Effect of additional mechanics used in intrusion with clear aligners on the movement of mandibular incisors: a finite element analysis

Abstract Background Mandibular incisor intrusion with clear aligners is biomechanically challenging because vertical displacement may be accompanied by unwanted labiolingual displacement. This finite element study evaluated the initial biomechanical effects of miniscrew-supported elastics with tooth-bonded or aligner-mounted buttons, lingual precision cuts, and power ridges during mandibular anterior intrusion with clear aligners. Methods A three-dimensional finite element model of the mandibular anterior segment with a clear aligner was constructed from publicly available anatomical data. One control and ten experimental models were analyzed. Models 1–6 combined tooth-bonded buttons, aligner-mounted buttons, or lingual precision cuts with one or two miniscrews, while Models 7–10 added power ridges to the corresponding button configurations. A 0.2-mm intrusive displacement was prescribed at nodes in the middle–incisal region of the mandibular incisors. Elastic-assisted models used a 100-g auxiliary force, and power ridge models incorporated 1° torque activation. Initial three-dimensional displacement and von Mises stress in the roots and periodontal ligament were evaluated. Results The greatest central incisor intrusion magnitude was observed in Model 1 (0.090 mm), followed by Model 3 (0.089 mm) and Model 7 (0.088 mm). Model 6 showed the smallest central incisor intrusion magnitude (0.068 mm), similar to the control model (0.069 mm). Lateral incisor intrusion was greatest in Model 7 (0.056 mm) and lowest in Model 6 and the control model (0.044 mm). Canine displacement was extrusive in all models. Labial displacement occurred in all configurations and was greatest in Model 1 (0.093 mm). In paired comparisons (1–7, 2–8, 3–9, 4–10), power ridge incorporation reduced labial displacement while maintaining comparable vertical intrusion. The highest root and periodontal ligament stress values were observed in Model 1. Conclusion Auxiliary mechanics altered the initial displacement and stress patterns during simulated mandibular anterior intrusion with clear aligners. Tooth-bonded button mechanics with one miniscrew produced the greatest intrusion but also the greatest labial displacement and stress concentration. Power ridge incorporation reduced labial displacement in paired comparisons. These findings should be interpreted as initial biomechanical responses and require clinical validation.