Localised force in direct-printed TC-85DAC clear aligners after thermal deformation and recovery cycles: a single-material in vitro study

Direct-printed clear aligners fabricated from shape-memory photopolymer resins have been introduced as an alternative to conventional thermoformed aligners. Tera Harz TC-85DAC is a photocurable shape-memory resin developed for direct aligner printing. This study aimed to evaluate the localised force generated by 0.5-mm direct-printed TC-85DAC clear aligners around the maxillary right central incisor after 50 thermal deformation–recovery cycles. This single-material in vitro study evaluated 12 direct-printed TC-85DAC clear aligners. An anonymised maxillary digital model was modified to retain the maxillary right central incisor and selected posterior teeth, with a rectangular attachment placed on the labial surface of the central incisor. Baseline force was recorded as T0. Each aligner was then subjected to 50 thermal deformation–recovery cycles, with force recorded after every 10 cycles from T1 to T5. Localised force was measured using Fuji Prescale pressure-sensitive film and analysed using image-processing software. Repeated-measures analysis of variance was used for statistical analysis, and intra-examiner reliability was assessed using the intraclass correlation coefficient. The mean force ranged from 5.07 ± 0.57 N at baseline to 5.27 ± 0.51 N after 50 cycles. The highest mean force was recorded after 10 cycles, at 5.49 ± 0.64 N. No statistically significant difference was detected across the six time points, F(5, 55) = 1.076, p = 0.384. The intraclass correlation coefficient was 0.87. Under the specific in vitro conditions tested, localised force remained relatively stable across 50 thermal deformation–recovery cycles, with no statistically significant change detected. Absolute force values were likely influenced by pressure-film interposition and should therefore be interpreted cautiously. Further studies using clinically representative models and comparator materials are required.