OBJECTIVE: The purpose of this research was to assess the effectiveness of clear aligners in treating various types of malocclusions when compared to fixed orthodontic appliances. METHODS AND QUALITY: The following databases were searched: EMBASE (Ovid), Medline (Ovid), the Cochrane Library, Latin America and the Caribbean Literature on Health Sciences (Lilacs), Web of Science and EBMR review until October 2024. Additionally, Google scholar, PubMed were also searched for completion for including all relevant articles. No restrictions were placed on language or publication date, and only randomized controlled trials (RCTs) were included in this review. Evaluation of the potential for bias in randomized controlled trials (RCTs) was carried out with the use of the revised Cochrane Risk of Bias instrument (ROB tool 2). The primary outcome was the treatment accuracy of clear aligners vs fixed appliances and included orthodontic tooth movement in terms of anteroposterior discrepancy, transverse discrepancy, vertical discrepancy and overjet. The secondary outcomes included the effectiveness of treatment, such as duration of treatment, periodontal health, root resorption and patient satisfaction. Available data was meta-synthesized using Review Manager 5.4. RESULTS: About 21 RCT studies were selected from a total of 600 records and involved 970 participants. All 21 studies included a comparison of the effectiveness of clear aligners vs fixed appliances. About 3 of the studies were assessed to be at high risk of bias, whilst 14 of the studies were assessed to be at unclear risk of bias, and only 1 study was found to be at low risk of bias. Based on the primary outcome, there was no significant difference in the ABO objective grading scores, Little Irregularity Index and PAR scores between the fixed appliances and clear aligner treatments. Meta-analysis was only possible for secondary outcomes. The scores for plaque index (MD = -0.76, 95% CI, -1.14 to - 0.38, P = .00001), gingival index (MD = -0.61, 95% CI, -0.78 to - 0.44, P = .00001) and bleeding index (MD = -0.71, 95% CI, -0.92 to - 0.49, P <
.0001) were significantly lower in clear aligners when compared to the fixed appliances. The patients quality of life at 6 months was significantly better for clear aligners compared with fixed appliances (MD = -4.37, 95% CI, -6.93 to -1.80, P <
.0001). Clear aligners also appeared to have a better outcome for chairside time, pain and root resorption. CONCLUSION: The overall quality of evidence from the included studies was low. Both clear aligners and fixed appliances worked well in treating simple malocclusions treated on a nonextraction basis. There was no significant difference in the ABO Objective Grading System, Little Irregularity index and PAR scores between the clear aligner and fixed appliance groups. There was low quality evidence available in favor of clear aligners for periodontal health and moderate quality evidence in favor of clear aligners for quality of life. More high-quality studies evaluating clear aligner treatment for treating complex malocclusions are required.