Finite element analysis of the biomechanical effect of clear aligners in extraction space closure under different anchorage controls

Clear aligners (CAs) have attracted increasing attention from patients and orthodontists because of their excellent esthetics and comfort. However, treating tooth extraction patients with CAs is difficult because their biomechanical effects are more complicated than those of traditional appliances. This study aimed to analyze the biomechanical effect of CAs in extraction space closure under different anchorage controls, including moderate, direct strong, and indirect strong anchorage. It could provide several new cognitions for anchorage control with CAs through finite element analysis, further directing clinical practice.A 3-dimensional maxillary model was generated by combining cone-beam computed tomography and intraoral scan data. Three-dimensional modeling software was used to construct a standard first premolar extraction model, temporary anchorage devices, and CAs. Subsequently, finite element analysis was performed to simulate space closure under different anchorage controls.Direct strong anchorage was beneficial for reducing the clockwise occlusal plane rotation, whereas indirect anchorage was conducive for anterior teeth inclination control. In the direct strong anchorage group, an increase in the retraction force would require more specific anterior teeth overcorrection to resist the tipping movement, mainly including lingual root control of the central incisor, followed by distal root control of the canine, lingual root control of the lateral incisor, distal root control of the lateral incisor, and distal root control of the central incisor. However, the retraction force could not eliminate the mesial movement of the posterior teeth, possibly causing a reciprocating motion during treatment. In indirect strong groups, when the button was close to the center of the crown, the second premolar presented less mesial and buccal tipping but more intrusion.The 3 anchorage groups showed significantly different biomechanical effects in both the anterior and posterior teeth. Specific overcorrection or compensation forces should be considered when using different anchorage types. The moderate and indirect strong anchorages have a more stable and single-force system and could be reliable models in investigating the precise control of future tooth extraction patients.