Effectiveness of Clear Aligners Versus Fixed Appliances in Correcting Mild to Moderate Crowding

Background: Fixed orthodontic appliances are widely regarded as the standard of care for managing dental crowding, yet their use is often limited by discomfort, aesthetic concerns, and oral hygiene challenges. Clear aligners have emerged as a patient-centered alternative, but high-quality comparative evidence in adults with mild to moderate crowding remains limited. Objective: To compare the effectiveness, treatment duration, pain experience, and patient satisfaction of clear aligners versus fixed appliances in adults with mild to moderate mandibular anterior crowding. Methods: In this parallel-group randomized controlled trial, 120 adults (18–35 years) with baseline Little’s Irregularity Index (LII) of 3–7 mm were allocated to clear aligner therapy or fixed pre-adjusted edgewise appliances. Standardized non-extraction protocols were used in both groups. Primary outcome was change in LII from baseline to treatment completion. Secondary outcomes included treatment duration, pain at 14 days (10-cm visual analogue scale, VAS), overall satisfaction at completion (10-item VAS composite), and early complications, including enamel decalcification and 3-month relapse. Data were analyzed using independent-samples t-tests and chi-square or Fisher’s exact tests with 95% confidence intervals. Results: Mean LII reduction was similar between clear aligners and fixed appliances (4.30 ± 0.88 vs 4.39 ± 0.91 mm; mean difference −0.09 mm, 95% CI −0.40 to 0.22; p = 0.56). Treatment duration was significantly shorter with aligners (8.4 ± 1.7 vs 12.1 ± 2.3 months; mean difference −3.7 months, 95% CI −4.42 to −2.98; p < 0.001). Pain at 14 days was lower (3.4 ± 1.2 vs 6.2 ± 1.8; p < 0.001), and satisfaction higher (9.1 ± 0.7 vs 7.4 ± 0.8; p < 0.001) in the aligner group. Enamel decalcification occurred in 0% of aligner patients and 8.3% of fixed appliance patients (p = 0.02), while early relapse rates were low and comparable. Conclusion: In adults with mild to moderate crowding, clear aligners achieved alignment comparable to fixed appliances but with shorter treatment duration, less early pain, higher satisfaction, and fewer enamel decalcification events, supporting their use as a patient-centered alternative in appropriately selected cases.