The effect of crown material type on the fracture strength of CAD-CAM fabricated crowns

Research on the mechanical performance, particularly the fracture resistance, of recently introduced glass-composite and hybrid ceramic resin materials used with additive manufacturing (AM) and subtractive manufacturing (SM) techniques, and indicated for definitive restorations, remains limited.

The purpose of this in vitro study was to evaluate and compare the fracture resistance of AM or SM crowns in different resin-based materials through fatigue cyclic loading and load-to-fracture testing.

A standardized maxillary molar preparation was used to fabricate a zirconia master die, which was then scanned and reproduced in resin using a digital light processing (DLP) 3-dimensional (3D) printer. Two resins for AM (Pro Resins Crown X and Flexcera Smile Ultra+) and 2 resins for SM (Shofu HC and Brilliant Crios), all containing inorganic fillers (glass or ceramic), were used to fabricate identical computer-aided design (CAD) crowns (n=15). These crowns were then cemented using a standard protocol. Specimens underwent fatigue cyclic loading via 1.2 million cycles at 49 N, followed by the load-to-fracture test using a universal testing machine. Statistical analysis included 1-way ANOVA and the Tukey post hoc test (α=.05).

All crowns withstood cyclic loading. A statistically significant difference in fracture load was observed across different crowns manufactured by using different resin-manufacturing technology pairs (P<.001). SM-S group exhibited the lowest fracture resistance (2184 ±660.2 N), whereas the other 3 groups exceeded 2500 N, with no significant differences among them (P>.05).

AM crowns demonstrated fracture resistance comparable to SM crowns during and after fatigue cyclic loading and load-to-fracture tests. All crowns showed fracture resistance loads higher than previously reported clinically acceptable load values, supporting their potential for clinical use.