Devices to Measure Tongue Force - a Critical Analysis

Introduction: For several years, researchers have been looking for methods to quantify the force or pressure exerted by the tongue. A lot of devices were constructed for this purpose. However, on Speech-Language Pathology clinical practice, tongue force is still evaluated by qualitative methods in which only perception and practical experience are used to classify this force. Quantitative evaluation is accomplished using instruments that show the numerical value of the force or pressure exerted by the individual, which makes the diagnosis of the tongue more accurate. The purpose of this study is to present a critical literature review about the devices to quantify tongue force. Methods: Through a bibliographic search in libraries and databases such as Medline, Lilacs, Bireme, Capes, and patent’s databanks, 120 studies on tongue force were reviewed. They cover the period until 2010 without initial period limitation. Thirty six different devices were described. Results: The devices were grouped into categories according to their technology: mouthpiece containing strain gauges (N=9), load cells (N=1) or force sensing resistors (N=2), pressure sensors attached on teeth or on palatal plates (N=7), dynamometers (N=3), bulbs filled with some fluid and connected to a pressure sensor (N=7) and other technologies (N=7). Some of them have shortcomes such as not being sensitive enough to small changes in force (dynamometers), difficulties in positioning reproducibility (bulbs and sensors attached to teeth), force direction different from clinical evaluation (sensors on palatal plates) and other specific points for each device. A critical analysis of the technologies is presented. Some studies describe the use of electromyography to estimate muscle force and were also discussed. Methodological differences made it difficult to compare the forces measured in different studies, as they depend of the degree of protrusion, the direction of the movement, the distance between mandible and maxilla, the tongue region in contact with the sensor, the area in which the pressure is exerted. A lack of reproducibility in any of these parameters might lead to significant variation in the obtained results. Conclusion: Several instruments to measure tongue force were found. All these methods can potentially help the professional in the evaluation of orofacial myology, making the diagnosis of tongue force more reliable. According to their specific design, devices are more indicated to different assessments of tongue force, as 15 different muscles are involved in tongue movements. Other advantages of the quantitative evaluation are the possibility to follow the evolution of the therapy, to facilitate the communication among professionals involved in the treatment of the patients and to make the prognosis of the treatment more accurate.