Fused filament fabrication (FFF): influence of layer height on forces and moments delivered by aligners—an in vitro study

Abstract

Objectives To investigate the effect of layer height of FFF-printed models on aligner force transmission to a second maxillary premolar during buccal torquing, distalization, extrusion, and rotation using differing foil thicknesses. Materials and methods Utilizing OnyxCeph3™ Lab (Image Instruments GmbH, Chemnitz, Germany, Release Version 3.2.185), the following movements were programmed for the second premolar: buccal torque (0.1–0.5 mm), distalization (0.1–0.4 mm), extrusion (0.1–0.4 mm), rotation (0.1–0.5 mm), and staging 0.1 mm. Via FFF, 91 maxillary models were printed for each staging at different layer heights (100 µm, 150 µm, 200 µm, 250 µm, 300 µm). Hence, 182 aligners, made of polyethylene terephthalate glycol (PET-G) with two thicknesses (0.5 mm and 0.75 mm), were prepared. The test setup comprised an acrylic maxillary model with the second premolar separated and mounted on a sensor, measuring initial forces and moments exerted by the aligners. A generalized linear model for the gamma distribution was applied, evaluating the significance of the factors layer height, type of movement, aligner thickness, and staging on aligner force transmission. Results Foil thickness and staging were found to have a significant influence on forces delivered by aligners, whereas no significance was determined for layer height and type of movement. Nevertheless, at a layer height of 150 µm, the most appropriate force transmission was observed. Conclusions Printing aligner models at particularly low layer heights leads to uneconomically high print time without perceptible better force delivery properties, whereas higher layer heights provoke higher unpredictability of forces due to scattering. A z-resolution of 150 µm appears ideal for in-office aligner production combining advantages of economic print time and optimal force transmission.

Effectiveness of different intrusion modes of maxillary anterior teeth with mini-implants in clear aligner treatment: a three-dimensional finite element analysis

“…At present, the research methods in oral biomechanics include clinical studies [ 6 , 11 ], in vitro studies [ 21 ] and FEA studies [ 12 , 17 ]. Due to the complex structure of human tissue, there are many factors influencing the intrusion effects of maxillary anterior teeth, such as the labiolingual angulation [ 22 ] and crown-root ratio [ 22 ] of maxillary anterior teeth, alveolar bone height [ 17 , 22 ], intrusive force value [ 6 , 12 ] and patient compliance. Therefore, it is challenging to control variables in clinical studies.…”