Clinical, biomechanical, and digital factors associated with refinement after the first series of clear aligners: A systematic review.

OBJECTIVES: To systematically identify, appraise, and synthesize the evidence on clinical, biomechanical, and digital factors associated with refinement-related outcomes after the first series of clear aligners. METHODS: This systematic review was conducted according to PRISMA 2020 and followed the Synthesis Without Meta-analysis (SWiM) guidance. Electronic searches were performed in PubMed/MEDLINE, Embase, Scopus, Web of Science, Cochrane Library, and Google Scholar. Clinical studies involving patients treated with clear aligners were included when they reported refinement, additional aligners, finishing aligners, midcourse correction, refinement plans, planned-versus-achieved discrepancies, or treatment-continuation outcomes after the first aligner series. Risk of bias was assessed using design-specific tools according to study design. Owing to heterogeneity in definitions, outcomes, units of analysis, and measurement methods, a structured narrative synthesis was performed. RESULTS: Twenty studies were included. Refinement-related outcomes were heterogeneously defined, including refinement aligners, additional aligners, finishing phases, refinement plans, midcourse correction, and first-refinement scans. The evidence suggested that refinement burden may be associated with malocclusion complexity, extraction treatment, interproximal reduction strategies, severe spacing, larger correction sequences, and movement-specific limitations. Rotations, intrusion, vertical correction, transverse expansion, and selected anterior movements showed reduced predictability. Remote monitoring appeared to reduce appointment burden but did not consistently reduce refinement need. Evidence for adjunctive technologies and machine-learning prediction remained preliminary. CONCLUSIONS: Refinement after the first aligner series should be interpreted as a multifactorial clinical outcome rather than a uniform finishing procedure. Standardized definitions and prospective studies are needed to clarify patient-, tooth-, movement-, and treatment-plan-level predictors. PROSPERO REGISTRATION NUMBER: CRD420261416896.