Ⅰ. Introduction
Maxillary sutures that separate the middle of the palate and the maxilla from the palatine bone are the important growth sites of the maxilla where the maxillary growth is possible to be modified. Dentofacial orthopedic appliances can be effectively used in growing patients with skeletal imbalances in order to improve skeletal relationships by manipulation and control of maxillary growth[
1]. The main concept of orthopedic treatment for maxillary discrepancies is to apply additional force to stimulate the separation of the midpalatal suture and the maxillary sutural system[
2].
Angelieri
et all .[
3] classified the midpalatal suture maturation into five stages, stages A - E, by observing cone-beam computed tomography (CBCT) images. However, it is impossible to regularly obtain CBCT in all pediatric patients to evaluate the maturational stages of the midpalatal suture due to ethical concerns about unnecessary radiation exposure[
4].
Recent studies have been conducted on relationships between the midpalatal suture maturation and skeletal development and reported that the maturation of the midpalatal suture is closely related to skeletal development[
5-
8]. These studies also have determined considerable variability in the chronologic age for ossification of the midpalatal suture[
5,
9]. However, there are the lack of previous investigations on utilizing skeletal maturity as a possible indicator to identify the maturational stages of the midpalatal suture.
Among several biologic methods to assess skeletal maturity, the skeletal maturation indicators (SMI) and the skeletal changes in the middle phalanx of the third finger (MP3) can be simply used by hand-wrist radiographs to evaluate skeletal maturity causing the least radiation risk[
10].
The purpose of this study was to evaluate the correlation between the maturation of the midpalatal suture and the skeletal maturity assessed by SMI and MP3 stages in children aged 7 - 15 years and to analyze the diagnostic reliability of SMI and MP3 stages in predicting the maturational stages of the midpalatal suture.
Ⅳ. Discussion
Maxillary discrepancy is one of the most common skeletal problems in orthopedic practice, which can mainly cause crossbite and dental crowding[
13]. An adequate procedure for correction of skeletal imbalances is to manipulate and control growth of the maxilla. The effects of growth modification treatment to improve dentofacial discrepancy in the maxilla can be manifested when the orthopedic force for splitting the midpalatal suture exceeds the limits required for orthodontic tooth movement[
14]. Also, the success or failure of the orthopedic treatment such as maxillary expansion and protraction relies on individual maturation levels of the midpalatal suture[
15].
According to Melsen[
9], as the maturation and the interdigitation of the midpalatal suture increase with increasing skeletal maturity, the effect of skeletal change is reduced whereas the effect of tooth movement is increased. In an adolescent reached to moderate levels of interdigitation of the midpalatal suture, it is possible to separate the suture with enough intraoral force across the palate with a jackscrew for expansion, but extraoral force from a facemask cannot exceed much force for protraction[
16]. Therefore, it is very important to understand individual maturational state of the midpalatal suture in growing patients to achieve the maximum skeletal change at optimal treatment timing and to predict the skeletal outcomes[
3,
17].
This study investigated whether the hand-wrist methods were able to be used as diagnostic alternatives to predict the maturational stage of the midpalatal suture. The 3 - dimensional images from CBCT can provide the exact amount of ossification of the midpalatal suture without image overlapping of surrounding structures; therefore, it allows a reliable diagnosis of the maturational stage of the midpalatal suture[
5]. However, it is impossible to regularly take CBCT with effective dose ranged between 19 and 368 μSv[
18] from every pediatric patients due to ethical concerns about unnecessary radiation exposure[
4,
18]. Radiation exposure to pediatric patients who are more radiosensitive than adults can be reduced by using reliable indicators such as hand-wrist radiographs with effective dose 0.16 μSv[
10] for predicting the midpalatal suture maturation instead of CBCT imaging.
The midpalatal suture maturation has been related with skeletal maturation as well as the transverse growth pattern of the maxilla[
19]. Individual skeletal maturity has been assessed in previous studies by hand-wrist[
11] and CVM methods[
20] for evaluating the adolescent growth peak. Although CVM method has been commonly used, it has some limitations for estimating skeletal age; for example, certain landmarks such as C2 and C3 could not be detected with the use of a thyroid collar for protection of the thyroid gland from radiation[
21] and the effect dose of a lateral cephalogram without a thyroid collar was higher than a hand-wrist radiograph as 5.03 μSv[
10]. As a result, hand and wrist methods have been shown to be safer for growing children in terms of the least radiation exposure and presented more reproducibility and accuracy in predicting skeletal maturity[
8,
10].
In this study, skeletal maturity evaluated by SMI and MP3 methods showed strong correlations with the midpalatal suture maturation, indicating that the midpalatal suture maturation is highly related to skeletal development. These results were similar to the findings of Jang
et all .[
8] who verified strong correlations between the midpalatal suture maturation and skeletal age. Although SMI and MP3 methods both showed relatively high Spearman’s coefficients, SMI showed higher coefficient as 0.905 than MP3 method with coefficient 0.830. This illustrates that SMI method is more suitable for estimating maturational status of the midpalatal suture.
While several previous studies have been only investigated on correlation of the midpalatal suture maturation with skeletal maturity assessed by hand-wrist methods, this study conducted not only on their relationships but also the diagnostic reliability of the hand-wrist methods for determining the maturational stages of the midpalatal suture. Positive LHRs were calculated to verify the validity of SMI and MP3 stages for estimating the maturational stages of the midpalatal suture. The range of the LHR varied from 0 to infinity and its interpretation was intuitive: the bigger the LHR, the greater the probability of disease[
22]. A result smaller than 1 indicated a decrease in the likelihood of disease while a result greater than 1 indicated an increase in the likelihood of disease[
23]. In this study, a positive LHR of 5 or more for any SMI or MP3 stage is considered to be a reliable diagnostic indicator for the estimation of any maturational stages of the midpalatal suture.
Based on the results in this study, SMI 1 - 2, SMI 3, SMI 4 - 6, and SMI 10 -11 can be used for reliable identification of stages A, B, C, and D & E, respectively (
Table 3) and MP3 FG stage and I stage can be used as valid indicator of stages C and D & E, respectively (
Table 5). None of patients before SMI 6 and MP3 FG was presented in stage D or E, resulting similar to a prior study[
8]. From a clinical point of view, these results are favorable since a patient before SMI 6 and MP3 FG should show a decent response to orthopedic treatment by modifying growth with more skeletal effect. In these instances, CBCT was unnecessary until SMI 6 and MP3 FG stage because these stages were correspondent to the midpalatal maturational stage C where the fusion of the midpalatal suture has not yet occurred.
On the other hand, patients at SMI 7 - 9 and MP3 G or H stage mostly distributed in stages C and D might need CBCT for evaluation of the midpalatal suture before making a decision for optimal treatment plan because initiated fusion of the midpalatal suture may hamper efforts to control sutural movement and reattachment[
9]. For patients at SMI 10 - 11 and MP3 I stage corresponding to stages D and E, surgically assisted or miniscrew-assisted palatal expansion may be a better choice to obtain effective skeletal expansion without side effects such as dental tipping, gingival recession, palatal tissue necrosis, and fenestration of buccal cortical bone[
24,
25].
In a previous research, it was proposed that less resistant forces and favorable skeletal changes can be obtained by growth modification treatment at stages A and B[
3]. Similarly, based on the results from this study, the prepubertal phases of skeletal maturation (SMI 1 - 2 and 3) can reliably correspond to the maturational stages A and B of the midpalatal suture. Thus, these results are able to support the findings of Baccetti
et all .[
26] that the most favorable skeletal changes can be achieved when dentofacial orthopedics is initiated prior to the pubertal growth spurt.
Although some previous histologic studies have indicated that there was large variability in chronologic age for ossification of the midpalatal suture[
9,
19,
27], chronologic age showed relatively high correlation with the midpalatal suture maturation in this study; correlation coefficients were 0.864 in male and 0.892 in female (
Table 6 and
7). These results correspond to the findings of Algelieri
et all .[
6], who stated that chronologic age was equally effective as skeletal maturity and able to be used as a viable alternative to evaluate the maturational stages of the midpalatal suture especially on the early stages when skeletal maturity is impossible to be assessed.
This study had a limitation related to the lack of interpretation on SMI 7 - 9 stages whether corresponding to the midpalatal suture stage C or D. Most of the patients in SMI 7 - 9 were distributed at stages C and D where are the critical border line to make a treatment decision whether try conventional orthopedic treatments. Therefore, further studies complementing this limitation would be encouraged to analyze the maturational stages of the midpalatal suture of growing patients in SMI 7 - 9 by using other maturity indicators found in hand and wrists.
Although the hand - wrist radiograph is the most common method to evaluate the skeletal development due to its objective and simple interpretation, high reproducibility, and minimal radiation exposure, it is not yet described as an absolute “gold standard” for the skeletal maturity[
28]. As a result, if more studies on prediction of midpalatal suture maturation with various other methods to assess the skeletal maturity will be proceeded, the midpalatal suture maturation can be more accurately determined.