Clear aligner therapy: a scoping review of treatment prediction, clinical effectiveness, and limitations.

Background: Clear aligner therapy (CAT) has significant predictability limitations, particularly in complex malocclusions. This scoping review maps discrepancies between digitally predicted and clinically achieved tooth movements across a broad evidence base. Objectives: To map the available evidence on the accuracy of CAT tooth movements and identify gaps in the current literature to guide future research. Eligibility criteria: Studies evaluating the accuracy or predictability of CAT tooth movements using quantitative methods (intraoral scanning with 3D metrology, cone-beam computed tomography, or cephalometric analysis) were eligible. Eligible designs included retrospective and prospective cohort studies, randomised controlled trials, and systematic reviews, published from 2001 up to June 2026 with no language restriction. In-office aligner systems and non-proprietary aligner systems were excluded from this review. Sources of evidence: PubMed and Scopus were searched in April 2026 and updated in June 2026, supplemented by manual reference list searching. Charting methods: Data were extracted onto a pre-piloted standardised form. A descriptive narrative synthesis was performed, organised thematically by movement type. Results: Of 6,865 records retrieved after removal of duplicates, 764 were selected after screening, 356 underwent full-text review, and 119 studies met inclusion criteria, including 70 retrospective studies, 12 prospective studies, and 4 RCTs. Early-generation Invisalign studies report approximately 50% mean accuracy. Rotational shortfalls averaged approximately 5°; torque was under-expressed at 35%-58%; overbite reduction achieved 28%-55% accuracy; arch expansion (73%-88%) predominantly produced tipping rather than bodily movement. Anterior open bite correction reached 58%-90% accuracy, while incisor intrusion was limited to 33%-53%. Based on limited studies, refinements were required in over 50% of cases and 17.2% necessitated conversion to fixed appliances. Conclusions: Available evidence, predominantly retrospective Level III-IV studies, supports over-correction strategies of 50%-100% for intrusions, 5°-15° for rotations and torque, and 1-2 mm for arch expansions; however, these estimates derive from heterogeneous, Invisalign-focused research and should not be applied as universal benchmarks. CAT is most reliable for anterior open bite correction under 3 mm. Hybrid approaches and informed consent regarding potential fixed appliance conversion are advisable for complex malocclusions. Adequately powered RCTs are needed to validate current clinical protocols.