The increase in the maxillary arch transverse dimension by means of rapid maxillary expansion (RME) has been a therapy in orthodontic practice and an indispensable tool for treating a maxillary transverse deficiency. This approach aims at separating the hemimaxillae, with consequent buccal movement of the posterior teeth and the alveolar process, indicated only when there is true maxillary atresia.

The ideal time for treating a posterior crossbite has been questioned, and it is not always possible to achieve rupture of the palatal suture. This happens especially at the end of growth, when there is ossification of the sutures, and the force dissipated by the palatal expander will cause buccal inclination of the anchoring teeth, and significant periodontal changes may occur in these teeth.

Over the years, many methods have been used to determine the maturation of facial sutures, especially the carpal radiograph, which identifies the patient’s skeletal age. It is noteworthy that the low correlation between skeletal and chronologic ages has been reported by Fishman, evidencing the need for individual indicators of the patient’s skeletal and facial growth stages. Thus, a method based on 11 indicators of bone maturity identified in the carpal radiograph was proposed; these are the events that occur successively until the end of adolescence. Mandibular growth has a strong correlation with the events of bone maturation of the hand and wrist, but this does not occur for the maxillary bones.

Likewise, the quantitative determination of ossification in the palatal suture with occlusal radiographs is unreliable, since the images of the vomer and other structures of the nose are superimposed on the suture area; this can lead to misinterpretation of the fusion stage of the palatal suture. Another aspect that jeopardizes this method concerns the direction of the x-ray beam in relation to the suture path, directly interfering with its visibility, which may classify the suture as “open” when it is not.

Taking into account the great variability among patients in relation to the time of sutural obliteration, it is necessary to develop an evaluation method for this suture.

Thus, Angelieri et al proposed, in 2013, an individual evaluation method of this structure with computed tomography. By observing the images of the suture in different stages of calcification, 5 maturational stages were determined: A, B, C, D, and E. Among these, treatment with RME would have less resistance and consequently greater skeletal effect in stages A and B than in stage C, where ossification areas are already observed along the suture. For patients in stages D and E, surgically assisted expansion is better indicated because at these stages fusion of the palatal suture has already occurred partially or totally.

In 2017, Grunheid et al studied different methods to predict the skeletal response to RME in 30 patients treated with maxillary expansion and corrective orthodontics. They concluded that their method based on the density ratio of the midpalatal suture had the best correlation with the amount of skeletal expansion compared with the other methods based on chronologic and skeletal ages, and the maturational stages. However, some limitations accounted for the retrospective data collection with a different expansion protocol and the period of evaluation after the corrective phase.

To better elucidate the prevalence of these maturational stages in patients whose RME prognosis is doubtful, in this study we aimed at identifying the different stages of maturation in postadolescents aged between 16 and 20 years. Therefore, we would justify requesting a cone-beam computed tomography (CBCT) for sutural diagnosis in patients in this age group, thus avoiding unnecessary surgically assisted maxillary expansion.

Material and methods

The research ethics committee of Sagrado Coracão University, Bauru, São Paulo, Brazil, approved this study under protocol number 1.064.999. All patients signed the donation form.

The sample of this study included 112 patients, 68 female and 44 male, aged 16 to 20 years, retrospectively selected from 2 private dental diagnostic imaging center clinics. Based on the inclusion criteria, we selected only patients between 16 and 20 years who had CBCT images for the diagnosis of retained teeth. The exclusion criteria were as follows: syndromic patients, cleft lip and palate, history of previous orthodontic treatment, or signs of any appliance at the examination (previous maxillary expansion as an early interceptive orthodontic phase may affect the suture status).

The tomographic images were obtained in a private clinic, from the same iCat scanner (Kavo; Imaging Sciences International, Hatfield, Pa) CT with standardization of the head position and the following specifications: 22 × 16 cm field of view, 40-second exposure, 120 kV(p), and 36 mA. This unit has a high-resolution sensor, which allows for images with a 0.4-mm voxel (volumetric picture element). To obtain the CBCT image in a standardized way, the patients were instructed to maintain their natural head position and occlude in their maximum habitual intercuspation.

Images for sutural evaluation were obtained in a standardized way. The image analysis software cursor was positioned in the patient’s sagittal plane, in both axial ( Fig 1 , A ) and coronal views ( Fig 1 , B ). In the sagittal plane, the cursor was positioned over the palatal suture ( Fig 1 , C ). After that, the final image was used in the axial plane for evaluation. In patients with a curved palate, 2 images were taken, 1 in which the sagittal plane line passes through the suture in the most posterior region ( Fig 2 , A ), and a second one with the cursor passing in the most anterior region ( Fig 2 , B ). Both were used to evaluate the maturation stage.

CBCT images: The main screen of the InVivo 5 program (Anatomage, San Jose, Calif) with A, axial, B, coronal, and C, sagittal views and reference lines. Note, in the sagittal view, that the orange line is positioned through the center of the hard palate.

For subjects with curved palate, 2 sagittal sections were used A , 1 for the anterior area and the other, B for the posterior area. Both images were used for determining the maturation stage.

For calibration, 2 evaluators (V.M.L., F.P.G.) analyzed the CBCT images to determine the maturation stage of the midpalatal suture of all patients. Any disagreements were discussed by them to obtain a final decision. The examiners used morphologic parameters of the suture described in a previous study. After that calibration process, the main researcher (V.M.L.) identified the maturational status of the midpalatal suture in 5 stages, A, B, C, D, and E, as described and illustrated in Figure 3 , for all patients.

Maturational stages A, B, C, D, and E: A, in stage A, the suture is seen as a relatively straight radiopaque line; B, in stage B, the suture appears as a sinuous line of high density; C, in stage C, there are 2 radiopaque, winding, and parallel lines separated by areas of low radiographic density; D, in stage D, the palatine bones become more radiopaque, and the suture is not seen in this area. Note that in the palatal area it is still possible to observe the 2 parallel radiopaque lines. E, In stage E, the sutures along the maxillary and palatine bonés are not seen; this indicates suture fusion.