Potential Research Waste Due to Primary Studies Overlap in Orthodontics Systematic Reviews: A Five-Year Analysis.

Objective To investigate how often primary studies are duplicated across orthodontic-related SRs and to quantify overlap using the Corrected Covered Area (CCA) methodology.Methods A comprehensive search was conducted in five databases to identify orthodontic-related SRs published. Eligible SRs were identified according to the Cochrane Handbook criteria. Overlap of included studies was evaluated using the Corrected Covered Area (CCA). Initially, the three most frequently published broadly defined orthodontic topics were analyzed: palatal expansion (PE), techniques to accelerate orthodontic tooth movement (TA), and clear aligners (CA). Thereafter, the most investigated subtopics among these areas were further assessed.Results A total of 430 systematic reviews (SRs) were included. Median [Q1, Q3] RCTs per SR was 1 [0, 1] for CA, 2 [1, 4] for PE, and 3 [2, 5] for TA. CCA values indicated slight overlap across broadly defined topics: 3.0% for TA (3.6% when considering only RCTs), 2.2% for CA (1.9% when considering only RCTs), and 0.8% for PE (1.2% when considering only RCTs). In contrast, when analyzing a subsample of similar outcomes/interventions in selected subtopics, the CCA ranged from 1 to 57%.Conclusions Median RCTs per SR were between 1 and 3 on the most frequently broadly defined orthodontic topics. Although CCA values indicated slight overlap when analyzing broadly defined orthodontic topics, high to very high overlaps occurred when analyzing similar interventions/outcomes. The repeated use of the same studies in research represents a significant potential for the waste of research resources, as SRs often fail to provide clinically meaningful, updated evidence or methodological improvements.