Influence of attachment designs in the insertion and removal force of clear aligners: An experimental study of strain sensors

Objectives: This experimental study analyzed the influence of attachment designs on the insertion and removal force of orthodontic clear aligners (CA). Material and Methods: Eleven CA (0.63 mm thickness) were manufactured with rectangle, beveled, distal slice, round wedge, pyramidal, and half-moon attachment shapes. The attachments were included in dental units 11, 12, 13, and 16, and absence of attachments in the control group. Analyses of the deformation stress (-) and expansion (+) of the CA were recorded six times using a strain gage during appliance insertion and removal. Descriptive analyses were calculated for all the study variables, followed by the analysis of variance test for repeated measures (significance level of 0.05). Results: Despite no attachments, CA still had low expansion (2.730; Standard deviation [SD] = 0.327) alteration. Rectangle horizontal scale in the dental unit 16 had the highest strain (−13.869; SD = 1.198 µm/m), similar to the half-moon type (−13.009; SD = 2.399 µm/m) in dental unit 11. CA with a beveled horizontal scale in dental unit 16 had a higher expansion threshold (5.337; SD = 0.453 µm/m) than the beveled low-profile horizontal scale in dental unit 12 (1.046; SD = 1.010 µm/m). Conclusion: Attachments significantly influence this behavior, with certain designs, such as the half-moon and rectangular types, producing higher stress and expansion values. The control group showed minimal strain, confirming the attachments’ role in guiding force distribution. These findings highlight the importance of attachment design in optimizing aligner performance and treatment effectiveness.