Biomechanical impact of beveling design on extrusion of a maxillary canine and a maxillary first molar: an in vitro and finite element analysis study

Objectives: To investigate the effect of beveling side (apical vs occlusal) on the extrusive biomechanics of clear aligners compared to unbeveled attachments when tracking issues occur. Materials and Methods: An in vitro Orthodontic Force Simulator (OFS) was used to simulate extrusion of a maxillary canine and first molar. Three attachment designs (beveled apical, beveled occlusal, and conventional rectangular) were digitally designed on the target teeth and directly milled in zirconia material. Aligners were thermoformed for each design and target tooth. The tooth-aligner mismatch was created on the target tooth up to 1.0 mm to simulate the tracking issue. Finite Element Analysis (FEA) was conducted to simulate the OFS experiment and analyze stress distribution and deformation. Results: The attachment designs yielded significant differences in extrusion forces and bucco-palatal moments on both teeth. Beveled apical attachments consistently produced the lowest forces and moments, especially as displacement increased. This was attributed to a sliding motion of the aligner along the tooth movement path, mitigating the negative effects of tracking errors. Rectangular and beveled occlusal attachments, while offering strong initial engagement, resulted in higher stress concentrations and variability in force delivery as the simulated aligner-tooth mismatch grew. Conclusions: The beveled apical design provides more predictable and consistent extrusion forces, reducing unwanted side effects, particularly for large movements and high risk of tracking issues.