Influence of the resin cement thickness on the fatigue failure loads of CAD/CAM feldspathic crowns

•We used a staircase method for evaluating cyclic loads-to-failure of crowns.•We compared the results from cyclic and monotonic testing.•50 μm was more favorable for the structural performance of the crowns than 500 μm.

Objectivesto evaluate the influence of the occlusal resin cement thickness on the cyclic loads-to-failure of feldspathic crowns and to compare the results to data from monotonic tests. A large range of cement thickness (50 μm and 500 μm) was tested, in order to better measure the influence of this variable.MethodsFeldspathic ceramic crowns (Vita Mark II blocks, Vita Zahnfabrik) were bonded to dentin analog dies (G10 (NEMA grade G10, International Paper), with occlusal resin cement thicknesses of 50 μm and 500 μm (Multilink Automix, Ivoclar). The dies were prepared with microchannels for water transport to the cement layer. After 96-h water storage, the specimens (n = 20) were submitted to cyclic loads (500,000 cycles at 20 Hz; initial maximum load = 40% of monotonic load, from previous data) following a staircase sensitivity design (step size = 25 N). Failure loads at 500,000 cycles were compared to monotonic failure loads (from a previous study with specimens produced by the same author, using the same materials, specimen configuration and cementation protocol).ResultsCrowns with an occlusal cement layer of 50 μm were more resistant than those cemented with 500 μm (246.4 ± 22.9 N vs. 158.9 ± 22.9 N), under wet cyclic testing conditions (p < 0.001). The fatigue failure loads were reduced compared to monotonic loads: to 37% of monotonic for 50 μm; to 53% of monotonic for 500 μm.SignificanceAn occlusal cement thickness of 50 μm was more favorable for the structural performance of feldspathic crowns than was 500 μm. Cyclic fatigue reduced failure loads well below those found under monotonic loading.