Predictability of lower incisor tip using clear aligner therapy

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.