An improved morphological staging method of midpalatal suture and its relationship with cervical vertebrate maturation (CVM) method

Background (1) Establish an improved morphological staging method of midpalatal suture. (2) Investigate the correlation between morphological stages of midpalatal suture (MPS stage) and cervical vertebrate maturation (CVM) stages. (3) Compare effects of traditional tooth-borne rapid maxillary expansion (RME) at different MPS stages. Methods 1076 CBCT images (675 females, 401 males, 6.0 to 21.0 years old) are included. MPS stages are classified based on observation of horizontal view. Correlation between MPS stage and CVM stage are investigated by Spearman correlation coefficient and diagnostic test analysis. Effects of traditional tooth-borne RME at different MPS stages were analyzed based on pre- and post-expansion dental casts. Results Five stages of midpalatal suture are established. Spearman coefficient between MPS stage and CVM stage is 0.803. Diagnostic pairs with the largest area under ROC curve (AUC) value are: CS 6 - MPS 5,CS 5 - MPS 4s2,CS 1 - MPS 1, CS 4 - MPS 4s1, CS 2 - MPS 1, CS 3 - MPS 3. 309/340 (90.9%) of individuals at CS 1-3 are at MPS 1-3, 31/340 (9.1%) are at MPS 4s1. 107/324 (31.2%) of individuals at CS 4 are at MPS 3, 151/324 (46.6%) are at MPS 4s1. Conclusion (1) An improved morphological staging method of midpalatal suture is established. (2) MPS stages have close relationship with CVM stages. (3) Pre-treatment CBCT is recommended for individuals at CS 4 to estimate the possibility of skeletal expansion with traditional tooth-borne RME. the correlation between MPS stage and CVM stage. (3) Case analysis to compare effects of traditional tooth-borne RME at different MPS stages.


Background
Midpalatal suture ossifies and fuses from posterior to anterior with aging [1]. Melsen et al. used autopsy material and reported that chronological ages of midpalatal suture fusion are different among individuals [2]. Persson et al. indicated that starting time of midpalatal suture fusion is strongly relevant with skeletal growth and development status [3].
Skeletal effects of tooth-borne rapid maxillary expansion (RME) highly depend on the ossification and fusion of midpalatal suture [4,5]. For traditional tooth-borne RME, skeletal effects (include opening of midpalatal suture and maxillary alveolar bone remodeling) decrease and dental effects (buccal tipping of maxillary molars) increase with aging [6]. Furthermore, clinical experience has proved the complications of traditional tooth-borne RME in matured adolescents, including external root 3 resorption, excessive tipping of maxillary teeth, and alveolar bone resorption et al [7][8][9].
Cervical vertebrate maturation (CVM) method established and optimized by Baccetti et al. is a commonly used indicator to predict individual growth stage [10][11]. Baccetti et al. preliminarily observed relation between CVM stages and RME effects by dividing samples into early RME group (CS 1-3) and late RME group , indicating that early RME group got lager proportion of skeletal expansion effect compared with late RME group [5]. Although using CVM stage to indicate optimal timing for maxillary expansion has some clinical significance, it is still indirect evidence due to unknown ossification and fusion status of midpalatal suture at specific CVM stage.
Surgical assisted or bone-borne RME currently used in orthodontic practice improve the possibility of skeletal expansion for individuals with partial or complete ossification and fusion of midpalatal suture [12]. Due to their invasive characteristics and complicated operation, traditional tooth-borne maxillary expansion is still regarded as regular therapy in orthodontic practice, especially for adolescents. Therefore, evaluation of midpalatal suture's ossification and fusion status is important when predicting the optimal timing for traditional tooth-borne maxillary expansion. Angelieri et al., as a pioneer study, classified five morphological stages to describe continuous process of ossification and fusion of midpalatal suture based on horizontal view of 140 CBCT images [13]. The relationship between midpalatal suture stages based on their study and CVM stages was also investigated and the most reliable diagnostic pairs are (CS 1-2) -(stage A-B), CS 3 -stage C and CS 5 -(stage D-E) [14].
Researchers assessed reliability, repeatability, intra-and inter-observer agreement of this classification method to evaluate its clinical prediction capability and found that prediction capability of this method is not optimistic. Clinicians should be cautious in interpretation of this classification method, and more studies are needed for improvement [15][16][17].
The aims of this study include: (1) Establish an improved staging method to describe the morphological characteristics of midpalatal suture.  CVM stage was recorded according to CVM method by Baccetti et al [10,11].
Dental casts measurements 5 9 patients took CBCT before traditional tooth-borne RME (T1) to record their MPS stage. Then maxillary dental cast was obtained and later Hyrax-type RME was delivered with 1-2 turns a day (0.25 mm per turn) until the orthodontist decided to stop activating ( Figure 2). Maxillary dental cast was obtained immediately after active expansion ended (T2).
Diagram of digital dental cast, landmarks identification and measurements are shown in Figure 3.
Lingual point on the maxillary first molar is located at the junction of the lingual groove with the palatal mucosa. Arch width at first molar level is defined as the distance between the lingual points of bilateral maxillary first molars. Arch width at second premolar, first premolar and canine level are also defined in this way [4]. Angulation of maxillary first molars defined by measuring the angle formed by the intersection lines passing through the mesio-buccal and mesio-lingual cusps. Angulation less than 180° indicates the possibility of molars' buccal tipping, while larger than 180° implies the possibility of molars' lingual tipping [4].
When analyzing expansion effects, total effect and average effect per activation were calculated. Characteristics of different stages on horizontal view are summarized in Table 2. CBCT images of each stage are shown in Figure 4. Diagrams to illustrate detailed characteristics of each stage are shown in Figure 5.

Frequency distribution of MPS stage and CVM stage
Frequency distributions of MPS stage and CVM stage are shown in Table 3.

Spearman correlation coefficient and diagnostic efficacy indicators
Spearman coefficient between MPS stage and CVM stage is 0.803 in total, 0.790 in females and 0.813 in males (Table 3). Diagnostic test results are shown in Table 4

Effect of RME at different MPS stages
7 Growth status, RME activation and measurements at pre-expansion (T1) and post-expansion (T2) are shown in Table 5. Total RME effects are shown in Table 6 (A), and average effects per activation are shown in Table 6 (B).
Average effects per activation Table 6

Correlation between MPS stage and CVM stage
It is reported that growth velocity and the occurrence of growth peak for maxilla and mandible are at different timing [19]. In our study, 90. We concern more on individuals at CS 4 for the feasibility of skeletal expansion with traditional tooth-borne RME. In the our study, 31.2% of individuals at CS 4 are at MPS 3, another 46.6% at MPS 4s1. This is obviously different for individuals at CS 3, in which 57.7% are at MPS 3, another 13.5% at MPS 4s1. Therefore, when growing from CS 3 to CS 4, quite a few individuals may go through start of midpalatal suture fusion from posterior to anterior. Therefore, for patients at CS4, it is recommended to take pre-treatment CBCT to observe the fusion and maturation status of midpalatal suture before including traditional tooth-borne RME into treatment plan.  Tables   Due to technical limitations the Tables are available as     Diagrams of morphological stages of midpalatal suture morphological characteristics. White:

Effects of traditional tooth-borne RME at different MPS stages
Low-density tissue. Light grey: Transitional area. Deep grey: High-density area. 16 Supplementary Files This is a list of supplementary files associated with this preprint. Click to download. Tables.pdf