Attachment technique as orthodontic aligner retention reinforcement: An in vitro study

Abstract
Objective: This study was aimed to compare the retention among orthodontic aligners according to the number of beveled attachments.
Material and Methods: Three types of 3D models were designed to mold three types of aligner samples. Model group A was without attachment. Model group B was with one attachment. Model group C was with two attachments. Sample aligners were fabricated using polyethylene terephthalate-glycol (PETG) sheets 0.8 mm (Erkodur). A pull-off device integrated into the Universal Testing Machine was manufactured to pull aligners from the model.  Data were analyzed with One-way ANOVA, SPSS (statistical Package of Social Sciences Version 28, IBM Co., New York, USA) to determine differences between three different groups of retention designs.
Results: The aligner retention was statistically significantly different for different numbers of attachments. Tukey post hoc analysis revealed that the mean increase from group A to group B was not statistically significant (P=0.416). Also, the increase from group B to group C was not statistically significant (P=0.114). However, the increase from group A to group C was statistically significant (P=0.009). The force peak was recorded when the aligner dislodged from the attachment. Thus, the group C representative produced two force peaks. The molar attachments were displaced first, followed by the premolar attachments.
Conclusion: The rectangular beveled shaped attachments are attachments that significantly reinforced aligner retention. Aligner with more rectangular beveled attachments is more difficult to pull off compared with aligner with less attachments or no attachments at all.