INTRODUCTION
Bruxism is defined as a repetitive jaw muscle activity characterized by tooth grinding or clenching accompanied with wearing of the teeth, and jaw muscle discomfort in the absence of a medical disorder. Bruxism has two distinct circadian manifestations: it can occur during the day or during sleep and is defined as awake bruxism or sleep bruxism respectively [1]. The etiology of bruxism is not totally clear however, some etiologic factors are; personality characteristics and psychosocial factors such as stress and central factors [2].
Bruxism leads to many negative outcomes affecting the muscles, such as inflammation, chronic local muscular contracture and localized muscular hypertrophy, which may in turn cause myofascial pain [3]. One of the most affected muscles due to bruxism is the masseter, the muscle that elevates the mandible [4]. Hypertrophy of the masseter muscle is an objective sign of bruxism. Additionally, fatigue or stiffness in the masticatory muscles, pain in the temporomandibular joint or headaches are subjective signs of bruxism. According to the literature, the vast majority of the general population experience episodes of bruxism during their lives. Thus, finding an effective treatment method for bruxism is crucial [5].
There is no certain treatment for Bruxism. However, the most recent recommendation is to follow the Multiple-P approach prior to medical drug regimens and invasive procedures. Different methods used in the conservative management of bruxism are known as the multiple-P approach; physiotherapy, plates, pep talk, pills and psychology [6]. Physiotherapy generally focuses on two objectives: decreasing the adverse effects of bruxism to the masticatory muscles and increasing self-awareness regarding this habit. These studies involve different interventions such as massage of the masticatory and cervical muscles, electrotherapy, therapeutic exercises, taping interventions or relaxation therapies [7]. Manual Therapy (MT) is a widely used physiotherapy modality which is known to be effective in the management of musculoskeletal problems [8]. MT is a passive, therapeutic approach used to target a variety of anatomical structures with the intent to create beneficial changes in the amount of pain a patient experiences. MT includes mobilization, manipulation, and treatment of the soft tissues or joints and is widely used to break fibrous adhesions, restore normal range of motion, reduce local ischemia, stimulate synovial fluid production, and reduce pain [9]. Another passive intervention used in physiotherapy is the Kinesio taping method. Kinesio Tape (KT) is a type of elastic therapeutic tape that was developed by Dr. Kenzo Kase and is used in many different situations with various aims. Advocates of KT state that it may promote different therapeutic objectives such as; improved circulation and lymphatic drainage, pain inhibition, reduction of delayed onset of muscle soreness or improvement in performance and coordination [10-12]. However, literature regarding which physiotherapy intervention is the most effective in bruxism is not clear. More clinical trials are necessary to clarify the effectiveness of different interventions.
Studies evaluating muscle thickness using Ultrasonography (US) [13, 14] and muscle thickness/width and cross-sectional area using Computed tomography [15, 16] have been conducted to assess changes in masseter morphology associated with orthognathic surgery. Although the muscle stiffness meter has been validated as a reliable method for evaluating muscle stiffness in the clinical setting, it only provides stiffness at certain points on the muscle [17, 18]. Ultrasound elastography is an imaging modality based on tissue stiffness or hardness, which is analogous to clinical palpation with ultrasonography for a malignancy. Unlike a physical examination, which allows only the subjective judgment of the stiffness of a lesion, elastography has the potential to quantify stiffness [19].
There are two elastographic techniques available as; strain and shear-wave elastography (SWE). Strain elastography produces an image based on the relative displacement of the tissue with manual compression of the transducer. The limitation of the strain technique is that the free hand probe pressure is difficult to standardize and the strain variations due to changes in the amplitude and velocity of compression that cannot be avoided. Meanwhile, SWE using the acoustic radiation force induced by the ultrasound push pulse generated by the transducer provides quantitative elasticity parameters, as well as displaying a visual color overlay of elastic information in real time [20].
In recent years, the ultrasound elastography (USE) has also been used to evaluate muscle stiffness and it was stated that the elasticity index (EI) ratio is a reliable method for determining masseter muscle stiffness [21, 22]. However, to the best of our knowledge, SWE has not been applied to follow-up treatment of masseter muscle changes.
Therefore, the purpose of this study was to compare the results of two different treatment modalities (Manual therapy intervention and Manual therapy plus Kinesio Taping Intervention) in patients with bruxism using shearwave ultrasonography (SWE).