Fatigue, Toughness and Compression Failure of a Printed Ceramic Hybrid

Objectives: The objective of this study was to assess the fatigue strength, fracture toughness and compressive load failure of Varseosmile Crown Plus relative to a control polymer infiltrated ceramic, Vita Enamic.
Methods: Step-stress fatigue was assessed by loading at 15N increments to failure or 245,000 cycles at 20Hz on disc shape specimens (n=10). Fracture toughness was assessed with the single edge v-notch beam method on bar shape specimens (n=6). Load-to-failure of crown shaped specimens (n=11) was assessed adhesively bonded to dentin analogs. A mandibular right first molar (#30) was prepared on a typodont, scanned and digitized to make twenty two dentin analogs (NEMA grade G10). A restoration was designed, and eleven crowns were printed or milled and then bonded to the G10 analog with self-adhesive resin cement. Results were recorded and compared between groups using two-sample t-tests.
Results: Vita Enamic demonstrated an average maximum tensile stress of 202MPa (±22.7). Varseosmile Crown Plus demonstrated an average maximum tensile stress of 164MPa (±43.8). The differences in failure load (p=.0106), number of loading cycles (p=.0004), number of steps (p=.0005) and tensile stress (p=.0264) were all statistically significant. Vita Enamic demonstrated an average fracture toughness of 1.343MPaÖm (±0.067). Varseosmile Crown Plus demonstrated an average fracture toughness of 0.878MPaÖm (±0.095). The difference in fracture toughness was statistically significant (p<.0001). The load to failure testing on crowns produced an average failure load of 2342.46N (±225.46) for Varseosmile Crown Plus and 1871.09N (±455.07) for Vita Enamic. The difference in compressive load to failure on crowns was significant (p=.008).
Conclusions: Varseosmile Crown Plus appears to demonstrate inferior fatigue resistance and fracture toughness relative to Vita Enamic. Load to failure results suggest high initial resistance to compression.