WO2020132763A1 - Device for correcting sleep bruxism by using a system for electrical stimulation of the mental nerve - Google Patents

Abstract

The invention relates to a device for correcting sleep bruxism by using a system for electrical stimulation of the mental nerve, which is portable and comprises the following components: (1) an occlusal splint containing an intrabuccal electronic neurostimulator formed by at least four capacitive pressure sensors for detecting interdental pressure, a microcontroller unit (MCU) that allows pressure signal data to be acquired and stimulation to be controlled by means of a pre-programmed algorithm, a power system for powering the microcontroller, a stimulus generator, and stimulation electrodes; and (2) an external base station comprising a power source for providing electricity to the neurostimulator by means of an inductive link and a wireless communication system with an interface on a computer for configuration and reporting.

Description

A DEVICE TO CORRECT THE BRUXISM OF SLEEP, THROUGH THE USE OF AN ELECTRICAL STIMULATION SYSTEM OF THE MENTONIAN NERVE.

5 Technical Sector

The technology is oriented to the health area, more particularly, it corresponds to an electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system of the mental nerve.

Previous Technique

Sleep bruxism (BS) is a repetitive mandibular muscular activity that is characterized by excessive clenching and grinding of the teeth when sleeping (Lobbezoo F. et al., 2013; Lobbezoo F. et al., 2008).

While this activity is carried out, a strong contact is generated between the surfaces of the upper and lower dental arches. The short-term consequences involve fatigue of the jaw-raising muscles upon awakening, due to increased clenching of the teeth, general fatigue and headache. The chronic effects cause significant deterioration of the

periodontium, severe dental wear, which can lead to tooth fracture and damage to the temporo-mandibular joint (TMJ) (Lobbezoo F. et al., 2008).

This disorder becomes a pathological condition when the person begins to manifest that he does not achieve a restful sleep or when he presents severe damage to the teeth.

One of the methods considered for the diagnosis of sleep bruxism has been polysomnography (PSG). However, the high cost, time consumption, and limitations of performing a diagnosis considerably limit its application as a diagnostic element in studies with 30 representative samples (Doering et al., 2008). Additionally, the fact

performing PSG on a patient means that they must wear uncomfortable sleep equipment and tests that are generally performed outside the environment where the subject normally sleeps. This has led researchers to develop devices capable of quickly and reproducibly measuring bruxist activity as a complement to clinical diagnosis (Ahlberg et al.,

2004; Kampe et al., 1997). Recently, devices have been developed that record the electromyographic activity of the mandibular levator muscles. Of those that are available on the market, the one that has shown greater precision in the records compared to PSG is 40 Bruxoff (Castroflorio et al., 2014; Manfredini et al., 2014).

Electromyography (EMG) is another method used to detect BS, it allows the electrical activity generated by the contraction of the muscles involved in mastication to be recorded, using surface electrodes connected to electromyography equipment. However, other types of 45 movements and activities that people do when sleeping can interfere

in the correct determination of bruxism events. On the other hand, over time various types of treatments have been implemented to reduce the adverse effects that BS generates. Among the most widely used are the use of an occlusal splint, a Botox injection and therapeutic relaxation treatments. However, no method has been found that is 100% effective in the long term.

The occlusal splint is a device that can be fixed or removable and is used only as a temporary solution, which helps to deprogram the muscle for an adjustment of the occlusion, avoids direct contact between the teeth and reduces the noise that occurs when making them grind. Polysomnographic records have been made to evaluate the muscular activity of subjects using splints, in which only a third of these have presented any change in the activity of the chewing muscles. Another interocclusal device is the trigeminal nociceptive suppression and tension suppression system, which corresponds to a trigeminal nociceptive system tension suppression plate that is generally positioned on the upper front teeth. Nociceptors are nerves that measure and respond to pressure, therefore, by stimulating these nerves, there is an inhibition of the mandibular levator muscles.

Among the less conventional treatments is the injection of botulinum toxin (Botox) into the masseter muscles, which has a paralyzing effect on the muscles, since it blocks the release of acetylcholine at the level of the motor plate, which reduces the masseter activity. However, the effect does not last more than five months and thereafter the treatment must be repeated. Therefore, it is only a temporary treatment. In addition, another disadvantage is that the treatment is expensive and requires a specialist doctor who has experience for the injection of this toxin, and thus avoid problems of paralysis of the mandibular muscles (Long et al., 2012).

Another type of treatment is related to the use of biofeedback therapies from an electrical stimulus to interrupt bruxism events when the person is sleeping, this because the human body does not have natural warning signals to counteract this condition. Biofeedback is generated when some initial stimulus of various kinds occurs in the receptor. Then, the stimulus is processed by the organism and generates a response that reaches the effector closing the feedback loop.

Devices that employ audible signals through hearing aids to interrupt sleep bruxism events are also known. As this alarm can be deactivated manually or deactivated automatically when bruxism decreases, after a certain time the subjects ignore this alarm. Several studies have published that the use of audible tones using EMG records cause a significant decrease in muscle activity when the subject is performing BS, but these effects are temporary (Lobbezoo et al., 2008). There is a device that uses this biofeedback method and it is on the market, it is the SleepGuard (Weinstein et al, 2001 (US 6,270,466)), which is based on the fact that when it detects a bruxism event, it uses auditory stimulation to alert to the patient. Takeuchi et al., (2001) evaluated the reproducibility, validity and utility of a splint that had a thin piezoelectric film inside, to measure the pressure exerted between the teeth, which was inserted at a depth of 1 - 2 mm below the occlusal surface. The device was called the intrasplint force detector (ISFD). They used a portable analog signal recording device to measure the EMG signals from the masseter muscle, and also recorded the ISFD data. The results indicated that the use of piezoelectric film has limitations, since it does not manage to accurately show the values of sustained force, however, it could reproduce bruxist behaviors with durations similar to those detected with the masseter's EMG.

Another study is the one developed by McAuliffe et al., (2015) where they performed clinical tests on a pressure sensor based on carbon black polymer. Using the sensor, they performed controlled mandibular movements in vivo to simulate bruxism and non-bruxism patterns. The examiners were able to differentiate bruxist from non-bruxist activities with sensitivity ranging from 80% to 100% and specificity from 75% to 100%.

On the other hand, treatments with electrical stimulation in different areas of the face seek to stop subjects who perform bruxism while sleeping, stop performing this activity by stimulating the muscles involved in chewing, or in the subcutaneous nerves. When stimulated, they provoke a reflex of inhibition of the elevation of the jaw. For example, in a study by Nishigawa et al. (2003) evaluated the effect of contingent electrical stimulation on the lips of bruxist patients. The results indicated that there was indeed a reduction in EMG activity overnight; however, the stimulation was applied only in the middle of the subjects' sleep period.

Electrical stimulation of the low-level trigeminal innervation area has been used, which provokes inhibitory responses in the mandibular contraction muscles; These periods of inhibition are the so-called exteroceptive suppression periods, which are divided into the short-latency (ES1) and the long-latency (ES2) or late suppression reflex (Lund et al., 1983). Not only have these reflexes been investigated by electrical stimulation in the trigeminal mandibular division, but their appearance has also been studied by electrical stimulation of inputs belonging to the trigeminal ophthalmic division. This is the case of the study carried out by Cruccu et al. [64], it was possible to register in 90% of the subjects, a period of suppression of the mandibular elevators after a stimulation of the supraorbital nerve.

On the other hand, it has been studied how the two reflexes can change by varying the maximum voluntary contraction (MCV) of clenching of the teeth and the intensity of the stimulus, obtaining a significant increase in reflexes as the intensity of the applied stimulus increases. , in addition to changes in the duration and depth of ES2 when going from 30% MCV to 50% MCV (Komiyama et al., 2005; Komiyama et al., 2009). Therefore, there are several works that indicate that ES1 and ES2 reflexes have a non-nociceptive origin (Hansen et al., 2002; Cruccu et al., 1998; Komiyama et al., 2010; Jadidi et al., 2009).

Another study on electrical stimulation to generate biofeedback was carried out by Jadidi et al. (2010), where the inhibitory responses in the bilateral muscular activity of the masseteros and temporals were examined when a short and long-lasting electrical stimulus was applied to different oro-facial locations. Both short-duration and long-term pacing at different oro-facial locations were estimated to produce similar bilateral inhibitory effects on the mandibular levator muscles, but with a different trend (Jadidi et al., 2010). The same researchers (Jadidi et al., 2007) designed a equipment capable of recording EMG activity by means of a surface electrode positioned in the anterior temporal muscle (Ta). This device known commercially as Grindcare, is made up of a recording and stimulation electrode that is positioned on the Ta muscle. The electrode records the electromyography in the muscle and applies the electrical stimulus to generate decreased muscle activity. This device is wirelessly controlled by a device that allows you to configure the parameters and perform the calibrations for its operation. Several researchers have evaluated this device, for example Needham and Davies (2013) who sought to determine if the use of this device can control or reduce the level of tightening activity in bruxists. In particular, in this study it was concluded that, although there was a decrease, the device did not eradicate bruxism completely and did not eliminate the habits that were carried out during the study period.

Based on the aforementioned background, one of the complications presented by these devices is related to the difficulty and discomfort when using the devices when sleeping. Another problem, particularly for devices that use EMG to measure the level of muscle contraction, such as Grindcare, is the discomfort of putting electrodes on your face and forehead every day. Therefore, the need to develop new equipment that allows solving sleep bruxism still persists, but in a way that does not generate discomfort and discomfort in the patient when using it.

References:

Ahlberg, J., Savolainen, A., Rantala, M., Lindholm, H., Kónónen, M. (2004). Reported bruxism and biopsychosocial symptoms: a longitudinal study. Community Dent Oral Epidemiol., 32 (4), 307-1 1.

Castroflorio, T., Deregibus, A., Bargellini, A., Debenadi, C., Manfredini, D. (2014). Detection of sleep bruxism: comparison between an electromyographic and electrocardiographic portable holter and polysomnography. Journal of Oral Rehabilitation, 41, 163-169.

Cruccu, G., Romaniello, A. (1998). Jaw-opening reflex after C02 laser stimulation of the perioral region in man. Exp Brain Res, 1 18, 564-568. Doering, S., Boeckmann, JA, Hugger, S., Young, P. (2008). Ambulatory polysomnography for the assessment of sleep bruxism. Journal of Oral Rehabilitation, 35, 572-576.

Hansen, P., Svensson, P., Arendt-Nielsen, L, Jensen, T. (2002). Human masseter inhibitory reflexes evoked by repetitive electrical stimulation. Clinical Neurophysiology, 1 13, 236-242.

Jadidi, F., Wang, K., Arendt-Nielsen, L, Svensson, P. (2009). Effect of stimulus parameters and contraction level on inhibitory responses in human jaw-closing muscles: Implications for contingent stimulation. Archives of Oral Biology, 54, 1075-1082.

Jadidi, F., Wang, K., Arendt-Nielsen, L, Svensson, P. (2010). Effects of different stimulus locations on inhibitory responses in human jaw-closing muscles. Journal of Oral Rehabilitation, 38 (7), 487-500.

Jadidi, F., Castrillon, E., Svensson, P. (2007). Effect of conditioning electrical stimuli on temporalis electromyographic activity during sleep. Journal of Oral Rehabilitation, 35 (3), 171 -183.

Kampe, T., Tagdae, T., Bader, G., Edman, G., Karlsson, S. (1997). Reported symptoms and clinical findings in a group of subjects with longstanding bruxing behavior. J Oral Rehabil, 24, 581 -587.

Komiyama, O., Wang, K., Svensson, P., Arendt-Nielsen, L, De Laat, A. (2005). Exteroceptive suppression periods in masseteric EMG: Use of stimulus-response curves. Archives of Oral Biology, 50, 994-1004.

Komiyama, O., Wang, K., Svensson, P., Arendt-Nielsen, L, De Laat, A., Uchida, T., Kawara, M. (2009). Relation between electrical stimulus intensity, masseteric exteroceptive reflex and sensory perception. Journal of Prosthodontic Research, 53, 89-94.

Komiyama, O., Wang, K., Svensson, P., Arendt-Nielsen, L., De Laat, A., Kawara, M. (2010). Magnetic and electric stimulation to elicit the masseteric exteroceptive suppression period. Clinical Neurophysiology, 121, 793-799.

Lobbezoo, F., Ahlberg, J., Glaros, AG, Kato, T., Koyano, K., Lavigne, GJ, De Leeuw, R., Manfredini, D., Svensson, P., and Winocur, E. ( 2013). Bruxism defined and graded: an international consensus. J. Oral Rehab., 40, 2-4.

Lobbezoo, F., van der Zaag, J., van Selms, M. K. A., Hamburger, H. L., Naeije, M. (2008). Principles for the management of bruxism. Journal of Oral Rehabilitation, 35, 509-523.

Long, H., Liao, Z., Wang, Y., Liao, L., Lai, W. (2012). Efficacy of botulinum toxins on bruxism: an evidence-based review, Int Dent J, 62, 1 -5.

Lund, JP, Lamarre, Y., Lavigne, G., Duquet, G. (1983). Human jaw reflexes. In: Desmedt JE (ed). Motor control mechanisms in health and disease (pp. 739-755). Raven Press, New York.

Manfredini, D., Ahlberg, J., Castroflorio, T., Poggio, CE, Guarda-Nardini, L., Lobbezoo, F. (2014). Diagnostic accuracy of portable instrumental devices to measure sleep bruxism: a systematic literature review of polysomnographic studies. Journal of Oral Rehabilitation, 41, 836-842. McAuliffe, P., Kim, JH, Diamond, D., Lau, KT, O'Connell, B. (2015). A sleep bruxism detection system based on sensors in a splint - pilot clinical data. Journal of Oral Rehabilitation, 42, 34-39.

Needham, R. and Davies, S. J. (2013). Use of the Grindcare device in the management of nocturnal bruxism: a pilot study. British Dental Journal, 215 (E1). Doi 10.1038 / sj.bdj.2013.653.

Nishigawa, K., Kondo, K., Takeuchi, H., Clark, G. T. (2003). Contingent electrical lip stimulation for sleep bruxism: A pilot study. Journal of Prosthetic Dentistry, 89, 412-7.

Takeuchi, H., Ikeda, T., Clark, G. (2001). A piezoelectric film-based intrasplint detection method for bruxism. J Prosthet Dent, 86, 195-202.

Weinstein, T. Devlin, K. Ulrich, C. Burns. “Bruxism biofeedback apparatus and method including acoustic transducer coupled closely to user’s head bones,” US Patent 6,270,466.

Brief description of the figures

Figure 1: Schematic of the electronic neurostimulator composed of a base station (A); and an intraoral neurostimulator (B).

Figure 2: Diagram of capacitive pressure sensors with a chip.

Figure 3: Evaluation of the energization system, where (A) corresponds to the primary circuit and (B) to the secondary circuit.

Figure 4: Results of the filtered circuit.

Figure 5: Results of electrical stimulation, for voltage (CH1) and current (CH2) signals at the electrodes when applying current pulses.

Figure 6: Evaluation of the neurostimular function, where the areas where the force is applied can be visualized.

Figure 7: Diagram of the neurostimulator operation with an occluder.

Figure 8: Results when applying pressure to the NIE sensors, where (A) corresponds to the capacitance and (B) to the state of the device.

Figure 9: Design of the prototype of the electronic neurostimulator (B) and operating in the occluder (A).

Disclosure of the Invention

The present technology corresponds to an electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system for the mental nerve. Advantageously, this device is easy and comfortable to use when the person is sleeping, and does not interrupt sleep. In addition, it is portable and does not use cables for its energization or operation, and it communicates wirelessly with an interface on a computer for its configuration.

This appliance is embedded in an occlusal splint and is flexible, so it can be adjusted to the shape of the dental arch. Optionally, a rigid splint can also be used. It can be positioned in the mouth to measure interdental pressure, detect high pressure events and apply an electrical stimulation imperceptible to the person through electrodes. This generates a decrease in the pressure exerted by the contraction of the mandibular elevator muscles.

The electronic neurostimulator comprises at least the following components:

to. an occlusal splint comprising within it an intraoral neurostimulator (NEI) (B) composed of at least 4 capacitive pressure sensors (f) of thickness between 0.5-0.6mm for the detection of interdental pressure; a microcontroller MCU (g) that allows acquiring the data of the pressure signal and controlling the stimulation by means of a pre-programmed algorithm; a power system to supply the microcontroller (MCU) (g); a stimulus generator (h); and stimulation electrodes (i); and

b. an external base station (A): comprising a power source to energize the neurostimulator via an inductive link and a wireless communication system for configuration and reporting.

This electronic neurostimulator allows to generate electrical current pulses in a range of 0.001 mA - 10mA, with a duty cycle that can vary between 0.01% - 99%, a frequency between 300 - 500Hz and with a maximum duration of 2 seconds of stimulation, to produce stimulation of the trigeminal sensory nerves.

Figure 1 shows a schematic of the electronic neurostimulator composed of the external base station (A) that includes a power source to energize the neurostimulator via an inductive link, where (a) corresponds to an amplification stage, (b) to the energy transmission and (c) energy delivery to the neurostimulator; and the intraoral neurostimulator (B) that comprises an energy system to feed the microcontroller (MCU), where (d) corresponds to the reception of energy and (e) to the storage of energy, at least 4 pressure sensors (f) to measure interdental pressure, a MCU microcontroller (g) that allows acquiring the data of the pressure signal and controlling the stimulation, the stimulus generator (h) and the stimulation electrodes (i), where said apparatus is hermetically encapsulated ( j). The specific detail of these components is presented below:

Capacitive pressure sensors (f) are of the preferred but not exclusive type, parallel plate capacitors, and allow the interdental pressure in the posterior, frontal and left and right lateral areas to be determined independently by means of a converter type chip (j) from capacitance to digital for capacitive measurements, which works by moving loads towards a capacitor periodically through switches, which allow the transmission and reception of data to the MCU (g), as can be seen in Figure 2. On the other hand, for To identify possible sleep bruxism events (BS), the MCU (g) incorporates a bruxism detection algorithm (ADB), where the signal being measured is interdental pressure. This algorithm uses a system of threshold detection and a signal duration in a window, where the signal sampling frequency is at least 5Hz; Sufficient sampling rate to obtain a digital signal without losing relevant data.

The stimulation electrodes (i) are of the preferred, but not exclusive, type, surgical steel, platinum or copper, and have a circular, square, oval or rectangular shape in their rigid or semi-rigid type, and are located in the chin area to bilaterally excite the mental nerve. These are those that are in contact with the mouth to apply the electrical stimulus in the area of the mental nerve. They have a diameter between 1 - 10mm and a thickness of 0.1 - 2mm, so they can be easily positioned inside the ferrule.

The NEI (B) is capable of communicating with a graphical interface on a computer using Bluetooth, so it does not use cables. Furthermore, to store the energy provided by the energizing system, it uses a rechargeable battery with a nominal voltage between 3.7V and a weight of less than 5g or a supercapacitor in the same range of electrical variables embedded in the same neurostimulator. In turn, the user interface allows you to configure the stimulation parameters, and the thresholds and recognition windows for bruxism and can be implemented on a smart mobile phone or a tablet or a computer.

The microcontroller (MCU) (g) controls the generation of stimulation pulses (of the square wave pulse train type) and generates the signal with a digital-to-analog converter (DAC). The applied stimulus is a biphasic wave with passive discharge to avoid the accumulation of electric charge in the stimulation zone. It can generate a constant current in the output in a range from 1 mA to 10mA. This stimulus originates from detecting interdental pressure with an intensity and time that is configurable for each user from the external configuration platform.

On the other hand, the base station (A) composed of the energization system, is in charge of supplying the power to the electronic circuit inserted inside the ferrule, specifically in the internal battery of the NEI (B). This is wirelessly charged with an external system to the splint through an inductive link. The power system is capable of keeping the electronics inside the splint running for as long as the subject is asleep (on average 8 hours). Advantageously, it has the ability to record interdental pressure and its distribution of forces by means of the 4 independent pressure sensors that it contains and generates a report of the bruxist activity of the time of use, for example, at night.

The electronics of the device are located inside the splint, which is preferably, but not exclusively, made of biocompatible silicone or acrylic which is sealed and allows it to be adjusted to different sizes of dentures.

Finally, this apparatus allows a decrease in the contractile activity of the muscles, and consequently in the interdental pressure, by applying current pulses to the mental nerve inside the mouth, achieving a desired inhibitory response. Application examples

Example 1 . Development of a prototype of an electronic neurostimulator.

A prototype of an electronic neurostimulator was designed to generate electrical current pulses to stimulate trigeminal sensory nerves. Different variables were evaluated to test the effectiveness of the system, which are detailed below:

1 .1 .- Base station.

Firstly, the base station that was wirelessly charged with an external system to the splint by means of an inductive link, and that was composed of:

• a primary circuit located in the base station and formed by a class D amplifier to perform wireless power; and a series resonant circuit; and

• a secondary circuit, in charge of ensuring the reception of energy in the NEI and the transformation of the signal from alternating to continuous, which was located inside the NEI and was made up of a parallel resonant circuit and a rectification and filtering (AC - DC ), to obtain a continuous voltage that allows energizing the neurostimulator system. Where the rectification stage incorporated a half-wave rectifier diode and the filter consisted of a capacitor in parallel to the resistive load to eliminate signal ripple.

For the implementation of the energy system, a serial topology was considered - parallel for its simplicity and efficiency. The primary energizing circuit had a series resonant inductor-capacitor (LC) circuit and the secondary circuit used a parallel resonant LC system. Both circuits were built with Litz cable and were of the planar type, and it was also possible to power up to a maximum distance of 20mm. Table 1 shows the detail of the circuits.

Table 1. Detail of the energizing circuits

It can be seen that the secondary circuit had a small value of inductance, this is because it is smaller than the primary to achieve insert it into the splint together with the electronic circuit; and had fewer turns. On the other hand, the quality factor (Q) was high enough to maintain its behavior when resonating. The resistance of the circuits was small, which helped reduce the amount of heat that could dissipate, especially in the secondary circuit, which was inside the ferrule. In both cases, the angle obtained at 1 MHz was very close to 90 ° (pure inductor).

On the other hand, the primary coil had a diameter of 25.5mm and an internal diameter of 4mm and the secondary coil had a diameter of 12mm and an internal diameter of 1.8mm, enough to incorporate it into the ferrule. Furthermore, the capacitors were implemented with ceramic material with dielectric with temperature coefficient X7R.

To test the operation of the wireless power system, an experimental test was carried out. At the output of the secondary circuit, a 68W resistance was used and the voltage drop between its terminals was measured, in addition to the current that circulated through the resistance.

Figure 3 (A) shows the voltage and current at the output of the primary circuit. Channel 1 of the oscilloscope (CH1) shows the current I3 and Channel 2 (CH2) shows the voltage V3 of the primary circuit. As can be seen, in the case of CH1 the current that was generated was sinusoidal and had an amplitude of 1.84A and an average current of -105mA, which indicates that it was centered at 0A. In the case of CH2, the primary circuit voltage was positive and had a maximum value of 9.6V. Then, the voltage and current that was generated in the secondary circuit were measured, results that are presented in Figure 3 (B). CH1 shows current I4 and CH2 shows voltage V4 of the secondary circuit. It can be seen that both signals were sinusoidal and the amplitude of current I4 was 1.36A centered at zero.

Figure 4 shows the secondary circuit current I4 (CH1), and the rectified and filtered voltage V5 (CH2). In this way, a voltage of 4.51 V was obtained in the 68W resistive load, with a direct current of 66mA. This voltage value is within the range allowed by the integrated battery charger, which has a maximum voltage of 7V.

Finally, it was possible to corroborate the operation of the wireless energy system, which fulfilled the necessary requirements to charge the internal battery found in the NEI.

1 .2.- Energy storage.

The energy storage inside the NEI, which is the continuation of the wireless power system, was evaluated. In this case, the voltage of the rectification and filter stage of the wireless energization reaches the circuit. Then the signal goes through a battery charger to ensure proper charging. Subsequently, the voltage goes through a voltage regulator that set it to 3.3V. This voltage is what was used to energize all the components of the electronic circuit. The battery that was selected to store the energy in the NEI was a rechargeable lithium-ion (Li-lon) battery, with a capacity of 70mAh and a nominal voltage of 3.7V and weighing less than 5g.

For this evaluation, the energy from the wireless power system was used to charge the battery. For this, a Li-lon battery charger was used that employed a constant voltage / constant current charging algorithm with selectable pre-conditioning and charge term. A configuration that adjusts to constant voltage regulation at 4.2V was used. It had an LED1 diode that served to alert when the battery was being charged. Then, the voltage was regulated to 3.3V.

To switch the NEI device on or off, a magnetic switch (reed switch) was used, which was normally open. When a magnet approached the switch, it closed and turned off the voltage regulator, thus interrupting the power supply to the entire circuit. The maximum output current it allowed was 100mA with a wide input voltage range (1.8V to 20V). Therefore, this component was adjusted to the requirements of the circuit.

1.3.- Capacitive sensors.

Parallel plate capacitive sensors were used to measure the level of clenching of the teeth. In this case, the variation in capacitance depended only on the distance between the plates when pressure was applied to them perpendicularly.

The sensors were made from commercial-grade flexible pcb boards where the copper foils were 35pm thick, resulting in 0.15mm thickness for dual-layer flex pcbs. A dielectric material was also used, which has the particularity of absorbing perpendicular forces and deforming; and it could also return to its original shape due to its elastic capacity. This dielectric material had a thickness of 90pm, so the sensors had a considerably small thickness. The cut copper foils joined with those of the dielectric to form the parallel plate capacitor.

The advantage of using these sensors is the ability to design sensor arrays with different sizes and shapes.

Then, the interdental pressure measurement system was designed, where a specialized tactile and proximity measurement chip with capacitive sensors was used, which was based on a switched capacitor circuit. The circuit worked by moving charges to a capacitor periodically using switches. Figure 2 shows a diagram of the sensor connection, as well as a bidirectional data line (SDA) and a clock input line (SCL) via serial interface with the microcontroller (MCU) (g). You can also see a flexible copper plate in the shape of the dental arch that had 4 copper rectangles (f), corresponding to the sensors. 1.4.- Electronic stimulus generator.

The stimulator is current controlled and features an adjustable current source and a stimulation pulse generation circuit. In order for the circuit to generate the stimulation waveform, the signal corresponding to a square wave pulse train had an amplitude of 3.3V, a variable frequency between 300 - 500Hz, and an adjustable duty cycle between 0 - 99%. On the other hand, the microcontroller (MCU) controlled these parameters and generated a signal with the help of a digital to analog converter (DAC). The applied stimulus was a biphasic wave with passive discharge to avoid the accumulation of electric charge in the stimulation zone, the current source was able to generate a constant current in a range from 1 mA to 10mA.

An experimental test run was performed by placing the electrode terminals inside a subject's mouth. The results can be seen in Figure 5, where channel 1 (CH1) indicates the voltage at the electrodes and channel 2 (CH2) shows the voltage at a 100W resistor, which is in series with the electrodes. This test was used to observe the waveform of the current flowing through the electrodes. By Ohm's law, it can be seen in CH2 that the current amplitude was 50GP \ // 100W = 0.5mA. It can also be seen that after the positive current pulse appeared the passive discharge of the capacitor in series to the electrodes.

1.5.- Stimulation electrodes

Electrodes were designed from flexible pcb plates, where each electrode had a radius of 3mm and a thickness of approximately 0.12mm, so they could be positioned anywhere on the splint.

An in vitro test was carried out on the stimulation electrodes, which consisted of immersing the electrodes in an aqueous environment simulating the conditions inside the mouth. For this, the electrodes were immersed in a glass with saliva and then pulses of current were applied with the electronic stimulator, to measure the voltage and current in the electrodes. The signals were measured with an oscilloscope, and the current was estimated by measuring the voltage in a 100W series resistance to the electrodes. The stimulation parameters were: 1 mA amplitude, 300Hz frequency and 10% duty cycle.

It could be obtained that the current had an amplitude close to 1 mA and that the voltage at the electrodes was adjusted to the impedance and the current, since the stimulator was controlled by current.

1.6.- Bruxism detection algorithm and graphic interface.

In order to identify possible sleep bruxism (BS) events, a bruxism detection algorithm (ADB) was implemented in the microcontroller (MCU). The signal that was measured was interdental pressure and was used to observe changes in the level of dental clenching. He algorithm used a threshold detection system and a signal duration in one window. The signal sampling frequency was 5Hz and the sampling rate was sufficient to obtain a digital signal without losing important data.

The first thing was to obtain an estimated value of the maximum pressure that the subject can exert, the maximum voluntary contraction (MCV). Therefore, when the device was started to be used, it was necessary to carry out a calibration that consisted of the subject clenching the teeth at MCV for 2 seconds to subsequently calculate the threshold value.

This algorithm seeks that the interdental pressure signal (Pl) exceeds a threshold corresponding to 25% MCV. Once it is exceeded, the cumulative integral of the signal is calculated in a window of 1 s, using the trapezoidal method. With the vector that has the accumulated integral, the slope of the integral is calculated. This slope is compared to a minimum slope value obtained from tests with pressure records. If the calculated slope does not exceed the minimum slope value, it means that it does not correspond to a BS event, then the signal Pl is sought to be less than the threshold. This ensures that the signal drops below the threshold for re-stimulation, preventing it from being stimulated more times until it encounters a new event. When the signal is below the threshold, the search for a possible bruxism event is started again (returns to the beginning of the algorithm). If the slope exceeds the acceptable minimum, the signal is considered a BS event and electrical stimulation begins for 2 seconds (time defined with respect to the duration of a BS squeeze event). When the 2 seconds of stimulation are completed, the stimulation ends and the signal is sought to be less than the threshold to return to the beginning of the algorithm.

In this way, the algorithm detects when there is dental clenching related to bruxism and electrically stimulates by evaluating the amplitude (threshold) and the duration of the signal (window) above the threshold.

1.7.- Implementation and programming tests

To configure the stimulation parameters and visualize the interdental pressure signal, a graphic interface was designed. This communicated with the intraoral neurostimulator (NEI) through a Bluetooth connection. In turn, Bluetooth communicated with the MCU, and data was sent and received wirelessly to the interface on the computer.

Example 2. Evaluation of the electronic neurostimulator in people suffering from bruxism.

2.1.- Determination of stimulation parameters.

Firstly, the value of the stimulation parameters had to be determined for each patient diagnosed with BS, so as to generate a decrease in the intensity of dental clenching. For what was necessary carry out tests applying electronic pulses with different stimulation parameters.

The tests were performed according to the “Clinical amnesiac protocol for the diagnosis of bruxism by Díaz et al. (2011) ”. For the test, the subject was placed in the Frankfurt plane, to position the skull so that the bite could be performed correctly. He was asked to clench his teeth at maximum voluntary contraction (MCV) for 4 seconds. Electrical stimulation was applied during the last 2 seconds, to later compare the segment to MCV under stimulation with respect to the segment without stimulation. The EMG activity of the anterior temporal muscle (Ta) was measured bilaterally to obtain the integrated EMG signal (EMGint), and the electrical stimulus was applied to the mental nerve inside the lower lip inside the mouth (vestibule fundus) . EMG was used to carry out the preliminary tests, since there is a proportional correspondence between bite force with EMG activity in isometric contraction.

In each of the tests, 6 records were made, plus a standard record in which only the teeth were clenched into MCV without applying electrical stimulation. In 3 of the 6 remaining records, electrical stimulation was applied randomly, without the subject knowing in which records it was stimulated. In this way, masking bias could be eliminated from the measurements.

EMG records were measured using the Biopac MP35 kit. Once the measurements were made, the data was analyzed and the area under the curve (ABC) of the segments with and without stimulation was calculated in each of the records, to calculate the percentage decrease in the signal when electrically stimulated. In total, 30 tests were performed on the bruxist subject, where 18 tests were performed using a square wave pulse with a frequency of 300Hz, and 12 tests at 500Hz. The applied current amplitude varied between 0.2 - 1 mA, and the duty cycle between 1-15%. For the cases in which a higher current was used, the work cycle was adjusted, taking care that the subject did not feel the electrical stimulus.

Table 2 shows the results of the tests carried out for stimulation pulses at 300 and 500Hz, and in ascending order of the amount of current applied to each pulse. These tests were repeated depending on the percentages of decrease obtained. In the case of stimulation at 300Hz, the greatest decrease was when pulses of 0.3mA of current amplitude were applied with a duty cycle of 10%, where the area under the curve (ABC) of the right anterior temporal muscle ( TaD) suffered a decrease of 29.03% when electrical stimulation was applied, with respect to the ABC of the segment before stimulation. While the ABC of the left anterior temporal muscle (Tal) decreased by 22.22%. In the case of stimulation at 500Hz, the greatest decrease was found when applying 1 mA pulses with a 3% duty cycle. On average, the TaD decreased by 30.42%, while the Tal muscle decreased by 20.92%. Another record in which a greater decrease was generated was that of 0.8mA and 6.25%. In this case, the TaD decreased by 26.09% and the Tal by 29.63%. In both cases the amount of current per pulse was the same. Finally, the results obtained from the stimulation tests indicated that it is possible to generate a response to decrease muscle contraction, by applying current pulses to the mental nerve inside the mouth.

Table 2. Results of stimulation tests

2.2.- Evaluation of the neurostimulator function with occluder

To evaluate the functioning of the neurostimulator, we started by positioning the NEI in an occluder to test its operation by applying pressure to it at different points, and additionally, to verify how the pressure is distributed in a dental arch. The areas marked with arrows in which force was applied to exert pressure on the NEI pressure sensors are shown in Figure 6. From the front view of the occluder, the points pressed were: in the posterior area of the occluder (F1), on the molars on the left (F2) and right (F3) side, and on the incisors (F4).

The test consisted of exerting pressure, vertically, on different points of the occluder, and visualizing the operation of the neurostimulator device on the graphic interface. 1 kg weight discs were used to exert pressure mounted on a base designed to place the discs. Figure 7 shows the complete system that was implemented to perform the test, where you can see the occluder with the NEI inside.

The NEI was conditioned with cables attached to a resistive load that simulated patient resistance, and in parallel an oscilloscope measurement tip was connected to visualize the electrical pulses. The graphic interface was located in the computer, in which the stimulation parameters, the detection threshold values and the minimum stimulation slope were configured. Additionally, real-time graphics of device status and pressure levels of each sensor were displayed.

Figure 8 shows the results of the test performed. In (A), the variation of capacitance of one of the sensors is shown, where the first activity was the posterior area of the occluder and it is shown enclosed in a bracket. The other events are displayed in the same way. The second zone was that of the molar on the left side, then that of the molar on the right side, and finally the anterior zone of the occluder. threshold exceeded), and when the threshold was exceeded, it went to state 4 (integration window) in which it is defined if it is a BS event, it calculated for 1 second the accumulated integral of the signal. At the end of the window of state 4, the slope of the integral was calculated, and if it exceeded the value of the minimum slope that was configured, it went to state 5, where an electrical stimulation was generated for 2 seconds. If at the end of the stimulation the pressure continued above the defined threshold value, it went to state 6, which sought the moment when the pressure dropped below the threshold. Once this happens, it is switched to state 3 to search for when the threshold is exceeded again. This was what happened in all records.

In the case of the last record (posterior occluder area), the duration of the event was shorter than the rest. Additionally, wireless Bluetooth communication worked correctly throughout the test with the device 1 meter away from the computer. The current pulses were generated only when the minimum value of slope of the accumulated integral was exceeded, and its duration was that programmed by software. Figure 9 shows the prototype implemented and working in occluder.

Claims

Claims 1 .- An electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system for the mental nerve, CHARACTERIZED because it is portable and includes at least the following components: to. an occlusal splint containing within it an intraoral electronic neurostimulator (NEI) (B) composed of at least 4 capacitive pressure sensors (f) for detecting interdental pressure; a microcontroller MCU (g) that allows acquiring the data of the pressure signal and controlling the stimulation by means of a pre-programmed algorithm; a power system to supply the microcontroller (MCU) (g); a stimulus generator (h); and stimulation electrodes (i); and b. an external base station (A) comprising a power source to energize the neurostimulator via an inductive link and a wireless communication system with an interface to a computer or mobile device (Tablet or smartphone) for configuration and reporting. 2.- An electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system for the mental nerve, according to claim 1, CHARACTERIZED because the capacitive pressure sensors (f) allow determining the interdental pressure in the posterior area , frontal and lateral left and right independently. 3.- An electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system for the mental nerve, according to claim 1, CHARACTERIZED because the stimulation electrodes (i) have a diameter between 1 - 10mm and a thickness 0.1 - 2mm and are located in the chin area inside the mouth to bilaterally excite the mental nerve. 4.- An electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system of the mental nerve, according to claim 1, CHARACTERIZED because the NEI (B) is provided with a rechargeable battery with a nominal voltage of 3 , 7V and weighing less than 5g or a supercapacitor in the same range of electrical variables embedded in the same neurostimulator. 5.- An electronic neurostimulator useful to correct sleep bruxism, by using an electrical stimulation system of the mental nerve, according to claim 1, CHARACTERIZED because the splint that contains it is flexible and made of biocompatible silicone, it is sealed and fits different sizes of dentures. 6.- An electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system of the mental nerve, according to claim 1, CHARACTERIZED because the splint that contains it is rigid and is made of biocompatible acrylic, it is sealed and fits different sizes of dentures. 7.- An electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system for the mental nerve, according to claim 1, CHARACTERIZED because it generates electrical current pulses in a range of 0.001 mA - 10mA, with one cycle working that varies between 0.01% - 99%, a frequency between 300 - 500Hz and with a maximum duration of 2 seconds of stimulation to produce stimulation of the trigeminal sensory nerves. 8.- An electronic neurostimulator useful to correct sleep bruxism, by using an electrical stimulation system of the mental nerve, according to claim 1, CHARACTERIZED because the stimulation originates when interdental pressure is measured in some combination of the 4 sensors pressure containing the neurostimulator. 9.- An electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system of the mental nerve, according to claim 1, CHARACTERIZED because the stimulation originates from detecting interdental pressure with an intensity and time that is configurable for each user from the external configuration platform. 10.- An electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system of the mental nerve, according to claim 1, CHARACTERIZED because it records interdental pressure and its distribution of forces using the 4 independent pressure sensors that Contains the NEI, and generates a report of bruxist activity during the time of use. 1 1 .- An electronic neurostimulator useful to correct sleep bruxism, by using an electrical stimulation system of the mental nerve, according to claim 1, CHARACTERIZED because the user interface allows you to configure the stimulation parameters, thresholds and windows for the recognition of bruxism, and it is implemented in a smart mobile phone or a tablet or a computer. 12.- An electronic neurostimulator useful for correcting sleep bruxism, by using an electrical stimulation system for the mental nerve, according to claim 1, CHARACTERIZED because the stimulation electrodes are of the surgical steel, platinum or copper type, and have a circular, square, oval or rectangular shape in its rigid or semi-rigid type.