SmartTrack, created by Align Technologies, has a lower initial insertion force and a longer working range compared with the older EX30 material to aid orthodontic tooth movement (OTM). Objectives: To investigate the effect of SmartTrack on OTM in vivo over a 25-day period, compared with the EX30 material. Methods: Aligners made of one of the two materials and programmed for 0.25 mm of buccal movement of a maxillary incisor were used in 33 subjects (17 females and 16 males), between 18 and 40 years old, for 22 h per day for 25 days, in a randomised, blinded manner. Results: SmartTrack achieved a significantly higher mean OTM (73.1% of planned tooth movement), compared with EX30 (42.8% of planned tooth movement) by day 14. No difference in OTM occurred from day 14 to 25. Conclusion: SmartTrack achieved a higher mean OTM compared with the EX30 material over a 25-day period. Schlagwörter: aligners, orthodontics, plastic, polyurethane, thermoplasticl