Current conservative therapies for ADD without reduction of the TMJ include patient relaxation and stress-reducing therapies; a soft diet; medications, such as analgesic agents or muscle relaxants; splints; and physiotherapy, such as ultrasound and gentle mandibular exercises. Surgical interventions include arthrocentesis, arthroscopy, and open joint surgery. Although some surgical procedures are aggressive, may lead to serious complications, and/or may be primarily reserved for patients who failed to improve following a reasonable course of nonsurgical therapy, surgery can also be used as primary treatment for patients with ADD without reduction of the TMJ.
The most common conservative therapy for ADD without reduction of the TMJ is the use of a splint. Splints can be classified into three major groups on the basis of function: stabilization splints (centric splints), distraction splints, and anterior repositioning splints. Although there are slight differences among the three kinds of splints, splint therapy generally does not reposition the disc on the condyle, although it allows the retrodiscal tissue to produce a pseudodisc where the condyle can function without limitation or pain. With splints, functional recovery of the TMJ can be obtained by adaptation of the retrodiscal tissue, without recapturing the displaced disc. Splint therapy can also decrease loading of the TMJ and remove the triggering mechanisms that program the neuromuscular system to maintain the mandible in an abnormal position [12–15]. Although several studies demonstrated that splint therapy significantly improved MMO and reduced subjective pain in patients with ADD without reduction of the TMJ, the effects of splints on ADD without reduction of the TMJ remain controversial [5, 16]. Haketa et al.  recently conducted a randomized clinical study evaluating the therapeutic efficacy between two treatment options for ADD without reduction: an occlusal splint and joint mobilization self-exercises. Their results suggested that joint mobilization self-exercises are an effective treatment option for improving jaw function and reducing pain and limitations of daily activities in patients with ADD without reduction. Kuboki et al.  reported that the elevator muscles are located behind the most posterior tooth and, therefore, the TMJ is always loaded when the elevators contract. It is usually necessary to wear splints for 6 months to 2 years, depending on the patient. Such long treatment periods can be a disadvantage in elderly patients with ADD without reduction of the TMJ. In addition, elderly patients with this condition have often had symptoms for a prolonged duration, and their disc frequently has an abnormal morphology. These factors can reduce the likelihood of achieving functional recovery of the TMJ with splint therapy. Moreover, although splints are considered one of the most effective treatment options available for ADD without reduction of the TMJ, further studies will be necessary to clarify the mechanism and efficacy of splint therapy.
Surgical intervention is another option for treatment of ADD without reduction of the TMJ. Current concepts in TMJ treatment suggest that a change in disc position is not the primary factor causing TMJ pain or dysfunction. Instead, alterations in joint pressure and a variety of biochemical constituents within the synovial fluid lead to derangement of the TMJ [18, 19]. Arthrocentesis is a simple method of flushing out the TMJ by placing needles into the superior joint space, which can be performed under local anesthesia or sedation. Arthrocentesis under sufficient pressure removes microscopic debris, pain mediators, and inflammatory cells and leads to improved movement by releasing adhesions. Although initially used to treat acute closed lock TMJ, the procedure has since developed into a treatment approach for chronic closed lock TMJ or degenerative joint disease. Several studies have reported the efficacy of arthrocentesis in treating ADD without reduction of the TMJ; however, the technique seems to be ineffective in certain conditions, such as those involving bony changes of the condyle, fibrous adhesions, and perforation of the disc .
TMJ arthroscopy is another type of minimally invasive surgery for treating TMJ disorders, which is usually performed under general anesthesia. Through arthroscopy, the joint can be explored, adhesions can be bluntly released or cut, and the disc can also be released. Murakami et al.  compared clinical short-term results of nonsurgical treatment, arthrocentesis, and arthroscopy for the management of ADD without reduction of the TMJ at 6 months after these procedures in similar age groups (mean ages of 30.4, 31.2, and 32.7 years, respectively). When the criteria for success were defined as an absence or significant reduction of pain, MMO >38 mm, and 6 mm minimum lateral and protrusive movements, the success rates were 55.6 % for the nonsurgical group, 70 % for the arthrocentesis group, and 91 % for the arthroscopy group. However, Schiffman et al.  reported that arthroscopy did not demonstrate statistically significant differences in effect over conservative interventions on all measured outcomes over the short- and long-term in patients (mean age, 31.8 years) with ADD without reduction. Further study is necessary to evaluate the effects of arthrocentesis and arthroscopic surgery in patients with ADD without reduction and structural alterations in the joint tissues, such as cartilage degradation and subchondral bone alterations.
Although disc repositioning with high condylectomy can be employed as an alternative method, with a high therapeutic success rate in ADD without reduction of the TMJ, disc repositioning may be an unreliable and ineffective strategy in patients with ADD without reduction of the TMJ and condylar erosion. Glycosaminoglycans, one of the main components of the TMJ, decrease significantly in patients whose symptoms have been present for a prolonged period, and these reduced levels can lead to disc degeneration. ADD without reduction of the TMJ and condylar erosion are frequently observed in patients with symptoms of a relatively long duration. Furthermore, the disc’s ability to bear heavy loads is impaired by the degeneration caused by disc displacement. Furthermore, Li et al.  reported that patients with ADD without reduction, particularly those in whom the disorder is bilateral, have a higher risk of rupture after repositioning the disc by arthroscopy. Therefore, disc repositioning may be considered only when the disc is minimally deformed and has a near-normal length [23–26].