# Use of Tens in the Diagnosis of Functional Mandibular Lateral Deviation
## 2 Material and Methods
### Experimental Protocol  
Neuromuscular recording was performed on 60 patients. First, alginate impressions of the upper and lower arches were taken and accurate dental casts were made for each patient. The midline asymmetry was measured in relation to the upper and lower incisal midline. Secondly, the discrepancy of the midline with respect to the upper and lower interincisal lines was evaluated. For each plaster model then, reference points were highlighted: a line that goes from the interincisal point of the maxilla up to the mandible, and a line on the right and left molar side on the horizontal plane. Later TENS was applied to relax the musculature and thus determine the rest position of the mandible, which was then measured and recorded. TENS was administered using an electro-stimulator specifically designed for dentistry called Myomonitor J5 (J5, Myotronics, Kent, WA, USA, [[https://www.myotronics.com/j5](https://www.myotronics.com/j5)]([https://www.myotronics.com/j5](https://www.myotronics.com/j5)), accessed on 4 December 2023). The electrical pulse delivered has a frequency of 0.66 Hz, which is why this type of stimulation is also called ULF (ultra-low frequency) TENS. The duration of the impulse is less than 500 us, and the amplitude is such that it does not evoke the upward movement of the mandible during the preparation phase (5 min) prior to recording the cranial jaw relationship. This amplitude of stimulation, defined as sensory amplitude, has been shown to be sufficient in inducing a reduction in the surface emg values of the anterior temporal and masseter muscles comparable to that obtained with motor amplitude ULFTENS, which requires a greater amplitude of stimulation and, therefore, more discomfort for the recipient. Stimulation is transferred to the subject by means of three electrodes, one positioned posteriorly on the neck (below the hairline, on the midline) and the other two anterior to the tragus, one on the right and the other on the left. The electrode on the back of the neck is the positive end of the stimulating circuit, while the negative end is split into the two anterior electrodes to allow symmetrical and simultaneous stimulation (Figure 1). The stimulation protocol involves 5 min of sensory amplitude stimulation, then the person is asked to open the mouth and a previously prepared occlusal registration material is injected onto the occlusal surfaces with a disposable syringe without needle. In our  
Figure 1: These photos show the application of TENS electrodes. case, this is a dental resin (Sapphire(tm) Acrylic Peripheral Impression Material, Keystone Industries, Gibbstown, NJ, USA, https:// dental.keystoneindustries.com/product/sapphire-acrylic-peripheral-impression-material/, accessed on 7 December 2023). The patient is asked to close the mouth and gently pull the lips together without manipulating the jaw or the face. One waits a minute for the jaw to return to the rest position obtained with ULFTENS and increases the amplitude of the impulse until a slight automatic upward movement of the jaw towards the upper jaw is obtained. This movement determines the impression of the teeth of the upper jaw in the resin placed on the occlusal surface. When the resin has a plastic consistency (approx. 1 min) it is removed from the mouth and placed on the plaster models awaiting its complete hardening. At this point, the child is discharged. When hardening is complete, the models are mounted on the Galetti articulator(Sevtis-Fisat s.r.l. Plastic Technology, Tianjin, China). In Figure 2, there is shown a patient who does not change her position after TENS [1,24]. With dental casts mounted in the articulator in the myocentric position with the interposed print, the change from the occlusal position was evaluated considering the initial reference lines; it was then calculated in millimeters and analyzed by a digital caliper. All measurements were performed twice, and the examiner's error was examined using the formula \(s(i)=\sqrt{\Sigma}d^{2}/2n\).