The Effect of Photobiomodulation on Temporomandibular Pain and Functions in Patients With Temporomandibular Disorders: An Updated Systematic Review of the Current Randomized Controlled Trials

Introduction: Temporomandibular disorders (TMDs) are the most prevalent non-dental origin orofacial pain conditions affecting the temporomandibular joints (TMJs) and/or orofacial muscles. Photobiomodulation therapy (PBMT) is a conservative way to improve function and reduce symptoms in TMD patients. This systematic review was conducted to update evidence about the effects of PBMT on pain intensity, TMJ movements, electromyography (EMG) activity, pressure pain threshold (PPT), and TMJ sound in patients with TMDs. Methods: A systematic literature search was conducted in Web of Science, PubMed/Medline, and Scopus databases using appropriate keywords and specific strategies from January 2000 to September 2022. Data extraction was done based on the inclusion/exclusion criteria. Results: A total of 40 studies were included. All included studies except one provided information on pain intensity; 27 studies showed a reduction in pain intensity in PBMT groups compared to control groups. Seven out of 15 studies, which reported maximum mouth opening (MMO), showed a greater MMO in PBMT groups than in placebo groups. In addition, the figures for passive maximum mouth opening (PMMO) and active maximum mouth opening (AMMO) in all the studies reporting PMMO and AMMO were higher in PBMT groups. In eight out of ten studies, lateral movement (LM) was greater in PBMT groups. Moreover, in three studies out of four, protrusive movement (PM) was reported to be greater in the PBMT group. Four out of nine studies showed a greater PPT in the PBMT group. Reduced TMJ sounds in the PBMT group were reported in two out of five studies. In addition, in most studies, no difference in EMG activity was detected between the two groups. Conclusion: This updated systematic review showed the promising effects of PBMT on the alleviation of pain and improvement in MMO. Using the infrared diode laser with a wavelength ranging between 780-980 nm, an energy density of<100 J/ cm2, and an output power of≤500 mW for at least six sessions of treatment seems to be a promising option for treating mentioned TMDs signs and symptoms based on the previously reported findings.

Temporomandibular Joint: Review of Anatomy and Clinical Implications

Temporomandibular joints (TMJ) are one of the most complex joints. Each one is located on one side of the face, and are composed of mandibular fossa, joint tubercle, and condylar process of mandible, separated by an articular disk. To these structures are attached ligaments and muscles, which will provide stability and movement. When TMJs work properly, jaw movements can be performed without pain or discomfort. It is important to mention that the complex formed by both TMJs will confront the maxillary with the mandibular bone and therefore will be related to the occlusion, linking these structures during growth and development.

[Characteristics of MRI and associated pathological features of the condylar cyst like lesions in temporomandibular joint]

Objective: To analyze the MRI characteristics and pathological features of the condylar cyst like lesions in temporomandibular joint (TMJ). Methods: The study was conducted retrospectively on TMJ images from 14 patients (2 males, 12 females, aged 10-71) who underwent MRI examinations, from January 2015 to December 2017 at Center for TMD and Orofacial Pain, Peking University School and Hospital of Stomatology including 2 patients with pathological results. The signals of the lesion, condylar bone and disc-condyle relationship were evaluated. Results: Cyst like lesions of 15 condyles from 14 patients were analyzed. All of the lesions showed hypersignal on T2WI (12/12), while most of them showed hypersignal on T1WI (8/11) and PDWI (11/12). Mostly the lesions were surrounded by hyposignal linear margin (12/15), with normal condylar bone signal (13/15). Disk displacement with reduction was discovered in 3 joints, while disk displacement without reduction was discovered in 8 joints and 4 joints had normal disk-condyle relationships. The pathological components of cyst like lesions included cartilage, loose connective tissue, hemorrhage and bone tissue. Conclusions: Differed from those of large joints like hips or knees, MRI characteristics of cyst like lesions of condyle in TMJ exhibited hypersignal imaging in both T1WI and T2WI, indicating that the components of cyst like lesions included granulation tissue, not fluid.

[MRI observation of condylar location and morphology in the patients with temporomandibular disc displacement]

Objective: To evaluate the mandibular condylar location and morphology in the temporomandibular joint disorders. Methods: One hundred thirty-seven TMD patients (age 37.5±16.1 years, male/female=39/98) were performed with MRI scan for temporomandibular joint (TMJ) from November, 2011 to April, 2019 in Department of Radiology,Hainan Hospital of General Hospital of Chinese PLA and General Hospital of Chinese PLA. The patients were classified into 3 groups according the disc displacement: disc without displacement (DWoD) (185 TMJ), disc displacement with reduction (DDWR) (17 TMJ) and disc displacement without reduction (DDWoR) (72 TMJ). The location (anterior position, central position and posterior position) and morphology (oval shape, flat shape and beaklike shape) of the condylar head were observed on the sagittal PDWI, and the long and short axes were measured on the axial T2WI. Another groups were classified into 3 subgroups according to the disc displacement of bilateral TMJ: bilateral normal disc location (biND) (74 cases), unilateral disc displacement (uniDD) (40 cases) and bilateral disc displacement (23 cases). The inter-condyle angle was measured on the axial T2WI. Results: There was no significant difference for the location of condylar head among DWoD, DDWR and DDwoR groups (χ(2)=7.435, P=0.115). The rate for flat condylar shape was significantly higher in DWoD group [83.9%(115/137)] than that in DDWoR group [50.7%(34/67)], and the rate for beaklike condylar shape was significantly lower in DWoD group [16.1%(22/137)] than that in DDWoR group [49.3%(33/67)] (χ(2)=23.521, P<0.001). The length of long axis presented significantly longer in DWoD group [(17.2±2.4) mm] than that in DDWR group [(15.4±2.0) mm] and that in DDWoR group [(14.7±2.7) mm] (P<0.05). The length of short axis presented significantly longer in DWoD group [(7.3±1.2) mm] than that in DDWR group [(6.5±1.3) mm] and that in DDWoR group [(6.1±1.4) mm] (P<0.05). The inter-condyle angle presented significantly larger in biND group (136°±13°) and uniDD group (132°±14°) than that inbiDD group (124°±17°) (P<0.05). Conclusions: The mandibular condylar morphology changes significantly presented in the patients with temporomandibular disc displacement for the temporomandibular disorders.

[Retrospective analysis of 4 rare cases of temporomandibular joint disc ossification]

Objective: To summarize the clinical manifestation and treatment of temporomandibular joint (TMJ) disc ossification, providing reference for clinical diagnosis and treatment of TMJ disc ossification. Methods: From January 2006 to January 2018, 4 patients with TMJ disc ossification (2 males and 2 females, aged 20-55 years with an average age of 35.5 years) which were admitted to the Department of Oral and Maxillofacial Surgery, Shenzhen Second People's Hospital were analyzed retrospectively. Ossification of TMJ disc was found in 4 cases during TMJ surgery. Two cases underwent partial ossification resection plus disc reduction and anchorage, and two cases underwent discectomy plus temporalis myofascial flap replacement. The causes, clinical manifestations and surgical effects of TMJ disc ossification were analyzed by comparing the maximal interincisal opening, visual analogue scale (VAS) score and MRI imaging indexes before and after operation. Results: The history of anterior disc displacement of TMJ in 4 patients was long (average 11.5 years). In clinic, TMJ disc ossification was characterized by TMJ pain and limitation of mouth opening. The maximal interincisal opening was (32.1±6.1) mm and the VAS score was (7.3±0.4) before operation. MRI showed that the displaced discs of the affected sides were displaced and the condyle bones were worn. During the operation, ossification of TMJ discs was found yellow and hard, and the original elasticity was lost. Pathologic findings showed that the TMJ disc cartilage were ossified to osteoid tissue. Under the microscope, bone cells scattered around the bone cells and red trabecular bone were seen, and there were bone trabecula formed. In a follow-up of one year, TMJ pain was significantly decreased [VAS: (1.7±0.2)], and the maximal interincisal opening was (38.5±2.2) mm. MRI showed that the TMJ disc returned to normal position, and the sign of repairing and reconstruction of condyle bone could be found. Conclusions: Long term displacement of TMJ disc may cause ossification with pain and limitation of interincisal opening. According to the degree and extent of ossification, partial ossification plus disc reduction and anchorage or discectomy plus temporalis myofascial flap replacement is feasible, and the clinical effects are satisfactory.

[Pilot study of trans-oral ultrasonography of temporomandibular joint in oblique sagittal plane]

This pilot study aimed to investigate the feasibility of trans-oral ultrasonography of the temporomandibular joint (TMJ) in oblique sagittal plane. Six volunteers who were receiving residency training at Hainan Hospital of General Hospital of Chinese PLA were recruited into this study, five of them had normal TMJ and one had anterior displaced disc all of which had been confirmed by MRI. A hockey-stick-shaped ultrasound probe was placed between the cheek and maxilla to push against the mucosa lateral to posterior maxillary tuberosity, and every volunteer underwent bilateral scans. The sonographic imaging were completed successfully on the six volunteers; the condyle, the superior and the inferior head of the lateral pterygoid muscle, the disc and the maxillary vein were clearly identified in all the twelve ultrasonographic scans. The feasibility of trans-oral ultrasonography of TMJ in oblique sagittal plane was confirmed.

[The relationship between temporomandibular joint disc displacement and condylar resorption and the comprehensive treatment protocol]

Temporomandibular joint (TMJ) anterior disc displacement (ADD) is one of the most common TMJ disease. However, the treatment of ADD have been far from reaching a consensus. In this article, we focused on the following three aspects: ①The relationship between ADD and condylar resorption. ②Whether disc reposition can stop condylar resorption or even make condylar regeneration. ③Proposing a more reasonable treatment pattern, that is TMJ-jaw-occlusion comprehensive treatment protocol.

[Displacement and tissue remodeling of temporomandibular joint disc]

Sounding takes the highest prevalence of the signs of temporomandibular disorders (TMD). The well accepted theory of the mechanism for temporomandibular joint (TMJ) sounding is the internal derangement typically characterized by disc displacement. However, according to literature, there are approximately one third of asymptomatic joints in population had disc displacement, and, on the other hand, there are one fourth of TMJ sounding patients had not signs or very limited signs of disc displacement. Replacing the displaced disc to the normal position via methods like surgical operation did not achieve satisfactory long-term outcomes. In this review, we discuss and analyze the possible remodeling of the joint disc displacement diagnosed with imaging based on the anatomy and pathophysiology.

[Physical therapy for temporomandibular joint anterior disc displacement without reduction]

Temporomandibular joint (TMJ) anterior disc displacement without reduction (ADDwoR) is a common type of temporomandibular joint disorders. Most patients experience limited mouth opening and joint pain at the same time. The standpoint of physical therapy is the function of the joint instead of the displaced disc. The treatment aims to make symptoms disappeared and joint function regained through 3M techniques, including modality, manual and movement. For ADDwoR patients with limited mouth opening within 2 month, manual therapy may reposition disc and the following splint and movement therapy can maintain disc-condyle relationship. Even so, restoring anatomical relationship is not the end of physical therapy. Enhanced health education and multidisciplinary cooperation are important for successful management of the ADDwoR patients.

[Understanding and treatment strategy for disc displacement of temporomandibular disorders]

Understanding and treatment strategy for disc displacement of temporomandibular disorders (TMD) were discussed in the present review. It has been strongly recommended by the author that the treatment strategy for disc displacement, one subtype of TMD, should be mainly the reversible conservative treatment methods. The most important goal of treatment for disc displacement is to recover the mobility and function of the joint in order to improve the quality of the patient's life. Comprehensive assessments both from somatic and psychological aspects for each TMD patient are necessary, especially for the patients with chronic pain. Although the role of surgical operative treatments is very limited in the general treatment strategy for TMD, it is still important for a few patients who had definite diagnosis of intra-articular disorders, severe symptoms affecting the quality of patient's life and failed to response to the correct conservative treatments. It should be very careful to treat the TMD patients by surgical operation or irreversible occlusion treatments changing the natural denture of the patient, such as full mouth occlusional reconstruction and extensive adjustment of occlusion.

[Intra-articular injections of hyaluronic acid for anterior disc displacement of temporomandibular joint]

Anterior disc displacement (ADD) of temporomandibular joint (TMJ) is regarded as one of the major findings in temporomandibular disorders (TMD). It is related to joint noise, pain, mandibular dysfunction, degenerative change and osteoarthritis. In the mean time, the pathological changes were found in synovial membrane and synovial fluid. Hyaluronic acid is a principal component of the synovial fluid which plays an important role in nutrition, lubrication, anti-inflammation and cartilage repair. The synthesis, molecule weight, and concentration of hyaluronic acid are decreased during TMD and cause TMJ degenerative changes. The clinical conditions, pathological changes, the mechanism of action for hyaluronic acid and the treatment of anterior disc displacement of TMJ are discussed in this article.

[Adaptive remodeling of temporomandibular joint following anterior disc displacement and treatment decision making]

Anterior disc displacement (ADD) of temporomandibular joint (TMJ) is one of the common oral diseases. The TMJ can be remodeled after disc displacement. The author's recent studies show that remodeled bilaminar zone is similar to the disc in composition and functions. The remodeled condyle can match the disc-like bilaminar zone. The new disc-condylar relationship can, to a certain extent, restore the function of the TMJ. Based on these studies, the author believes that the adaptive remodeling in TMJ has important guiding significance for clinical treatment and discusses the views of the treatment decision for various stages of temporomandibular disorders.

[MRI analysis of the effect on mandibular retrusion with anterior disc displacement treated by using Herbst appliance]

Objective: To investgate the effect of Herbst appliance on the growth and remodeling of the temporomandibular joint (TMJ) in class Ⅱ patients with mandibular retrusion by using MRI. Methods: Between December 2010 and October 2014, 12 class Ⅱ patients (11-16 years old) with mandibular retrusion were chosen. The patients were divided into two groups. The control group included 7 patients (14 joints) with normal disc condyle relationship and the anterior disc displacement (ADD) group included 5 patients (10 joints) with anterior disc displacement. The MRI images of TMJ were measured, including condylar height, joint space index and disc position ratio, before and after the treatment. Results: The condylar height of the patients in the control group was significantly increased (P<0.001) after treatment, and no significant difference in joint space index (P=0.821) and disc position ratio (P=0.146) was found. The joint space index of the patients ([-14.70±8.82]% and [4.90±11.35]%) in ADD group changed significantly (P<0.001) after treatment, and no significant difference in condylar height (P=0.294) and disc position ratio (P=0.120) was found. Conclusions: The normal disc condyle relationship was beneficial to the reconstruction of the condylar process, and the increase of the condylar height. The condyle moved forward in patients with anterior disc displacement after treatment.