Oral Breathing and Head Posture

Oral breathing has been reported to cause changes in human head posture. The head position relative to the cervical spine is the result of integration at the central nervous system level of different external and internal inputs, including visual, cutaneous, musculotendinous, and vestibular receptors.

Breathing is one of the prime functions fulfilled by man, and it can have considerable effects on the morphology and on the craniofacial and cervical functions.1–3 Ricketts4 maintained that head extension represents a functional answer to facilitate oral breathing (OB) in order to compensate nasal obstruction. Tecco et al5 studied the changes in head posture in mouth breathing girls after treatment with rapid maxillary expansion (RME). They reported that RME is able to increase the capacity of the nasopharyngeal airways and leads to significant changes in the craniocervical angles.

In a study undertaken on healthy young adults, OB was artificially induced by nasal obstruction. The authors evaluated the relationship between the true vertical and the nasion-tragus line as well the C7-tragus line, and found significant differences in extension of the neck as measured by the C7-tragus/vertical line angle, with the other (nasion-tragus/vertical line angle) showing greater variability.6 

Another study evaluated the influence of total nasal obstruction and the absence of vision on head posture (singly and combined). The results indicate that total nasal obstruction, by the use of a nose clip, induces a change in head posture (head elevation).7 

It has been noted that there are changes in the association between the nasopharyngeal resistance and the variations of the craniocervical parameters (with reduction in craniocervical angulation through head flexion) following a tonsillectomy or adenoidectomy,8–10 rapid maxillary expansion (RME),5 and after cortisone therapy in children with asthma and chronic rhinitis. In one study on children suffering from allergies, the use of a cortisone nasal spray (budesonide) reduced nasal resistance, thus causing an increased flexing of the head.11 To approach the problem from another direction, no significant variation in airway resistance was seen after cranial extension obtained by manipulation.12 

The existing correlations among OB, craniocervical posture, and craniofacial development indicate that further confirmation is needed in the morphogenetic consequences of bronchial asthma and of chronic allergic rhinitis.13,14 

The aim of this research was to analyze the influence of OB, not necessarily connected to an upper airway obstruction, on head posture in children in order to establish possible postural alterations associated with OB, before the same might condition their development.

The sample included 35 oral breathing (OB) children and 35 physiological breathing (PB) children, consecutively admitted in the Department of Orthodontics, University of Palermo, who needed orthodontic treatment. The first group of OB subjects comprised 14 (40%) boys and 21 (60%) girls (age 5–13 years, average 8.8 years, SD ± 2.2 years). All patients had a history of OB, confirmed by their parents and the medical history. On clinical examination these patients showed lip inefficiency at rest, dental crowding in the upper arch, “adenoidal facies,” and reduced maxillary transverse dimension with unilateral or bilateral crossbite.

Evaluation of the breathing pattern for most of this group showed a diaphragmatic mode of inhalation with underexpansion of the thorax and a reduced mobility of the nostrils suggesting a reduced patency of the upper airway. OB was shown by water vapor condensed on the surface of a mirror placed outside the mouth. The cause of OB was not established.

The second group of PB subjects comprised 16 (46%) boys and 19 (54%) girls (age 7–13 years, average 9.7 years, SD ± 1.6 years). These children were chosen at random from a group of children who had varied orthodontic problems, but who did not have a past history or any clinical signs of OB.

Exclusion criteria for both groups included previous or ongoing orthodontic treatment, vestibular or equilibrium problems, visual, hearing or swallowing disorders, and facial or spinal abnormalities (ie, torticollis, scoliosis, or kyphosis). A teleradiograph was taken of each subject (70 in total) in the natural head position (NHP), and all teleradiographs were evaluated cephalometrically. The parents of all patients gave informed consent for participation in the study.

Fourteen angular and three linear measurements that formed the basis of the postural and craniofacial analysis and airways dimension15–17 were measured by hand for each subject. A ruler and a protractor accurate to 0.5 mm and 0.5° were used. The Ad2-PNS value was measured in all subjects in the OB group. On the basis of the obtained data the group was divided into two subgroups of 12 and 23 patients: subjects with values ≥15.5 mm and subjects with values ≤15 mm. The association between the increases in the nasopharyngeal resistance, using an active anterior rhinomanometer, and Ad2-PNS values ≤15 mm, encouraged the choice of this measurement in order to differentiate between the patients.18 The cephalometric points, lines, and angles used in the study are shown in Figures 1 and 2.

In the postural recording method, the radiographs were taken with the subject standing in NHP as described by Şahin Sağlam and Uydas.19 Duplicate determinations were also carried out for all the linear and angular variables measured on the lateral cephalometric radiographs by two orthodontists. The measurements were undertaken 2 weeks apart and no significant differences were found for any of the craniofacial and airway variables in the two data sets (paired t-test).

The measurement error was calculated using 20 radiographs (10 randomly chosen from OB and 10 from PB) and Dahlberg's formula. For linear distances the error varied from 0.4 mm (H-MP) to 0.75 mm (H-CV3ia-RGN) with a mean of 0.52 mm, while for angles the error varied from 0.40° (CVT/HOR) to 0.80° (OPT/NSL) with a mean of 0.65°.

Cephalometric variables are presented as mean, standard deviation (SD), and the lowest and highest values. The Student's t-test was used to determine if significant cephalometric differences existed between the OB and the PB children.

Three subgroups representing those with normal values, increased values, and reduced values compared with the standard values,20 were created within each group (OB and PB). A chi-square test was used to analyze the data. The purpose was to see if the different value of a craniocervical parameter, in both groups, was due to an excessive flexion on PB or an exaggerated extension on OB. Within the OB group, two further subgroups were created with Ad2-PNS values less than 15 mm and greater than 15.5 mm. A Student's t-test was used to compare the values between these two subgroups.

Statistical significance was set at the value P = .05. Data were analyzed using the Primer of Biostatistics for Windows (version 4.02).21 

When OB children were compared with PB children, the following craniocervical angles were significantly greater: NSL/OPT (P < .0001), NSL/CVT (P < .0001), FH/OPT (P < .0001), FH/CVT (P = .005), and NSL/ VER (P < .0001). The distance MGP-CV1p was significantly smaller (P < .0001) as was angle MGP/OP (P < .0001) and angle OPT/CVT (P = .036).

A lower position of the hyoid bone, as measured by a greater distance H-MP (P = .009) was present in OB children. An increase in the maxillomandibular plane angle (ANS-PNS/Go-Me, P < .0001) and an increase in angle ANB (P = .023) were seen in the OB group (Table 1).

Tables 2 and 3 show the ratio and number distribution for each variable as well as the normal, increased, and decreased values for the OB and PB groups. In particular, PB patients present a greater proportion of children with an increased value for MGP/OP (P = .012) and MGP-CV1p (P < .001), and a smaller proportion of children with decreased value for OPT/CVT (P = .022) and increased values for angle ANS-PNS/Go-Me (P = .009). In OB patients an increased number of children with an increased value of NSL/OPT (P = .038) was always evident.

Table 4 shows the measurements of all craniocervical variables in the two subgroups: Ad2-PNS ≥15.5 mm and Ad2-PNS ≤15 mm. No statistical differences were found for any of the cephalometric parameters between the two subgroups.

Oral respiration alters the muscle forces exerted by the tongue, cheeks, and lips upon the maxillary arch. Intraorally, the dentist might expect to find a narrow maxillary arch with a high palatal vault, a posterior crossbite, a Class II or III dental malocclusion, and an anterior open bite.22 

The purpose of this study was to assess whether there was a relationship between OB and variables of head posture in children before these same variables might influence their development. An abnormal posture of the head changes the load in several joints of the craniovertebral region, resulting in unfavorable dentofacial and craniofacial growth.23 

Our main finding is that in OB patients a well-defined postural picture is often evident: reduction of cervical lordosis and increased extension of the atlanto-occipital joint to maintain the Frankfurt plane horizontal. Further analysis of the data with the chi-square test confirms this result. Only MGP/OP and MGP-CV1p suggest an excessive craniocervical flexion in the PB subjects.

Several studies have shown that OB is connected with a variation in the head posture and with a increased craniocervical extension1 in order to increase the dimension of the airway24,12 and the oropharyngeal permeability4 with mandibular and lingual postural modifications, and of the soft palate as well.25 

Some authors have evaluated the patency of the upper airways using cephalometric techniques and established a connection between the reduction of the nasopharyngeal space and the increase of the craniocervical angle.26,27 

Even if no association emerges between obstruction of nasopharyngeal space and craniocervical extension, we cannot conclude that craniocervical extension does not depend on the superior airway obstruction, owing to the absence of information about the nasal resistances in this study. In fact, the OB subdivision in Ad2-PNS ≥15.5 mm and ≤15 mm only underlines the different adenorhinopharyngeal conditions of these patients, without revealing any details about nasal resistance.

However, there are studies which have demonstrated, by rhinomanometric tests, a significant relationship between a smaller distance Ad2-PNS or impaired nasal breathing and a wide craniocervical angulation and forward inclination of the cervical spine.1,28 

In our analysis, the ANB angle and the intermaxillary divergence (ANS-PNS/Go-Me) are present and prevailing in OB patients, which agrees with other studies.29 These skeletal measurements indicate a tendency for OB children to present a dolichofacial Class II skeletal pattern.

The hyoid bone is located in a lower position in OB patients. Other studies found a correlation between a lower hyoid bone position in relation to the mandibular plane and increase in craniocervical extension.30,31 However, Bibby32 supported the stability of the hyoid position which should not be influenced by the postural anomalies of oral breathers.

• OB causes an increase in head elevation and a greater extension of the head related to the cervical spine and influences hyoid bone position and intermaxillary divergence.

• OB during growth may alter NHP, as well as craniofacial morphology.

• Changing the mode of breathing from oral to nasal early in adolescence may promote a tendency towards normalization of the craniofacial dimensions with growth.