Mechanical, optical and surface properties of 3D-printed and conventionally processed polyamide 12.

Background: Polyamide-based materials are suitable for three-dimensional (3D) printing.

Objectives: The aim of the study is to examine the impact of aging on the mechanical, surface and optical properties of polyamide 12.

Material and methods: A total of 116 specimens were examined, comprising 58 conventionally processed polyamide 12 (PA12_C) specimens and 58 3D-printed polyamide 12 (PA12_3D) specimens. The modulus of elasticity was determined before and after mechanical and thermal aging with 1,000, 3,000, 9,000, and 1,000, 3,000 and 7,000 cycles, respectively. The surface roughness (Ra), Ra change (ΔRa) and color change (ΔE) were examined before and after chemical aging (1, 12 and 36 days, with artificial saliva, coffee and red wine) using surface profilometry and color spectroscopy. The Kruskal-Wallis test, Mann-Whitney U test and Bonferroni-Holm correction were employed, with a significance level of p < 0.05.

Results: Before and after mechanical aging, the modulus of elasticity for PA12_3D showed significantly higher values (761 MPa and 747 MPa, respectively) in comparison to PA12_C (515 MPa and 455 MPa, respectively; adjusted p < 0.001). Additionally, before and after thermal aging, the modulus of elasticity for PA12_3D exhibited significantly higher values (833 MPa and 705 MPa, respectively) compared to PA12_C (516 MPa and 458 MPa, respectively; adjusted p < 0.001). The Ra of PA12_3D was higher than that of PA12_C at the baseline (0.41 μm compared to 0.31 μm, respectively), and remained higher during the aging process. The ΔRa values were small for both groups. The ΔE was significantly higher for PA12_3D compared to PA12_C after 12 days (6.2 (PA12_3D) compared to 4.8 (PA12_C), adjusted p = 0.003) and 36 days of storage in red wine (8.2 (PA12_3D) compared to 6.8 (PA12_C), adjusted p = 0.003). After 36 days of coffee storage, the observed changes were found to be statistically significant (8.6 (PA12_3D) compared to 6.7 (PA12_C), adjusted p < 0.001).

Conclusions: The 3D-printed polyamide 12 demonstrated higher rigidity, Ra and discoloration compared to the conventionally processed polyamide 12. However, not all of the observed parameter differences were significant or clinically relevant. These differences may impact clasp retention, biofilm formation and aesthetic appearance. Nevertheless, the clinical efficacy of 3D printing may be significant.