Effect of centrifugal time and speed of post-processing on the accuracy, surface characteristics and mechanical...

The study aimed to examine the effect of centrifugation time and speed on the accuracy, surface characteristics, and mechanical properties of temporary crowns printed using digital light processing (DLP). Experimental groups were centrifuged at different durations (1 and 5 min) and speeds (100, 500, and 2500 rpm), whereas the control group underwent ultrasonic cleaning with isopropanol for 5 min. Evaluation parameters included three-dimensional accuracy (trueness and precision) of the inner and margin surfaces. Surface morphology was examined using scanning electron microscopy, and roughness parameters (Sa, Sq, Sz) were quantified. Mechanical properties, including flexural strength (FS), flexural modulus, and fracture load, were evaluated using a three-point bending test. Inner surface trueness and precision improved with increased centrifugation time (P < 0.0001; P < 0.0001) and speed (P = 0.0011, P < 0.0001). Margin surface trueness and precision were influenced by centrifugation speed (P < 0.0001; P = 0.0001), but not by time (P = 0.9231; P = 0.2389). Accuracy in the 500 rpm/5-min group was comparable to the control group. Surface roughness decreased with increasing centrifugation intensity; Group F (2500 rpm for 5 min) showed lower Sa (0.287 ± 0.137 μm) and Sq (0.739 ± 0.449 μm) values. Flexural strength (FS) increased with increasing time and speed, with Group F (158.5 ± 18.73 MPa) exceeding the control group (119.8 ± 11.04 MPa; P = 0.0009). Centrifugation time and speed of post-processing significantly influenced dimensional accuracy, surface characteristics, and mechanical properties of DLP-manufactured temporary crowns. The 5-min/500 rpm and 5-min/2500 rpm conditions yielded the highest trueness and precision, whereas 2500 rpm for 5 min might provide optimal surface quality and strength.