Additive manufacturing or 3D printing is becoming increasingly popular in the daily clinical practice due to its versatility, lower cost, and adequate accuracy when compared with traditional subtractive manufacturing (or milling) [1,2,3,4,5,6,7,8]. The use of 3D printers allows the conversion from a digital treatment plan to an analogic/real life outcome, resulting in a full integration with the digital workflow [2,3,4,5,6,7,8,9,10,11,12,13].

Most 3D printers used in dentistry are based on Stereolithography (SLA) or Digital Light Processing (DLP). While in SLA, a laser beam cures each individual layer, in DLP, a digital projector screen is used to project the entire layer, resulting in faster printing times. After cured, samples are washed, usually in 99% isopropyl alcohol, followed by post-curing in various combinations of curing unit, time, temperature, immersion in media, among others [6, 7, 9].

Resins currently available on the market for preparing 3D-printed dental restorations are considered biologically safe [13]. Nevertheless, this safety depends on the 3D printing workflow as resins for 3D printing contain more photo-initiators when compared with conventional resin composites [1, 14, 15]. This results in the presence of unreacted photo-initiators and monomers after the printing process, which may be minimized during the post-polymerization processes [1, 14, 15].

With the rapid increase in the number of available 3D printers and post-polymerization devices, along with a lack of standardization about printing workflows, there is increasing concern about the influence of the different components of the 3D printing workflow in the properties of 3D printed parts [1,2,3,4,5, 7,8,9,10,11,12,13,14,15]. This concern becomes even more critical considering that there are several 3D printers available in the market, ranging from very affordable, open-platform, hobby-like 3D printers, to professional grade 3D printers with closed-platform and completely validated workflows [13,14,15].

Literature reports both printing parameters and post-processing methods influence the physical–mechanical properties of 3D printed parts [2, 3, 6, 9, 13, 14, 16,17,18,19,20,21,22,23]. Nevertheless, most studies used open-platform 3D printers, different curing chambers with different curing times, in a not fully validated workflow. This lack of standardization prevents the understanding of how, or if, the 3D printer parameters and the post-polymerization parameters could influence the final properties of a 3D printed part. Therefore, it is unclear whether different 3D printers could influence the physical–mechanical properties of 3D printed parts if an adequate post-curing protocol were to be used.

In order to identify if the 3D printer would impact the physical–mechanical properties of 3D printed resins, this study evaluated the flexural strength and color stability of 2 resins for 3D printing, considering 2 situations: a fully validated 3D printer + different post-curing methods compared to no previous 3D printing + different curing methods. The null hypothesis tested was that there would be no difference between 3D printed and non-3D printed parts after the post-polymerization processes.