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.