OBJECTIVE: To compare the three-dimensional root parallelism (mesiodistally and buccolingually) between orthodontic therapy with the Invisalign clear aligners (CA) and fixed appliances (FA) among the first premolar-extraction patients, using cone-beam computed tomography (CBCT). MATERIALS AND METHODS: Sixty participants with similar American Board of Orthodontics discrepancy index scores as baseline characteristics were included and divided into CA and FA groups (30 per group). Post-treatment mesiodistal and buccolingual root parallelisms were analysed through CBCT using Invivo 6.0.3 software. Descriptive and analytical statistics were performed with a p <
0.05, considered statistically significant. RESULTS: Mesiodistal dental root parallelism in the U1-U2 and L1-L2 pairings between CA and FA groups were found to be significantly different with inferior parallelism in the CA group (p <
0.05). Conversely, the U3-U5 and L5-L6 pairings exhibited superior parallelism in the CA group (p <
0.05). However, other pairings, including U1-U1, U2-U3, U5-U6, U6-U7, L1-L1, L2-L3, L3-L5, and L6-L7, showed no significant differences in mesiodistal parallelism between groups (p >
0.05). Regarding the buccolingual dental root parallelism, significant differences were also noted in the U5-U6 and L5-L6 pairings with superior parallelism in the CA group (p <
0.05). However, in the U1-U1, U2-U3, U3-U5, U6-U7, L1-L1, L2-L3, L3-L5, and L6-L7 pairings, no significant differences in buccolingual parallelism were observed (p >
0.05). CONCLUSION: In this study, our findings indicate that in cases involving the extraction of first premolars, Invisalign clear aligners may offer comparable or even superior three-dimensional root parallelism compared to fixed orthodontic appliances, with the exception of the mesiodistal dimension in upper and lower incisors, where their performance is less effective.