Mouth Breathing and Its Impact on Sleep-Disordered Breathing

The most recognizable symptom of abnormal sleep is snoring because it is so easily identifiable and monitored. Nighttime mouth breathing (NMB), however, is not so easily discernible and yet is the most frequently occurring symptom of abnormal sleep. Since snoring is so easily measured, it receives a majority of research interest. Of 50 randomly selected studies analyzing sleep-disordered breathing (SDB) reviewed by the authors, 98% used snoring to study these sleep issues, while only 2% used NMB.

Urschitz et al found that occasional and habitual snoring is present in 63.7% of children.¹ Stevens and Bergersen found that 37.2% of children "snored at all," while NMB was present in 43% of children.² Bergersen et al found that NMB was present in 69% of children aged from 2 to 13 years and snoring was present in 64%.³ Daytime mouth breathing, on the other hand, was present in 54%.³ This indicates that children can mouth breathe while sleeping at night yet not breathe orally during the day.

Snoring only occurs when one sleeps, and it most often occurs while the individual is in the supine position; however, it can occur while in a more vertical sleeping position as well. Because snoring requires an open mouth while sleeping and usually involves mouth breathing, when one prevents oral breathing, the individual is forced to breathe through the nose, which can eliminate snoring. Such a reduction in NMB reduces both the number of symptoms present and their severities, but does not usually reach complete correction in every person.

There appear to be multiple factors to SDB besides the mechanical impingement of the base of the tongue forcing at least a partial collapse of the anterior wall of the oropharynx. One theory explains how a shortening in the length of pharyngeal dilator muscles can contribute to upper airway collapse.⁴ Meurice et al suggested that open-mouth breathing while sleeping decreases the efficiency of the dilator muscles by reducing their length since these muscles are positioned between the mandible and the hyoid bone.⁵ This reduction of muscle length tends to reduce the resistance to collapse of the airway. Oral breathing may be influenced by changes in nasal breathing resistanceas well as by obstructive sleep apnea.⁶ There is also a reduction of masseter muscle electromyographic activity during NMB.^6,7 This might also help explain the presence of increased vertical facial growth in mouth breathers. Mouth opening alone during sleep without oral breathing can also increase the collapse of the airway.⁵

Nasal resistance to breathing influences mouth breathing⁸ and can be the result of allergies and septum and turbinate interference. Of course, tonsil and adenoid enlargement has a significant effect on mouth breathing. Another cause can be the counterclockwise rotation of the mandible⁹ and the movement of the hyoid bone in an inferior and posterior direction. Other possible factors are food and other allergies, premature birth, obesity, and reduction of muscle activity while sleeping with less lung capacity due to a horizontal sleeping position during expiration.¹⁰ When the airway becomes narrow, the suction created by an increased airflow results in further collapse of the pharyngeal walls.¹¹

According to Hawkins, the two most important causes of mouth breathing are allergies and adenoid enlargement.¹² Guilliminault and Akhtar proposed that the most important influence on airway size is a combination of muscle coordination with genetics (epigenetics),¹⁰ since sleep reduces the masseter muscle tone and the supine sleeping position encourages constriction of the airway.¹³ Continuous oral breathing in young children can result in dry mouth with local inflammation as well as abnormal swallowing and esophageal reflux and allergies causing swelling of the tonsils and adenoids.¹⁰ Montgomery-Downs and Gozal found that secondhand smoke can influence mouth breathing,¹⁴ while Sahin et al noted that parental smoking influences habitual snoring in children.¹⁵ Several researchers have stated that the most important factor is to establish normal nasal breathing, which can best be accomplished by eliminating mouth breathing.^13,16,17

During sleep, if the external pterygoid muscles relax, the mandible is allowed to open without any opposing force, which is normally needed to maintain its anterior position. Lessened muscular activity between the symphysis and hyoid bone reduces the force needed to maintain proper anterior positioning of the mandible while sleeping.¹⁸ Any mouth breathing during sleep will allow the mandible and the base of the tongue to impinge against the anterior wall of the oropharynx and, combined with the lengthening of the pharyngeal dilator muscles, can cause further airway constriction. A half-inch opening of the mouth during mouth breathing can be estimated geometrically to close the airway about 6 mm. With an oral pharyngeal airway in a child measuring about 7 mm or 8 mm wide, major problems in air exchange in the lungs may result.

Since NMB is the most prevalent symptom of SDB, its presence being 69%,³ and because of its close association with abnormal nasal breathing, this study tested the importance of NMB and its relationship to other symptoms and their severities.

The data for this retrospective study was obtained from 243 dental professionals, including general dentists, pediatric dentists, and orthodontists, practicing in the United States, all of whom have been similarly trained to analyze and treat children with SDB. Twenty-five of the 27 symptoms listed in an SDB questionnaire (Figure 1) were used for the various studies. Symptoms Nos. 6 and 7 on the questionnaire were combined due to their small sample size and similar description of apnea, while NMB was the independent factor analyzing its relation to the other 25 symptoms.Two main samples were used to obtain the data (Table 1). The first sample was acquired from 1,034 children aged 4 to 13 years (along with a subsample of 1,010) at the introduction of treatment (T1). This sample was used for analyzing the relation of NMB with children who do not mouth breathe at night (non-nighttime mouth breathing [Non-NMB]). These comparisons were made for various analyses involving: the incidence of both NMB and Non-NMB in the population; the various symptoms and their individual severities as well as their indexes (which consist of the sum of the number of symptoms and their severities); the percentages of influence of NMB and Non-NMB individuals on the 25 various symptoms (Table 2, columns C through G); the ranking according to differences between NMB and Non-NMB for the symptoms, severities, and their index values (Table 3); and the influence of NMB and Non-NMB on the five grades of sleep severity (Table 4). Another sample consisted of 220 children that had reported treatment changes from T1 to the end of a 6.5-month treatment period (T2). This data was presented to compare treatment success (T1 to T2) for both NMB and Non-NMB children (Table 5). A review of the most significant of the various analyses (Table 6) using "t" ratios and correlations statistics consisted of eight categories.

The purpose of these various analyses was to determine the relative impact that mouth breathing might have on the different measures of SDB incidence and treatment. The data for these several analyses are found in Table 6, while the sleep questionnaire used in this study is shown in Figure 1. The treatment appliance used was the HealthyStart^® Habit Corrector^® (Ortho-Tain, Inc., orthotain.com) (Figure 2). Statistical tests determined there were no differences between males and females, and as a result their data was pooled.

Several separate studies were used to determine if NMB exerts a greater effect on various SDB symptoms in comparison to children who do not mouth breathe. The first study (Table 2, columns D and E) separated those children who mouth breathe from those who do not and indicated that the NMB group was statistically more influential in 88% of the 25 symptoms studied (Table 2, column J, P = .001). NMB had a greater presence in 22 of 25 symptoms (P = .001) with a mean ratio of 5.4 times greater than the Non-NMB group (Table 2, columns F and G). The relative influence of NMB on each symptom varied from 69.5% to 94.5% (Table 2, column F) compared to the Non-NMB group (Table 2, column G), which ranged from 5.5% to 30.5%.

The second study investigated the possible impact that NMB has on each of the 25 symptoms their severities, and their indexes (consisting of the addition of the symptoms and their severities for each patient). Symptoms Nos. 6 and 7 were combined due to their similarities and small sample sizes. This study indicated the differences ("t" ratio) between the 25 symptoms and ranked them in descending order of the influence of NMB over Non-NMB (Table 3, column C). Significant differences in the number of symptoms favoring NMB over Non-NMB (22 of 25, ie, 88%, had significance at P = .001, and three had less significance of P = .01 and P = .05) are shown in Table 3, column D.

The severities of the symptoms had similar results with 84% having a significance of P = .001, one with P = .005, and three cases showed non-significance (Table 3, column G). The index showed similar results: 88% with P = .001 and 12% with non-significance (Table 3, column J). The conclusion from this study (Table 3) shows the significant predominance of NMB over Non-NMB in 92% of the symptoms, their severities, and indexes.

The third study (Table 4) involved comparisons between the five grades of symptoms and indexes. Each of these five severity grades indicated significant differences (P values of .001, .005, .001, .001, .001) favoring NMB (Table 4, column C). The mean index amount was 47.5% higher (36.8 vs 19.3) for NMB than for Non-NMB. The fourth study (Table 5) compared those cases with NMB initially present (T1) in order to use correlation statistics ("r") to determine which symptoms were more influenced by NMB than others (Table 5, column E) in a sample of N = 220. The results showed that 72% of the symptoms were significantly influenced by NMB, while 28% were not. The fourth study (Table 5) was to investigate if treatment with the HealthyStart appliance was more successful when NMB was present or not present. Columns H and I of Table 5 show the percentages of correction for the NMB group (Table 5, column H) and the Non-NMB group (Table 5, column I). Only 16% of symptoms (four of 25) exhibited significant differences (Table 5, column J), equally distributed between the two groups (NMB and Non-NMB), while 84% had no difference in treatment success between the two groups. As a result, statistics indicated that 84% of those symptoms with more NMB had the same success in treatment than those with less NMB (Table 5, columns H through J).

Table 6 reviews eight research categories with the 10 most influential symptoms affected by NMB for each category. The statistical results of the 80 tests represented show all but three (96%) had significance, supporting the positive impact that NMB has on SDB.

Abnormal sleep issues in children can be categorized into several major symptoms and their severities; 27 such symptoms are listed on an SDB questionnaire (Figure 1) that clinicians can utilize and which parents fill out. When present, the symptoms and their severities can exert an enormous impact on the well-being of a child. It is important to know how often these harmful issues occur in a developing young person. To best address this question, parents were asked about the purpose of their visit to the dental office (among the aforementioned 243 dental professionals), and 464 answered that they either were not knowledgeable about their child's sleep problems or were at least interested in only their child's dentition and not in possible sleep issues. These parents were then given the aforementioned sleep and speech questionnaire (Figure 1) to fill out, and the responses indicated that 92.5% of the children in this group had a mean 7.7 symptoms per individual. In other words, nine out of every 10 children in the sample (N = 464) had a mean of 7.7 symptoms, while only one out of 10 was indicated to be symptom-free.

The mean severity of these symptoms was 16.8, indicating a mean sleep severity index (SSI) of 24.5 (7.7 + 16.8). This SSI amount (24.5) would be a grade 3 and would indicate a moderate problem with a recommendation for treatment.

To assess the seriousness of a child suspected of having a sleep problem, the number of symptoms listed on the SDB questionnaire appear to be less important than their severities. The SSI was developed to assess the sum of these two variables. The severity indicators of grades 1 through 5 range from 0 to approximately 100 in a sample of 1,034 children aged from 4 to 13 years (Table 4). The ranges of these indexes are separated into five grades of severity with different treatment recommendations for each. It can be seen that at grade 1 (Table 4), the incidence of NMB regarding the index is 1.8 times greater than Non-NMB (P = .001). At grade 5, the ratio is 79.5 to 0 favoring NMB (P = .001). This further establishes NMB as having a major influence on SDB.

Table 6 summarizes the 10 most dominant symptoms in relation to NMB for various analyses. All symptoms are represented in the eight separate categories of Table 6 except excess sweating.

A non-published study by the authors (N = 1,008) of the effects of nasal congestion on mouth breathing at night was tested by comparing the severity of NMB to both difficult and impossible nasal breathing at T1. There was no statistical difference in NMB between these two variables of nasal insufficiencies; however, there was a significant difference (P = .001) in the severity of NMB between nasal insufficiencies and normal nasal breathing. The difficult and impossible nasal breathers had 52% more severity in NMB than normal breathers, which indicates that difficult and impossible nasal breathing has a strong association with NMB.

Other factors can influence NMB, such as finger or thumb sucking, pacifier and nipple bottle use, sleeping position,^19-22 gravity, obesity,^23-26 and enlarged tonsils and adenoid tissue.^27,28 Because mouth breathing can be corrected with appliance use or myofunctional therapy, this is an indication that it is probably an acquired habit, particularly since it is easily developed at a young age and can be easily corrected at early ages. A young child with a cold can often develop interference with normal nasal breathing, which can easily develop into a mouth-breathing habit.

This study tested the possible impact of NMB on 25 symptoms associated with SDB using three samples of data provided by parents of 4- to 13-year-old children. The following conclusions can be made: (1) Statistically significant results were indicated in 92% of the measured symptoms, their severities, and their indexes regarding the influence of NMB on SDB. (2) The influence of NMB increases the severity of the symptoms, while children who do not nighttime mouth breathe have less severity of SDB. (3) The presence of NMB in a child tends to increase the severity of 72% of the symptoms measured. (4) NMB is considered to have a major impact on the severity of SDB and is the most prevalent of all symptoms measured, being present in 68% of cases; the next most common symptom is waking up at night, at 52%. (5) Clinically, it is important and advantageous to address NMB in order to produce an effect on most other symptoms of SDB.

Dr. Bergersen is the innovator of the appliance used for treatment in this study and an advisor on the board of the company that manufactures and distributes the appliance. He volunteers his time and takes no compensation for this role. While neither Drs. Bergersen or Stevens-Green has commercial interest in the product or the company, they both share a family relationship with the owners and chief executive officer of the company.

Earl O. Bergersen, DDS, MSD
Former Assistant Professor for 25 years, Northwestern University Dental School, Graduate Orthodontic Department, Chicago, Illinois; formally in Private Practice in Orthodontics, Winnetka, Illinois

Brooke Stevens-Green, BS, DDS
Private Practice, Pontiac, Michigan

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