Effects of variable attachment shapes and aligner material on aligner retention

Abstract

Objective: To evaluate the retention of four types of aligners on a dental arch with various attachments. Materials and Methods: For this study, three casts were manufactured, two of which contained attachments (ellipsoid and beveled), and one without any attachments to serve as a control. Four types of aligners were thermoformed: Clear-Aligner (CA)-soft, CA-medium, and CA-hard, with various thicknesses, and Essix ACE. Measurements of vertical displacement force during aligner removal were performed with the Gabo Qualimeter Eplexor. Means and standard deviations were next compared between different aligner thicknesses and attachment shapes. Results: CA-soft, CA-medium, and CA-hard did not present a significant increase in retention, except when used in the presence of attachments. Additionally, CA-medium and CA-hard required significantly more force for removal. Essix ACE demonstrated a significant decrease in retention when used with ellipsoid attachments. The force value for Essix ACE removal from the cast with beveled attachments was comparable to that of CA-medium. Forces for aligner removal from the model without attachments showed a linear trend. Essix ACE did not show a continuous increase in retention for each model. Overall, ellipsoid attachments did not present a significant change in retention. In contrast, beveled attachments improved retention. Conclusions: Ellipsoid attachments had no significant influence on the force required for aligner removal and hence on aligner retention. Essix ACE showed significantly less retention than CAhard on the models with attachments. Furthermore, beveled attachments were observed to increase retention significantly, compared with ellipsoid attachments and when using no attachments. (Angle Orthod. 2015;85:934-940.)

Scanning electron microscopy evaluation of aligner fit on teeth

“…Different aligner systems have various designs, for example: a scalloped gingival border (Invisalign) or a straight border with different widths (CA-Clear Aligner of 2-3 mm). Dasy et al 19 demonstrated that edgeless aligners generated significantly lower forces than did those with a wider edge. The increased force might be due to the enhanced stiffness caused by material shape.…”

“…In contrast, the measurements obtained in the current study demonstrated a better fit of the less stiff and, thus more flexible, aligner material. The difference may be explained by the fact that Dasy et al 19 analyzed aligners built with the same material (glycolmodified polyethylene terephthalate by Scheu Dental) while, in this study, the CA-Clear Aligner material was compared with Invisalign SmartTrack aligners, which are multilayer aromatic thermoplastic aligners. The exact composition of the material is patented.…”

Clear Aligner Treatment with “In-Office” Virtual Model Set-Up and 3D Printing.

“…The absence of attachments in the simulation of the same displacement produced a force system comparable to uncontrolled tooth inclination. Dasy et al reported an experiment comparing vertical displacement force of two kinds of attachments (ellipsoid and beveled rectangular attachments), and found that the beveled attachments increase retention significantly compared with ellipsoid attachments or no attachment [10] .…”

Risk Factors of Composite Attachment Loss During Orthodontic Clear Aligner Therapy

“…Bond failure or patient neglect can cause attachment loss from the tooth surface. Attachment loss can induce signi cant clinical problem that may prolong treatment time, increase the number of re-visit, and the prognosis of the treatment [11].…”