Effects of attachment design and location on derotation of mandibular second premolars : A finite element analysis

To assess the effects of attachment design and location on derotation of mandibular second premolars through the finite element method.

A mandibular model consisting of teeth, periodontal ligament (PDL), trabecular/compact bones, attachment, and clear aligner was created. Tooth 35 was positioned with 30° mesial rotation. Seven treatment scenarios were planned to analyze the derotation movement, i.e., Model 1: no attachment; Model 2: buccal vertical rectangular attachment (VRA); Model 3: buccal beveled VRA (bVRA); Model 4: lingual VRA: Model 5: lingual bVRA; Model 6: buccal and lingual VRAs; and Model 7: buccal and lingual bVRAs. Derotation activation was 1.2° for each aligner. Tooth displacement, aligner deformation, and stresses produced in the PDL and the aligner were analyzed.

The highest value for tooth displacement (0.087 mm, 0.51°) was detected in Model 7, while Model 1 exhibited the lowest value (0.067 mm, 0.39°). Model 7 created the least deformation of the clear aligner (0.469 mm) and the highest stresses in the PDL (6.780 MPa) and the clear aligner (101.258 MPa), whereas Model 1 induced the highest deformation of the clear aligner (0.523 mm) and the lowest stresses in the PDL (6.253 MPa) and the clear aligner (62.667 MPa). Greater derotations were observed in models with bVRA than in those with VRA in the same placement and in models with attachments on both surfaces than in those with attachment on one surface.

bVRAs placed on both the buccal and lingual surfaces provided the most controlled and predictable derotation movement. Aligner deformation and stresses produced in the PDL and the clear aligner showed biomechanical harmony with the movement.