Comparison of residual monomer content in permanent crown materials fabricated by additive manufacturing at different thicknesses

With the development of the digital world today, the demand for faster and more esthetic solutions has increased. In dentistry, the time-consuming nature of conventional prosthesis fabrication and the requirement for technical expertise have brought alternative production methods to the forefront. Following a digital workflow with 3D printing technology, fixed restorations can be designed and manufactured using scans obtained from patients. Thanks to 3D printers, more personalized and precise fixed restorations can be achieved. However, further research is needed regarding the long-term performance and biocompatibility of restorations produced with this method. In this study, different permanent crown resins used in dentistry for the fabrication of permanent crown restorations with 3D printers were investigated, while Cerasmart Nano Hybrid Ceramic Block material was included as the control group. A total of six different materials and four subgroups for each material were defined. Each group contained n=8 specimens, yielding a total of 24 groups and 192 specimens. Samples of two different thicknesses (2 mm and 4 mm) were produced from each brand and immersed in an ethanol/water solution for either 1 week or 1 month. The eluates obtained were analyzed for monomer release using an HPLC device. For intergroup comparisons of the parameters, the Kruskal–Wallis test was used, while Dunn's test was applied to identify the groups responsible for the differences. For pairwise comparisons based on thickness and time, the Mann–Whitney U test was performed. The highest mean release value of Bis-GMA was measured in the Bego – 4 mm – 1 month group (360.16 ± 133.71 ppm), while the lowest was in the DentaFab – 2 mm – 1 week group (7.88 ± 3.1 ppm). For TEGDMA, the highest mean release was observed in the Bego – 4 mm – 1 month group (1250.74 ± 92.02 ppm), and the lowest in the DentaFab – 2 mm – 1 week group (12.67 ± 3.69 ppm). The highest mean release value of UDMA was in the Bego – 2 mm – 1 month group (20.03 ± 4.43 ppm), whereas the lowest was in the Formlabs – 2 mm – 1 week group (1.84 ± 0.97 ppm). For HEMA, the highest mean release was measured in the Bego – 2 mm – 1 month group (6.85 ± 5.33 ppm), while the lowest was in the DentaFab – 2 mm – 1 week group (0.47 ± 0.48 ppm). In the Bego group, the monomer that showed the most relative increase with thickness was TEGDMA, and the fastest release with time was observed for UDMA. In the NextDent group, TEGDMA showed the greatest relative increase with thickness as well as the fastest release with time. In the Formlabs group, HEMA showed the most relative increase with thickness, while UDMA had the fastest release with time. In the Saremco group, Bis-GMA showed the greatest relative increase with thickness, whereas TEGDMA exhibited the fastest release with time. Additionally, the 1-month HEMA release value was the only parameter that decreased with increasing thickness. In the DentaFab group, HEMA showed the most relative increase with thickness, while Bis-GMA demonstrated the fastest release with time. It was determined that residual monomer release varies depending on the brand of permanent crown resin used, the storage period, and the material thickness. The study showed that UDMA and HEMA were the monomers with the lowest release, remaining below toxic thresholds and therefore considered clinically safe. In contrast, Bis-GMA (Bego and Formlabs) and TEGDMA (Bego) exceeded toxic limits in some groups, highlighting the importance of considering potential biological risks in clinical applications of these materials and underlining the need to take these findings into account when selecting alternative materials. Keywords: 3D printing, permanent crown resin, high-performance liquid chromatography, residual monomer