Effect of thickness and aging on key mechanical properties of 3D-printed crowns

With the growing demand for additively manufactured resin restorations, this study investigated the effects of cleaning time and thermal aging on key mechanical properties of digital light processing (DLP)-fabricated resins for permanent crowns, and assessed how crown thickness (1.25, 1.50, 1.75, and 2.0 mm) influences fracture load. Specimens were ultrasonically cleaned in isopropanol for 180, 210, and 240 s and post-cured for 30 min, and either stored in water (37°C, 24 h) or aged for 10,000 thermal cycles (5-55°C). Vickers hardness, flexural strength, shear bond strength, fracture load, and fit were assessed. Cleaning time affected only Vickers hardness, while thermal aging resulted in significantly degraded mechanical properties. Fracture load increased with thickness but decreased after aging, from 1240.3 ± 261.4 N to 955.3 ± 145.3 N for 2.0 mm crowns. Marginal gaps ranged from 54.09 to 79.43 µm, and internal gaps from 46.62 to 101.55 µm, and both decreased after aging. Crown thickness and thermal aging significantly impacted mechanical properties, whereas cleaning time had minimal impact. For durability and resistance to maximum clenching forces, a 2 mm thickness is recommended. These findings offer valuable insights into optimal post-processing and design to enhance the clinical longevity of DLP-fabricated crowns.