The sleep apnea (or sleep apnoea) syndrome is a sleep disorder involving abnormal pauses in breathing or abnormally low breathing during sleep.  Pauses in breathing are called apnea and abnormally low breathing is called hypopnea. 
Apnea is generally defined as a cessation of air flow lasting for 10 seconds or more and may occur 5 to 30 times or more per hour.  Hypopnea is generally defined as a reduction in air flow of at least 50% for at least 10 seconds. 
Three types of sleep apnea are described: central (CSA), obstructive (OSA) and mixed (combination of central and obstructive) sleep apnea.  In CSA, breathing is disrupted by a lack of neurological control of the respiratory effort; in OSA, by a physical upper airway obstruction despite to respiratory effort. 
It is estimated that the sleep apnea syndrome, and particularly obstructive sleep apnea, afflicts an estimated 2-5% of the general population.  Adults but also babies and children may be affected by sleep apnea.  Sleep apnea is more common in men than in women. 
Sleep apnea may be diagnosed by an overnight sleep test called polysomnogram (PSG).  This test enables determining indexes reflecting the severity of the disease: Apnea Hypopnea Index (AHI) and Respiratory Disturbance Index (RDI).  The AHI corresponds to the quantity of apneic events per hour of sleep.  Above 5 for AHI, the patient is considered as suffering from sleep apnea, and the severity may be quantified. 
The disease is quantified in terms of respiratory disturbance per hour.  Mild disease begins at 2-3 apneas per hour and in the more severe cases, it may raise up to one hundred or more per hour. 
Another test for assessing sleep apnea is oximetry.  This test may be performed at patient's home.  Oximetry aims at monitoring saturation of hemoglobin and is a very sensitive method. 
People suffering from sleep apnea undergo sleep fragmentation and intermittent, complete or nearly complete, cessation of ventilation during sleep with potentially severe degrees of oxyhemoglobin unsaturation.  Symptoms associated with sleep apnea are daytime sleepiness, slower reaction time, cognitive dysfunction, cardiac dysrhythmia, pulmonary-artery hypertension, congestive heart failure.  Hypersomnolent sleep apnea patients may be at risk for excessive mortality from these factors as well as an elevated risk for accidents when driving or operating other potentially dangerous equipment. 
While sleeping, a normal individual is “at rest”, breathing is regular and oxygen levels stay fairly constant.  Any sudden drop in oxygen or excess of carbon dioxide strongly stimulates the brain's respiratory centers to breath. 
In central sleep apnea, the brain's respiratory control centers are imbalanced during sleep.  In CSA patients, basic neurological controls for breathing fail to give the signal to inhale, causing the individual to miss one or more cycles of breathing and leading to a drop of oxygen level and an increase of carbon dioxide level. 
It is generally admitted that the mechanism of obstructive sleep apnea syndrome involves anatomic or functional abnormalities of the upper airway which result in increased air flow resistance.  These abnormalities may include narrowing the upper airway due to suction forces developed during inspiration, the effect of gravity pulling the tongue back to the pharyngeal wall and/or insufficient muscle tone in the upper airway dilator muscles, especially the genioglossus.  In apneic patients, the latency time of implementation of the genioglossus is elongated.  Moreover, in the case of obese patients, the presence of excessive soft tissues in the anterior and lateral neck applies pressure on internal structures and narrows the airway. 
It is admitted that the main reason for snoring and obstructive sleep apnea is the relaxation of the tongue and pharyngeal walls.  In awaken patients, these tissues have normal air tone and air passes in and out of the lungs during respiration.  During sleep of apneic or snoring patients, the musculature retaining these tissues relaxes.  When air is inspired, the tongue and the posterior walls of the pharynx collapse, causing snoring or partial or complete obstruction of the airway. 
The lack of respiration implies inadequate blood oxygenation (hypoxia) and raises the carbon dioxide levels (hypercadmia).  Hypoxia induces diverse effects on the body, especially increase of the heart rate or cyanosis.  At worst, death may occur.  However, in general, the oxygen desaturation that occurs induces a transition to a lighter sleep stage, usually without wakefulness.  This transition brings a return to tonicity of the muscles of the upper airway, allowing normal breathing.  The person then return to a deeper sleep stage and the process is repeated. 
This fragmentation of the sleep induces a poor quality of the sleep, resulting in persons feeling tired and falling asleep at inappropriate time during the day and to other symptoms described above. 
Moreover, some studies have shown that hypoxia promotes angiogenesis which increases vascular and tumor growth and higher incidence of cancer mortality. 
A first action to limit sleep apnea and especially obstructive sleep apnea comprises lifestyle changes, such as avoiding alcohol or muscle relaxants, losing weight, quitting smoking.  Patients may also sleep at a 30-degree elevation of the upper body or in a lateral position. 
The most widely used treatment of obstructive sleep apnea is continuous positive airway pressure (CPAP) to maintain the airway of the patient in a continuously open state during sleep.  The patient typically wears a facial mask connected to a CPAP machine which generates required air pressure.  The method has been found very effective but suffers from some limitations, especially because a significant proportion of sleep apnea patients do not tolerate CPAP. 
Another treatment of obstructive sleep apnea implies surgical procedures.  Different methods were proposed, for example nasal surgery, surgery of soft tissues or bone surgery, however, failures were reported.  The poor success of these interventions, combined with high morbidity from some of these surgical interventions is not in favor of a surgical treatment of sleep apnea. 
Pharmacological treatments were also proposed to stimulate the upper airway muscle to reduce apnea or to lower blood pH to encourage respiration, such as with acetozamide.  However, until now, disappointing results were obtained and side effects were reported. 
Other non-chirurgical treatments were proposed to treat obstructive sleep apnea, especially using oral devices and appliances.  These treatments are based on the fact that people suffering from sleep apnea often present an important anatomical change during sleep.  Especially, a change in the soft tissues such as tongue, soft palate, pharyngeal walls and/or palatine tonsils is often observed.  These modifications also affect craniofacial skeleton. 
It was also observed that anatomical abnormalities favor sleep apnea, such as for example craniomaxillofacial abnormalities or retrognathims, for example the position of the jaw. 
Some appliances work to mechanically retain the tongue, preventing it from falling backwards or helping to reduce the collapse of the soft palate such as in EP2181678 or in US2012/145166.  Patent application US2012/0145166 discloses an intra-oral mandibular advancement appliance comprising a tongue rest designed for preventing the patient's tongue from falling, under the influence of gravity, towards his throat during sleep. 
Some devices were also described which actively pull on the tongue to keep it forward during sleep, such as in WO2011/060103, in WO2009/096889 and in EP0679378.  European patent application EP0679378 discloses a device for preventing snoring comprising a stirrup and a tongue component movably mounted on the end of the stirrup.  The stirrup is loaded by means of a spring such that the tongue component can press the tongue away from the rear soft palate while allowing swallowing. 
Devices were also proposed which actively push the lower jaw forward, thereby pulling the tongue slightly forward such as in US2009/178684 and in US2007/079833. 
These devices are intended to prevent the patient from exerting muscle forces on soft tissues of upper airways.  However, these intraoral devices do not provided significant improvements in sleep apnea, except in mild to moderate cases. 
Moreover, most of the devices of the prior art are associated with movements of teeth over time or with problems with the mandibular joint and mandibular muscles.  Such side effects are related with the fact that the muscle involvement in the mandible or tongue advancement is forced, not induced.  This kind of device is called active device or orthopaedic device.  By “active device”, it is meant a device that employs external forces to induce anatomical changes.  Active devices should be understood by contrast with functional devices.  By “functional device”, it is meant a device that achieve anatomical changes—in the present invention, more particularly changes in the position of the jaw, the tongue and/or or the pharyngeal walls—by using the body's own natural forces.  Functional devices change the functional patterns of the muscular system by causing the muscle to work. 
Beyond obstructive sleep apnea, snoring and other airway disorders are also caused by a wrong position of the tongue and/or a relaxation of pharyngeal walls.  Other airway disorders may be for example linked to breathing through the mouth. 
There is thus a need for new intraoral appliances that enable relieving obstructive sleep apnea syndrome, snoring and/or other airway disorders, that overcome above mentioned issues and that are well tolerated by patients.  Especially, the device of the present invention presents the advantage of being easy to use, not expensive, easily adaptable, easy to manufacture and not inducing side effects usually associated with prior art devices.  The device of the invention is a functional device. 
In patent application US2008/190437, the Applicant proposed a first functional device inducing reflex mandibular advancement.  The device of US2008/190437 comprises means for exerting pressure on the mucous zone covering the mental spines of the lower jaw.  The pressure on the mucous zone covering the mental spines induces a reflex mandibular advancement resulting in the opening of upper airways.  As mandibular advancement is induced and not forced, the functional device of US2008/190437 does not lead to movements of teeth overtime and to problems with the mandibular joint and mandibular muscles.  Results obtained on patient with this device were very encouraging and the Applicant continued searching to provide even more efficient device. 
The tongue is mainly made of muscles.  Especially, the tongue comprises four extrinsic muscles (genioglossus, hyoglossus, styloglossus and palatoglossus) which originate from bone and extend to the tongue.  The main function of these extrinsic muscles is moving the tongue, enabling protrusion, retraction and side-to-side movement. 
Especially, the genioglossus enables protrusion of the tongue.  The genioglossus muscle is also the only pharyngeal dilator muscle.  As a consequence, a stimulation of the genioglossus may induce a dilatation of the pharynx, opening upper airways. 
Tongue is an explorative element, especially the tip of the tongue.  When a foreign body is present into the mouth of an individual, the tongue explores it, without conscious control from the individual.  During the exploration, extrinsic muscles of the tongue are solicited, especially the genioglossus and an induced movement of the jaw occurs at the same time.  The movement of the jaw and the advancement of the tongue during exploration lead, among other effects, to the opening of the upper airway. 
Therefore, the Applicant carried out an extensive research relative to the placement of a foreign body into the mouth of a patient afflicted by sleep apnea syndrome, snoring and/or other airway disorders to induce reflex exploration of the tongue and leading to tongue and jaw advancement and consequently to airway opening.  In other words, the device of the invention intends using the sensitive propensity of the tongue to induce tongue movement. 
According to the Applicant's understanding, the tongue reiterates or not its reflex exploration of the foreign body depending of its shape and of its ability to move. 
The Applicant showed that a ball-shaped element was particularly appreciated by the tongue for exploration, even more if the ball-shaped element is movable. 
The present invention thus relates to a novel intraoral device comprising upper cooperating means adapted to cooperate with the upper jaw and lower cooperating means adapted to cooperate with the lower jaw, characterized in that the device comprises a bracket fixed in the cooperating means, said bracket supports a target aiming at attracting the tip of the tongue; said target being centered, in a transverse plane, with regard to the cooperating means. 
In one embodiment, stimulating means for stimulation of the tongue muscles, preferably the genioglossus, involving reflex exploration of said means by the tongue comprise a target able to rotate on itself.  In a preferred embodiment, the target is carried by a bracket.  In a preferred embodiment, the target is ball-shaped. 
In the device of the invention, means for stimulation of the tongue muscles, preferably the genioglossus, are also able to exert pressure on the mucous zone covering the mental spines of the lower jaw.  Therefore, but without willing to be bound by a theory, it is the Applicant understanding that the device of the present invention both promotes:                a reflex mandibular advancement by pressure on the mucous zone covering the mental spines of the lower jaw; and        a reflex exploration by the tongue leading to genioglossus stimulation and tongue advancement.         
According to the Applicant's understanding the following occur when a user bears the device of the invention:
During apnea, the lower jaw moves backward.  In patients bearing the device of the invention, when the lower jaw moves backward, it encounters the target.  The target exerts a pressure on the mucous zone covering the mental spines of the lower jaw.  As explained above, a reflex mandibular advancement occurs in response to pressure.  It is though that the tongue then explores the mouth in order discover the origin of the pressure.  When the tongue explores the target, the genioglossus is stimulated.  The stimulation of the genioglossus has at least two effects:                it induces the dilatation of the pharynx, opening upper airways; and        it muscles the genioglossus.         
The invention thus relates to a device for inducing reflex exploration by the tongue and reflex mandibular advancement leading to induced tongue and jaw advancement.  The device of the invention thus induces airways opening and may be used in the treatment, prevention and/or correction of obstructive sleep apnea syndrome, snoring and/or other airway disorders. 
The use of the functional device of the invention is intended to strengthen the genioglossus so that it retrieves sufficient muscle tone in order to induce correct dilatation of the pharynx.  The stimulation of the genioglossus obtained by using the device of the invention is expected to lead to a correction of airway disorders, especially of obstructive sleep apnea syndrome.  In one embodiment, using the device of the invention enables a reeducation of the genioglossus.