SSs) to regain a nonpainful maxillomandibular relationship. Adjunctive therapies to splint therapy are LLLT and medications (such as CH Alpha, a liquid containing bioactive collagen peptides, and a patented compound called Fortigel).

Treatments range from simple self-care practices and conservative treatments to injections and open surgery.(Fig. 1) Most experts agree that treatment should begin with conservative, nonsurgical therapies, with surgery left as the last resort. Many of the treatments discussed here work best when used in combination.