Impact of removal frequency on site-specific force profile and dimensional stability of clear aligners in relation to dental crowding

This in vitro comparative study examined the effects of high removal frequency on force generation and gap width changes in direct-printed aligners (DPAs) compared with thermoformed aligners (TFAs), considering different tooth positions and crowding conditions. A total of 104 aligners, comprising 26 pairs of DPAs and 26 pairs of TFAs, were fabricated for both crowded and noncrowded maxillary arch models. Force measurements were conducted at initial placement and after every 20 removal cycles for up to 100 cycles, whereas gap width analyses were performed at initial placement and after 100 removal cycles. Statistical analyses were performed to evaluate the force and gap width changes, with a focus on site-specific differences. DPAs demonstrated significantly lower initial forces and maintained consistent force levels over increased removal frequencies, irrespective of crowding conditions. Conversely, TFAs exhibited higher initial forces, with significant force decay over time, particularly in crowded models. DPAs also showed improved fit over time with decreased gap widths, whereas the gap widths of TFAs increased, particularly in the gingival areas. DPAs offer superior dimensional stability and force predictability over TFAs while maintaining consistent performance across different tooth positions and crowding scenarios.