###### Abstract  
(1) Background: the aim of this study was to investigate the transmittance levels of aligners in relation to different thermoforming disks and printers after 14 days of in vitro aging. (2) Methods: the transmittance level of 18 aligners was investigated. Three printers were used to create the aligner: Carbon L1, Prodways LD20 and RapidShape D100+. Each printer produced 6 aligners: three were made of Zendura FLX material and three of Scheu Ca Pro+. Each sample was subjected to spectrophotometry analysis of its transmittance levels, for a total of 54 measurements at T0. Then, all samples were aged in vitro at a constant temperature in artificial saliva supplemented with food coloring for 14 days each. The spectrophotometry protocol was repeated, and the same 54 measurements were collected at T1 (after aging). The resulting data were analyzed and compared by means of ANOVA (\(p<0.05\)). (3) Results: all tested aligners revealed lower transmittance values after aging. Scheu Ca Pro+ aligners showed higher transparency at T0, but a significant worsening of its aesthetic at T1. On the other hand, Zendura FLX aligners presented slightly reduced transmittance levels before aging, which, however, remained more stable after 14 days, showing no significant difference. In the specific, aligners produced by Prodways LD20 printers showed better optical properties than the others, both at T0 and T1. (4) Conclusions: Differences in pre-and-post-aging optical properties of aligners are influenced by the manufacturing process. Both the thermoplastic disks and the printers, thanks to new technologies, played a positive role in the final transparency of the product, which improved in all values compared to previous studies.  
or +
Footnote †: journal: Applied  
1
Footnote 1: email: _Applied_  
Received: 8 November 2022  
Accepted: 21 November 2022  
Published: 23 November 2022  
###### Abstract  
(1) Background: the aim of this study was to investigate the transmittance levels of aligners in relation to different thermoforming disks and printers after 14 days of in vitro aging. (2) Methods: the transmittance level of 18 aligners was investigated. Three printers were used to create the aligner: Carbon L1, Prodways LD20 and RapidShape D100+. Each printer produced 6 aligners: three were made of Zendura FLX material and three of Scheu Ca Pro+. Each sample was subjected to spectrophotometry analysis of its transmittance levels, for a total of 54 measurements at T0. Then, all samples were aged in vitro at a constant temperature in artificial saliva supplemented with food coloring for 14 days each. The spectrophotometry protocol was repeated, and the same 54 measurements were collected at T1 (after aging). The resulting data were analyzed and compared by means of ANOVA (\(p<0.05\)). (3) Results: all tested aligners revealed lower transmittance values after aging. Scheu Ca Pro+ aligners showed higher transparency at T0, but a significant worsening of its aesthetic at T1. On the other hand, Zendura FLX aligners presented slightly reduced transmittance levels before aging, which, however, remained more stable after 14 days, showing no significant difference. In the specific, aligners produced by Prodways LD20 printers showed better optical properties than the others, both at T0 and T1. (4) Conclusions: Differences in pre-and-post-aging optical properties of aligners are influenced by the manufacturing process. Both the thermoplastic disks and the printers, thanks to new technologies, played a positive role in the final transparency of the product, which improved in all values compared to previous studies.  
Keywords:orthodontic aligners; transparency; spectrophotometry; materials; 3D +
Footnote †: journal: Applied