The present study aimed to evaluate the treatment changes by the MEAW technique in treating anterior open bite patients with TMD. All patients, except two patients, did not present TMD symptoms throughout treatment. The two patients presented mild discomfort and did not get worse. Therefore, it appears that the MEAW technique might be a viable treatment option for patients who are not able to choose surgery as a treatment of choice. The MEAW treatment approach might help unload the joint and reduce the risk of relapse of TMD symptoms during orthodontic treatment.
The temporomandibular disorder (TMD) is defined as a set of functional and pathological conditions affecting the temporomandibular joint (TMJ), masticatory muscles and tissue, and their adjacent components .The relationship between occlusal factors, orthodontics, and TMD remains controversial. Based on the previous literature, orthodontics in the normal population “neither produces nor cures” the TMD .In clinical practice, the most common chief complaints are pain, articular sounds (clicking and creaking), limited mouth opening, and disrupted jaw movements . Among the symptoms, pain is the most urgent problem that plagues patients’ daily lives and is often the main reason they seek help . Michelott  suggests that orthodontic treatment should be avoided until the pain is relieved.
It is necessary to conduct X-ray screening for patients with TMD symptoms before initiating orthodontic treatment. This will help the orthodontist determine whether the patient is in the quiescent or progressive stage, so as to avoid problems in the subsequent orthodontic treatment. Orthodontic treatment, to improve the masticatory function and aesthetic, can be considered once the TMD is stabilized [18, 19].At present, most experts recommend conservative treatment for mild to moderate TMD patients to stabilize the TMD. Conservative treatment usually results in satisfactory clinical outcomes. Most importantly, patients are more receptive of a more conservative approach [20, 21, 22]. Occlusal stabilization splints have always been the main treatment method for jaw dysfunction and the most common treatment method in oral instruments . Occlusal splints aim to “unload” the condyles to relieve discomfort and muscular pain. Splints may help prevent the progression of TMD and can be beneficial for reducing pain .It is generally recognized that splints are useful in the conservative treatment of TMD [25, 26]. Once the TMD symptoms are alleviated through splint therapy, the possibility of recurrence or exacerbation of TMD symptoms by orthodontic treatment is very low. Orthodontic treatment combined with the use of a splint is effective for reducing pain and restricting mandibular movement, but not for joint sound [27, 28].
Anterior open bite is considered one of the most challenging dentofacial deformities to treat . Extrusion of the upper and lower incisors is a common way of correcting the anterior open bite, which can be achieved through vertical elastics, extrusion arches , or a MEAW appliance .
The present study shows that the MEAW technique can be a viable and effective option in correcting severe skeletal open bites in patients with TMD without utilizing TADs or other auxiliaries. However, the biggest drawback of this technique is that it relies on the patient’s cooperation. With poor cooperation, there are serious consequences. Moreover, it is not easy to achieve counterclockwise rotation of the occlusal plane because of the extrusion of the anterior teeth rather than the intrusion of the molars. At the same time, extruded anterior teeth are unstable and prone to relapse .
It has been well documented that molar intrusion is necessary for the mandible to be rotated counterclockwise, as well as to reduce the lower face height and facial convexity. In this study, from the maxillary superimposition of the non-extraction group (Table 3, Figure 3), the upper molars were intruded by 0.81mm and distalized about 0.9mm, which is challenging to achieve without using TADs. In non-extraction group, distal tipping more than 10° provided space for resolving the crowding and retracting the upper incisors as well (Table 3, Figure 3). Unfortunately, the uprighting of the mandibular molars caused extrusion of the mesial cusp by about 1.0 mm (Table 3, Figure 3). It seems that the MEAWs are not sufficiently effective in controlling the mandibular molars; an additional modality to control lower molars is required.
In recent years, it has become popular to use temporary anchorage devices (TAD) to correct anterior open bites . Several case reports have illustrated the successful use of TADs in non-growing skeletal open bite cases that obtain “orthognathic surgery-like” results. TADs have elevated open bite correction in non-growing patients and have created higher levels of success .
Current evidence suggests that using the MEAW appliance in conjunction with TADs allows the lower molars to be intruded effectively with mild extrusion of the incisors. They also documented counterclockwise rotation of the mandible, which closed the anterior open bite and reduced the lower facial height to improve facial esthetics . In further studies, we need to compare the long-term stability of open bite correction using the MEAW technique only and using the MEAW technique in tandem with TADs or other appliances.
Due to the nature of retrospective studies, the present study has limitations. Severe skeletal open bite with TMD is relatively rare condition, so the sample size was not ideal. TMD evaluation was based on clinical examination and not all patients had MRI or 3D imaging. In addition, the sample was derived from a single institution. Therefore, the generalization of the results of this study should be limited and carefully interpreted.