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Objective The aim of this study is to assess if low-level laser therapy (LLLT) alleviates pain after the placement of orthodontic alignment archwire and if there could be a specific indication for the usage of LLLT according to the amount of dental crowding. Materials and Methods Ninety subjects were included and randomly assigned to the tested group (orthodontic treatment and LLLT), placebo group (orthodontic treatment and simulated LLLT), and control group (orthodontic treatment only). Inclusion criteria are age between 13 and 30 years, completely erupted mandibular teeth, and lower crowding of ≥3 mm. Exclusion criteria are spaces or diastema in the lower arch, ectopic teeth, treatment plan including extractions or the use of auxiliary devices, and previous orthodontic treatment. Patients reported the pain experienced by using a numeric rating scale, ranging from 0 to 10, at specific time intervals, that is, 2 hours, 6 hours, 24 hours, and from day 2 to 7. Kruskal–Wallis H Test was used to assess differences in the maximum pain and pain experienced at each time interval among the three groups and in the maximum pain reported among subjects with different degree of crowding. Results The final sample consisted of 84 patients, 41 male and 43 female patients, with a mean age of 16.5 ± 2.8 years. The pain experienced at each time interval and the maximum pain score were significantly lower in the tested group, whereas no differences were found between control and placebo groups. Moreover, no differences were found in the pain experienced among subjects with mild, moderate, and severe incisor crowding in all groups. Conclusions LLLT is effective in alleviating the intensity and duration of pain experienced by patients after the engagement of alignment archwire. However, there is no specific indication for the usage of LLLT according to the amount of crowding.