Abstract
BACKGROUND/PURPOSE: Fixed lingual retainers (FLRs) often experience structural instability, including poor adaptation, and the untwisting of spiral wires, which can lead to unwanted tooth movement. Digital workflows have enhanced the appliance's accuracy. This study evaluated the water sorption (W(sp)), water solubility (W(sl)), staining resistance, and flexural performance of three-dimensionally printed resin (3DR) to determine its optimal design for FLRs. MATERIALS AND METHODS: Cylindrical 3DR specimens were immersed in distilled water and artificial saliva for 7, 14, and 30 days. W(sp) and W(sl) were measured according to ISO 4049 guidelines. Color stability was analyzed after 7 days of immersion in staining solutions using the CIEDE2000 formula. Straight 3DR specimens with various cross-sectional shapes and dimensions underwent a three-point bending test, comparing mechanical properties to multistrand stainless-steel wire (MSW). Statistical analysis was performed using a one-way ANOVA with Tukey's post-hoc test (P < 0.05). RESULTS: W(sp) and W(sl) values remained within ISO standards, with no significant changes over time. Specimens exposed to red wine, grape juice, and curry exhibited color changes exceeding the acceptability threshold of 1.77, while other solutions caused minimal discoloration. Hemi-elliptical cross-sections demonstrated significantly greater flexural strength than round designs. Although all 3DR specimens fractured before reaching the 2.0-mm deflection limit, some designs exhibited comparable bending strength to MSW while maintaining sufficient flexibility for physiological tooth movement. CONCLUSION: A hemi-elliptical 3DR design (1.0 mm thick and 2.0 mm wide) demonstrated stability in the oral environment, moderate stainability, and mechanical performance comparable to MSW, supporting its feasibility for FLRs.