Effects of airway problems on maxillary growth: a review.

The volume of air passing through the nose and nasopharinx is limited by its shape and diameter. Continuous airflow through the nasal passage during breathing induces a constant stimulus for the lateral growth of maxilla and for lowering of the palatal vault. Maxillary morphological differences exist between patients with airway problems and control groups, identifying a potential etiological role in these patients. The purpose of this article was to review the literature on the interaction between airway problems and expressed maxillary morphology including specific dental and skeletal malocclusions. Statistically significant differences were found between patients with airway problems and control groups, in maxillary skeletal morphology including shorter maxillary length, more proclined maxillary incisors, thicker and longer soft palate, narrower maxillary arch and higher palatal vault.

INTRODUCTION

The volume of air passing through the nose and nasopharinx is limited by its shape and diameter.1 The causes of nasal obstruction and mouth breathing may be hypertrophied adenoids and tonsils, chronic and allergic rhinitis, nasal traumas, congenital nasal deformities, foreign bodies, polyps, and tumors.2 One of the most common causes of mouth breathing in children is hypertrophy of pharyngeal tonsils.3

According to Moss’s functional matrix concept,4 nasal breathing allows proper growth and development of the craniofacial complex. Thus, continuous airflow through the nasal passage during breathing induces a constant stimulus for the lateral growth of maxilla and for lowering of the palatal vault.5 On the other hand, midface hypoplasia can lead to upper respiratory tract obstruction.6

Naso-respiratory function and its relation to craniofacial growth are of great interest from 1980’s to present, not only as an example of basic biological relationship of form and function but also because of great practical concern to pediatricians, otorhinolaryngologists, allergists, speech therapists, orthodontists, and other members of health-care community as well.7

Most of the literature examining the relation between airway problems and craniofacial morphology are interested in obstructive sleep apnea. Obstructive sleep apnea, one of the most common airway problems, is a potentially life-threatening condition in which the patient suffers periodic cessation of breathing during sleep, which impairs the quality of life.8

The purpose of this article was to review the literature on the interaction between airway problems and expressed maxillary morphology including specific dental and skeletal malocclusions.

EFFECTS ON SAGITTAL PLANE

Lateral cephalometry is one of the most important imaging techniques that has been used to investigate the facial characteristics of patients with airway problems.9 Several cephalometric differences between patients with airway problems and control samples and a variety of morphologic characteristics specific to these patients have been reported7,9–27 but little information has been presented concerning maxillary growth.

McNamara7 reported that in patients with airway obstruction, superimposition on the internal structures of the maxilla reveals a slight downward and forward movement of the maxillary molars and a lesser extent of the upper incisors, and even with a normal antero-posterior relationship between mandible and maxilla the increase in anterior facial height and the slight relative posterior displacement of the maxillary complex caused the face to become more retrognathic.

Pae at al9 investigated the cephalometric characteristics of patients with severe obstructive sleep apnea and they showed that patients with severe obstructive sleep apnea may have a short facial height and a deep overbite, the antero-posterior relationship of the mandible to the maxilla may not be the primary reason for the large overbite, and they speculated that obstructive sleep apnea problems in patients may be associated with the vertical skeletal disharmony of the oral cavity.

Most of authors reported that the PNS-posterior pharyngeal wall measurements were reduced in all obstructive sleep apnea subjects.28–30 Seto et al30 and Lowe at al31 reported a statistically significant shorter ANS-PNS length in obstructive sleep apnea patients. Lowe at al31 reported that the position of the maxilla did not show any significant difference from the control subjects, however, it was smaller antero-posteriorly. Some of the authors observed changes in the inclination of the hard plate.32–37

Race is an important factor on craniofacial morphology even both in patients with airway problems and normal population. Wong at al1 made an inter-ethnic comparison of craniofacial morphology of patients with obstructive sleep apnea and they reported that Malay subjects with obstructive sleep apnea had a shorter maxillary length compared with other racial groups. This is surprising because Chinese morphology is generally less prognathic than that of Malays.1

Lam et al38 made a computed tomographic evaluation of the role of craniofacial and upper airway morphology in obstructive sleep apnea in Chinese population and they concluded that craniofacial factors and upper airway morphology contributed to severity of obstructive sleep apnea in Chinese subjects. Similarly, Endo et al39 made a cephalometric evaluation of craniofacial and upper airway structures in Japanese patients with obstructive sleep apnea and they stated that the morphological characteristics specific to Japanese patients with obstructive sleep apnea.

Lateral cephalometric characteristics of the soft tissue structures include a long soft palate, a long large tongue, and a long pharynx.9 Some of the studies reported that soft palate length was increased in patients with airway problems.10,16,19,20,22,28,30,31,40 In addition, soft palate length increases with age,41 and so that studies must match control subjects for age.28 Soft palate area was increased in all obstructive sleep apnea patients.28,42 Increase in soft palate thickness in obstructive sleep apnea patients was not statistically significant in some studies,28,29 and was significant in others.16,20–31 Johal and Conaghan28 reported that palatal angle (ANS-PNS-uvula) was significantly more obtuse in male obstructive sleep apnea subjects and because all other maxillary skeletal measurements detected no significant differences, the discrepancy appeared to be with the soft palate and its orientation.

EFFECTS ON TRANSVERSAL PLANE

Maxillary transverse deficiency is one of the most common skeletal anomalies in craniofacial region.43 The relationship between maxillary constriction and the etiology of airway problems is not clear.28 There are not enough studies evaluating transverse dimensions of the maxilla in patients with airway obstruction. Mouth-breathing individuals have been classically described as narrow, V-shaped maxillary arch, a high palatal vault, proclined upper incisors and a Class II occlusal relationship.7

There are some studies showing that there is a strong relationship between air way resistance and high palatal vault.28,44 However, these results were not in agreement with other studies who did not find differences in palatal heights between patients with airway problems and control subjects.30,45 Although Cistulli et al45 examined the influence of maxillary morphology in sample of patients with Marfan’s syndrome and a high vaulted palate is very characteristic of this syndrome, they surprisingly did not find any differences in palatal heights.

Johal and Conaghan28 evaluated the maxillary morphology in obstructive sleep apnea with a cephalometric and model study and the made following conclusions:

Maxillary morphological differences exist between obstructive sleep apnea and control subjects, identifying a potential etiological role in obstructive sleep apnea.

Statistically significant differences exist between obstructive sleep apnea and control subjects, in both maxillary skeletal morphology and oropharyngeal dimensions.

Study model analyses demonstrated that obstructive sleep apnea subjects differ significantly from control subjects in palatal height measurements.

Principato46 evaluated the upper airway obstruction and craniofacial morphology and he reported that low tongue posture seen with oral respiration impedes the lateral expansion and anterior development of the maxilla. Neeley at al47 stated that the effects upon nasal airflow resistance and subsequent growth are unpredictable and therefore airflow issues alone may not be a primary reason to increase the transverse dimension of the nasal base. In some of the studies, authors observed maxillary construction in patients who presented with constricted nasopharingeal dimensions and altered respiratory function.30,48,49 On the other hand Shanker et al50 found no relationship between palatal arch width and respiratory function.

CONCLUSIONS

The review of the literature indicates the interaction between respiratory function and maxillary growth pattern. Maxillary morphological differences exist between patients with airway problems and control groups, identifying a potential etiological role in these patients. Statistically significant differences were found between patients with airway problems and control groups, in maxillary skeletal morphology. In sagittal plane; maxillary length was shorter, maxillary incisors were more proclined, soft palate length and thickness were increased. In transversal plane; patients with airway problems presented narrow, V-shaped maxillary arch, and a high palatal vault.