key: cord-0014241-1t0icobq authors: Maspero, Cinzia; Tartaglia, Gianluca Martino title: 3D Printing of Clear Orthodontic Aligners: Where We Are and Where We Are Going date: 2020-11-18 journal: Materials (Basel) DOI: 10.3390/ma13225204 sha: cd6970d806396a4ffda76978d07c561cf5383f87 doc_id: 14241 cord_uid: 1t0icobq nan A study by Jindal et al. [28] presented a successfully 3D printed 0.75 mm thick clear aligner using Dental Long Term (LT) ® clear resin (Form Labs, Somerville, MA, USA) and compared its mechanical and geometrical properties to a conventionally manufactured thermoformed Duran clear dental aligners. Authors suggested that 3D printed resin-cured clear dental aligners are more suitable because they have better geometric accuracy and mechanical resistance. Dental LT resin is an approved Class IIa biocompatible material with high resistance to fracture and it is ideal for hard splints, retainers, and other rigid direct-printed long-term orthodontic appliances. Its use for a direct 3D printing of clear aligner was not described before, and authors are omitting the major limitation of their study-the lack of clinical data to evaluate performance of Dental LT resin and its durability during the use by patients. The cytotoxicity of directly 3D printed clear aligners from three different materials was also studied [29] . Three different aligners were compared: printed using Accura 60 ® SLA (3D Systems, Rockhill, South Carolina), Dental LT ® clear resin (Form Labs, Somerville, MA, USA) and Invisalign ® (Aligntech, San Jose, CA, USA). Similarly, Dental LT resin and Accura 60 ® SLA are not approved for direct printing of 3D aligners and were not previously tested and described for this purpose. The study confirmed that Invisalign ® material was the least cytotoxic, followed by Dental LT ® and Accura 60 ® . However, to our knowledge, Invisalign ® aligners are not directly 3D printed. The lack of clinical data is similarly the main limitation of this study. In early 2018, EnvisionTEC Inc. announced launch of E-Ortholign, a new material for the direct 3D printing of clear thermoformed aligners [27, [30] [31] [32] . This clear resin is marketed as biocompatible, stable, flexible and strong material for the direct 3D printing of esthetic retainers [30, 33, 34] . Nowadays, there is no marketed and approved resin suitable for the direct 3D printing of clear aligners. Direct 3D printing of aligners offers several advantages over conventional fabrication: edges are softer and do not need trimming or smoothing; undercuts analysis is digitally defined; intra-aligner thickness is customizable, which may reduce the need of attachments, reducing the transparency of clear aligners [35] . Cone-beam computed tomography and three-dimensional orthodontics. Where we are and future perspectives Adult patients' adjustability to orthodontic appliances. 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