The Under Tie Wing Area in Orthodontic Brackets: Structural Design, Biomechanics, and Clinical Implications – A Quasi-Systematic Open-Source Review

Background: The under tie wing area of orthodontic brackets represents a critical interface between bracket and ligature, yet it has not been systematically examined as a distinct anatomical and functional entity. This quasi-systematic review aims to synthesize available evidence from open-source literature on this region from engineering, biomechanical, and clinical perspectives. Methods: Four open-source databases were searched: PubMed/MEDLINE, PubMed Central, Google Patents, and the Cochrane Library (inception–March 2026). Search terms included "orthodontic bracket," "ligation," "ligature," "tie wing," "under tie," and "laceback." Inclusion criteria: original research, patents, or clinical technique descriptions addressing the under tie wing area; English; open-source access. A standardized form extracted study characteristics, engineering data, biomechanical data, clinical data, and quality indicators. Quality was assessed using adapted tools (NIH, JBI, customized patent assessment). This quasi-systematic review followed adapted PRISMA 2020 reporting principles where applicable. Narrative synthesis was performed across engineering, biomechanical, and clinical domains. Results: Forty-two studies met inclusion criteria (18 peer-reviewed articles, 16 patents, 8 clinical technique descriptions). Patent literature consistently defines the under tie wing area as a concave recess beneath tie wings with geometric parameters (curvature radii 0.010–0.030 inch, undercut depth 0.005–0.020 inch) intended to receive ligatures and reduce stress risers. Twin bracket configurations create distinct mesial and distal under tie wing regions. Biomechanical studies confirm this area as the primary load-bearing surface during ligation and torque expression, with tie wing deformation documented under clinical loads (0.02–0.05 mm separation). Friction studies confirm ligation method significantly influences resistance to sliding. Clinical literature establishes "under tie" as synonymous with laceback for space closure and anchorage reinforcement; specialized techniques include double-ligation for rotated teeth and doubled-over ligature configurations. Evidence quality was moderate overall, with strong engineering data but limited high-level clinical trials. Conclusions: This review provides, to our knowledge, among the first evidence-synthesized frameworks positioning the under tie wing area as a bridge between bracket engineering and clinical biomechanics. Structural and procedural understandings are fundamentally interconnected, with engineered geometry enabling specific clinical techniques. Key evidence gaps include quantitative characterization across commercial bracket systems and correlation of geometric parameters with clinical outcomes. This framework reframes a routinely overlooked bracket feature as a biomechanically strategic element in orthodontic therapy.