A Review of Research Studies on Sleep-Disordered Breathing in Children Relevant to Dental Professionals

Children with sleep-disordered breathing (SDB), which might include obstructive sleep apnea (OSA) when severe or other more mild manifestations of abnormal sleep often referred to as upper airway resistance syndrome (UARS) or primary snoring (PS),^1-6 have symptoms that typically vary considerably from adults, as does their incidence.^7-9 The incidence of OSA, for example, in children is about 1% to 4%.^10-15 This is in stark contrast to adults where it can occur from 4% to up to about 24% depending on age, sex, height, weight, and other factors.^16-21 This disparity is attributed to several reasons, such as the comparative sizes and configurations of tonsillar and adenoid tissues^22-25 as well as the soft palate,^19,26 and differences in anatomical form and neuromotor tone of the respective airways.²⁷ The most prevalent time of a child's increased size of lymphoid tissue is between the ages of 2 and 6 years,²⁸ although size increase can occur as young as at birth and continue until about age 12 years.^29,30 Compared to adults children generally have a stiffer wall of the airway that resists its change in shape and resists collapsibility from pressure from the base of the tongue.^31,32

Although OSA is less prevalent in children than in adults, it is extremely serious due to its potential effect on the cardiovascular system,^27,33 such as increased blood pressure, endothelial dysfunction, pulmonary hypertension, and cor pulmonale.^34-36 Children, however, exhibit the effects of SDB, OSA, UARS, and PS differently than adults in that the neurocognitive and behavioral symptoms occur quite frequently, are more obvious, and can severely alter a child's life.^5,37-39

With several important symptoms associated with abnormal sleep in children^40-42 a symptom analysis is applicable at an early age, even as young as almost at birth, since many of these factors that may be present could affect early growth, particularly of the mandible and maxillary arch widths.^43-46 From birth to about 20 months, major changes in mandibular advancement occur that can alter an infant's class 2 profile to a more normal class 1 appearance. After 20 months a fairly constant maxillo-mandibular relation becomes permanently established.

Facial morphology appears to be related to abnormal sleep and airway narrowing, affecting such aspects as head posture,⁴⁷ facial growth (following adenoidectomies),⁴⁸ mandibular size (short mandibular body),⁴⁹ vertical facial pattern (retrognathic mandible, open bite),⁵⁰ and various craniofacial characteristics (steep mandibular plane, high angle face).^51,52 Because the causes of sleep and breathing dysfunctions are numerous, interactive, and illusive, consistently achieving a complete correction becomes difficult and often even impossible.^53-55 Although adults may have some similar symptoms as children,^53,56 treatment is usually more successful in a child because of the impact of growth and its positive effect on the ease, completeness, and stability of treatment.

Studies that have analyzed these various symptoms, such as hyperactivity, daytime sleepiness, snoring, attention deficit, headaches in the morning, etc, and their associations with other diagnostic markers have often observed an alteration of oxygen in the blood and a frequent degree of oxygen reduction (oxygen desaturation)^6,57 associated with abnormal sleep issues. In an analysis of 1096 research studies on childhood symptoms in relation to various baseline factors (OSA, SDB, snoring, etc), the present author found that 77.4% of these studies had significant relationship of these symptoms to blood levels of oxygen, while 22.6% indicated no such significant relationship. In other words, hypoxia, which is an oxygen reduction of 3% or more and which can be tested by a finger clip that analyzes blood coloration, is probably a major factor in the various morbidity elements of sleep disturbances.

Oral appliances have garnered increasing interest as a treatment option, particularly for adult snoring. This is evidenced by the many such appliances available to the dental profession. In 1997 there were 15 various appliances available,⁵⁸ in 2006 there were 80,⁵⁹ and by 2012 there were 120.⁶⁰ Most, if not almost all, of these appliances are for adult snoring, and they function by advancing the mandible in an anterior direction several millimeters beyond an end-to-end incisal relation. The designs of these appliances are inappropriate for growing patients since their use would result in a class 3 (protrusion of the mandible in relation to the maxilla) malocclusion. This advancement procedure would stimulate mandibular growth that typically does not relapse.⁶¹

Appliance techniques, however, have been used in children to modify abnormal sleep issues. One such appliance is a modified monobloc. Research on this appliance consisted of 20 patients aged 4 to 8 years with a similar control sample.⁶² Treatment results indicated a reduction of the apnea-hypopnea index (AHI) within a 6-month period while the monobloc appliance was worn only at night.⁶² Other results from this study showed no change in oxygen desaturation of the blood, with few significant changes in the length of the face and width of the upper posterior arch, a lowering of the hyoid bone, and a reduction in overbite.

Villa et al described the use of an oral appliance in a sample of 14 patients aged 4 to 10 years with a control sample of nine cases during a 6-month treatment period.⁶³ Significant results were obtained for snoring, apnea, restless sleep, sleepiness, irritability, tiredness, thirsty in the morning, oral breathing, and nasal stuffiness. Insignificant findings occurred for nightmares, school problems, and morning headaches. Tonsillar enlargement was consistently reduced in 67% of the treatment group. Interestingly, none of the symptoms consistently received 100% correction. These findings again show that most or perhaps all of the partial corrections indicate that multiple causes are probably present. In this same study, blood oxygen levels increased but did not reach significance. These studiesindicate that oral appliances are capable of producing significant improvements in at least some childhood sleep abnormalities.^62,63

Lymphatic enlargement (tonsil and adenoid tissue) is considered to be the most important risk factor for OSA in children.^64,65 Research, however, has found that adenotonsillar surgery (tonsil and adenoid surgical removal [T and A]) corrects OSA in less than 25% of children and 10% in obese youngsters.^66-68 Significant changes, however, were noted in hyperactivity, depression,^69-71 snoring, asthma, oxygen desaturation, obstructive AHI,^72,73 and bed wetting,^74-76 although other studies found no improvement in bed wetting.^73,77 According to the Friedman analysis,⁷⁸ only grade 3 (tonsils almost touching each other) and grade 4 (tonsils actually touching) are severities that are usually recommended for surgical removal. An unpublished analysis by the present author on 881 children between ages 4 and 12 years found that only 9% were in grades 3 and 4, and therefore, according to the aforementioned parameters, would be recommended for surgery. Grade 3 comprised 8.2% of the 881 children sampled while grade 4 consisted of 1% incidence. Considering this small percentage (9%) of children where surgery would be recommended while discounting other factors such as tonsillitis and the low incidence of the AHI level in children (1% to 5%),^15,55 most children would not be candidates for surgery. It would appear that T and A might not be as effective as expected as a treatment solution for the many adverse sleep symptoms given that only 9% are candidates for the surgery.

One prevalent orthodontic solution for these sleep issues is rapid palatal expansion (RPE). In the author's experience as a practicing orthodontist, after performing expansion procedures with RPE on children, patients often commented that they were now able to breathe through their nose. This would occur after providing about 3 mm to 6 mm or more of expansion. RPE is a highly efficient procedure in which the mid-palatal suture is separated but the posterior teeth do not tip as a result of the expansion force. Simultaneously, space is created between the maxillary central incisors for crowding corrections, and the nasal cavity volume can be increased.

The significant and insignificant changes in symptoms after RPE therapy vary and are often inconsistent. Several studies analyzed various treatment changes,⁷⁹ which are summarized in Table 1. The table presents 20 symptoms separated into five categories based on the significance of the results of treatment. The symptoms with the most consistent significant results were apnea, snoring, AHI, oxygen saturation, and daytime sleepiness.^79-84 The results of the other symptoms also are reviewed in Table 1. Among the 12 symptoms that are reported with nonsignificant results is daytime mouth breathing. Mouth breathing while sleeping was not tested. Oxygen saturation improvement and AHI were found to be stable 12 years after RPE therapy.⁸⁵ The mid-palatal suture closes at around the end of puberty, and RPE should not be done once this suture is closed unless surgery is used to open the suture prior to appliance use in a more mature person.⁸⁶

Other studies found that RPE enlarged the nasal cavity volume by 11.3%⁸⁷ and 15.2%⁸⁸ and the nasopharynx by 16.2%⁸⁸ but did not increase the oropharyngeal volume.^88,89 Significant increases in volume of the palatopharynx were found to be 35%⁸⁹ and 59.6% (mm²).⁹⁰ No changes in volume were found in the nasopharynx,^89,90 however there were changes in the width of the nose⁹¹ and pyriform apertures,⁸⁴ as well as increases in ventilation.⁹² Several other surgical procedures can affect various sleep issues such as uvulopalatopharyngoplasty, genioglossus advancement, hyoid myotomy suspension,⁹³ maxillo-mandibular advancement,^94-96 tracheotomy, midline glossectomy, septoplasty, radiofrequency ablation, transpalatal advancement, and hyoid advancement.^97,98

Two surgeries of particular interest to dental professionals are maxillomandibular and mandibular advancement. Two meta-analyses addressed these procedures and indicated that the mean of the maxillomandibular advancement studies⁹⁶ reduced apnea (N = 627) 95.4% (from 34.7 to 1.6) and AHI (N = 627) 85.1% (from 63.9 to 9.5) and increased oxygen saturation (N = 402) 22% (from 71.9 to 87.7). This procedure advanced the maxilla a mean 8.7 mm and the mandible 10.7 mm while increasing the oropharynx (N = 230) 6 mm (109%). Both the AHI and the oropharyngeal length appeared stable at 4 years post-surgery (N = 16).⁹⁷ Another study (N = 9) indicated the oropharynx increased its mean width 10 mm with a maxillary advancement of 6 mm and a mandible increase anteriorly a mean of 10 mm.⁹⁸ After a post-surgical follow-up of a mean of 8.2 months the oxygen saturation increase remained stable as did the number of apneas as a result of the surgery.

The mandibular advancement surgery (meta-analysis, N = 57) resulted in a mean advancement of the mandible of 16.1 mm with an 81% improvement of AHI (from 45.7 to 8.7) and a 23.8% change in oxygen saturation (from 71.9 to 89).⁹⁹

Oral appliances are capable of advancing the mandible; procedures can be removable or fixed. Two studies have indicated that an increase in condylar growth is produced by such procedures,^61,100 one of which indicated that mandibular growth was 54% (11.1 mm vs 7.2 mm) greater than the control sample during a 3.3-year period of appliance wear.⁶¹ Another study using a removable mandibular advancement appliance for a 6-month period showed an increase of oxygen saturation of 7.9% (from 88 to 95) and an increase in airway volume of 19.4% (from 12,140 mm³ to 14,500 mm³).¹⁰¹

Continuous positive air pressure (CPAP) has been used for children, but there have been few studies on its efficiency. CPAP has been shown to be effective in reducing various symptoms; however, relatively low cooperation among children is a problem. Various motivation rates indicate 39% to up to 70% of children using CPAP use it properly.^102-104 The use of CPAP has been shown to significantly improve snoring, sleepiness, oxygen saturation, and AHI,¹⁰⁵ while another study showed a 54% relapse of AHI and blood saturation with CPAP.¹⁰⁶ Positive findings regarding OSA, snoring, and daytime sleepiness are also seen in adults.^106,107

A significant procedure on its own or in combination with other procedures, such as RPE and T and A, is myofunctional therapy (MFT).^108,109 In one study it was particularly effective for AHI (91% improvement), mouth breathing (69%),¹⁰⁹ and lip closure (83%).¹⁰⁹ In a review of 22 research studies,¹¹⁰ a positive change was found in AHI in children, who obtained a 62% improvement, and in adults, in whom improvement was 50%. Interestingly, these symptoms (except AHI) can be corrected with exercises and, therefore, are habits that probably can be altered with muscular retraining and strengthening. MFT, however, depends greatly on the skill of the therapist as well as the cooperation of the child and parent. Ieto et al found cooperation in adults to be 85% in a sample of 39 patients treated for 3 months.¹¹¹

Mouth breathing seems to be a critical element in the correction of childhood SDB, because when corrected, it prevents the collapse of the oropharynx by keeping both the mandible and the base of the tongue from impinging on the anterior wall of the oropharynx thus preventing its collapse. The elimination of nighttime mouth breathing also promotes proper nasal breathing, which can increase the nasal airway.

In a study by Stevens et al analyzing 501 cases submitted by dental professionals, nighttime mouth breathing was found to have an incidence of 46% (in patients aged 2 through 12 years), which was the highest frequency among all 27 symptoms studied.¹¹² Other symptoms with the next highest incidence were snoring at all (36%), talking in sleep (33%), bruxism (33%), difficulty listening to others, and frequently interrupting (32%). Of the 10 most frequently occurring symptoms, four are related to dentistry (nighttime and daytime mouth breathing, snoring, and bruxism). Snoring was more common among children aged 4 years and younger (59%), and it decreased to 19% by age 13 years and older. Snoring decreased 68% during this period while mouth breathing decreased 32%. Children who mouth breathe during days and nights had eight other associated symptoms present (snoring at all, difficulty listening and often interrupts, talks in sleep, allergic symptoms, fidgets with hands or does not sit quietly, restless sleep, teeth grinding, and feels sleepy and/or irritable during the day). This study stressed that mouth breathing is an extremely important symptom to correct in children, and this belief is shared by other researchers.^113-115 The fact that about 67% of oral breathing is correctable by MFT¹⁰⁹ indicates that this symptom is probably mostly due to a repetition acquired-type habit.

Oropharyngeal constriction, which is often the result of nighttime mouth breathing due to oxygen deficiency, seems to be have an important influence on the endocrine system and the brain's ability to rid itself of toxins produced by daytime brain activity, in particular beta amyloid. Oxygen deficiency and the lack of brain cell size reduction during sleep are possible causes of neurocognition symptoms.¹¹⁶ Reducing oropharyngeal constriction is best accomplished by eliminating nighttime mouth breathing.

In addition to improving daytime brain activity, there are a number of reasons why the correction of nighttime mouth breathing in children is important. First, nighttime mouth breathing is the most frequently occurring symptom and is associated with seven other symptoms.¹¹² Second, pharyngeal constriction involves the oropharynx and is directly caused by the mandible and tongue drifting posteriorly during sleep, which occurs because the genioglossus muscle has its origin in the genial tubercle of the lower jaw.^117,118 Third, airway volume is reduced in cases with retrognathic mandibles.^99,119 Fourth, mouth breathing is a good predictor for OSA.¹²⁰ Fifth, persistence of mouth breathing after T and A surgery (in 56% of cases) can be improved with MFT.⁸⁰ Sixth, oral breathing reduces pharyngeal resistance to its collapse and increases OSA.^121-123 Additionally, mandibular advancement increases the size of the oropharynx and lessens OSA.^98,99,123 Lastly, mouth breathing remains consistently high in incidence with little self-correction over time to age 13 years and older.¹¹²

Nasal breathing resistance appears to initiate oral breathing and symptoms of SDB⁵ and can occur during infancy.¹²⁴ Common causes of nasal breathing resistance are allergic rhinitis, which tends to increase with age,¹²⁵ along with septal deviation, nasal congestion, and adenoid enlargement. According to Massler, adenoid swelling occurs in about 85% of children that have difficulty breathing through the nose.¹²⁶ In an unpublished survey by the present author of 940 cases, 22.8% had difficulty in nasal breathing while 1.1% could not breathe at all nasally and 76.2% breathed normally without interference through the nose. Statistically, there was no significant difference in the frequency of nighttime mouth breathing between "difficult" and "impossible" nasal breathing; however, there was a significant difference (P = .001) in the severity of nighttime oral breathing between patients with normal nasal breathing (being less severe) and those with difficult and impossible nasal breathing. This comparison indicates that there is a strong association between abnormal nasal breathing and increased severity of nighttime mouth breathing. Nighttime mouth breathers are reported to breathe this way about 69% of the sleeping time, while nasal breathers breathe through their mouth at night about 4% of the time.¹²⁷

Proper nasal breathing seems to be the key to successful breathing, and this can often be accomplished with any procedure that eliminates mouth breathing.^114,128 Additionally, the pharyngeal airway must be stimulated to be opened sufficiently to allow the proper exchange (in both speed and volume) of air (oxygen and carbon dioxide), and this is accomplished by the elimination of mouth breathing 78.6% of the time.⁶³

Shintani et alfound that snoring with SDB in children occurred as early as age 22.7 months.¹²⁹ This, together with an increase in adenoid tissue within a very small square area, is also a factor for SDB problems and can occur as early as 1 to 4 years of age.^124,125 This in turn can decrease the nasopharyngeal airway, which also has a deleterious effect of causing mouth breathing. Abnormal AHI can occur during the first 6 weeks of life.¹³⁰ Other factors that are believed to have an influence on mouth breathing and snoring in infancy are related to secondhand smoke,¹³¹ while nipple bottle feeding (without mother's milk), which does not provide the infant with advantageous immune protection against respiration infections and lymphoid swelling,¹³² can also be an issue. The relation between allergic rhinitis and SDB is strongest in children.¹²⁴ All of these factors, together with the lack of mandibular advancement and a high narrow developing palate, as well as pacifier sucking habits and bottle feeding, may contribute to early developmental problems.

Acquired thumb sucking can start even in the womb where a fetus may develop such a habit.¹³³ Thumb or finger sucking habits can contribute to several harmful developmental issues. For example, having the thumb or finger positioned in the palate displaces the tongue inferiorally within the mandibular body. Since the thumb is narrower than the tongue, the upper posterior arch becomes narrower, especially when a vacuum is created with sucking. This narrowing can become so severe (≥7 mm) that the mandible shifts to one side to make the occlusion more comfortable for the patient.¹³⁴ This results in a displacement of the mandible and usually involves a cross-bite on one side. All of these factors tend to affect the nasal airway and encourage mouth breathing.¹²⁹

Thumb sucking also interferes with proper anterior mandibular growth and, together with the increased protrusion of the maxillary incisors, can interfere with normal swallowing and may often produce an anterior open bite. These factors tend to encourage mouth breathing. Along with the development of a retrognathic mandible from pacifier use and finger sucking in particular, these factors can increase overjet,¹³⁵ reduce nose width,¹³⁶ and restrict the size of the upper airway.¹¹⁹ When an infant sleeps on his or her back, the muscles that maintain an anterior position of the mandible during the day relax, and this combined with the contributory effect of gravity allows the lower jaw to be displaced posteriorly. Because the tongue is attached to the mandibular body, any distal drifting of the mandible also allows the base of the tongue to impinge on the anterior wall of the oropharynx. A child that snores usually has his or her mouth open while sleeping. The snoring is a result of the partial closure of the oropharynx with increased inspirational effort, which speeds up the diminished airflow that vibrates the uvula and soft palate. Open-mouth breathing, snoring, and hypopnea present in SDB can occur at 1 year of age.^31,70

Obviously, if T and A surgery is indicated in a child with a stage 3 or stage 4 tonsillar enlargement as per the Friedman analysis,⁷⁸ or if a child cannot breathe through the nose, a referral to a sleep clinic or otolaryngology specialist is recommended prior to consideration of treatment with an oral habit appliance. The least invasive and simplest procedure should be the initial goal of treatment of SDB. Dental professionals should be knowledgeable of abnormal sleep issues, particularly since so many symptoms are associated with the oral cavity. Also, dental professionals are well positioned to observe these issues since children theoretically receive dental check-ups every 4 to 6 months from about 2 years of age or younger into adulthood.

To summarize, mouth breathing is a fairly common symptom among children and should be corrected to establish normal nasal breathing. Mouth breathing is likely a repetition-developed habit since it can be corrected 67% of the time by MFT.¹⁰⁰ Mouth breathing increases OSA and can predict OSA, and can increase pharyngeal wall collapse even though children have a stiffer pharyngeal wall than adults. Mouth breathing does not self-correct much up to 13 years and beyond; it alsoencourages SDB and reduces the nasal airway. Finally, mouth breathing and snoring, as well as SDB, can occur by 1 year of age, while AHI can be present at 6 weeks of life. Because thumb sucking can occur before birth, it is probable that mouth breathing also can occur at birth.

Symptoms of SDB include primary snoring, mouth breathing, and interrupted breathing (hypopnea) as well as OSA. SDB is present with retrognothic mandibles. It along with oral breathing is stimulated by difficulty in nasal breathing.

RPE can be used to increase the nasopharyngeal, palatopharyngeal, and nasal cavity volumes; however, these increases can relapse 1 year later, and this procedure does not increase oropharyngeal volume. RPE can improve OSA, oxygen desaturation, snoring, apnea, and AHI. On the other hand, restless sleep, mouth breathing, and headaches have had inconsistent results with RPE. Symptoms that showed no improvement were irritability, school problems, nightmares, allergies, night sweating, bruxism, bed wetting, and interrupts.

MFT helps improve AHI by 91%, mouth breathing by 69%, lip closure by 83%, and OSA by 62%. A retrognathic mandible can restrict the sizeand volume of the upper pharyngeal airway. Mandibular advancement increases the size of the oropharynx and lessens OSA. The use of CPAP can improve snoring, oxygen desaturation, and AHI, but a 54% relapse has been shown in the latter two symptoms. Cooperation with CPAP in children is quite variable, ranging between 39% and 70%. OSA is a critical symptom for the child due to its potential effect on the cardiovascular system; it is present in 1% to 4% of children and 4% to 24% of adults.

Oxygen levels in blood are affected by sleep problems and can be very critical. T and A surgery corrects OSA in less than 25% of children and in less than 10% of obese children. Grade 3 (Friedman scale) is present in 8.3% and grade 4 in 1% of children ages 4 to 12 years. Lymphoid swelling is greatest from 2 to 6 years of age but can occur at birth and up to age 12 years.

Finally, regarding nasal resistance, allergic rhinitis is present in infancy and encourages oral breathing and SDB in infants. Allergic rhinitis generally increases with age, particularly during early adulthood.

Dr. Bergersen was an assistant professor at Northwestern University Graduate Orthodontic Department in Chicago, Illinois, for 25 years. He also was formerly in private practice in orthodontics in Winnetka, Illinois.