To establish a staging method to describe the morphological development of midpalatal suture of Chinese population, to investigate the distribution of chronological age of this method, and to explore its clinical application in determining the timing of upper rapid palatal expansion.

This study is a retrospective observational study. 1076 CBCT images (Female: 675, Male: 401, Age range: 6.0~20.9 years old) are included. Morphological stages and corresponding features of midpalatal suture are classified and summarized according to images on horizontal view. Relation between midpalatal suture stages and chronological age ranges are performed by frequency and proportion analysis.

(1) Five stages of midpalatal suture are established, with Stage 4 divided into two substages: Stage 4s1 and Stage 4s2. (2) Majority of samples between 6.0~10.9 years old are at Stage 1~2 (Female: Stage 1~2: 81%. Male: Stage 1~2: 87%). Majority of samples between 11.0~12.9 years old are at Stage 3, accounting for 60%. Majority of samples between 13.0~13.9 years old are at Stage 3 and Stage 4s1, with larger proportion of Stage 3 than Stage 4s1 (Female: Stage 3: 46%, Stage 4s1: 38%. Male: Stage 3: 54%, Stage 4s1: 36%). Majority of samples between 14.0~14.9 years old are at Stage 3 and Stage 4s1, with larger proportion of Stage 4s1 than Stage 3 (Female: Stage 3: 29%, Stage 4s1: 54%. Male: Stage 3: 26%, Stage 4s1: 56%). Majority of samples between 15.0~20.9 years old are at Stage 4~5 (Female: Stage 4~5: 94%. Male: Stage 4~5: 90%).

The morphological staging method of midpalatal suture established in this study indicates that it is necessary to take CBCT exams for potential tooth-borne rapid maxillary expansion treatments in 13.0~14.9 years old individuals to clear the maturation and fusion status of midpalatal suture.

Morphological stage; Midpalatal suture; Fusion; Chronological age