Micro-computed tomography evaluation of aligner fitting on anchorage attachments

To evaluate the fit of clear aligners (CAs) manufactured from different materials and thicknesses to anchorage attachments using micro-computed tomography-based (Micro-CT) three-dimensional and two-dimensional analyses.

Forty CAs fabricated from different thicknesses and materials (0.50 mm CA-Soft, 0.625 mm CA-Medium, 0.75 mm CA-Hard polyethylene terephthalate glycol [PET-G], and 0.75 mm CA PRO-Hard ABA) were fitted onto a master model with rectangular attachments on the first and second premolars. Micro-CT scans were obtained to assess the air gap between the aligner and attachment. Total air-gap volume was calculated using three-dimensional volumetric analysis, while mean gap width was measured in predefined two-dimensional sections. Adjusted mean differences were interpreted using a practical relevance threshold of 20 μm.

CA PRO-Hard showed the lowest mean three-dimensional air-gap volume, but differences among groups were not statistically significant (P > 0.05). Two-dimensional analysis revealed localized differences in aligner-attachment adaptation. The most pronounced and practically relevant differences were detected in the palatal and gingival sections (P < 0.001), where PET-G groups showed greater gap widths than CA PRO-Hard and exceeded the 20 μm threshold. In the sagittomedian section, mean differences also exceeded 20 μm, but confidence intervals indicated cautious interpretation. No statistically significant or practically relevant differences were observed in the transversomedian (P = 0.054), buccal, frontomedian, mesial, or occlusal sections.

Micro-CT enabled detailed assessment of CA fit. Although volumetric analysis showed no significant material-related differences, section-based analysis demonstrated localized adaptation differences, particularly in palatal, gingival, and sagittomedian regions. CA PRO-Hard showed superior fit in these areas.