To the best of our knowledge, it was the first time that the biomechanical properties of polymer-infiltrated ceramic crowns on one-piece zirconia implants after long-term chewing simulation were examined. The present in vitro study investigated the biomechanical properties concerning surface wear and bond strength. No fractures occurred during long-term chewing simulation, and the abrasion of the crowns was macroscopically visible. There are several reasons for the fracture resistance:

Firstly, the layer thickness prescribed by the manufacturer could be strictly adhered to.

Due to the sizes of the probational implants, enough friction surfaces on the implants could be ensured and fracture and debonding was less likely.

Lastly, the occlusal force of 50 N appointed in the chewing simulator is distinctly lower than the maximum in vivo bite force of approximately 700 N [8]. 50 N roughly imitates light biting [9].

El Zhawi et al. also investigated wear and fatigue fracture of PICN crowns (Vita Enamic) but attached to composite abutments instead of zirconia implants [10]. They tested VE crowns after long- and short-term biomechanical loading. The specimens from the long-term mechanical loading group, which are most likely to be compared to our study, did not undergo any pull-off tests. In both studies, no failure occurred during or after mechanical loading. A remarkable difference between the results of both studies was seen in surface wear of the crowns which was much higher in our study despite the lower load of 50 N instead of 200 N. The materials’ characteristics may explain the relatively high wear of the crowns. Compared to composites and dentin-like materials, zirconia is a very rigid material. During chewing simulation, the implant does not move so there is only one component of the system to absorb the occlusal force which may result in high wear. Even though surface wear was macroscopically visible, abrasion may also prevent the system from catastrophic failure, namely, fractures in the implant.