Influence of attachment bonding protocol on precision of the attachment in aligner treatments

Aim Precise bonding of attachments in aligner treatment is crucial to achieve the intended tooth movement. Thus, we evaluated five different bonding protocols for attachments used in aligner treatments with the goal of identifying the most precise protocol. Methods One ellipsoid and one rectangular attachment were exemplarily chosen and examined. All attachments were bonded using the same template aligner, which was produced by thermoforming. The bonding process was repeated 30 times with each protocol for statistical analysis. The protocols differed in the type of composite used (high viscous, low viscous), the additional application of a perforation in the attachment reservoir, and the use of a two-phase procedure with high viscous composite. All bonded attachments were laser scanned and compared to the attachments of a master model using a surface/surface matching algorithm to determine the precision, i.e., highest aberrations (maximum vertical distance) between the attachment of the master and results obtained from the various bonding protocols. Furthermore, the excessive amounts of composite bonded around the attachments were measured and compared. Results The two-phase procedure had a median aberration of 0.13 mm and a median amount of excessive composite of 7.40 mm 2 (ellipsoid attachment). With the low viscous composite without a perforation in the template reservoir, similar results were achieved (median 0.13 mm) regarding the maximum vertical distance, but had an excess area of 33.50 mm 2 . Conclusion In this in vitro study, the bonding protocol influenced the precision of bonded attachments. The bonding protocol with high viscous composite without a perforation in the attachment reservoir was the most inaccurate. The use of a low viscous composite or attachments made by a two-phase procedure with high viscous composite revealed more precise results.