The digital workflow has gained popularity in dentistry, and numerous acrylic-based photosensitive resins are now available for additive manufacturing of crowns and bridges. However, there are still many aspects to be investigated concerning the 3D printing process of restorative polymers. A review study on 3D-printed provisional materials revealed that their fracture strength tends to be higher than that of conventional acrylic restorations and comparable to their milled provisional counterparts [1]. However, regarding other physical properties, varying results were reported [1], which can be attributed to several factors including differences in printing layer thickness [2], printing orientation [3], [4], [5], equipment used [6], resin composition [2], and post-processing procedures [7], [8], [9], [10].

After 3D printing, the conversion of monomers to polymers is not complete, necessitating post-processing steps. The initial step involves washing the printed restorations in a solvent to remove residual monomers. This step is crucial to improve surface properties and also because residual monomers can have cytotoxic or allergic effects on human cells [11], [12], [13]. Isopropyl alcohol is commonly used for washing, although other solvents have been tested [8], [14], [15]. Isopropyl alcohol was shown not to affect the flexural strength of temporary resins [16], whereas tripropylene glycol monomethyl ether has been suggested to enhance accuracy and precision of polymers [8]. A study showed that an ultrasonic bath is more effective than a rotary washer or simple immersion in the solvent for eluting residual monomers [14]. Additionally, a 3-min ultrasonic or rotary washer bath with isopropyl alcohol has been found to improve cell viability compared to soaking the resin [14]. However, the effects of routinely used solvents, such as absolute ethanol, on the characteristics of 3D-printed resins are still uncertain.

Subsequent to washing, the degree of CC conversion (DC) in 3D-printed polymers is enhanced through UV light-polymerization chambers. UV polymerization time and intensity may improve DC and influence the mechanical and optical properties of the polymers [4], [9], [10], [17]. A previous study showed that increasing UV time beyond 60 min does not significantly increase the DC or affect the flexural strength with different polymerization temperatures [17]. Another study observed that the surface accuracy of an acrylic-based resin was similar when UV exposures for 15 min or 30 min were used at the same temperature [18]. However, the impact of post-curing on different 3D printing resins may vary due to their unique compositions, including initiators and monomers. Despite studies evaluating the effect of post-processing steps on surface and optical properties of 3D-printed resins [4], [8], [9], [10], [14], [15], [16], [17], [18], limited information exists on fracture toughness and gloss [19] and particularly when all tests are conducted using the same specimen across different methodologies. In addition, a comparison between short vs. longer UV exposure times could provide valuable insights for clinicians and laboratories during post-processing of additive-manufactured restorative polymers.

This study aimed to evaluate the effect of different post-processing protocols on selected properties of three commercial 3D printing restorative resins for provisional restorations. We assessed the use of absolute ethanol as an alternative to the commonly used isopropyl alcohol for washing the uncured resin. Furthermore, we investigated the possibility of optimizing the post-curing process by using shorter UV times (5 or 10 min) compared to a 30-min UV light-polymerization. The tested hypotheses were as follows: (i) the type of solvent would not influence the selected properties, and (ii) increased UV post-curing times would improve the performance of the 3D-printed polymers.