Predictability of lower incisor tip using clear aligner therapy

Abstract

Abstract Background Uprighting incisors is particularly important with clear aligner therapy as incisor tip determines the mesio-distal space needed in the arch, and consequently the fit of the aligner. The objective of this study was to investigate the accuracy of ClinCheck ® software to predict lower incisor tip by comparing digitally prescribed movements with actual clinical outcomes and to determine whether the presence of a vertically orientated rectangular composite attachment influences the efficacy of incisor tip. Methodology This retrospective study included 66 lower incisors from 42 non-extraction adult patients treated using the Invisalign ® appliance. Twenty-one incisors had vertical attachments, while 45 incisors did not have any attachments. Lower incisor tip was measured at T0 (pre-treatment), T1 (predicted post-treatment) and T2 (achieved post-treatment) on digital models using metrology software. The change in position from T0 to T1 and T0 to T2 was measured from the estimated centre of resistance (C Res ) of each tooth. The estimated centre of rotation was plotted relative to the C Res to describe the type of orthodontic tooth movement (OTM) predicted and achieved. Results Predicted incisor tip and achieved incisor tip were positively correlated ( R 2 = 0.55; p < 0.001). For every degree of tip planned 0.4 degrees of tip was achieved. The presence of an attachment resulted in 1.2 degrees greater tip ( F = 3.7; p = 0.062) and 0.5 mm greater movement of the predicted apex of the tooth ( F = 4.3; p = 0.042) compared with the no attachment group. The type of OTM achieved differed from the type predicted. Sixty-seven percent of incisors investigated were predicted to move by root movement, while 46% achieved this type of movement. Conclusions The amount of lower incisor tip achieved was on average substantially less than the ClinCheck ® displayed. Vertically orientated rectangular attachments are recommended where large root movement is planned, and their presence slightly improves apex movement.