Evaluation of different treatment modalities in patients with disc displacement with reduction using systematic review and meta-analysis

INTRODUCTION

Temporomandibular disorders (TMDs) is a collective term for a group of musculoskeletal conditions, in-volving pain and/or dysfunction in the masticatory muscles, temporomandibular joints (TMJs), and asso- ciated structures [1]. These symptoms include joint and muscle pain, restricted mandibular movements, and joint sounds. Disc displacement with reduction (DDwR) is an internal TMJs’ derangement, where the articular disc moves medially/laterally (with or without intermittent locking), or anterior to the condylar head [2]. Joint clicking may or may not be present in DDwR presentations, which can include discomfort and/or dysfunction. Anteri-or repositioning splints (ARS), thermal packs (moist heat fomentation), physiotherapy, such as ultrasound (US) therapy, jaw relaxation through soft food consumption, refraining from gum chewing, and oral parafunc-tional habits, coupled with jaw exercises to correct poor posture, are the most frequently suggested non-surgical treatment modalities for TMDs and DDwR [3, 4]. Other interventions, including medication, physical therapy, and occlusal splints, have been suggested to address the symptoms of TMDs [5]. One of the primary conservative therapies for myofascial pain and disc displacements with or without reduction is stabilization splint therapy, reported with some success in the literature [6]. Non-steroid anti-inflammatory medicines (NSAIDs), sedatives, antidepressants, muscle relaxants, and vitamins, are among the medications used in the pharmacological therapy of TMDs [7]. Furthermore, parafunctional habit therapy, occlusal splints, and physical therapy techniques, such as laser, acupuncture, and ultrasound, can be employed [8]. Studies have examined the efficacy of physical therapy and splint approach in patients with disc displace-ment without reduction [9-13], but treatment modalities for DDwR are lacking. There is a need for compara-tive studies and reviews evaluating the efficacy of different modalities currently employed in the management of DDwR. Additionally, some older randomized controlled trials (RCTs) have strongly questioned beneficial effects of specific splints in the management of these conditions [14-16]. However, in terms of evidence-based literature, a direct comparison between splints, ultrasound, and laser therapy, compared with home exercise programs, counselling, and patient education, in the treatment of DDwR has not been assessed comprehensively. Therefore, the current systematic review seeks to provide a quantitative analysis of the efficacy of different treatment modalities in patients diagnosed with DDwR.

MATERIAL AND METHODS

This systematic review was conducted according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines and the Cochrane Handbook [17]. The protocol for the study was registered in the International Prospective Register of Systematic Reviews (PROSPERO, reg. No: CRD42024508856) before initiation.

FOCUSED QUESTION

The study question was as follows: Is there a difference in the efficacy of splints, ultrasound, and laser therapy compared with home exercise programs, counselling, and patient education, in pain and maximal mouth opening in patients diagnosed with symptomatic DDwR?

SEARCH STRATEGY

Electronic records, including PubMed/Medline, Cochrane Central Register of Controlled Trials, Scopus, and Embase, published from January 2011 to September 2024, were searched by two reviewers. Additional sources, such as Google Scholar and cross-references were explored. Also, reviewers searched emerging re-search registries, such as the Clinical Trial Registry India and the National Institutes of Health Trials. For un-published studies, the authors were contacted. To maintain a thorough screening, a manual search of oral surgery- related journals was carried out. Two reviewers formulated the search strategy by employing controlled ter-minology, including Medical Subject Headings (MeSH), key terms, and synonyms related to “temporoman-dibular joint disc displacement,” “displacement with reduction,” “occlusal splint,” “ultrasound”, “high-level laser therapy”, combined with “AND” “OR” “Boolean algorithms”. During the search, no language restrictions were imposed. The search strategy was first formulated for PubMed, and then adjusted to meet the requirements of other databases. Clinical trials and RCT filters were applied for PubMed during the search. We also explored and browsed through the first 100 results on the Google Scholar search engine to locate potentially relevant articles. Rayyan, a free online systematic review tool, eliminated duplicates. In addition, two reviewers independently performed title and abstract screening of articles in Rayyan. The selected ti-tles/abstracts were then read in entirety by the same two reviewers to determine their eligibility. Conflict at any stage was resolved through discussion with a third reviewer.

ELIGIBILITY CRITERIA

The population, intervention, comparison, and outcomes (PICOS) tool was utilized for inclusion criteria, as follow: 1) population – adult patients diagnosed with symptomatic DDwR at present or within the last 6 months; 2) intervention – splints (occlusal splint, anterior repositioning splint, and lingual splint), ultrasound, and laser therapy; 3) comparison – home exercise program, counselling, patient education on pain and maxi-mal mouth opening; 4) outcomes – pain and maximal mouth opening; 5) study design – randomized con-trolled trials.

DATA EXTRACTION

A tabulated form was filled by two reviewers to extract data, which was subsequently verified by a third reviewer. The authors discussed and resolved conflicts mutually. For each study, the extracted data included author and year of publication, country, sample size, outcome assessed, and conclusion.

QUALITY ASSESSMENT

Two reviewers assessed methodological qualities of the included studies, while a third reviewer was con-tacted for consensus. The Cochrane Handbook for systematic reviews of interventions’ risk of bias (version 5.1.0) tool was employed to assess the quality of identified RCTs [18].

STATISTICAL ANALYSIS

The studies were divided into three categories: splints versus ultrasound, laser versus splints, and laser versus ultra­sound. Each study’s values and findings were presented independently. Difference in mean and standard deviation served as the foundation for a meta-analysis. The results were summed together using a random effects model and standardized mean difference (SMD) with a 95% confidence interval. I-squared (I2) statistic and and chi-square (2) test were utilized to assess heterogeneity. Significant statistical hetero-geneity was defined as a 2 test result of p < 0.1 [19]. Review Manager, version 4.2 for Windows software (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark) was used for data analysis.

ASSESSMENT OF HETEROGENEITY

The following results were reached after assessing he­terogeneity with Cochran’s test and I2 statistics: between 0 and 40% – heterogeneity not significant; between 30% and 60% – moderate heterogeneity; between 50% and 90% – substantial heterogeneity; between 75% and 100% – significant heterogeneity [20].

PUBLICATION BIAS

Begg’s funnel plot was employed to assess publication bias [21], and its asymmetry indicated publication bias and other biases related to sample size.

RESULTS

STUDY SELECTION FINDINGS

The initial database search identified 245 studies. After removing duplicates, primary screening, and secondary screening, five studies were included in the systematic review and meta-analysis [22-26]. The flow dia­gram in Figure 1 presents the detailed descrip-tion of screening process, with reasons for exclusion.

CHARACTERISTICS OF THE INCLUDED STUDIES

As shown in Table 1, data from five studies were evaluated, including a total of 509 patients with TMJs DDwR [22-26]. Among the included studies, three studies were conducted in Turkey [23, 25, 26], one study in Iran [22], and one in Saudi Arabia [24]. All studies compared the efficacy of splints, lasers, and ultrasound with controlled lines of treatment in pain reduction and increase in maximum mouth opening (MMO). Interven-tions employed splint therapy (occlusal splints and ARS), and comparators being physical therapy, counsel-ling, drug therapy, education, self-care, and management instructions for outcomes evaluated (joint pain, clicking, range of motions, MMO, and lateral movements). It was found that all interventions evaluated were equally effective, and provided improved and satisfactory results for patients with DDwR, while one study found a significant reduction in joint sounds in ARS compared with other modalities [22].

ASSESSMENT OF METHODOLOGICAL QUALITY

There was a substantial risk of bias across most domains, with a particularly high risk in selective reporting and incomplete outcome data. The strongest domain was random sequence generation. Quality assessment suggested that the quality of evidence may be compromised and the results should be interpreted cautiously (Figure 2).

META-ANALYSIS

Evaluation of reduction in pain and assessment of mouth opening was observed to measure the effectiveness of splints, ultrasound, and laser in patients dia­gnosed with DDwR.

EVALUATION OF REDUCTION IN PAIN

Laser versus splints: The overall pooled effect estimate showed SMD of 0.37 (–0.88 to 0.14) favoring laser, and signifying that reduction in pain on average was 0.37 times lesser in using laser (p > 0.05) (Figure 3) [22, 24, 25]. Laser versus ultrasound: The overall pooled effect estimate revealed SMD of 0.22 (–1.86 to 1.41) favoring laser, and indicating that reduction in pain on average was 0.22 times lesser in using laser (p > 0.05). There was substantial heterogeneity (I² = 88%) between the two studies, suggesting significantly different results achieved (Figure 4). Splints versus ultrasound: The overall pooled effect estimate showed SMD of 0.04 (–1.36 to 1.28) favoring splints, and signifying that reduction in pain on average was 0.04 times lesser in using splints (p > 0.05) (Figure 5).

EVALUATION OF MMO

Laser versus splints: The overall pooled estimate demonstrated SMD of 0.47 (–0.86 to 0.08) favoring la-ser, and signifying that MMO on average was 0.47 times lesser in using laser (p < 0.05). The effect size (–0.67) sug­gested a moderate clinical benefit of splints compared with laser (Figure 6). Splints versus ultrasound: The overall pooled estimate showed SMD of 1.43 (–1.84 to 4.69) favoring ul-tra­sound, and signifying that mouth opening on average was 1.43 times wider in using ultrasound (p > 0.05). There was substantial heterogeneity (I² = 98%) between the two studies, indicating markedly different results achieved (Figure 7).

FUNNEL PLOT

The funnel plot did not show significant asymmetry, indicating the absence of publication bias. However, with the small number of the included studies, this conclusion should be interpreted with caution (Figure 8).

DISCUSSION

The multifaceted nature of TMDs and difficulties in identifying potential etiology make their management extremely complex. TMDs’ treatment aims to reduce pain, improve mobility, and postpone the advancement of internal derangement. It is exceedingly challenging to achieve the intended treatment outcomes due to the complex etiology of TMDs, particularly in individuals with acute pain and limited jaw motion. Conservative, non-invasive therapy techniques are the mainstay of managing DDwR cases. Low level laser therapy, occlusal splints, and ultrasound therapy, are among the most successful procedures, whether used alone or in a combination. In a study, Ricardo et al. [27] advocated for physiotherapy and viscosupplementa-tion to symptomatically manage the initial presentation of DDwR. Laser therapy has biostimulatory properties, resulting in tissue regeneration, inflammation control, and analgesia. Its mechanism of action enhances adeno- sine triphosphate (ATP) production by penetrating soft tissue, stimulating mitochondrial activity. This plays a role in reducing muscle hyperactivity, improving vascularization around TMJs, and controlling synovitis and capsulitis. Moreover, laser therapy contributes to joint pain reduction, mandibular function improvement, and a relatively better quality of life of DDwR patients. Its non-invasive nature and the absence of adverse effects make it a safe and patient-friendly solution [25]. A systematic evaluation was carried out by Zwiri et al. [28], assessing the impact of lasers on TMJ difficulties. Databases were searched until 2020, and 32 compara-tive studies involving 1,172 patients were found evaluating the efficacy of lasers in treating pain. The trials showed a considerable reduction in pain during laser application, and it was determined that, in comparison with conventional treatment, laser provided satisfying results in patients with continuous pain. Occlusal splints are custom-made dental devices, which help to mechanically stabilize TMJs by decom-pressing the joint and directing the mandibular condyle into a more physiologic position. This minimizes stress on joint structure and encourages muscular relaxation. Clinical outcomes demonstrate considerable reductions in joint noises and pain as well as better jaw movement, particularly when splints are worn con-tinuously throughout sleep [29]. Ebrahim et al. [30] in their systematic review concluded that splint therapy reduced pain in the management of TMJ disorders, and could be used as effective modality. Ultrasound therapy offers thermal and non-thermal therapeutic benefits. It enhances microcirculation, in-creases cellular metabolism, and provides deep tissue heating, which relaxes masticatory muscles and pro-motes tissue healing. Ultrasound successfully alleviates discomfort, joint clicking, and inflammation, while increasing the mandibular range of motion. It is particularly effective for relieving myofascial pain and muscle tightness [29]. Combination therapy, involving splints and ultrasound, has shown superior outcomes com-pared with either modality alone. Patients undergoing combined treatment report faster functional recovery, greater pain relief, reduced joint noises, and improved mouth opening. The mechanical correction of splints complements the anti-inflammatory and healing effects of ultrasound, offering a comprehensive approach for managing DDwR. This systematic review was conducted to provide an overview of comparative analysis on the efficacy of splints, ultrasound, and laser therapy in patients with TMJs DDwR. The efficacy of various modalities was assessed in terms of reduction in pain and MMO. The results of the review suggest that all the interventions evaluated were effective and provided satisfactory results in patients with DDwR, while the pooled estimation through SMD concluded that for reduction in pain, laser was inferior to splints [0.37 (–0.88 to 0.14)], laser was inferior to ultrasound [0.22 (–1.86 to 1.41)], and splints were inferior to US (–1.36 to 1.28). Whereas for mouth opening, it was observed that laser was inferior to splints [0.47 (–0.86 to 0.08], and US was superior to MMO than splints [1.43 (–1.84 to 4.69]. In our research, only pain reduction and MMO outcomes were evaluated. One of the limitations of our study is that a pooled assessment of the effect of these interventions on joint sound, joint clicking, lateral movements etc., was not carried out. Also, only open-access literature and full-text articles available through institutional access were included in the analysis. A network MA of all available literature on different modali-ties for DDwR would provide a greater level of evidence, and guide practice management in this TMD. In addi-tion, the number of included studies for qualitative synthesis as well as for quantitative analysis based on our eli- gibility criteria in the MA was small. Only five studies were included in our analysis. Larger studies with a longer follow-up would have strengthened the findings of our review, thus we consider that another limita-tion of the study. The Cochrane risk of bias tool for randomized controlled trials, reliable methods for qualitative data syn-thesis, and adherence to PRISMA guidelines, all contribute to the strengths of this systematic review. The selected studies had low variability of reported issues, no potential or inevitable sources of bias, and good overall quality, according to the quality evaluation. Laser therapy, occlusal splints, and ultrasound are conservative therapies for DDwR. While each technique has an unique mechanism and benefits, their tailored application can improve patients’ quality of life by ad-dressing joint mechanics and soft tissue inflammation. These non-invasive techniques form the cornerstone of current TMDs’ care, offer dependable relief with minimum risk.

CONCLUSIONS

The findings of our study shed valuable insights on the efficacy of splints and ultrasound in managing DDwR, particularly in terms of pain reduction and MMO improvement. The results suggest that splints and ultrasound interventions hold promise as feasible the- rapeutic options for patients suffering from this condition. Notably, splints demonstrate efficacy in alleviating pain, while ultrasound appears to be more effective in enhancing MMO.

DISCLOSURES

1. The approval of the Bioethics Committee for the research: Not applicable. 2. Assistance with the article: None. 3. Financial support and sponsorship: None. 4. Conflicts of interest: None.

References