Upper Airway Resistance Syndrome

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Continuing Education Activity

Upper airway resistance syndrome, commonly known as UARS, is a disorder included with many others that encompass an umbrella of conditions characterized as a sleep-related breathing disorder. UARS was aimed at understanding what was not historically covered by Obstructive Sleep Apnea Syndrome (OSAS). Stated, patients suffering from UARS do show a decrease in oxygen saturation while sleeping, as observed in patients suffering from OSAS during a clinical sleep study. Even though their oxygen levels remain in the "normal" range, patients suffering from UARS can still suffer from metabolic and cardiovascular consequences we see presented in patients who have been clinically diagnosed with OSAS. This activity explores the vital role of an interprofessional team in the evaluation and management of bruxism.


  • Describe bruxism, and how bruxism can be identified as a risk factor for those patients suffering from UARS.
  • Explain the evaluation of patients with UARS.
  • Outline a treatment plan with appropriate oral appliances for patients with UARS.


Sleep-related breathing disorders (SRBDs) connect the clinical spectrum of chronic snoring, upper airway resistance syndrome (UARS), obstructive sleep apnea syndrome (OSAS), sleep-disordered breathing (SDB), respiratory sleep disorders, and sleep-related breathing disorders. These terminologies have been collectively described as abnormal breathing during sleep, historically based on the recording technologies and knowledge of the time.[1] However, with all these terms helping to advance the field of UARS, are we utilizing all of our available resources collectively to help correctly diagnose and, most importantly, correctly treat patients suffering from UARS? Initially, UARS syndrome was aimed at understanding what was not covered by OSAS in hopes of prompting specialists to go further than the obvious. It aimed at pushing specialists, including dentists, to identify pathologies promptly and to extract any pre-existing research towards the features of SDB. What is used to monitor SDB has been evolving and changing, which allows for recognition differently, yet this does not mean this is necessarily better than before. The technology used to monitor SDB changed over-time, allowing recognition of SDB differently but not necessarily better.[1]

Currently, we have a better understanding of the development of SDB, and its evolution with aging, leading to comorbid-OSAS. Although OSAS was identified greater than 30 years ago, no formal training is given to current physicians in recognizing or treating the condition.[2] Analyzing the issue further, it is evident that these problems need to be recognized earlier in onset, identifying what can be done to prevent development in patients with associated risk factors for UARS. There is enough knowledge to date regarding UARS, OSAS, and SDB to go beyond these definitions and to proactively recognize these problems differently to lead to the prevention of the symptoms in UARS. This is where the role of Dentist come into play. Dentists can help with the recognition of non-hypoxic sleep-disordered breathing earlier than what may have been diagnosed by a general healthcare provider.[1]

In a study conducted by Mello de Godoy and colleagues, when comparing patients with UARS to those with mild OSA, it was evident that they had increased levels of fatigue, reported worse sleep quality with impaired productivity in everyday activity and social relationships, while also having much higher scores with regards to anxiety and depression.[3] UARS has been discussed and researched for more than 15 years, yet, there is still no clear consensus on what diagnostic criteria should be used or whether UARS represents a distinct syndrome from OSA, obstructive sleep apnea.[3]

The role of dentistry in recognizing sleep disorders is becoming more prevalent and more significant. Dentists play an essential role in co-managing patients who present with the main complaint of light snoring accompanied by mild/moderate OSA. The practicing dental professional has the functional opportunity to assist patients at a variety of levels. Dentists can start with the recognition of a sleep-related disorder by a simple dental examination. The next step would be to refer the patient to the patient's general practitioner for evaluation. The general practitioner would then like to refer the patient to a sleep medicine physician, where the patient can undergo proper sleep study testing. Lastly, dentists will be able to assist in the management of sleep disorders by creating an oral appliance worn during sleep by the patient. Almost every discipline in dentistry, including dental hygienists and orthodontists, needs to be aware of sleep disorders and their potential impact on the overall well-being and health of the patient.[4]

Some authors had also suggested that UARS symptoms closely resemble those of the functional somatic syndromes. The common signs and symptoms of UARS in addition to excessive daytime sleepiness and sleep-onset insomnia include unrefreshing sleep, sleep fragmentation, bruxism, muscle pain, heartburn, diarrhea, headaches, depression, and orthostatic syncope.[3] In 2013, an international consensus was obtained on a pragmatic and straightforward definition of bruxism as constant masticatory muscle movement that is described by clenching and/or grinding of the teeth by bracing or thrusting of the mandible. Furthermore, this definition is more specific in terms of whether it is during sleep or when the patient is awake, making it dependent on the circadian phenotype.[5]

The essence of this paper will be on the significance of recognizing bruxism, which is a movement disorder that creates the condition where a patient grinds or clenches their teeth while sleeping. Patients who present with sleep bruxism can unconsciously grind or clench their teeth while asleep, unconsciously doing so, helping to alleviate the upper airway restrictions resulting in UARS.


The anatomy of the upper airway consists of the nasopharynx, oropharynx, and hypopharynx. The oropharynx includes the tongue, teeth, maxilla, mandible, the hard and soft palate, uvula, tonsils, and the hyoid bone. The hyoid bone is involved in the muscular action of the oral cavity, for example, moving the lower jaw inward and outward. This movement is essential for the behavior of bruxism. When a patient falls asleep in the supine position, the muscle relaxation, along with gravity, causes the base of the tongue to approach the posterior wall of the pharynx.[1]

UARS is the disorder occurring in the faciomaxillary region, toward which much relevance, and focus have not been given to the field of dentistry.[2] Individuals who complain of excessive daytime sleepiness or daytime tiredness are suspected of suffering from UARS. Neither OSAS nor a polysomnographic study that shows a change in respiratory parameters indicates an increased upper airway resistance. One of the main parameters of UARS includes flow limitation during sleep. Patients present with arousals from sleep. These arousals are associated with an increase in respiratory effort leading to sleep fragmentation. Sleep fragmentation then results in excessive daytime sleepiness for patients suffering from UARS.[3]

Upper airway resistance syndrome has been often overlooked simply due to how UARS is diagnosed. Sleep-disordered breathing is traditionally diagnosed by polysomnography (PSG) without measurement of esophageal pressure (PES). Breathing-related EEG arousals are not inspected.[4] Untreated UARS individuals can present a low quality of life and, over time, can develop cardiovascular consequences. Over a significant amount of time, sleep, and daytime symptoms, such as fatigue, insomnia, and depressive mood, in untreated UARS usually increase. If left untreated over time, UARS could cause hypertension, cardiovascular, and metabolic consequences. In order to avoid the consequences previously mentioned, early diagnosis and proper treatment should be offered to UARS patients as early as possible.[3]


Due to the limited diagnosing criteria for UARS, little information is available regarding the portion of the population who actually suffer from this condition. However, OSAS prevalence is 2% to 4% in men and 1% to 2% in women of average age as found in recent international studies.[5] Other articles claim the prevalence of OSAS is around 4% for men and 2% for women in the age-group of 30 to 60 years.[1] In the general population, at least 5% of men and 8% of women report suffering from excessive daytime sleepiness. Since many factors can attribute to daytime sleepiness, these figures can't assume this percentage of the population suffers from UARS.

History and Physical

UARS diagnosis is suspected in individuals with complaints of excessive daytime sleepiness or daytime tiredness, coupled with the patient and or relative complaining of the patient's loud snoring. No OSAS and a polysomnographic study with respiratory parameters can be indicative of increased upper airway resistance. The main respiratory parameter Sleep Medical Physicians focus on is flow limitation during sleep. UARS patients present with frequent sleep arousals associated with an increase in respiratory effort. These frequent sleep arousals lead to sleep fragmentation, ultimately resulting in excessive daytime sleepiness. The polysomnographic studies of these patients also showed sequences of breaths with flow limitation, which were interrupted by abrupt arousals witnessed by the patient's sleeping partner.[3]

Historically, the definition of UARS syndrome was aimed at recognizing the pathology not covered by 'OSAS' and also to prompt specialists to go further than the obvious. It aimed at pushing specialists to recognize pathologies earlier and to elicit research in the developmental features of sleep-disordered-breathing (SDB).[6] Untreated UARS individuals can present a low quality of life and may develop cardiovascular consequences. Over a significant amount of time, sleep and daytime symptoms, such as fatigue, insomnia, and depressive mood, in untreated UARS usually increase, and can lead to undesired consequences of poor productivity at work.[3]

Since the patient is asleep and unaware of their actions, awareness of tooth grinding is typically noted by a sleep partner or family member. This tooth grinding is reported by 8% of the population. Because grinding of the teeth requires the movement and involvement of the mandible, sleep bruxism is a behavior classified as a 'sleep-related movement disorder'. Current publications indicate that sleep bruxism is a direct result and or consequence of sleep-related micro-arousals. Sleep-related micro-arousals are defined by a rise in autonomic cardiac and respiratory activity. These micro-arousals can occur up to 8-14 times per hour of sleep. The putative roles of genetic factors and upper airway resistance in the genesis of rhythmic masticatory muscle activity and sleep bruxism are under investigation.[7]


In healthy individuals, bruxism should be considered a risk factor rather than a disorder. Even though a risk factor is an attribute that could potentially increase the probability of a disorder, it does not "guarantee" that disorder will become present. A disorder is defined as a condition that results in a harmful dysfunction to the patient, which ultimately causes harm to the patient, resulting in a negative impact on the patient's overall health and well being.[5] 

There is still a lack of supporting evidence to be considered conclusive. However, in some individuals, the evidence of bruxism could be a positive consequence for the bruxer. Grinding of the patient's teeth could be a compensatory movement for the bruxer in order to prevent the patient from waking up due to the amount of difficulty the patient is having keeping a patent airway, resulting in respiratory arousal. A patient waking up in order to catch their breath is classified as respiratory arousal. Respiratory arousals are essential for these patients in order to prevent a collapse in the airway while asleep or even to restore the patency of the airway while the patient is sleeping. Hence, why the sign of nighttime bruxism is a legitimate early indicator of UARS. We call this a "positive" consequence for the patient because, ultimately, the behavior of bruxism is allowing adequate airflow for the patient while sleeping. To sum this all up, patients presenting with bruxism may not be clinically diagnosed with OSAS due to the patient adapting over time to not result in full hypoxia due to upper airway resistance. Damage to the dental hard tissues such as cracked teeth, repetitive failures of restorative work/prosthodontic constructions, or mechanical wear of the teeth (for example, attrition) may also be indicators of sleep bruxism.[5]

Treatment / Management

Dentists have the most significant opportunity to see and recognize patients who may be suffering from UARS. Their primary objective is to inspect your mouth and observe the teeth. By examining the teeth, dentists can help identify problems and facilitate treatment options. For patients who suffer from primary snoring and mild to moderate OSA, the American Academy of Sleep Medicine (AAOSM) has recommended patients try wearing an oral appliance while they sleep.[4] When fitted and worn appropriately, the oral appliance has been suggested to act by maintaining the activity of the masseter muscles that control the movement of the lower jaw. The oral appliance can also assist in protracting the tongue. The oral appliance is also responsible for holding the mandible in an increased vertical and protrusive position. By maintaining this position, the oral appliance reduces the airflow resistance in the upper airway. Oral appliances are more cost-effective and less cumbersome than the traditional continuous positive airway pressure (CPAP) machine.

Patients who suffer from UARS can also benefit from the use of an oral appliance. These patients, to a lesser degree, may tolerate their symptoms with a lower oxygen concentration.  This could be beneficial for these patients that might not meet the full criteria to be diagnosed with OSAS. Patients with relatively less daytime sleepiness can also benefit from wearing an oral appliance while sleeping. Patients suffering from a lower frequency of apnea may also benefit from an oral appliance. Oral appliances are also a great treatment option for those patients with UARS who are intolerant of CPAP or those who refuse surgery.[8] The roles of the physician and the dentist have been defined by the Association of American Sleep Disorders. This group has published guidelines about the appropriate use of oral appliance therapy.[4]

Oral appliances vary depending on which specific appliance can accomplish the treatment goal recognized by the dentist. Most oral devices are comprised of thermoplastic materials with retainers and support. Oral appliances are custom made by dentists. Oral appliances come in multiple styles and variations; again, all depends on the outcome that's trying to be achieved for the best treatment for the patient. The first device is a mandibular repositioning device (MRD) or a mandibular advancement device (MAD). Both of these devices can be created to be titratable. The MRD and MAD function by engaging one or both of the dental arches to modify mandibular protrusion. For a patient to be treated with an MRD or a MAD, first, the dentist must make a dental impression, along with creating a centric relation record, along with a protrusion record. The next oral appliance that can be used to treat patients suffering from UARS is a tongue repositioning device or a tongue retaining device. These devices help maintain the positioning of the tongue while a patient is sleeping in the supine position and prevent the tongue from sliding posteriorly, restricting the patient's airway. Other oral appliances used to treat patients who suffer from UARS include soft palate lifters and tongue retainers.

Lastly, oral appliances used in combination with a CPAP machine can help alleviate symptoms associated with UARS. When used together, the oral appliance allows pressurized air into the oral cavity, with the added benefit of the patients not having to wear the bulky headgear or nasal mask required with a traditional CPAP machine. When an oral appliance is worn by a patient while also using the CPAP, the patient avoids the common problem of air leaks, and this also eliminates the feeling of claustrophobia that is a common feeling associated with CPAP treatments. The oral appliance is worn in conjunction while using the CPAP, and the oral appliance works by moving the tongue anteriorly to enlarge the airway. Moving the tongue anteriorly results in enlarging the patient's airway. The cross-sectional size of the airway can be increased by the simple movement of the mandible or the tongue anteriorly. It is not clear whether this movement increases the cross-sectional area of the airway or if this changes the entire shape of the airway.[4]

Differential Diagnosis

Several pathologies can present themselves as UARS, such as obstructive sleep apnea syndrome, sleep-related breathing disorder, respiratory sleep disorder, and sleep-disordered breathing. Even though all these terminologies have different titles, they all can be summed up by describing a patient who experiences abnormal breathing during sleep.


UARS is the intermediate between that of normal subjects and that of patients with mild-to-moderate sleep apnea syndrome. Any neurological abnormality absence gives UARS a good prognosis. Also, UARS is potentially reversible if treated early. The best outcome for the patient is strongly dependent on the early discovery and help of the patient's dentist. However, some studies suggest that untreated UARS has an increased risk of arterial hypertension. It can also evolve into obstructive sleep apnea.[9]


If left undiagnosed and untreated, UARS patients usually present with a low quality of life and could potentially suffer from complicated cardiovascular consequences. Over time, if left untreated, UARS patients see an increase in sleep and daytime symptoms. Daytime symptoms of UARS patients include fatigue, insomnia, and depressive mood.[6] 

UARS patient's main characteristic of esophagic pressure (Pes) negativity can cause a diastolic leftward shift of the interventricular heart septum and a consequent ventricular "collapse" overtime if left untreated. These cardiovascular consequences are a direct result of the long-lasting flow limitation episodes a patient experiences during their sleep. These flow limitation episodes can induce a small increase in end-tidal carbon dioxide (PetCO2). This small increase in end-tidal carbon dioxide can also stimulate the sympathetic nervous system activity. This small increase in end-tidal carbon dioxide could cause hypertension, cardiovascular, and metabolic consequences observed in UARS patients. Some studies suggest that untreated UARS has an increased risk of arterial hypertension.[10]

An increase in inflammatory markers can also happen in non-treated UARS individuals. If the crowded airway or narrow jaws are not corrected, these consequences could develop. UARS patients will then be left with the complaint of worsening "functional" symptoms, which potentially may lead to the development of local polyneuropathy.[9]

Pearls and Other Issues

Sleep apnea, or OSAS, historically has been diagnosed by a Sleep Medicine physician. However, as we have discussed in his article, its management is interdisciplinary. The Dentist has the vital role of first screening patients for OSA or URAS risk factors. Risk factors for OSA or UARS include retrognathia, a palate with an extremely high arch, tonsils that are consistently enlarged, or a tongue that is larger than normal for the patient's oral anatomy. Probing questions asked by the Dentist regarding poor sleep, sleep position, obesity, hypertension, morning headaches, or orofacial pain are also necessary identifiers.  Most importantly, as discussed at length in this article, the more critical identification of bruxism by a tooth examination. Next, the Dentist is responsible for referring to an appropriate health professional as indicated. Still, for the majority of Dentists, this requires the Dentist to bring awareness to the patient and reaching out to the patient's primary care provider. For the sake of hierarchy, giving the patient meets the required criteria, referring the patient to a Sleep Medicine Specialist. Finally, it will be the responsibility of the Dentist to create and provide oral appliance therapy followed by the recommended regular dental and sleep medical follow-up.[11] 

The monitoring is one of the most critical steps because if a patient isn't comfortable with the appropriately chosen treatment regimen, the patient isn't going to use it, resulting in the patient not benefiting from treatment, potentially leading to cardiovascular and metabolic consequences. In addition to an adequately chosen oral appliance based on the patients' needs and goals, it requires provider expertise in all fields of medicine to appropriately and successfully treat our patients suffering from UARS. Oral appliance effectiveness is vital in managing OSA caused by UARS.

Enhancing Healthcare Team Outcomes

Effectively identifying and ultimately treating bruxism for the goal of reducing UARS in patients suffering from UARS relies on effective interprofessional communication and continuity of care throughout the entire diagnosing process. As stated earlier, in medicine, there is a specific chain of commands and hierarchy of order that must be followed in order to properly diagnose and treat our patients.

When discussing UARS, this chain of commands starts and could also ultimately end with the dental professional. The interprofessional communication will start with the dental professional identifying the bruxism/teeth grinding of the patient on the dental exam. Further, follow up questioning performed by the patient's primary care provider, then a visit to the sleep medicine Doctor, where if no changes in the patient's oxygen levels are detected during periods of sleep, that patients symptoms can be managed and treated by a simple oral device, created by their dentist.

Article Details

Article Author

Margaret Maggard

Article Editor:

Marco Cascella


7/17/2021 1:10:04 PM



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