Objective: To determine the optimal method to correct rotations of conical teeth using thermoplastic appliances with and without attachments. Introduction: Despite the increasing popularity of clear aligner therapy, there are still questions as to its effectiveness, efficiency, case selection and limitations. It has been reported that the full prescription for clear aligners is not expressed, and that the mean accuracy of any type of tooth movement using clear aligners is only 41% (Drake, 201213). One of the major limitations of clear aligner therapy is the correction of rotated conical teeth, especially canines and premolars (Kravitz, 200814). According to Simon et al (2014)12, mandibular premolar derotation has the lowest predictability of movement and accuracy with clear aligners. This is due to the fact that conical teeth lack interproximal undercuts, and as a result, the aligner tends to slip as derotation is attempted (Kravitz, 2008; Simon, 2014). To address this limitation, the use of resin bonded attachments, interproximal reduction, overcorrection, auxiliaries, or adjusting aligners with thermopliers has been recommended - however the effectiveness of these methods has not been well established. Materials and methods: The design of this in vitro study was prospective and experimental. A comparative study was performed to examine the effect of attachment location and the number of attachments on rotational control of conical teeth relative to control, which was rotational control with no attachments. Total rotation correction was recorded as an angular measurement after placement of each aligner, as measured on a digital scan (Ortho Insight 3D) using Geomagic Design software. Results: Results of a one-way ANOVA showed that there were no statistically significant differences between the six groups. The group with a rectangular attachment on the buccal surface had the highest overall rotational correction. Conclusion: Attachments appear to mildly improve rotational correction of the mandibular right second premolar. Increasing the number of attachments does not appear to aid rotational control, as the group with a single buccal attachment had the highest overall rotational correction. Multiple attachments, and adding attachments to adjacent teeth, appear to impede rotational correction in this study. Keywords: aligner, attachment, auxiliary, orthodontic, rotation