Temporomandibular disorders affect the quality of life, causing pain and limitations in jaw movements [1] . After dental pain, temporomandibular disorders are the most common cause of orofacial pain and have the potential to produce chronic pain [2] . The temporomandibular joint (TMJ) is a complex anatomical structure that plays an important role in the ability to speaking, chewing, and swallowing [3] This is achieved through mandibular movements, these are the displacements that the jaw can perform thanks to the dynamics of rotations and translations in a three-dimensional manner [4] .

Transcutaneous Electrical Nerve Stimulation (TENS) has been studied as a non-invasive therapy for these disorders, demonstrating effectiveness in relieving pain and relaxing muscles [5] , this is achieved through the use of functional low-voltage electrical impulses delivered via electrodes on the skin, which reduce the sensation of pain and allow for physiological muscle elongation [6] . TENS inhibits nociceptive impulses from nerve fibers, thereby activating endogenous mechanisms known as “diffuse inhibitory controls” [7] . TENS for TMJ works through electrical stimulation, which allows the muscles involved in the TMJ, such as the masseter and temporalis, to relax and improve mobility by reducing stiffness. Additionally, it increases blood circulation, helping to reduce inflammation and promote healing of this condition. Contraindications for TENS include patients with pacemakers, as the electrical impulses can interfere with their functioning, and patients with infections or neoplasms, as it can worsen their condition. The risks of the therapy include irritation in the area where the electrodes are placed and overstimulation, which can cause muscle fatigue. Therefore, it should be performed professionally to ensure correct application. However, its specific use in TMJ disorders requires further research.

Aurelié et al., compared TENS with low-level laser therapy, ultrasound therapy, and occlusal splints, finding that 67% of patients treated with TENS no longer experienced discomfort while chewing and opening their mouths, compared to only 53% with occlusal splints. No significant differences were found with ultrasound therapy [8] .

This study explores the impact of TENS on patients with temporomandibular disorders before orthodontic treatment, aiming to contribute to the scientific literature. It evaluates maximum mouth opening, mandibular lateralization, and pain perception before and after TENS. The results are expected to enrich scientific knowledge and offer more effective treatments for these disorders.

Evaluate the effectiveness of transcutaneous electrical nerve stimulation in mandibular deprogramming in patients at the Orthodontics Clinic of the Juarez Autonomous University of Tabasco.

A paired samples T-test analysis was conducted for before/after measurements for each of the variables before and after the application of TENS. A significant difference was found for mouth opening with a P-value less than 0.001. It was observed that the mean value of mouth opening before the application of TENS was 37.7 ± 6.4 mm, and after using TENS, the value found was 44.6 ± 5.88 mm ( Table 1 ). These values indicate an improvement in the maximum mouth opening movement of 18.3%.

Additionally, due to the high correlation coefficient found, it was decided to explore whether there was a model explaining the relationship between the values before and after. Thus, a simple linear regression method was applied, and it was found that the scatter plot followed a linear trend ( Figure 1 ), Equation (1) serves as a predictive model for the before and after relationship. Moreover, Equation (2) shows the coefficient of determination that indicates the explained variation is up to 90.5% accurate; the remaining 9.5% is due to unexplained variations, which may be attributed to factors such as the level of temporomandibular disorder and the individual anatomy of each patient.

$\text{Y}=0.8705\text{x}+\mathrm{11.79.}$ (1)

$R^2=\mathrm{0.905.}$ (2)

The average value of right laterality before the application of TENS was 3.86 ± 1.57 mm, and after the therapy, an average of 5.43 ± 1.21 mm was found ( Table 1 ). The results for left laterality improved from an average of 3.13 ± 1.63 mm to a value of 4.53 ± 1.61 mm ( Table 1 ). Protrusion was 4.01 ± 1.7 mm and after 40 minutes of therapy, its value was 5.36 ± 1.32 mm ( Table 1 ).

Pain perception showed a significant difference with a confidence level of 99% and a significance level of 1%. It was observed that the mean value before the application of TENS was 4.56 ± 2.045 mm, and after the use of TENS, it was 2.03 ± 1.5 mm ( Table 1 ).

a. Comparison of the mean before and after TENS therapy.

Regarding the consulted scientific literature, there are articles evaluating the outcomes of transcutaneous electrical nerve stimulation in the TMJ. It is important to note that within the limitations of this study, there was no control group to ensure that the intervention is responsible for patient improvement, as placebo effects were not verified. Similarly, the bias that may exist with the VAS is due to the variability of evaluations, as they are subjective and dependent on each patient’s individual pain perception. Similar studies have sought to determine the effectiveness of TENS. Authors such as Zhang et al. found that pain reduction and increased range of opening were better following the application of TENS (P = 0.007). Compared to the results of this study, it can be determined that the results are consistent, as our confidence level was 99% [10] .

Other authors, like Barile, analyzed the effects of TENS application with an emphasis on pain through recruited clinical trials; similar to this project, there is a decrease in pain intensity, suggesting that TENS can also be included in therapies for treating TMD [11] .

Additionally, in other research such as that by Aurélie et al., it was found that there is a significant functional improvement in mandibular opening movement, achieving values up to 19.46% higher. In this study, the improvement in the range of this movement was 18.3% [8] .

After the observation and analysis of the obtained data, it can be concluded that applying transcutaneous electrical nerve stimulation (TENS) at ultra-low power for 40 minutes, with a duration of 300 microseconds and a frequency of 4 Hz, resulted in a significant difference before and after using the device in terms of maximum opening, as well as lateral and protrusive movements. In patients with Temporomandibular Disorders (TMD), TENS proves to be effective in providing short-term pain relief, significantly contributing to the reduction of painful symptoms experienced by these patients.

In addition to its analgesic effects, TENS produces immediate muscle relaxation, which can improve patients’ quality of life. However, it is important to consider that this technique should be viewed as a complementary therapy, as it does not address or correct the underlying etiology of TMD. Despite this limitation, TENS therapy stands out as a non-invasive treatment that does not require surgery and is not painful, making it a generally well-tolerated option for most patients. This acceptance and tolerability favor its incorporation into comprehensive therapeutic regimens for managing Temporomandibular Disorders.