Abstract
Introduction: Root tip (orthodontic movement of the root in a mesio-distal direction) occurs when a high moment-to force ratio is applied to the crown of a tooth. In this situation the centre of rotation is located approximately at the incisal edge. Uprighting incisors in the coronal plane is particularly important with clear aligner therapy (CAT). The tip of a tooth determines the amount of space it occupies (mesio-distally) and subsequently the fit of the aligner.
Objectives: To investigate the ability of ClinCheck® to accurately predict lower incisor root tip by comparing simulated movements with actual clinical outcomes and to determine whether the presence of a vertically orientated rectangular composite attachment influences the efficacy of root 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. A customised method for measuring tip and classifying orthodontic tooth movement (OTM) type was developed. Lower incisor root tip was measured at T0 (pre-treatment), T1 (predicted post-treatment) and T2 (achieved post-treatment) on digital models using metrology software (Geomagic Control X). The change in position from T0 to T1 (predicted) and T0 to T2 (achieved) was measured from the estimated centre of resistance (CRes) of each tooth. The estimated centre of rotation (CRot) was plotted relative to the CRes to describe the type of tooth movement predicted and achieved.
Results: A positive correlation was found between predicted root tip and achieved root tip (R2 = 0.55; p< 0.001). For every degree of root tip planned 0.4 degrees of tip was achieved. The presence of an attachment resulted in 1.2 degrees greater root tip (F=3.7; p =0.062) and 0.5mm 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 only 46% achieved this type of movement.
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Conclusions: The amount of root tip achieved was on average substantially less than the ClinCheck® displayed. Vertically orientated rectangular attachments are recommended where substantial root movement is planned, and their presence slightly improves apex movement.