The hard palate is one of the central structures of the stomatognathic system, and it presents great anatomical and clinical importance, as it assists in different orofacial functions, including breathing.1,5 When there is an imbalance between the structures of the stomatognathic system due to airway obstruction, or due to changes in the direction of growth and development of the face, the hard palate may change and adapt its morphology, position, and function.2,3,5 In this study, the dimensions of width and height of the posterior region of the hard palate in patients of different sexes, and skeletal and breathing patterns were assessed. It was also investigated if there was an association between the measurements of the hard palate and the volumes of the upper airways and maxillary sinuses. It was found that sex and facial type influence the dimensions of the hard palate, and there was an association between the measurements of the hard palate and the volumes of the maxillary sinuses and upper airways.
About the morphometric analysis of the hard palate, significant differences were found between sexes, and among the facial types, for some measurements. Males had greater width of the hard palate at the first molars region, and greater values of height of the hard palate at the first premolars region, corroborating previous studies.19,20 For facial types, in general, dolichocephalic individuals presented greater height of the hard palate in the first premolars and molars regions, whereas brachycephalic patients had greater width of the hard palate in the first premolars region. In view of this result, it is possible to observe the influence of the vertical growth trend in the shape of the hard palate, since the greater vertical tendency of growth (dolichocephalic) presented greater height of the hard palate, while the greater horizontal tendency (brachycephalic) showed greater width of the hard palate. These results corroborate the theories presented by Vucic et al. (2019)2 and Miranda-Viana et al. (2020)3 that the bone structures of the craniofacial complex adapt to variations in craniofacial growth trends. Conversely, two previous studies reported no significant differences among facial types for linear measurements of the hard palate.21,22 However, these studies were performed on plaster models, which present deformations inherent to molding and plastering, while in our study the hard palate was evaluated by means of CBCT scans, which provide three-dimensional images with no magnification or distortion. No significant differences were identified among the different skeletal malocclusions for the hard palate morphometry. This may be related to the fact that the skeletal malocclusions are defined by the position of the mandible in relation to the base of the skull, not influencing the width and / or height of the hard palate. To our knowledge, no other study in the literature has performed this type of analysis. Therefore, further studies are encouraged in order to confirm or refute our hypothesis. In regard to the breathing pattern, no significant difference was observed between mouth and nasal breathing for the morphometric analysis of the hard palate, which is in disagreement with prior researches.6,7,23 These different findings are believed to have occurred because these studies were carried out using plaster models. Another factor is that, differently from our sample of adult patients, these studies were carried out in children, in which the bone and integumentary tissues are not yet fully developed. Thus, we believe that the body may adapt to the breathing pattern after the individual is fully grown.
A linear regression was developed to investigate a possible relationship between the hard palate measurements and the volumes of the upper airways and maxillary sinuses. It was found an association between the width and height of the hard palate at the level of the first premolars and the volumes of the upper airways (total volume) and nasopharynx; and between the hard palate width and the volume of the oropharynx. According to our results, the greater the height of the hard palate, the lower the volume of the upper airways; and the greater the width of the hard palate, the higher the volume of the upper airways. It was also found an association between the width and height of the hard palate at the level of the first molars and the volume of the maxillary sinuses, in which the greater the width and height of the hard palate, the greater the volume of the maxillary sinuses. Grauer et al. (2009)24 and Gupta et al. (2016)25 reported an association between the facial width (distance from right to left zygomatic bone) and the upper airway volume. Their results seem to corroborate those of the present study, in which the width of the hard palate showed to be related with the volume of the upper airways, since, although we have measured different bones, both studies assessed the horizontal dimensions of craniofacial structures. Regarding the association between the hard palate and the volume of the maxillary sinuses, this is the first work to perform this analysis. Thus, it is not possible to compare our results with the literature. Therefore, future studies evaluating this association are encouraged, since the results reported here may contribute to additional clinical information, and to assist in the elaboration of the treatment planning in different areas, such as orthodontics, surgery, and otorhinolaryngology.
The authors consider that the relationship between the linear measurements of the hard palate at the first premolars region and the volume of the upper airways may be due to the craniofacial growth trend. Dolichocephalic patients have a tendency of vertical craniofacial growth, presenting a narrower and deeper hard palate. On the other hand, brachycephalic patients have a tendency of horizontal craniofacial growth, presenting a regular and larger hard palate.3,21,23 This is in concordance with the results of this study, in which dolichocephalic and brachycephalic individuals presented greater values of height and width of the hard palate, respectively, at this region. In addition, the study of Fernandes et al. (2017)26 observed a trend towards vertical growth when the oropharynx permeability is reduced. In our research, dolichocephalic patients presented lower volume of the airways at the oropharynx region than brachycephalics. Given these characteristics, there is an indication that the width and height of the posterior region of the hard palate are associated with the volume of the upper airways, as patients with greater height and width of the hard palate presented lower and greater values of volume, respectively.
In view of the results presented and discussed, we understand that the association of the linear dimensions (width and height) of the posterior region of the hard palate with the volumes of the upper airways and maxillary sinuses shows the clinical and anatomical importance of this bone, which may provide clinical information for procedures involving the airways and/or the maxillary sinuses. Therefore, future studies investigating this clinical relationship in the areas of oral and maxillofacial surgery, orthodontics and otorhinolaryngology are encouraged.