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

STATEMENT OF PROBLEM: 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.

PURPOSE: 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.

MATERIAL AND

METHODS

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).

RESULTS

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).

CONCLUSIONS

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.