Transversal maxillary constriction is a critical problem frequently encountered and must be resolved first. The literature has no consensus on the safe age limit for maxillary expansion. The maturation stage of the MPS differs between individuals according to chronological age. Thus, predicting the successful outcome of RME protocols is challenging, especially in young adults [3, 14]. CBCT is a reliable method for describing MPS maturation and predicting RME. [4]. However, only some patients can obtain CBCT images, because it may cause more radiation and increase patient costs.

The onset of fusion of the midpalatal suture has been associated with the rate of skeletal development and the transverse growth pattern of the maxilla [3]. The skeletal developmental stage is evaluated from hand-wrist [15] or cephalometric radiographs (CVM) [8]. Sagittal images of cervical vertebrae indicate the skeletal developmental stage [16].

Pichai et al. [17] reported that developmental stage detection by vertebral analysis from cephalometric radiographs reduces radiation exposure and is as valid as hand and wrist radiographs. Our study used the 6-stage method defined by Baccetti et al. [8]. Thus, the phase separation can be made quickly.

Lee and Mah [18], Mahdian et al. [19], Jang et al. [20], and Angelieri et al. [21] reported a correlation between CVM and MPS maturation stages. In our study, a high correlation coefficient was observed between CVM and MPS stages, revealing that MPS maturation was associated with skeletal growth. However, for the evaluation of MPS maturation stages, positive likelihood values of 10 and above, which can be considered a reliable diagnostic tool for a particular CVM stage, were found to be variable [22].

When positive LHR values of each CVM stage were analyzed to evaluate each stage of MPS maturation, the results showed that CS2, CS5, and CS6 could be used to reliably identify stages B, D, and E, respectively. Another study observed that only CS2 and CS3 could be used for the reliable identification of stages B and C [21].

In the last two stages of MPS maturation (D and E), mucosal ulceration, prominent buccal tipping of posterior teeth, severe pain, and gingival recession and external root resorption, which are complications of an unsuccessful RME application, may be encountered. Thus, surgical support may be a better approach for maxillary expansion [23,24,25,26,27].

We should note that stages D and E, which show MPS fusion before the CS4 stage, were not observed in the same way as in the previous studies [19,20,21]. In addition, Kwak et al. [28] showed that, similar to our research, suture fusion in patients with CS5 and CS6 did not occur in all cases. Our study observed MPS stage C in 16% of postpubertal subjects in CS5. This finding explains why the midpalatal suture separates in some postpubertal patients. Studies of human autopsies have shown significant interindividual differences in the onset of closure and progression of closure with age [3, 29, 30].

Regarding the age of the patients, our study found that MPS fusion started at the age of 15 in males and 12 in females. Mahdian et al. [19] reported that fusion began at 12 in females and 13 in males, while Jang et al. [20] reported that it started at 11. In addition, Angelieri et al. [21] observed suture fusion in patients aged 14–18 years. Studies support that suture maturation is more strongly associated with skeletal development than age.

Although the exact correspondence of the stages cannot be said, there is a strong relationship between the CVM and MPS maturation stages when the results of our study are examined. It has also been shown that the suture is not fused before CS4 and that palatal expansion can be performed without surgery. Clinicians should remember that the midpalatal suture is not the only factor in the expansion achieved with conventional RME procedures. It should not be forgotten that other sutures, such as zygomaticotemporal, zygomaticofrontal, and zygomaticomaxillary sutures with which the maxilla is in contact, also play a role in the effectiveness and success of the treatment [31, 32].

The correlational nature of the statistical analysis and the different numbers of patients between the CVS groups in the sample group are the main limitations of this study. Further studies with larger study groups can provide valuable insights into this subject. Also, artifacts may appear on radiographs of young children during the initial phases of skeletal development. The CVM method exhibits low consistency among different observers when assessing variations in vertebral body shapes. Additionally, the timing between CVM phases remains not entirely clear.