It has been recognized that identifying the obstructive sites of the upper airway is important because different combinations of obstructive tissues from the Waldeyer's lymphatic ring may influence craniofacial growth in a different way[25; 27–29]. Nevertheless, some researchers debated that the respiratory mode and obstruction sites[13; 31] were unrelated to craniofacial morphology.
The adenoid and tonsil are not the only determinants in craniofacial morphology which is also affected by other factors, such as family heredity, self-adaptability and so on. Therefore, conflicting conclusions may have been drawn in previous studies mainly because of the sample size and sample collection. In addition, the adenoid and tonsil have physiological hypertrophy and age-dependent characteristics, which was fully reflected in the current study. Thus, it is crucial to take the role of age into consideration.
In the present study, a relatively large sample size from consecutive orthodontic cases was used, aiming to represent the real world population. The population involved a large variety of phenomena from which a control group was set as a benchmark. In addition, statistical methods such as chi-square test and regression analysis were used to avoid the direct comparisons of quantitative measurements.
In this study, we showed that adenoid hypertrophy tended to lead to Class II maxillo-mandibular relationship with mandibular retrusion and high mandibular plane angle. While tonsillar hypertrophy showed a trend in the opposite direction, leading to Class III maxillo-mandibular relationship with mandibular protrusion. By stepwise regression, we found that SNB was the most sensitive variable which could best differentiate craniofacial characteristics of adenoid hypertrophy and tonsillar hypertrophy. Above all agreed with the previous studies. Moss developed the widely discussed “functional matrix theory” suggesting that development of the craniofacial bones depends on the balance between different tissues within the “matrix” of oro-facial capsule. When the upper airway is obstructed, there are postural and functional alterations in the oro-facial system in order to search for a more efficient airflow [35–38]. For example, enlarged tonsils occupied a considerable space in the oropharynx and forced the tongue to be postured forward[10; 27–29; 36; 39]. The pressure of the tongue on the anterior portion of the mandible acted as a stimulation and activated forward growth of the mandible[13; 28; 29]. Thus, tonsillar hypertrophy might be related with horizontal craniofacial growth[27–29].
As for adenotonsillar hypertrophy, we found that it did not show a mean facial profile of adenoid hypertrophy and tonsillar hypertrophy but were rather similar to adenoid hypertrophy, which rejected the null hypothesis. Both subjects with isolated adenoid hypertrophy and adenotonsillar hypertrophy had a retrognathic mandible, an increased maxillo-mandibular sagittal discrepancy and an increased mandibular plane angle, which was known as the “adenoid face” [14; 15; 21; 25; 40]. Moreover, compared with isolated adenoid hypertrophy, subjects with adenotonsillar hypertrophy tended to have a more severe skeletal class II relationship and a larger mandibular plane angle, although it was not significant. It indicated that the obstruction would be more severe when both adenoid and tonsil were hypertrophied. As a consequence, children could adopt a position with larger mouth opening to cope with a more severe airway obstruction and they preferred the posture of opening mouth which led to an clock-wise rotation of the mandible and an inferior position of the tongue. This result is further confirmed by one study concerning dental occlusion and obstruction sites of upper airway. In the study, the highest rate of class II relationship was detected in adenotonsillar hypertrophy, higher than isolated adenoid hypertrophy.
It needs to be pointed out that the craniofacial patterns mentioned above only represents population characteristics. Even though a certain group of people might share specific craniofacial features, individual’s growth and development varies. In our study, there was a relatively high proportion of skeletal class III in subjects with isolated tonsillar hypertrophy, but skeletal class I and skeletal class II still accounted for a large proportion. The same was true for isolated adenoid hypertrophy.
It should also be noted that growth patterns of adenoid and tonsil were observed in our study. Hypertrophy of adenoid and tonsil was normal in early childhood and probably was an index of immunological activity. Growing adenotonsillar tissue narrowed the upper airway to variable degrees in early childhood and the degree of airway obstruction decreased with age, which was supported by another study. The adenoid reached peak at age 6 and showed small increases at age 10 (possibly associated with the sex hormones at puberty), which was consistent with the Linder-Aronson’s longitudinal study. The tonsil reached peak at 5 to 6 years of age, which was supported by Shintani's findings. The adenoid hypertrophy lasted longer than tonsil hypertrophy, which might be the reason for that the “adenoid face” is more common in patients.
The present study surely could not avoid limitations. First, since it was a retrospective study, there might be some inadequacies in documentations and special condition controlling. For example, respiratory control during cephalometric scanning might have some impact on upper airway. Second, this study was based on lateral cephalograms, which could be further carried out with cone beam computer tomography (CBCT) and with evaluations of upper airway resistance and ventilation functions. Third, influenced by ethical aspects, although we tried to exclude syndromes, congenital malformation and severe bone deformity and so on, samples from orthodontic population were not a fair representation of the healthy population. Fourth, household hereditary should be considered in the facial pattern analysis in future studies. Last, the study was based on Asian children and may not be applicable to other populations.