Enamel wear and fatigue resistance of 3D printed resin compared with lithium disilicate.

Statement of problem: The effect of 3-dimensional (3D) printed crown materials with lower flexural strength but higher ductility than lithium disilicate on enamel wear and fatigue resistance is unknown.

Purpose: The purpose of this in vitro study was to compare the enamel wear and fatigue resistance of a 50% filled 3D printed crown material with lithium disilicate.

Material and methods: Disks of a 3D printed crown material (Ceramic Crown; SprintRay Inc) and lithium disilicate (IPS e.max CAD; Ivoclar AG) (n=8) were tested for wear in a custom Alabama wear testing device which applied a 20-N load and 2-mm horizontal slide. The test was run for 400 000 cycles at 1 Hz in a 33% glycerin solution. Cusps of extracted human molars were used as the antagonists. The volumetric wear of the restorative material and enamel antagonists were measured every 100 000 cycles using a profilometer. Worn specimens were examined with a scanning electron microscope. Human molars were prepared for occlusal onlay preparations, and 1.2-mm 3D printed (Ceramic Crown) or lithium disilicate (IPS e.max CAD) restorations (n=10) were bonded to the teeth with resin cement. Restorations were subjected to 2 million cycles of fatigue loading (50 N, 1 Hz) in water against a Ø7.8-mm steel ball. Restorations were monitored for cracks every 100 000 cycles with transillumination and every1 million cycles with microcomputed tomography (µCT). After fatigue, specimens were fractured in a load-to-failure test. Fractured specimens were examined with µCT. Statistical analyses were performed with 2-way mixed ANOVAs and a t test (α=.05).

Results: The wear and opposing enamel wear of lithium disilicate was greater than the 3D printed material at every interval of cycles tested (P<.001). None of the restorations showed signs of internal cracks up to 2 million cycles of fatigue. No statistical difference was found in the load-to-failure fracture load of the 3D printed (2574 ±303 N) or lithium disilicate (2396 ±277 N) restorations (P=.110).

Conclusions: For the conditions tested, the 3D printed crown material demonstrated less wear than lithium disilicate and created less opposing enamel wear. All the occlusal onlay restorations survived 2 million cycles of fatigue at a 50-N load without signs of cracks. These results provide some support for the use of these restorations at 1.2-mm occlusal thickness when bonded with a resin cement.