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Objective: This study aims to determine how the individual operator's level of clinical experience influences the quality of treatment delivered with the Invisalign system (Align Technology, San Jose, CA, USA) under identical conditions. Quality was assessed using the Peer Assessment Rating Index and Little Irregularity Index. Treatment duration, the number of regular/emergency appointments and the total number of aligner sets required were also defined. Methods: The initial and final models of 81 adult patients selected according to strict criteria and who underwent Invisalign Full (now Invisalign Comprehensive) treatment were 3D printed, scanned with a CS 3600 intraoral scanner (Carestream, Rochester, NY, USA) and entered into CS Model+ measuring software (Carestream) to evaluate the Peer Assessment Rating Index and Little Irregularity Index semiautomatically. Based on when their treatment began, patients were grouped into periods T0, T1 and T2 with treatment delivered by three different orthodontists, all of whom had a different level of clinical experience. All data were analysed statistically. Results: The treatment results of the different operators and for the different periods did not vary significantly. There were also no significant differences in treatment duration, or the number of regular/emergency appointments and total aligner sets. Conclusion: In the case of highly standardised structures (clinic) and processes (treatment protocols), orthodontists with comparable postgraduate training can provide the same treatment quality (treatment results) despite having different levels of clinical experience. Keywords: aligner, expertise, Invisalign, Irregularity Index, Peer Assessment Rating Index, treatment quality