Effectiveness of Space Closure by Clear-aligners Using Two Attachment Types

Objectives: To evaluate force levels produced by a series of Invisalign® smart track aligners and to investigate the effectiveness of two types of attachments proposed by Align Technology to maximize tooth translation during space closure.
Methods: Ten randomly selected teeth (canines and premolars) were either fitted with either vertical attachments (N =5) or optimized attachments as proposed by Align technology (N =5) to maximize tooth translation during space closure. The ClinCheck® for each patient/tooth was planned such that the movements to be investigated were performed in the respective quadrant with no other teeth movements. Resin replicas of the patients’ teeth models prior to the start of the investigated movement were produced and mounted in an Orthodontic Measurement and Simulation System (OMSS). Each aligner was fitted to the model, the force systems were measured and the movements were performed until no more forces/moments were generated. Each aligner was tested five times simulating clinical use of the clear aligners by the patients. Then, the next aligners were installed and the measurement repeated. Tooth movement ranged between 2-7.5 mm. Maximum peak forces produced by each type of attachment group as well as effectiveness of each attachments group were compared using two-sample t-test. Alpha was set at 0.05.
Results: There was no significant difference in the mean peak force levels between the two attachments groups (P=0.83). However comparing the planned and simulated tooth movements revealed that the effectiveness of the vertical attachments groups was statistically significant higher (98.9%) than that of the optimized attachments group (44.7%) (P=0.003).
Conclusions: Although force levels produced by both vertical and optimized attachments for tooth movement to close extraction spaces are similar, vertical attachments are more effective in controlling tooth movement than optimized attachments in closing extraction spaces.