Biomechanical Effects of Different Auxiliary-Aligner Designs for the Extrusion of an Upper Central Incisor: A Finite Element Analysis

Abstract

Aim. To evaluate the biomechanical effects of four different auxiliary-aligner combinations for the extrusion of a maxillary central incisor and to define the most effective design through finite element analysis (FEA). Materials and Methods. A full maxillary arch (14 teeth) was modelled by combining two different imaging techniques: cone beam computed tomography and surface-structured light scan. The appliance and auxiliary element geometries were created by exploiting computer-aided design (CAD) procedures. The reconstructed digital models were imported within the finite element solver (Ansys® 17). For the extrusion movement, the authors compared the aligner without an attachment with three auxiliary-aligner designs: a rectangular palatal attachment, a rectangular buccal attachment, and an ellipsoid buccal attachment. The resulting force-moment (MF) system delivered by the aligner to the target tooth and the tooth displacement were calculated for each scenario. Results. The maximum tooth displacement along the z-axis (0.07 mm) was obtained with the rectangular palatal attachment, while the minimum (0.02 mm) was obtained without any attachments. With the ellipsoid attachment, the highest undesired moments Mx and My were found. The rectangular palatal attachment showed the highest Fz (2.0 N) with the lowest undesired forces (Fx = 0.4 N; Fy = −0.2 N). Conclusions. FEA demonstrated that the rectangular palatal attachment can improve the effectiveness of the appliance for the extrusion of an upper central incisor.

Optimal Position of Attachment for Removable Thermoplastic Aligner on the Lower Canine Using Finite Element Analysis

“…We tried to use the loading condition of 0.15 mm which was used in previous studies [ 19 ], but the analysis did not converge due to excessive deformation of the PDL in the extrusion attachment model. The reason for this is the material properties of PDL reported in the previous literature use stress–strain curve values, whereas, our study was applied in the hyperelastic properties were considered using the Ogden model [ 19 , 23 ]. Therefore, the stresses and strains generated in the PDL have been shown to be different between previous and our studies.…”

“…RTA was designed for each orthodontic treatment situation, and RTA was implemented with thickness of 0.3 mm based on previous literature ( Figure 2 b) [ 19 ]. The material properties of each component except for PDL were applied with reference to previous literature ( Table 1 ) [ 18 , 19 , 22 , 23 ].…”

“…In the four orthodontic treatment models, “tie contact” was applied assuming complete union and bonding state among bone, teeth, PDL and attachments, whereas a friction coefficient of 0.2 was applied by assuming a sliding state for the surface of contact among RTA, teeth and attachment [ 23 ]. The four orthodontic treatment models completely controlled the side and bottom of the bones so that movement and rotation did not occur in all directions ( Figure 3 a–d).…”

“…Therefore, our study built a mandibular canine model and performed FEA. Based on previous studies, the thicknesses of the cortical bone, mucosa and PDL were set to 2 mm, 2 mm, and 0.2 mm, respectively [ 22 , 23 , 26 , 27 ] ( Figure 5 b,c). A single tooth shape was considered to compare the displacement and rotation according to the position of attachments, and the mandibular canine was extracted from the mandibular CBCT image ( Figure 5 c).…”

“…For rotation attachments, a nine attachment positions were simulated by combining two attachments at each lingual and buccal sides of the tooth, respectively ( Figure 6 d). Previous literature was referenced for the material properties of the cortical bone, cancellous bone, mucosa, PDL, the teeth and the attachments, and the applied parameters are presented in Table 1 and Table 2 [ 20 , 22 , 23 , 24 , 25 ]. All components were formed using the tetrahedral element (C3D4).…”