Influence of build direction, post-polymerization time, and aging on the fracture resistance and marginal and internal discrepancies of three-dimensional printed provisional crowns

To evaluate the effect of build direction, post-polymerization time, and aging on the fracture resistance, failure mode, margin quality and Marginal (MD) and Internal Discrepancies (ID), and degree of conversion of tridimensional (3D) printed provisional crowns using the liquid crystal display technique (LCD). A left mandibular first molar was prepared and scanned. After, a full crown was designed (ExoCad) and exported to the LCD-printer software. One hundred and eighty crowns were printed at two build directions (30°, 90°) and post-polymerized for different periods (15, 30, 45 min). Half of the samples were aged (ST) in distilled water (37 °C/90 days). The marginal quality of the crowns was evaluated by the Schriwer method under a stereomicroscope (40x). The replica technique was used to measure the MD and ID and measured under a stereomicroscope (10x), through 20 reference points defined in 5 regions: Occlusal (O), Cusp (CP), Axial (AX), Chamfer (CH), and Finish Line (F). After, the crowns were cemented onto the respective dies using temporary cement and submitted to compression test (ISO150, 1 mm/min, 100 kgf).The failure mode was classified by Burke’s fracture mode. The degree of conversion was evaluated through Fourier Transform Infrared Spectroscopy. The data (μm) of MD and ID and fracture resistance (N) were subjected to ANOVA (3 factors) and Tukey’s test (5%); Weibull analysis was also performed for fracture resistance data (N). For MD, ID and fracture resistance ANOVA revealed that all factors (P < .001) were significant. For aged groups, the crowns printed at 30° showed lower MD (Tukey). The O_90_30 min (172.13^A μm) and O_90_15 min (170.20^A μm) groups showed the highest ID values. Higher resistance values were observed for the 30_45 min (844.30^A N), 30_30 min (835.35^A N), and 90_30 min (820.62^A N) groups (Tukey). In the margin analysis, 98.6% of the crowns printed at 30° showed smooth margins without defects. The most prevalent fracture mode (41.7%) was Burke type 5. The degree of conversion (DC) increased with increasing post-polymerization time and aging. Printing provisional crowns at 30° provided lower crown MD and ID, as well as higher fracture resistance. A post-polymerization time of 30 min resulted in higher crown fracture resistance, while aging reduced the resistance of the crowns.