Objectives: Despite the widespread adoption of clear aligner therapy (CAT), its effectiveness in managing rotations remains debated. This systematic review aims to evaluate rotational accuracy in adults and the influence of treatment variables—such as attachments, interproximal reduction (IPR), and staging. Methods: Following PRISMA guidelines, seven databases and two grey literature sources were searched up to July 2025. Eligible studies assessed rotational accuracy in patients treated exclusively with clear aligners, using 3D digital model superimposition. Primary outcomes included percent accuracy, lack of correction (LC), or mean absolute error (MAE). Risk of bias (RoB 2, ROBINS-I) and certainty of evidence (GRADE) were assessed. Results: Twelve studies (one RCT, eleven non-randomized) were included, showing wide heterogeneity in aligner systems, tooth types, outcome measures, and adjunctive strategies. Reported accuracy ranged from 36% to 85%, averaging around 65%. LC values varied from 0.7° to 4.5°, and mean MAE was about 2.3°. Incisors and molars showed higher predictability, whereas maxillary canines and premolars remained the least reliable. Attachments and IPR were widely used, but their effectiveness was inconsistent. Staging protocols were generally set at 2°/aligner and most studies adopted 7–14-day wear schedules. Nearly all investigations showed moderate-to-serious risk of bias, and certainty of evidence was rated low to moderate. Conclusions: CAT shows limited yet improving predictability in rotational movements, with performance strongly influenced by tooth morphology and staging. Attachments, IPR, and overcorrections may contribute but lack consistent validation. Given the low certainty and high risk of bias of current evidence, these findings should be interpreted cautiously. Well-designed RCTs with standardized protocols are required to develop reliable clinical guidelines.

Background/Objectives: Skeletal Class II malocclusion due to mandibular retrusion is frequently treated with functional appliances, yet their impact on temporomandibular joint (TMJ) structures, specifically the articular disc, remains debated. This systematic review aimed to critically assess quantitative morphological and positional TMJ changes (disc, condyle and glenoid fossa) evaluated with CBCT or MRI in growing skeletal Class II patients treated with functional appliances and to explore whether these changes are associated with the onset or prevention of temporomandibular disorders (TMDs). Methods: The review followed PRISMA guidelines and was registered in PROSPERO (CRD420251028803). Electronic searches were performed in PubMed, Scopus, Web of Science, Cochrane Library, and Embase from inception to December 2025, complemented by manual screening. Inclusion criteria comprised controlled clinical studies in patients aged 8–16 years with skeletal Class II malocclusion due to mandibular deficiency, treated with removable or fixed functional appliances, with pre- and post-CBCT/MRI quantitative TMJ assessment. Risk of bias was evaluated using RoB 2 (RCTs) and ROBINS-I (non-randomized studies); overall certainty was appraised with GRADE. Results: From 937 records, 8 studies met the inclusion criteria. Articular disc outcomes were reported in fewer studies: disc position/morphology was generally stable, and when changes were observed they were favourable (partial improvement/normalization in selected cases). Importantly, no included study reported new treatment-induced disc displacement or new-onset TMD symptoms at the end of treatment. Across studies, the most consistent findings concerned condylar adaptations, commonly described as anterior and/or superior positional changes and remodelling of the condyle–fossa unit. Evidence certainty was limited by heterogeneity and methodological constraints, resulting in low to very low confidence for several outcomes. Conclusions: Functional appliance therapy in growing skeletal Class II patients may be associated with TMJ adaptations, predominantly involving the mandibular condyle, while limited available data may suggest disc stability and no reported short-term clinical TMD onset in included controlled studies. However, due to the limited and heterogeneous evidence base, these findings should be interpreted cautiously, and well-designed prospective studies with standardized 3D imaging outcomes and longer follow-up are needed, particularly for disc-specific endpoints.