Airway-centric orthodontics: a review on oral appliance therapy as a simplified solution to obstructive sleep apnea

Introduction

Background

“You that seek what life is in death, now find it air that once was breath.”—Baron Brooke Fulke Greville, “Caelica 83”.

Air, breath, and life are synonymous. Breath sustains life and every cell of the several billion that constitute the human body’s need to breathe. Surprising though, the intersection of evolutionary biology, function, and biomechanical modulation of the craniofacial skeleton struggles to find a central position in clinical orthodontics and oral health sciences.

Any decrease in breath on the other hand has numerous dangerous and potentially dangerous effects for all life. Obstructive sleep apnea (OSA) is one such disease characterized by episodes of upper air passage collapse during sleep accompanied by hypoxia and sleep arousals. Patients with OSA may complain of various signs and symptoms such as daytime sleepiness (1), snoring and choking and gasping during sleep (2), nocturia (3), morning headaches (4), increased sedentary fatigue (5), unrefreshing sleep (6), and chronic insomnia (7) making a positive diagnosis of OSA difficult (8). Risk factors predisposing to OSA include obesity, large neck diameter, male sex, increasing age, post-menopausal status, and disturbances of the craniofacial region (6,9).

While polysomnography (PSG) remains the gold standard for testing for OSA, the use of home sleep apnea testing (HSAT) has emerged as a reasonable alternative with a sensitivity and specificity of 79% the use of several questionnaires such as the Stop Bang, Epworth Sleepiness Scale (ESS), and the Berlin Scale also have seen a wide acceptance in the clinical setting (6).

Rationale and knowledge gap

OSA prevalence is increasing, Benjafield et al. reported an OSA (mild to severe) prevalence of 936 million persons between 30 to 69 years, and 425 million persons between 30 and 69 years have OSA (moderate to severe) globally, according to the diagnostic criteria of the American Academy of Sleep Medicine (10). The prevalence rates of OSA in different regions vary with rates from 3% (females) to 10% (males) (11) to rates as high as 78% (females) to 90% (males) being reported making it one of the commonest sleep disorders (12). The rising challenge of obesity brings an increasing focus on OSA. There is a need to address the address the etiology, pathogenesis, and management strategies for OSA. The role craniofacial anomalies have been receiving much attention as contributors for OSA (6), with a lot of recent studies focusing on the role of malocclusion and craniofacial anomalies as contributory factors for OSA bringing to fore the role of dentists in early diagnosis and management of OSA (13,14).

There exist diverse modalities for the management of OSA with lifestyle modifications such as abstinence from alcohol, exercise, changes in sleep position to name a few being the least invasive (6). Skeletal and soft tissue surgeries have also been recommended as management strategies (15). Positive air pressure (PAP) has emerged as the mainstay in the treatment of OSA. Continuous PAP (CPAP) was first tried in 1981 and is the most common delivery in use subsequent modifications such as bilevel PAP (BPAP) have provided better results. Technological advancements such as auto CPAP (ACPAP) and Auto BPAP (ABPAP) have led to better results (16). However patient compliance with PAP devices have been challenging. There is also the emerging recognition that effective management of OSA needs an interdisciplinary approach (17).

Dentists often examine various structures such as the tongue, tonsils, soft palate and evaluate jaw position routinely thus making them an important part of the multidisciplinary team for the management of OSA (18). The use of oral appliances which reposition the jaws during sleep in the management of OSA is a promising field because of better tolerance in patients intolerant to PAP appliances (6) leading to the emergence of a new field in dentistry i.e., dental sleep medicine.

Objective

This review presents an all-inclusive view of OSA in the context of evolutionary cranio-skeletal development, collates current knowledge regarding OSA prevalence in contrast to issue or subject specific reviews. The biologic effects of OSA have been added to ensure a holistic view of the condition. Special emphasis that has been placed on the recommendations on diagnosis of OSA using simple diagnostic aids routinely used by dentists and management of OSA using relatively simple oral appliance therapy (OAT) are deliberated.

OSA: cause & ramifications

The term “Pickwickian syndrome” that’s sometimes used for the syndrome became coined by the famous early twentieth-century doctor, William Osler, who apparently was a reader of Charles Dickens. The description of Joe, “the fat boy” in the pickwick papers suits flawlessly with the clinical image of a person with OSA syndrome. The effect of OSA on overall health is also well established, 50% of cardiac patients have a varying degree of OSA and a causative link between OSA, stroke, and coronary artery disease is also well established in literature (19,20). Yet the underlying problems remain surprisingly undiagnosed. A systematic review and meta-analysis by Chen et al. in 2021 shows that 80–90% of cases go undiagnosed with a huge health liability and risk (21). There is flippancy and embarrassment over seeking help or a consultation over sleep problems and snoring.

OSA is related to the enhanced crumpling of the upper air passage. The pharyngeal critical closing pressure (PCRIT) defines the point at which the air passage collapse occurs. Impaired muscle tone, mandibular and tongue position add to the collapse. The increased effort to maintain respiration in a compromized air passage is accompanied by an enhanced serum carbon dioxide and diminished oxygen levels (22,23). The respiratory distress is related to cortical arousal and an increase in sympathetic neural activity with spikes in blood pressure, heart rate and a predisposition towards cardiac arrythmias (8). Multiple sleep wake cycles complicate the issue with serious health consequences.

Search strategy

PubMed/Embase/Scopus/Web of Science databases were searched for studies that mentioned sleep apnea, obstructive sleep apnea, OSA in the title and mentioned oral appliance, myofunctional in the title or abstract. The following search strategy was put into the advanced research intelligence system (AriS) chart using python software (Figure 1). The articles were sub divided into clinical trials, comparative studies, and systematic reviews and meta-analyses. The following were the search terms used: (sleep apnea [Title] OR obstructive sleep apnea[Title] OR OSA[Title]) AND (appliance[Title/Abstract] OR oral appliance[Title/Abstract]) AND (systematic review[Title] OR meta-analysis[Title]).

Figure 1 ArIS chart demonstrating distribution of articles from the AI search. ArIS, advanced research intelligence system; AI, artificial intelligence.

OSA: an evolutionary basis

Evolutionary biology has been a serious contributor to this emerging silent epidemic as some have termed it (24). Bipedalism, an erect posture, a collapsible oropharynx, all led to a progressive set of factors where a minor variation could have unprecedented outcomes on the airway and breathing. Bipedalism of homo sapiens came at a price, the scaffolding had to support the weight of the cranium, brain posture became an issue and the larynx descended. Migration into the grasslands and the introduction of pursuit hunting led to an increased demand for oxygen in our ancestors which was provided by mouth breathing. The process of verbal communication and language affected tongue position and posture. If the tongue rested completely in the oral cavity, it would not impede the airway, but phonation and articulation would be a challenge, so the tongue came to lie in the oropharynx setting the stage for compromising airway with even small variations in position and posture (25).

A growing concern in evolutionary biology was the possibility of a progressive reduction of the size of the human jaws, this is made out by comparisons of medieval skulls with modern skulls in which the medieval skulls have shown little or no evidence of malocclusion, had ample space for the tongue, and showed a minimal prevalence of mandibular third molar impactions, all of these traits are found compromized in modern human skulls. Craniofacial development was linked to changing dietary and chewing habits from coarse to more refined food (26) and anthropologists set about building a link with the reduction in the size of the jaws (27). Some experts in dental anthropology, infer that malocclusion has accelerated in the last 150 years or so in technologically advanced communities (28).

Observations on the effect on muscle posture modifying facial growth are present in published literature (29). Obstructions in the naso-respiratory passages have been found to promote a clockwise rotation in the growing mandible thereby leading to increase in anterior vertical facial height and decrease in posterior vertical height leading to retrognathia and open bites (30,31). Harvold has demonstrated the impact of impaired nasal breathing on craniofacial development. Obstructed airway leads to an extended cranio-cervical extension and a forward head posture to maintain patency of airway which unfortunately does not happen during sleep (32).

Dentists on the other hand have seen malocclusions from the prism of genetics only, ignoring an increasing body of evidence which focusses on the epigenetic/phenotypic events leading to malocclusions (33).

What Mew postulated in his philosophical paper suggesting the disruption of resting oral posture by environmental factors guiding skeletal growth patterns and genesis of a dental malocclusion which is defined by muscle patterns primarily of the tongue (34) has now found experimental evidence in the work of Engelke et al. who have demonstrated the formation at least two functional components in their bio-functional model reaffirming the role of muscle posture in oral skeletal development (35). These findings present an interesting evolutionary pathway for the development of OSA (Figure 2) and are summarized in Table 1.

Figure 2 Hypothetical correlation between OSA and evolution (14,25-27,30,34,35). OSA, obstructive sleep apnea.

Biologic burden of OSA

The complex interrelationship between sleep and health has been widely recognized. Disturbed sleep is in numerous studies found associated with diseases of cardiovascular and metabolic systems. There is also emerging evidence that sleep disorders increase the risk of breast, prostate and colorectal cancers (36-40).

OSA has also been found to be associated with several systemic diseases and the intermittent hypoxia caused by OSA has been consistently found to predispose patients to cardiovascular diseases, insulin resistance and neural damage (8).

Cardiovascular diseases

OSA contributes to cardiovascular disease by affecting various paths of the cardiovascular system. Episodes of OSA produce central hemodynamic effects such as hypercapnia, intrathoracic pressure oscillation and produce arterial oxygen desaturation in addition to causing sleep disruption. This causes a fall in cardiac flow rate, decreased stroke volume and diminutions in cardiac rate (41). The post apnea period is typified by a pronounced transitory increase in systemic arterial pressure. The peripheral circulation is also affected with vasoconstriction being observed in the forearm and finger (42).

The increased cerebral blood flow seen during periods of apnea is followed by a sudden decline in the post-apnea period leading to fluctuations in the partial pressure carbon dioxide (PaCO₂) and causing breathing disability during sleep (43). In the pulmonary circulation OSA produces cyclic patterns of vasoconstrictions and vasorelaxations leading to fluctuations in pulmonary arterial pressure (44).

Endothelial damage by induction of endothelial cell apoptosis (45), increased levels of cell death markers serum nucleosomes, double-stranded DNA (19) and the presence of increased levels of cellular adhesion molecules [intercellular adhesion molecule (ICAM), vascular cell adhesion molecule (VCAM), and E-selectin] all point to endothelial insult as a key event predisposing to the occurrence of other vascular events such as cardiovascular death, unstable angina and myocardial infarction with stratified hazard ratios as high as 6.01 for cardiovascular events occurring in OSA patients (46).

Insulin resistance

Knowledge that obesity is a factor in both OSA and insulin resistance leading to type 2 diabetes has led to postulations of relationships between OSA and insulin resistance (47), causal relationships between the two were however difficult to generate because of the presence of confounding factors such as smoking, body mass index (BMI), age, etc.

The nurses’ health study cohort found a relative risk for diabetes of 1.48 between occasional snoring vs. non-snoring, adjusting for other diabetes risk factors attenuated to relative risk to 1.41 showing that snoring and by extension OSA being an independent risk factor for type II diabetes (48). while the complex interrelationship between OSA and type II diabetes gets slowly unraveled the results of various clinical trials point out to intermittent hypoxia as a factor in causing insulin resistance and glucose intolerance in OSA patients.

Increased levels of catecholamines, the increased sympathetic neural traffic and amplified levels of cortisol by the effects of OSA on hypothalamic-pituitary-adrenal axis are other possibilities by which OSA predisposes to insulin resistance (49).

Neural damage

Neurobehavioral impairments such as sleepiness, fatiguability, impaired memory and poor concentration are seen in most adults with OSA. While investigating reasons for these, Macey et al. (50), Morrell et al. (51) have found marked reductions in the gray matter of the hippocampus, cingulate cortex and Broca’s area using magnetic resonance imaging (MRI).

Higher levels of brain infarctions (25%) in comparison to normal obese controls (6%) and increased levels of CD40 ligand (CD40L) and P-selectin markers for cerebrovascular disease have been demonstrated by Minoguchi et al. in persons with OSA (52).

In the peripheral nervous system consistent functional impairment, with demyelination of motoneurons has been found in OSA and a correlation between the oxyhemoglobin desaturation and the severity of peripheral nerve dysfunction have been observed (8).

OSA and the immune system

The sleep immune crosstalk has recently received much attention (53) and thus it would only be logical that OSA would lead to impairments in the immune system.

Increase in T helper cells and alteration in the T_helper/T_regulator ratios are noted in patients with OSA. Significant reductions in the peripheral dendritic cell population and reductions in B lymphocytes have also been found in patients suffering from OSA pointing to the presence of immune impairment in OSA (54).

In addition to impairments in the immune system OSA has also been shown to cause a dysregulation of circulating cytokines. Pro-inflammatory cytokines such as the interleukins 6, 12, 17, and 23, tumor necrosis factor alpha, and matrix metalloproteinase (MMP)3 were increased whereas MMP2 and tumor necrosis factor-like weak inducer of apoptosis (TWEAK) levels were decreased (55).

While the data on immune dysregulation in OSA patients is rather recent, immune dysregulation also seems to predispose OSA patients to certain types of cancers and influence oncological outcome (56,57).

The results of the quoted literature are consolidated in Table 2.

Malocclusion and its relation to OSA

Recent systematic reviews and metanalysis have found that the worldwide prevalence of malocclusion is 56% with no gender variances. Africa (81%) had the highest prevalence was seen in followed by Europe (72%), America (53%) lowest prevalence was seen in Asia (48%) with prevalence rates of class I (74.7%; range, 40–96%), class II (19.56%; range, 2–63%), and class III (5.93%; range, 1–20%) (58,59).

Craniofacial disharmony is reflected in cases of OSA. The most common features of disharmony seen in cases of OSA are bimaxillary retrusion, decreased mandibular length, reduced cranial base angle with a shortened cranial base and increased lower anterior facial height amongst these the decreased mandibular length has been found to dispose most to OSA (60,61). Multiple regression analysis have demonstrated increased overjet and a class II malocclusion as significant risk factors for OSA, however racial variations exist and lateral cross bite was the most prominent transverse dimension predisposing to OSA (13,61-63).

An elongated face with a dolichoprosopic pattern, steep mandibular plane angle, high arched narrow palate, also find a positive association with OSA (Figure 3) (64).

Figure 3 Patient with OSA demonstrating classical long narrow face with collapsed arch. (A) Frontal view demonstrating increased facial height with vertical maxillary excess (arrow). (B) Side profile demonstrating small and retrognathic mandible (arrow). (C) Intraorally a narrow palate with a high palatal vault (arrow) is seen. (D) Occlusal radiograph demonstrating reduced transverse maxillary dimension (arrow) and collapsed palate. These images are published with the patient’s consent. OSA, obstructive sleep apnea.

Considering all of these findings together, the classical pathogenesis begins to emerge. A narrow palate with a mouth breathing habit would imply increase nasal airway resistance and altered tongue posture. Increased overjet with crowding would prevent lip closure further aggravating the problem (65). The mandibular retrognathia associated with slackening of the genioglossus and mentalis muscles, hypotonia of the circumferent musculature would produce a fall back of the base of tongue in supine position with partial or complete airway obstruction (66). A skeletal class II pattern in patients with OSA would be associated with an underdeveloped/posteriorly positioned mandible with associated soft tissue and muscle attachments. The articles of this section are summarized in Table 3.

Defining airway centric orthodontics

Is health merely an absence of disease or infirmity? Could malocclusion fall into a definition of a disease? Orthodontics has struggled with its own identity of coming to terms with malocclusion and health (67). However, the ‘tooth’ paradigm has been centric to dentistry, the central focus being fixing crooked or diseased teeth and restoring an occlusion from a skill based and technique centric model using technology and materials. The industry has offered cookbook solutions with newer materials and a ’stepwise’ methodology often dictating professional trends. In the 1940’s the World Health Organization (WHO) proposed a larger definition of health correlating not just the absence of disease and infirmity but well-being and quality of life (68). Airway centric orthodontics brings into sharp focus the need for a link between orthodontics, oral medicine, sleep medicine, a concept of health with focus on cell anatomy, biology, physiology pathology and shifting a paradigm away from cosmetic or smile design which by association tend to diminish a specialty that is so deeply rooted in health and well-being. It brings a new paradigm of diagnosis and holistic treatment with appliances, techniques and technology being relegated to a secondary role (69). After all moving teeth and remodelling the craniofacial skeleton is a biologic and cellular phenomenon which could only work if all the cellular blocks are in harmony and alignment.

Diagnosis of OSA

OSA and sleep disordered breathing requires a joint workup with a physician to confirm the level of the problem. There has been a lot of debate over whether only sleep experts should be diagnosing and managing OSA, nevertheless OSA has been diagnosed and managed by confluence of specialties in dentistry and several studies have shown that the treatment outcomes do not vary on the type of expert diagnosing and managing OSA (70,71).

There is no physical examination that is specific for OSA, however the signs and symptoms (Table 4) that point out to the probability that a patient has OSA are as follows:

• Overweight/obese (72);
• Neck circumference (>17 male, >16 female) (72);
• Greater waist to height ratio (73);
• Male (6);
• Crowded oropharyngeal airway (74);
• Elder age group (6);
• Post menopausal status (6).

There exist several tools which would aid in assessment of OSA in a non-sleep clinical setting most sensitive among these is the Stop Bang questionnaire, essentially this looks at snoring (S), tiredness (T), observed pauses in breathing (O), blood pressure (P), the ESS (75) and the Berlin questionnaire are also used to predict OSA, however these alone should not be used to diagnose OSA (76,77).

Volumetric estimation of airway is possible by use of computed tomography (CT), MRI, acoustic imaging techniques and acoustic pharyngometry are in use today to estimate the degree and severity of OSA (78).

Home sleep testing/portable sleep testing reduce the necessity for patients to be tested in a sleep lab/hospital settings and recent introduction of devices such as Alice PDX, WatchPAT, etc. have provided results similar to lab PSG and are acceptable as alternatives to PSG in patients without comorbidities, home sleep testing devices report a respiratory event index (REI) in contrast to the PSG (79-82).

PSG however still remains the gold standard for identifying OSA and determining its severity (76,83). PSG provides an apnea-hypopnea index (AHI) (84). Based on AHI scores, OSA can be grouped into four categories:

• Normal (AHI <5 events/h);
• Mild OSA (AHI 5–15 events/h);
• Moderate OSA (AHI 16–30 events/h);
• Severe OSA (AHI >30 events/h).

Mild to moderate OSA is amenable to OAT, severe and central apnea’s need CPAP, nasal CPAP or oscillating positive airway pressure (OPAP) support apart from a detailed medical investigation (85,86).

Though dentists gather a vast array of records including a detailed personal and family history and perform cephalometric and model analysis, these have been with the defined purpose of estimating space to bring about an optimal occlusion with a consequent smile and/or an aesthetic facial outcome. While the utility of various cephalometric and model analysis in the diagnosis of OSA has been recognized quite early (87,88), the entire focus on cephalometric and model analysis in routine practice has been on creating metrics for tooth movement and adjusting teeth in a given occlusion (69). The assessment of skeletal disharmony is routine but so is the tendency for looking at a camouflage and compromise even before offering a more aggressive surgical correction of the jaw bases. This tendency has found favor and is promoted by the industry who tend to define extraction decisions related to a particular appliance. There is an inherent need to bring airway centric focus in the process of diagnosis.

Dental treatment goals need a redefinition beyond teeth and smiles. Improvement of upper airway patency and promotion of nasal breathing should be a primary objective (85). It is possible to outline a simple airway inclusive process in dental evaluation as proposed by Jayan and Kadu (89).

• Preliminary screening in all patients, adults or children, using an ESS or similar Stop Bang analysis;
• Distinctive clinical indicators for a compromized airway;
• Lip incompetency with oral breathing;
• Crumpling of chin;
• Adenotonsillitis;
• Airway grading of Mallampati more than grade III;
• Dark circles under the eye;
• Distended uvula;
• Severe clockwise rotation of the mandible;
• Tiny nares and high and narrow nose;
• Macroglossia and crenations.

It is also imperative for dentists to leverage the routine records that are collated for diagnostics and treatment planning. A lateral cephalogram in natural head position provides good information with a number of analysis being available for assessing risk and potential airway collapsibility along with mandibular position, tongue position (Figure 4) (90). The inherent disadvantage is that the cephalogram is recorded in an erect posture and is two-dimensional (2D). Cone beam CT (CBCT) evaluations offer three-dimensional (3D) airway assessments apart from a physical estimation of the skeletal structures (91). The results of various studies quoted in this section are summarized in Table 5.

Figure 4 Lateral cephalogram of class 2 malocclusion with features predisposing to OSA. a: increased vertical height; b: small and retrognathic mandible; c: increased symphyseal length; d: clockwise rotation of mandible; e: skeletal open bite. OSA, obstructive sleep apnea.

Airway centric orthodontics: revising the clinical treatment paradigm

Much has been debated on early treatment, one phase or two-phase intervention. The reality remains that an essential amount of craniofacial growth is accomplished by 4 years of age. Almost complete development (90%) of the craniofacial complex is completed by 12 years of age and so it must follow that aberrant growth, morphologic features of sleep disordered breathing in adults may be a carryover from childhood issues that remain unaddressed both due to a lack of detail by the treating dentists and also the cognitive bias of treatment only once all the permanent teeth have erupted by a large segment of the lay population and the profession.

There is a need for orthodontists being sensitive to the reality of OSA as they play an important role in the diagnosis and management of OSA albeit as part of an interdisciplinary team.

OAT has emerged as one of the accepted modalities of management of OSA especially so in patients who do not tolerate the PAP devices (16), while early research has focused on OAT in patients with mild and moderate OSA (92) emerging evidence indicates that these devices could be beneficial to patients with severe OSA also especially in cases where CPAP has not been successful (93,94).

Comparisons of OAT with PAP devices have largely focused on the improvement in the AHI scores and thus OAT are often reported to be less efficacious in comparison to PAP for PSG parameters (95). In clinical practice, irrespective of the comparative measures used the better compliance and better health benefits achieved by OAT offset the inability of OAT to match the PAP devices in reducing apneic events (96).

Management of OSA in adults

Broadly OSA can be managed using three stratagems of behavioral modification, treatment devices and surgical intervention.

Drug therapy and behavioral modification

Drugs such as eszopiclone, acetazolamide, naltrexone, physostigmine, donepezil, and fluticasone have been tried out in the therapy of OSA, however there is insufficient scientific evidence to recommend the long-term use of these drugs in the treatment of OSA (97).

Behavioral modification including diet modifications (98) low energy diet (99) diet and exercise (100,101) have all been found to be beneficial in reducing the severity of OSA and achieving reduction of AHI scores (102). The findings of the articles quoted in this section are summarized in Table 6.

Treatment with devices

The benchmark treatment for OSA continues to be CPAP and modifications such as BPAP, auto-titrating PAP (APAP), and humidified PAP (103). However, poor compliance is reported in around two-thirds of patients on PAP devices (6) and thus recent devices come with modifiable pressure profiles that result in greater patient compliance, however the compliance rates still continue to be an area of concern (16,104).

OAT

The oral cavity is an important component of the airway, the anterior boundary of the upper airway is formed by the upper and lower incisors and the piriform rim. The superior boundary is formed by the cranial base, the posterior boundary by the cervical vertebrae, and the inferior boundary is formed by the hyoid bone. The width of the palate, the separation between the ascending rami, and the middle cranial fossa are lateral determinants of airway size. The pharyngeal muscles, turbinates, tonsils, soft palate, tongue, adenoids, and nares line these structures which define the bony skeletal limits (67), Thus providing the dentists and orthodontists with opportunities to leverage these factors for the management of OSA. The challenge for the orthodontists is to address any craniofacial structural deformity that could directly or indirectly influence the airway and to look at the possibility of OAT in addressing OSA.

The first documented use of an oral appliance to improve respiration comes from Pierre Robin who in 1921 demonstrated the use of a monoblock appliance for a case of the Pierre Robin syndrome which essentially led to mandibular advancement with tongue and hyoid repositioning for the management of the Pierre Robin sequence (105).

There are over 100 types of oral appliances available for the treatment of OSA differing in terms of mechanism of action, location and materials used (106). These appliances can be grouped as follows:

• Palatal lift appliances/soft palate liners;
• Tongue retaining devices/tongue stabilizing devices (TRDs/TSDs);
• Mandibular advancement devices (MADs)/mandibular repositioning devices (MRDs)/mandibular advancing appliances (MAAs).

Drug-induced sleep endoscopy (DISE) a procedure fist recommended in 1991 to accurately locate the position of upper airway collapse during induced sleep is now being used to discern the value of OAT in patients who have failed CPAP or previous surgery (107,108).

Palatal lift appliances or soft palate liners

These were initially used for the treatment of snoring by applying pressure on both the soft palate and uvula thereby reducing palatal vibrations, this was also found to increase airway space and hence were also used for OSA treatment (105,109). However, these appliances are rarely seen in clinical use exclusively for the management of OSA (106). Several devices such as the Tübingen palatal plate used for the management of the Robin Sequence also improve OSA parameters (110).

TRDs/TSDs

TRD/TSDs work on the principle of clasping the tongue in a forward position and not allowing it to proceed downward because of negative inspiratory pressure thus maintaining airway patency. A variety of TRD designs are available and have shown to significantly reduce the AHI scores in over 71% of patients (111,112) and TRDs are ideal for use in edentulous patients and patients with unhealthy dentition in whom other OAT is precluded (113).

MADs

The American academy of dental sleep medicine in 2014 gave an evidence-based definition for an effective appliance in the treatment of OSA and snoring and have constructed the definition for MAD as they are the most effective and clinically widely used OAT appliance (114).

Titratable functional appliances have been the precursors to the MADs for adults, MADs as the name suggest reposition or advance the mandible and base of tongue leading to tightening of the supra hyoid, infrahyoid, genioglossus, and geniohyoid muscles causing an increase in pharyngeal airway space and resultant decrease in the PCRIT (115) an important consideration in MAD therapy is the amount of mandibular advancement possible since devices in which advancement is not beyond centric occlusion do not effect airway size and in general the degree of mandibular attachment dictates the efficacy of MAD devices (105). MADs have generally shown optimum results at a 50% protrusion and protrusion beyond 50% has not shown any added benefits, the effect of less than 50% protrusion is not yet clearly documented (116,117).

Boil and bite devices

The simplest MAD device available are the boil and bite devices such as the Sleep Pro 1 and SnoreRx consist of a thermoplastic material which can be heated and the patient bites on these blocks and allows the material to set. The boil and bite devices suffer from improper fit and fall out easily, nevertheless these devices have also been found to improve AHI scores (118).

Customized MADs

Customized MADs are better tolerated than the prefabricated boil and bite (119), devices and come in two models, the one piece or monobloc appliances and the two piece or duo bloc appliances which consist of two blocks connected to each other, the two piece appliances come with the added benefit of being adjustable serially titrable i.e., the mandibular protrusion in these devices can be adjusted gradually allowing the patient to slowly adjust to maximum protrusion in contrast to the monobloc devices. Isacsson et al. have reported similar efficacy rates in their multicentric trial and Ishiyama et al. found better results for the monoblock devices in their meta-analysis (120-122).

The advent of digital impressions, computer-aided design (CAD)/computer-aided manufacturing (CAM) and 3D printing have led to the emergence of several Food and Drug Administration (FDA) approved MAD appliances such as Narval, Pantera, and Somnodent avant which are 3D printed and the Prosomnus Micro2 which is a CAD/CAM milled appliance (Figure 5) (123), these come with the benefits of being less bulky and have a better fit and have also shown a good response in severe cases of OSA (117,124).

Figure 5 Mandibular advancement using the Micro 2 device demonstrated on casts. (A) Frontal view. (B) Lateral view.

The MAD appliances are usually delivered with the mandible obtruded to two-thirds of its maximal protrusion (Figure 6). A second sleep study after the patient is well accommodated and has some relief would be an indicator of success of the therapy. Monitoring every 6 months and then annually after the first year is recommended in various guidelines (113).

Figure 6 Mandibular advancement using the Micro 2 device in an adult patient with radiographs showing marked increase in airspace. (A) Pre appliance insertion showing retruded mandible (arrow). (B) Lateral cephalogram showing collapsed airway (box). (C) Post appliance insertion with mandibular advancement (arrow). (D) Lateral cephalogram showing increased airway space (box). These images are published with the patient’s consent.

Selection of patients for OAT

The key to successful management of OSA by OAT would be appropriate patient selection. A stable dentition, minimum of 6–8 teeth/arch, good oral and periodontal health are prerequisites for a patient to be subjected to MAD appliances, though no absolute contraindications exist the presence of loose crowns, pre-existing temporomandibular disorders (TMDs), bruxism, micrognathia are relative contraindications (106,120).

Patients likely to benefit from MAD appliances are likely to be younger females, patients with a lower BMI and smaller neck circumference (120).

Efficacy of OAT

In consonance with the WHO definition of health the authors believe that the efficacy of OAT should be assessed on the basis of improvement in the quality of life indicators. Narratives of OSA efficacy have largely been affected by comparisons to CPAP and physiological indicators and the AHI index (106).

There exist ample evidence from several randomized control trials (RCTs) for the use of OAT in OSA especially in patients not compliant with PAP devices (97,98,107,112,125-131), this evidence is further supplemented by several systematic reviews and meta-analysis (112,116,117,122,130-133). all of these have reflected on the fact that OAT and PAP devices provide comparable health outcomes, with PAP devices showing a greater reduction in OSA severity as assessed by PSG.

The systemic effects of OAT have also been widely studied for over 2–8 years with OAT bringing about modest but significant benefits on cardiovascular outcomes, blood pressure, cognitive function, depressive symptoms, headache and quality of life (93,126,134-138).

Adverse effects of OAT

Temporomandibular joint (TMJ) discomfort or pain is the most common complaint of patients being treated with MADs occurring in over 37% of patients after a year of use according to a questionnaire study (139).

Increased salivation, dry mouth, bad taste in the mouth and occlusal changes have also been reported (118,140). Alterations in cephalometric measurements have also been found post use of MAD devices (141,142). The results of various studies quoted in this section are summarized in Table 7.

Surgical management

Surgical interventions in adult OSA are never the first line of treatment and are only considered after other modalities have failed or cannot be implemented (143). The cases need careful evaluation and possible impact on airway and alleviation of symptoms.

Nasal surgeries such as septoplasty (with or without turbinate reduction) have been found to reduce sleepiness in a RCT (144). Tonsillectomies are recommended for adults with tonsillar hyperplasia although evidence of contribution of tonsillar hyperplasia to adult OSA is still unclear (145).

Oropharyngeal surgeries such as uvulopalatopharyngoplasty and modifications such as laser-assisted uvulopalatopharyngoplasty, radiofrequency palatoplasty, Z palatoplasty involve reduction of palatal bulk by removal of uvula, part of soft palate and tonsil and closure of tonsillar pillars (146). These are the commonest surgical procedures being performed for adult OSA with success rates of 50% and cure rates of 16% (147).

Procedures on the tongue such as reduction glossectomies have been found to improve quality of life while reducing daytime sleepiness (147), and have provided variable success rates, ranging from 35% to 62% (148).

Maxillomandibular advancement (MMA) surgeries involve osteotomies (Le Fort 1 and bilateral mandibular ramus sagittal split) of the maxilla and mandible followed by counter clockwise advancement of the inferior portion of the maxilla and anterior mandible leading to a forward displacement of attached soft tissues, tensioning the pharynx with resultant increase of the pharyngeal air space (146,149). These procedures also lead to better facial aesthetics (150,151). MMA surgeries demonstrate a high success rate (86–90%) and are the only treatment modalities demonstrating cure rates similar to CPAP (152). MMA surgeries are usually done as part of a multilevel or staged surgeries with stage 1 consisting of soft tissue surgeries and MMA as stage 2 surgeries (143).

Surgically assisted rapid palatal expansion (SARPE) and micro implant assisted rapid palatal expansion (MARPE) are modalities for increasing the transverse maxillary dimensions in individuals with transverse deficiency (153). This expansion has the secondary effect of decreasing airway resistance and increasing airway space. Both modalities have been found to decrease rate of respiratory disturbances in OSA (154).

Genial advancement, tracheostomy and surgical implantation of a hypoglossal nerve stimulation device that has been deemed safe, feasible and efficacious in two trials are the other surgical procedures used in adult OSA (155,156). Table 8 summarizes this section.

OSA in children

Pediatric OSA is pathogenetically different from adult OSA because of the role played by multiple risk factors such as airway collapse, impaired neuromuscular tone, hyperplasia of tonsils and surrounding lymphoid tissue and growth-related changes contribute to pediatric OSA. Childhood obesity is a growing concern, and any screening must consider this essential aspect (157). According to the International Classification of Sleep Disorders (ICSD)3 (158), OSA can be diagnosed by either of two sets of diagnostic criteria. The first set of criteria for OSA includes the presence of at least one of the following: (I) snoring; (II) labored, paradoxical, or obstructed breathing during the child’s sleep; or (III) sleepiness, hyperactivity, behavioral problems, or learning problems. The PSG criterion for diagnosis requires either (I) one or more obstructive events (obstructive or mixed apnea or obstructive hypopnea) per hour of sleep or (II) obstructive hypoventilation, manifested by PaCO₂ >50 mmHg for >25% of sleep time, coupled with snoring, paradoxical thoracoabdominal movement, or flattening of the nasal airway pressure waveform. It would be necessary to emphasize that these criteria are for use only in children under 18 years, though for ages 13–18 years the adult criteria may also be used (17). The pediatric sleep questionnaire is recommended as an adjunct to PSG analysis (159). In addition, HSATs with oximetry, DISE and dynamic MRI are used in diagnosis of pediatric OSA (160).

Management of pediatric OSA

Management of pediatric OSA differs from adult OSA in a multitude of ways, surgical management gains primary importance with adenotonsillectomy becoming the gold standard surgical treatment, with a metanalysis demonstrating resolution of PSG findings in 83% of patients (161). In children with deficient jaw size or with syndromes such as Pierre Robin sequence and trencher Collin syndrome MMA surgeries have proven to be beneficial (157). In cases where MMA surgeries cannot provide the desired increase in space, distraction osteogenesis is emerging as a viable alternative as the gradual maxillary/mandibular advancement provides for better soft tissue adaptation. The decreased PSG parameters are stable in the long run (17,161).

MAD appliances are when used in children will stimulate cartilaginous growth at the condyles and a recent metanalysis has found MAD devices in children to be most effective when used before the pubertal peak (162). In cases of transverse nasomaxillary deficiency the use of rapid maxillary expansion (RME) or MARPE has been found to reduce AHI scores in the short-term while there is insufficient long-term data. These devices bring about a transverse expansion of the palate, maxillary base and nasal floor with a downward shift of the nasomaxillary complex thereby decreasing airway resistance and increasing airway space (163,164).

Increased vertical face dimension is one of the classic findings in patients with OSA, this is largely caused by a clockwise rotational growth of the, to counteract this a vertical pull headgear with intraoral maxillary micro implants favoring a counter clockwise mandibular growth with concomitant reduction in vertical facial height (165) has also been tried with mixed results precluding any recommendations (166).

The findings of this review on pediatric OSA are summarized in Table 9.

Strengths

This review charts the spectrum of OSA from its evolutionary basis to the biological effects, diagnosis and treatment of the condition from the perspective of orthodontists.

Limitations

Being a literature review in the context of OSA and orthodontics not all aspects of OSA have been discussed. The review has utilized literature published in the English language only and hence data from other language articles are not included. The literature search may have missed out on a few relevant publications.

Conclusions

Airway centric orthodontics underlines a major shift from the tooth paradigm to a larger definition of health and well-being. OSA is major medical disorder that can have serious health consequences in both children and adults. An anthropologic predisposition consequent to bipedalism, phonetics, and the erect posture of homo sapiens has been further compounded by a progressive reduction in the size of the jaws, malocclusions, altered dietary patterns, obesity and societal change. There exists a need to screen all pediatric and adult patients for OSA in an orthodontic setting, a simple questionnaire procedure can be incorporated into the initial history taking and record keeping. Though diagnosis of OSA is based on PSG/HSAT parameters, the orthodontist would be able to identify the altered skeletal morphology which could impede the airway. OAT therapy achieves the alteration of mandibular/tongue position affecting airway dynamics and lowering the PCRIT. Surgical correction of maxillomandibular bases becomes essential in extreme cases. Maxillary expansion by SARPE/MARPE/RME/distraction osteogenesis could alter the nasal airway volume and the resistance to airflow.

OAT has emerged as a treatment of choice in the management of OSAs with several RCTs demonstrating the utility of OAT. This is especially in patients who are not amenable to PAP devices with MADs being the most common and effective devices available to orthodontists to manage OSA.

Slowly but surely a bridge is being built between orthodontics, oral medicine, oral, surgery and sleep medicine leading to the creation of multidisciplinary teams which will serve the specialty of dentistry well in enhancing its image rather than being relegated to a niche segment of cosmetics and aesthetics alone. It’s time to redefine the paradigm.

Acknowledgments

The authors acknowledge Medeva Knowledge Systems, New Delhi, and Dr. Uday for the AI-Based Literature Search and Collation, and acknowledge Dr. Goutham Reddy & Dr. Rezin Aziz, Department of Orthodontics, Coorg Institute of Dental Sciences for data from their dissertation on “Comparative assessment of changes in pharyngeal airway space in cases of obstructive sleep apnoea with a customized mandibular repositioning appliance—a clinical study”.

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned by the Guest Editor (Chung H. Kau) for the series “Managing Craniofacial and Dentofacial Disorders—Simplified Solutions for Difficult Situations” published in Frontiers of Oral and Maxillofacial Medicine. The article has undergone external peer review.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://fomm.amegroups.com/article/view/10.21037/fomm-23-1/coif). The series “Managing Craniofacial and Dentofacial Disorders—Simplified Solutions for Difficult Situations” was commissioned by the editorial office without any funding or sponsorship. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. Written informed consent was obtained from the patients for publication of their images.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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