Dentofacial Morphology of Mouth Breathing Children

1Specialization Course in Orthodontics and Facial Orthopedics, EFOA, Alfenas, MG, Brazil 2Department of Orthodontics, Faculty of Dentistry, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil 3Discipline of Orthodontics, Faculty of Dentistry of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil 4Department of Otorhinolaryngologics, Faculty of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil


INTRODUCTION
Nose breathing associated with the normal functions of chewing and swallowing and posture of tongue and lips provides correct muscular action stimulating adequate facial growth and bone development (1). Dentofacial morphology can be altered by dysfunctions, such as nasorespiratory obstruction depending on the magnitude, duration and time of occurrence (2).
When nose breathing is disrupted by adenoid and tonsil hypertrophy, rhinitis, nasal septum deviation, among others (3,4), there is a prevalence of mouth breathing. Mouth breathing may lead to postural changes such as lowered position of the mandible, raised position of the head, low posture of the hyoid bone and anterior inferior position of the tongue (1,2,5). It has also been shown that such postural changes may be related to specific dentofacial characteristcs and morphological changes (6).
According to Paul and Nanda (7), there is much evidence that mouth breathing produces deformities of the jaws, inadequate position or shape of the alveolar process and malocclusion and results in the development of "adenoidal facies" or "long face syndrome" (8,9). The aim of the present investigation was to verify skeletal and dental relationships of mouth and nose breathing children.

MATERIAL AND METHODS
Thirty-five children of both sexes ranging in age from 7 to 10 years were selected from the Orthodontic Service of the Faculty of Dentistry of Ribeirão Preto, USP. The children were submitted to otorhinolaryngological and dental evaluations that consisted of anamnese, specific physical examination, nasofibroscopy, cavum radiographs and cephalometrical analysis. The children were evaluated in the Otorhinolaryngology Department of the Faculty of Medicine of Ribeirão Preto, USP and they were further separated into 2 groups: nose breathers (N = 15) and mouth breathers (N = 20) according to the results of clinical, physical and nasofibroscopic examinations and cavum radiographs based on methods proposed by Cohen and Konak (10).
Nose breathers met the following criteria: 1) light or no alteration in the radiographic exam; 2) nasopharynx obstruction less than 30% detected by nasofibroscopy exam; 3) no history of orthodontic treatment. Mouth breathers demonstrated: 1) evident alteration in the radiographic exam; 2) nasopharynx obstruction greater than 60% (some patients presented 100% obstruction that could be associated to allergic rhinitis, hypertrophy of palatal tonsil, among others); 3) no history of orthodontic treatment.
Standard lateral cephalometric radiographs were obtained to evaluate the skeletal and dental characteristics of both groups. The cephalometric radiographs were traced on 0.002 inch acetate paper and dental and skeletal anatomic landmarks were located and used for the angular and linear measurements ( Figure 1).
The data were submitted to statistical analysis using the GMC program, 7.7 version. The non-parametric Mann-Whitney U test was used. The level of significance was set at p<0.01.

RESULTS AND DISCUSSION
The statistical analysis indicated that there was a statistically significant difference (p<0.05) for SNA and SNB angles. The maxilla and mandible were more retrognathic in the mouth-breathing group (Table 1). These results are in agreement with the literature (3,11,12) . The maxillae were more retrognathic owing to upper airway obstruction resulting from the hypoplasia of the maxillary sinus and narrowing of the nasal cavities. Trask et al. (13), Martins (14) and Santos-Pinto et al. (15) verified that the mandible was retrognathic in relation to the cranial base. The SNB angle was less in the allergic mouth breathers and the SNA angle did not present alterations. Ricketts (16) reported that the SNB angle was located more posteriorly in relation to the cranial base because the forward and downward tongue posture was even more marked when the nasopharynx was filled with adenoid tissue. Therefore, it was speculated that respiration was one factor predisposing to malocclusion of teeth due to the influence of tongue posturing and possibly even the positioning of the mandible, which was maintained downward and backward in the growth phase. According to the results obtained in this study, mouth breathing interfered in the anteroposterior position of the maxilla, because of a reduction of air flow in the nasal cavity. This leads to nasal and paranasal hypoplasia and reduction of tongue pressure against the palate where deviation in the vertical growth, as the mandible remains downward and backward in relation to the cranial base, can occur.
The ANB angle was not statistically different between groups (Table 1), which is in agreement with Bresolin et al. (11) who studied both nose and mouth breathers with allergic rhinitis.
Angular measurements of vertical skeletal relationships were significantly different between groups. The angular relationship of the sella-nasion to the mandibular plane (SNGoGn) was larger in the mouth breathing group ( Table 1). The NSGn angle was significantly larger in the mouth breathing group (Table  1). In children with nasal obstruction, there was a dorsal rotation of the mandible. Linder-Aronson et al. (9) and Solow et al. (17) reported that nasal obstruction can also alter the airway and, subsequently, facial growth. The mouth breathers had longer faces and their mandibles had more obtuse gonial angles, resulting in a vertical growth pattern (8,9,12,15,18,19).
There were no statistically significant differences for maxillary molar height, mandibular molar height, IMPA, 1.SN and 1.1 between groups (Table 2). It can be supposed that, as the mandible rotated downward and backward in the mouth breathers, the fulcrum was located in the region of the permanent first molar. In relation to the height of both maxillary and mandibular molars, Santos-Pinto (12) found the same results. However, Subtelny (3) and Rubin (19) reported that mouth breathers have more developed vertical alveolar process in the posterior region of the dental arches.
The results found in the literature about the inclination of the maxillary and mandibular incisors (1.SN, IMPA and 1.1) are controversial because McNamara Jr. (1) and Paul and Nanda (7) concluded that maxillary incisors were protruded in the mouth breathers, justified by interposition of the hypertonic lower lip between maxillary and mandibular incisors provoking labioversion of the maxillary incisors. However, Subtelny (3) and Solow et al. (17) saliented that maxillary incisors are found retroclinate in these patients in relation to the S-N line and Tarvonen and Koski (20) reported that the mandibular incisors pre- Data are reported as means ± SD. See Figure 1 for explanation of abbreviations. *p<0.05; **p<0.01; ns = not significant (Mann-Whitney U test). Data are reported as mean ± SD. See Figure 1 for explanation of abbreviations. There were no statistical differences between the two groups (Mann-Whitney U test).