Korean J Orthod.  2024 Nov;54(6):359-373. 10.4041/kjod24.016.

Evaluation of different designs of 3D printed clear aligners on mandibular premolar extrusion using force/moment measurement devices and digital image correlation method

• Baik JC
• Choi YK
• Cho Y
• Baek Y
• Kim SH
• Kim SS
• Park SB
• Kim KB
• Kim YI

• KMID: 2561598
• DOI: http://doi.org/10.4041/kjod24.016

Abstract

Objective
This study aimed to investigate the effect of three-dimensional (3D) printed clear aligners (CA) with different designs on the extrusion of mandibular premolars using a force/moment measurement system and digital image correlation (DIC).
Methods
The forces and moments applied to the mandibular canines, first and second premolars were measured using a multi-axis force/ moment transducer when an extrusion of 0.5 mm was planned, assuming the mandibular first premolars were intruded by 1 mm. In addition, displacement and strain changes in the CA were analyzed using the DIC method. CA designs were categorized based on the presence of first premolar attachment and subdivided into equigingival margins, 1-mm extended margins, equi-margins with 1-mm thickness and height, and equi-margins with 1-mm reduced buccolingual width. The CA was printed directly at a thickness of 0.5 mm, and the experiments were conducted at 37°C.
Results
The results showed that attachment played an important role in the extrusion of first premolars in both the force/moment measurement system and the DIC method. Intrusion was observed without attachment, even though extrusion was planned. CA designs apply greater force to the cervical region by extending the margin or reducing the buccolingual width, thereby improving extrusion efficiency.
Conclusions
Force and moment changes in direct 3D printed CA are complex and difficult to predict; however, modifying aligner designs, such as extending the margin or reducing buccolingual width, and using appropriate attachments could minimize unwanted tooth movement, optimize planned treatment, and increase treatment predictability.

Keyword

Aligners; Extrusion; Force; Moment

Figure

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  Figure 1 A, Apparatus virtual design (the mandibular left 1st premolar: 1 mm intrusion). B, Printed apparatus model. C, Attachment design and position.

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  Figure 2 Various aligner designs. A, Group 1 (equi-margin) without attachment; B, Group 1 (equi-margin) with attachment; C, Group 2 (1-mm extended margin) without attachment; D, Group 2 (1-mm extended margin) with attachment; E, Group 3 (equi-margin with 1-mm thickness and height) without attachment; F, Group 3 (equi-margin with 1-mm thickness and height) with attachment; G, Group 4 (equi-margin with reduced buccolingual width) without attachment; and H, Group 4 (equi-margin with reduced buccolingual width) with attachment.

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  Figure 3 Compare aligner thicknesses (bottom view). A, Group 1 (equi-margin) and Group 4 (equi-margin with reduced buccolingual width); B, Group 1 (equi-margin) and Group 3 (equi-margin with 1-mm thickness and height); C, Group 1 (equi-margin) and 3 (equi-margin with 1-mm thickness and height), and Group 4 (equi-margin with reduced buccolingual width). Grey: Group 1, Red: Group 3, Green: Group 4.

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  Figure 4 Coordinates of data from apparatus. Centered on the facial axis of a clinical crown, we designated the X-axis to represent the mesial/distal direction, the Y-axis for the buccal/lingual direction, and the Z-axis for the occlusal/gingival direction. Fx was delineated as the proximal direction, Fy as the buccal direction, and Fz as the occlusal direction. Additionally, positive values were assigned to buccal tipping as Mx, mesial tilting as My, and distal-in rotation as Mz.

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  Figure 5 The force/moment measurement system overview.

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  Figure 6 Experimental set-up for digital image correlation method. A, Images taken using two cameras; B, Clear aligner after speckle pattern coating; and C, Aligner mounted on the experimental apparatus.

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  Figure 7 Displacement field in surface load with attachment. A, Group 1 (equi-margin); B, Group 2 (1-mm extended margin); C, Group 3 (equi-margin with 1-mm thickness and height); and D, Group 4 (equi-margin with reduced buccolingual width).

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  Figure 8 Displacement field in surface load without attachment. A, Group 1 (equi-margin); B, Group 2 (1-mm extended margin); C, Group 3 (equi-margin with 1-mm thickness and height); and D, Group 4 (equi-margin with reduced buccolingual width).

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  Figure 9 Major principal strain with attachment. A, Group 1 (equi-margin); B, Group 2 (1-mm extended margin); C, Group 3 (equi-margin with 1-mm thickness and height); and D, Group 4 (equi-margin with reduced buccolingual width).

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  Figure 10 Major principal strain without attachment. A, Group 1 (equi-margin); B, Group 2 (1-mm extended margin); C, Group 3 (equi-margin with 1-mm thickness and height); and D, Group 4 (equi-margin with reduced buccolingual width).

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