Korean J Orthod.  2022 Jul;52(4):258-267. 10.4041/kjod21.126.

Validation of three-dimensional digital model superimpositions based on palatal structures in patients with maximum anterior tooth retraction following premolar extraction

• Liu J
• Koh KM
• Choi SH
• Kim JH
• Cha JY

• KMID: 2532104
• DOI: http://doi.org/10.4041/kjod21.126

Abstract

Objective
This study aimed to evaluate the superimposition accuracy of digital modes for measuring tooth movement in patients requiring anterior retraction after premolar extraction based on the proposed reference regions.
Methods
Forty patients treated with bilateral maxillary first premolar extraction were divided into two groups: moderate retraction (< 7.0 mm) and maximum retraction (≥ 7.0 mm). Central incisor displacement was measured using cephalometric superimpositions and three-dimensional (3D) digital superimpositions with the 3rd or 4th ruga as the reference point. The Wilcoxon signed-rank test and linear regression analyses were performed to test the significance of the differences and relationships between the two measurement techniques.
Results
In the moderate retraction group, the central incisor anteroposterior displacement values did not differ significantly between 3D digital and cephalometric superimpositions. However, in the maximum-retraction group, significant differences were observed between the anteroposterior displacement evaluated by the 3rd ruga superimposition and cephalometric methods (p < 0.05).
Conclusions
This study demonstrated that 3D digital superimpositions were clinically as reliable as cephalometric superimpositions in assessing tooth movements in patients requiring moderate retraction. However, the reference point should be carefully examined in patients who require maximum retraction.

Keyword

Digital models; Cephalometrics; Dental cast analysis; Palatal ruga

Figure

• 

  Figure 1 Reference co-ordinate system for measuring the amount of tooth movements. A and B, Reference co-ordinate system for cephalometric superimposition. A, X-axis: a line through the maxillary central incisor tip and the mesio-buccal cusp tip of the first maxillary molar on the initial cephalogram. Y-axis: plane perpendicular to X-axis through Sella. B, Superimposition of the maxilla along the palatal plane registered at anterior nasal spine (ANS). C and D, Reference co-ordination system for three-dimensional digital superimposition. The green box is the occlusion plane perpendicular to midpalatal raphe, which passes through tip of the central incisor and mesio-buccal cusp tip of the first maxillary molars. The green, blue, and red arrows indicate the X, Y, and Z axes, respectively. C, Occlusal view. D, Sagittal view. PNS, posterior nasal spine.

• 

  Figure 2 Definition of landmarks for the superimposition of three-dimensional digital model. A, Superimposition using third ruga: medial 1/2 of third ruga and the following regional palatal vault. B, Superimposition using fourth ruga: medial 1/2 of fourth ruga and the following regional palatal vault. Palatal vault region, Anterior border line - the line connecting the interdental contact points between the 2nd premolar and 1st molar on either side. Posterior border line - the line connecting the interdental contact points between the 1st and 2nd molars on either side. Lateral border line - the anteroposteior lines are 10 mm away from the lines in contact with the palatal gingival margins of the posterior teeth and parallel to occlusal line through central groove of the posterior teeth bilaterally.

• 

  Figure 3 In maximum retraction case, change of the ruga and digital superimposition. A, Pre-treatment. B, Post-treatment. C and D, Tooth movement of superimposed three-dimensional models in the maximum retraction case. C, Superimposition using the third ruga. D, Superimposition using the fourth ruga.

• 

  Figure 4 Scattergrams and regression lines for the central incisor movements measured on the cephalogram and three-dimensional digital model. A, B, C and D, in the moderate retraction group. E, F, G and H, in the maximum retraction group. A and E, Horizontal movements of central incisor (Xd). X-axis: cephalometric superimposition (Xd_ceph); Y-axis: 3rd ruga digital superimposition (Xd_3rdR); B and F, Horizontal movements of central incisor. X-axis: cephalometric superimposition; Y-axis: 4th ruga digital superimposition (Xd_4thR); C and G, vertical movements of central incisor (Yd). X-axis: cephalometric superimposition (Yd_ceph); Y-axis: 3rd ruga digital superimposition (Yd_3rdR); D and H, vertical movements of central incisor. X-axis: cephalometric superimposition; Y-axis: 4th ruga digital superimposition (Yd_4thR).

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