Comparative Analysis of CAD-CAM Workflow Variations on the Marginal and Internal Gaps and Fatigue Behavior of Ceramic and Resin Composite Dental Crowns.

Objectives:  To analyze the marginal/internal gap and the fatigue behavior of crowns made of two different materials, using four combinations of a digital workflow-two intraoral scanners (IOSs) and two milling machines.

Materials and methods:  Crowns were made considering three factors: IOS (a confocal microscopy-based scanner: TRIOS 3-TR; or a combination of active triangulation and dynamic confocal microscopy: Primescan-PS), milling machines (four-axis: CEREC MC XL-CR or five-axis: PrograMill PM7-PM), and restorative material (lithium disilicate-LD or resin composite-RC) (n = 10). The bonding surface of each crown was treated and bonded to each respective glass fiber-reinforced epoxy resin die using a dual-cure resin cement. A computed microtomography analysis was performed to access marginal/internal gap. The specimens were subjected to a cyclic fatigue test (20 Hz, initial load = 100 N/5,000 cycles; step size= 50 N/10,000 cycles until 1,500 N, then if specimens survived, the step size was increased to 100 N/10,000 cycles).

Statistical analysis:  For data analysis, three-way analysis of variance and Kaplan-Meier with log-rank (Mantel-Cox) test were performed (α = 0.05).

Results:  TR resulted in a smaller axial-occlusal angle and occlusal gap, and five-axis milling resulted in a smaller marginal gap, axial-occlusal angle, and occlusal gap. Angled points and occlusal surface showed a tendency for overmilling. RC crowns displayed higher survival rates and a more pronounced topography compared with LD independently of the scanning and milling method. LD crowns produced with a five-axis milling machine resulted in higher fatigue performance and rougher topography compared with a four-axis machine.

Conclusion:  RC crowns displayed better fatigue behavior compared with LD, while LD benefited from a five-axis machine for improved survival probability.