Assessment of Dentofacial Characteristics and Pharyngeal Airway in Children with Class II Malocclusion and Mouth Breathing

Introduction

During the course of growth period, diverse etiologic features like dentoalveolar development, maxillary and mandibular growth, tongue and lips functions, and eruption of the teeth may cause malocclusion. The features in sagittal malocclusions are proclination of incisors, short and hypotonic upper lip, and incompetent lips with convex profile.¹

Correct muscle activity stimulates proper facial growth and bone development when nose breathing is combined with regular eating and swallowing processes, as well as posture of the tongue and lips.² However, depending on the severity, duration, and time of occurrence, dysfunctions such as nasorespiratory blockage can affect dentofacial morphology.³ Ricketts observed that the key features of the respiratory obstruction syndrome are presence of hypertrophied tonsils or adenoids, mouth breathing, open bite, cross bite, and narrow external nares.⁴ Mouth breathing can cause postural changes such as the mandible being lowered, the head being lifted, the hyoid bone being lowered, and the tongue becoming anterior inferior.²³

Mouth breathing has also been shown to alter the lower third face, mandibular rotation, and excessive mandibular angle in studies. Nasal obstruction affects muscular function, which can lead to dentofacial abnormalities.⁵⁶

The size of the pharyngeal space is mostly influenced by the growth and size of the soft tissues that surround the dentofacial skeleton.⁷ Reduced pharyngeal airway passage can be caused by cranial anomalies such as mandibular or maxillary retrognathism, small mandibular body, and backward and downward rotation of the jaw.⁸ Reduced space between the mandibular corpus and the cervical column may cause posterior changes in tongue and soft palate posture, impair respiratory function during the day, and possibly cause nocturnal problems such as snoring, upper airway resistance syndrome, and obstructive sleep apnea.⁹

The occlusion of the upper and lower pharyngeal airways, as well as mouth breathing, is linked to vertical growth pattern. Vertical growth patterns and class II malocclusions are necessary to indicate anatomic predisposing factors if this association exists.¹⁰ Early diagnosis, evidence-based explanation of etiology, and assessment of functional aspects may be critical for the restoration of normal craniofacial growth and stability of treatment needs in growing patients with skeletal discrepancies and clinical symptoms of adenoid facies.¹¹¹²¹³

The aim of this prospective cross-sectional clinical investigation was to compare dentofacial features and pharyngeal airway in children with skeletal class II malocclusion with or without mouth breathing habit to healthy children with normal craniofacial relationship. Any significant correlations between the various cephalometric characteristics and the airway morphology of the children were also examined.

Materials and Methods

The Research Ethics Committee of our Institution approved the study (Cert. No. ABSM/EC/2011), which was in accordance with the 1964 Helsinki declaration and its later amendments. Informed written consent from the parents and oral assent from the participating children were obtained.

Eligibility Criteria

• 1 Children with normal skeletal class I jaw relation (difference between SNA and SNB (ANB) angle between 0° and 3°).

• 2 Children with untreated skeletal class II division I malocclusion (ANB > 5°) and point of contact on the occlusal plane from A (AO) ahead of point of contact on the occlusal plane from B (BO) (>1 mm).

• 3 Children with untreated skeletal class II division I malocclusion (ANB > 5°) and AO ahead of BO (>1 mm) with confirmed mouth breathing habit.

Anteroposterior jaw relationship (ANB angle, Fig. 1) was corroborated by the Wits appraisal.

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Fig. 1 Cephalometric tracing of angular measurements. Cephalometric landmarks and reference planes for angular measurements: (1) SNA, (2) SNB, (3) ANB, (4) gonial angle, (5) articular angle, (6) saddle angle, (7) upper incisor to NA, (8) lower incisor to NB, (9) upper incisor to SN, (10) upper incisor to palatal plane, (11) lower incisor to mandibular plane, (12) interincisal angle, (13) SN-MP, (14) mandibular plane to palatal plane, (15) occlusal to mandibular plane angle, and (16) (N-S-Gn) Y-axis. Abbreviations: ANB, difference between SNA and SNB; NA, Nasion - point A; NB, Nasion - point B; SN, Sella - Nasion; SNA, Sella - Nasion - point A; SNB, Sella - Nasion - point B; SN-MP, Sella Nasion- Mandibular plane angle.

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Exclusion Criteria

• 1 No symptoms of upper respiratory and any other pharyngeal pathology including enlarged adenoids.

• 2 No previous surgery of palatine or pharyngeal tonsils.

Lateral cephalograms were obtained under standardized conditions.¹⁷ All subjects were positioned in the cephalostat with the sagittal plane at a right angle to the path of X-rays. The Frankfort plane was parallel to the horizontal plane, the teeth were in centric occlusion, and lips were lightly closed.

All radiographs were manually traced with a 2H lead pencil on 0.003 inch acetate paper, and the following angular and linear measurements were recorded by a single investigator and double-checked by other investigators for proper landmark identification. Each patient in our study had a total of 31 cephalometric measurements, 16 of which were angular and 15 of which were linear¹⁸ (Figs. 1 and 2). McNamara analysis was used to determine upper and lower airway width¹⁹ (Fig. 3).

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Fig. 2 Cephalometric tracing of linear measurements. Cephalometric landmarks and reference planes for linear measurements: (1) anterior facial height, (2) posterior facial height, (3) facial height ratio, (4) length of maxillary base, (5) length of mandibular base, (6) SN, (7) point A to Nasion perpendicular, (8) PoG to N perpendicular, (9) sella to articulare, (10) articulare to gonial angle, (11) gonial angle to gnathion, (12) nasion to gonial angle, (13) sella to gnathion, (14) overjet, and (15) overbite. Abbreviations: PoG, Pogonion; SN, Sella- Nasion.

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Fig. 3 Cephalometric measurements for airway. (1) McNamara's upper pharynx dimension (PM-UPAW: minimum distance between the upper soft palate and the nearest point on the posterior pharynx wall). (2) McNamara's lower pharynx dimension (U-MPAW: minimum distance between the point where the posterior tongue contour crosses the mandible and the nearest point on the posterior pharynx wall). Abbreviations: PM-UPAW, Pterygomaxillare-upper pharyngeal airway; U-MPAW, Uvula - middle pharyngeal airway.

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Statistical Analysis

All statistical analyses were performed using the Statistical Package for the Social Sciences, version 20.0. Arithmetic mean and standard deviation values were calculated for each measurement. For multiple comparisons, one-way analysis of variance and a post hoc Tukey honestly significant difference (HSD) test was used. Pearson's correlation was done to correlate the significant variables with airway width. When the p-value was less than 0.05, it was considered to be significant.

Results

A total of 60 children were included in this study. The mean age of the children was 11 ± 1.44 years, while the gender distribution was 33 boys and 27 girls. Intergroup comparison of age and gender revealed that there were statistically no significant differences between the groups.

When angular measurements in groups II and III were compared with those in group I, we found statistically significant differences in the following measurements: Sella - Nasion- point B (SNB) ANB, lower gonial angle, saddle angle, interincisal angle, mandibular plane to palatal plane angle, y-axis (p < 0.001, Table 1), mandibular plane angle, occlusal plane to mandibular plane angle, upper incisor to NA, and lower incisor to NB (p < 0.05, Table 1).

When linear measurements between group II and group III were compared and analyzed with group I, we found statistically significant differences in the Jarabak's ratio, N-Go, overjet, and overbite (p < 0.001, Table 2).

In the present study, children in group I recorded a mean upper airway measurement of 16.25 ± 2.573 mm, which was within normal range values. Intergroup comparison revealed statistically significant differences in upper pharyngeal airway widths among the three groups. Upper pharyngeal airway width was found to be significantly decreased in group III (mean = 9.85 ± 1.785 mm, p < 0.001, Table 3) followed by group II (mean = 11.05 ± 2.012 mm, p < 0.001, Table 3).

Children in group I recorded a mean lower airway measurement of 9.8 ± 1.399 mm, which was within normal range values. However, there were no statistically significant differences in lower pharyngeal airway widths across the groups in our study, and there were no correlations between lower pharyngeal airway width space and craniofacial growth pattern or malocclusion types.

Post hoc Tukey HSD analysis of the intergroup comparison of the results revealed significant differences between groups II and III in certain dentofacial measurements such as upper and lower gonial angles and saddle angle (major angles); vertical measurements such as mandibular plane to palatal plane and y-axis; and dental measurements such as overbite, overjet, and lower incisor to NB and Mandibulae plane (MP) (Table 4).

When correlations among dentofacial variables and upper airway were analyzed in children of group II, we observed that the variables like upper incisor to NA, lower incisor to NB, lower incisor to MP, overbite, and interincisal angle showed a fair to good correlation with upper airway width (Table 5).

When correlations among dentofacial variables and upper airway were analyzed in children of group III, ANB, as length of ramus (ar – Go) angle, upper incisor to palatal plane, overjet, and overbite showed a good correlation with upper airway width (Table 6). However, we found a fair correlation between SN-MP and Nasion – gonion (N-Go) measurements with the upper pharyngeal airway width (Table 6).

Discussion

The growth and function of the nasal cavities, nasopharynx, and oropharynx are all tightly linked to appropriate skull growth. Several studies have found a link between pharyngeal structures and dentofacial and craniofacial structures in both adults and children.²⁰²¹

It has also been discovered that certain dentofacial features and morphological changes are linked to postural modifications.²² Because of a possible link between upper airway size and structure and sleep-induced breathing difficulties, attention has recently been drawn to uvulo-glosso-pharyngeal dimensions. Obstructive sleep apnea sufferers have abnormal skeletal and soft tissue patterns that restrict airway space, according to research.²³²⁴

We chose children aged 9 to 13 years for our study because these preadolescents have the best chance of receiving early diagnosis and timely care.

The ANB angle was used to determine the anteroposterior skeletal jaw relationship in our investigation, and the Wits appraisal confirmed it. Rotation and vertical growth of the jaws, anteroposterior position of the nasion, and vertical distance between points A and B are all factors that influence the ANB angle, according to Hussels and Nanda.²⁵ The ANB angle, on the other hand, has been described by Oktay²⁶ and Ishikawa et al²⁷ as one of the most trustworthy and accurate assessments of the anteroposterior jaw relationship. As the ANB angle is a popular cephalometric parameter in clinical orthodontics, it was used to categorize the children in our study.²

Our findings revealed substantial variations in numerous dentofacial and airway width parameters across the three groups of youngsters in both angular and linear measurements.

Average values for upper and lower airway width in this age group are stated to be in the range of 15 to 20 mm and 9 to 15 mm, respectively.¹⁹²⁸ Children of group I exhibited upper and lower airway measurements within normal range values. However, intergroup comparison revealed statistically significant differences in upper pharyngeal airway widths among the three groups, with group III children obtaining the narrowest measurements, followed by group II (p < 0.001, Table 3). This was in accordance with a previous study by Paul and Nanda who found greater prevalence of mouth breathing and nasopharyngeal airway obstruction in subjects with class II malocclusions.²⁹

There were no statistically significant differences in lower pharyngeal airway widths across groups in our study, and there were no correlations between lower pharyngeal airway width space and craniofacial growth pattern or malocclusion type. This backs up prior research.²¹²⁸³⁰

In this study, we found that children in group III had significantly larger ANB angles (p < 0.001, Table 1), which showed a strong negative correlation with upper pharyngeal airway width (–0.575, Tables 6). These findings are in accordance with those of Ceylan and Oktay who reported that the oropharyngeal space was reduced in subjects with an enlarged ANB angle.²¹ Subjects with posterior mandibular rotation exhibited smaller upper airway dimensions, according to Akcam et al.³¹ This demonstrates a close link between the upper airway dimension and the jaws' posture.

According to Ferrario et al, orthodontic diagnosis should be based on more than one anteroposterior examination.³² Other anteroposterior determinants such as the Wits assessment, SNB, A-N Perpendicular, and Pog-N Perpendicular showed statistically significant differences in both groups II and III, supporting the reliability of the ANB angle, which was utilized to identify our participants. Furthermore, the upper airway width was found to have a significant correlation with all of the above anteroposterior tests (Tables 5 and 6).

From these findings, we can infer that children with increased anteroposterior jaw measurements and skeletal mandibular retrognathism were more likely to have narrower upper pharyngeal airway space.

Although our study did not classify children according to their growth patterns, we observed significant increases in the following (vertical) dentofacial measurements, namely SN-MP and y-axis, with the greatest increase in group III. The SN-MP and N-Go measurements in group III showed a fair correlation with the upper pharyngeal airway width (Table 6). Further, a significantly smaller Jarabak's ratio was found in group III as compared with group I, reflecting a significantly shorter posterior face height and a vertical growth pattern in this group (p < 0.001, Table 2).

Our findings were in accordance with another study⁸ that reported that the nasopharyngeal airway in hyperdivergent individuals was significantly narrower than that in normo-divergent individuals.

In our study, we found that preadolescent children with skeletal class II and skeletal class II with mouth breathing had narrower upper pharyngeal airways, which significantly correlated with key anteroposterior and vertical dentofacial measurements, specifically SNB, ANB, SN-MP, and N-Go. These children's dental measurements, such as upper incisor to NA, lower incisor to NB, lower incisor to MP, overbite, and interincisal angle, showed a fair correlation with upper airway width (Tables 5 and 6).

In our study, it is possible that the retruded position of the jaw in children in groups II and III caused the tongue base to be positioned more posteriorly and inferiorly, reducing oropharyngeal airway space. In people with mandibular retrognathism, it is known that the tongue position is more backward, and that contact with the soft palate might result in a posterior placement of the soft palate and restriction of the oropharyngeal airway.³³

To breathe through the mouth, one must maintain an oral airway, which is achieved by shifting the mandible and tongue downward and backward, as well as tilting the head back. These variations in posture could have an impact on the connection between teeth as well as the direction of jaw growth, which could shift lower and backward.³⁴

This work used two-dimensional cephalometric films to assess pharyngeal airway width rather than airway flow capacity, which would have necessitated a more complicated three-dimensional cone-beam computed tomography and dynamic estimation.³⁵ Further, as we had used lateral head films for airway measurement, we could not measure the anteroposterior dimensions of the airway, and therefore could not determine three-dimensional volumetric measurements. While the cephalometric view produces a two-dimensional image that is unavoidably constrained, it has the advantage of being simpler and more easily available than computed tomography scanning or magnetic resonance imaging. Although we found significant correlations between many dentofacial measurements and upper pharyngeal airway widths among children with skeletal class II with and without mouth breathing, we recommend that further investigations including a larger sample size of children as well as evaluation of other airway parameters such as airway volume and airflow capacity will allow a better understanding of the relationship between respiratory function and craniofacial morphology.

Conclusion

Our study found significant differences in many of the dentofacial measurements between the children of the three groups, with greater sagittal as well as vertical jaw discrepancies in children with malocclusion. Children with class II malocclusion with mouth breathing had the greatest vertical jaw discrepancy.

We found a significantly decreased upper pharyngeal airway width in children with malocclusion, with the narrowest airway observed in children with class II malocclusion with mouth breathing. No significant differences were observed in lower airway widths among the groups.

Based on the findings of this study, we may conclude that children with class II malocclusion with mouth breathing seemed to have significant narrowing of the upper airways. Certain dentofacial characteristics such as increased sagittal and vertical discrepancy and anterior tooth proclination seem to be definitely correlated with a decreased upper pharyngeal airway width, which could help identify children at increased risk of sleep disordered breathing.