Scanning electron microscopy analysis of aligner fitting on anchorage attachments

Purpose: The aims of the study were (1) to evaluate the fitting of three different aligners (Invisalign [Align Technology, Santa Clara, CA, USA], CA Clear Aligner [Scheu-Dental, Iserlohn, Germany] and F22 [Sweden&Martina, Due Carrare, Italy]) on anchorage attachments using scanning electron microscopy (SEM), and (2) to analyze the influence of 2 different types of resin used to build attachments on aligner fitting. Methods: Using STL files of a patient, six resin casts were obtained and rectangular attachments were bonded on them. Conventional bulk-fill resin was used to build upper attachments while a flowable resin was used to build the lower ones. Passive aligners were adapted on each cast and then sectioned buccolingually. Microphotographs of the obtained sections were performed using a SEM and then micrometric measurements of aligner fitting on anchorage attachments were recorded. Results: Analyzing the overall fitting of upper arch aligners, Invisalign provided a significantly better fitting with respect to F22 (P = 0.009); differences were not significant when comparing Invisalign with CA Clear Aligner, and CA Clear Aligner with F22. Analyzing the overall fitting of lower arch aligners, F22 provided a significantly better fitting with respect to CA Clear Aligner (P = 0.008) and Invisalign (P = 0.011). The analysis showed a significantly better fitting on upper attachments, built using conventional bulk-fill resin (P = 0.034). Conclusions: Invisalign, CA Clear Aligner and F22 have comparable performance in terms of fitting on anchorage attachments. Conventional bulk-fill resin provides the best fitting on anchorage attachments.