Effect of thermal cycling on the mechanical properties of conventional, milled, and 3D-printed base resin materials: a comparative in vitro study

Abstract

Purpose The purpose of this study is to evaluate the impact of thermal cycling on the mechanical properties of conventional, milled, and 3D-printed denture base materials. Methods Unigraphics NX software was used to design the sample data, after which denture base resin samples were fabricated using conventional polymerization (conventional), milling, and 3D-printing techniques. Flexural strength, Vickers hardness, and impact strength of each group of samples were evaluated both before and after 10,000 thermal cycles in distilled water at 5 °C and 55 °C (n = 8/group). Statistical analysis of the data was conducted using the Kruskal-Wallis H test, Weibull analysis and Spearman correlation analysis. Results The flexural strength and impact strength of the 3D-printed group significantly decreased after thermal cycling (P = 0.001), whereas no significant differences were observed before and after thermal cycling in the conventional or milled groups (P > 0.05). No significant correlation was found between flexural strength and impact strength for any of the groups. The Weibull modulus of 3D printed groups for both flexural and impact strength decreased after thermal cycling. The Vickers hardness of the conventional group increased significantly after thermal cycling, while Vickers hardness significantly decreased in the milled or 3D-printed groups (P < 0.05). Conclusion Compared with the conventional or milled groups, thermal cycling had a more pronounced effect on the flexural strength, Vickers hardness, and impact strength of the 3D-printed group. These findings indicate that further improvements (e.g., material composition, printing parameters and post-processing) in the mechanical properties of 3D-printed materials is necessary before clinical application.

Keywords

• Denture base materials
• Milled
• 3D-printed
• Thermal cycling
• Mechanical properties