Biomechanical force profiles and force decrease of direct printed versus thermoformed aligners with different trimlines: an in vitro analysis

Background This in-vitro study aimed to evaluate and compare the biomechanical force profiles of thermoformed and direct-printed aligners with different gingival trimlines during facial and palatal translation of a maxillary central incisor. Methods A 3D-printed model with a mounted central incisor was used to simulate 0.25 mm of bodily movement. Forces were recorded in three axes (Fx, Fy, Fz) using a multi-axis force sensor. Three aligner types (thermoformed with straight trimline: TFA S , and direct-printed with either straight: DPA S or garlanded trimline: DPA G ) were tested ( n = 10 each). Vertical, transverse, and sagittal force components and their decrease were analyzed. Forces were recorded over 60 min to characterize initial force delivery and early stress relaxation under standardized in vitro conditions. Results Thermoformed aligners exhibited the highest sagittal forces during facial movement (Fx − 0.70 N), while DPA G demonstrated significantly lower forces (Fx − 0.25 N; p < .001). During palatal translation, DPA S reached peak forces of 0.57 N, whereas DPA G showed lower, more controlled forces ( p < .001). Vertical forces (Fz) were significantly higher in TFA S (− 0.10 N), while DPA remained near zero or slightly extrusive ( p < .001). Conclusions In this in vitro model, DPA, particularly DPA G , showed lower sagittal force values and smaller vertical force components. In the first 60 min, DPA showed a pronounced early force decrease. Longer observation periods are required to describe force behavior beyond the initial seating phase.