Survival of resin infiltrated ceramics under influence of fatigue

Purposeto evaluate influence of cyclic fatigue on two resin infiltrated ceramics and three all-ceramic crowns manufactured using CAD/CAM technology.Materials and methodsCAD/CAM anatomically shaped crowns were manufactured using two resin infiltrated ceramics (Lava Ultimate and Vita Enamic), two reinforced glass ceramic milling blocks (IPSEmpress CAD and IPSe.max CAD) and a veneered zirconia core (IPSZir CAD). IPSe.max CAD and IPSZir CAD were milled into 0.5 mm thick anatomically shaped core structure which received standardized press-on veneer ceramic. The manufactured crowns were cemented on standardized resin dies using a resin adhesive (Panavia F2.0). Initial fracture strength of half of the specimens was calculated using one cycle load to failure in a universal testing machine. The remaining crowns were subjected to 3.7 million chewing cycles (load range 50–200 N at 3 s interval) in a custom made pneumatic fatigue tester. Survival statistics were calculated and Weibull modulus was measured from fitted load-cycle-failure diagrams. Scanning electron microscopy was performed to fractographically analyze fractured surfaces. Data were analyzed using two way analysis of variance and Bonferroni post hoc tests (α = 0.05).ResultsDynamic fatigue resulted in significant reduction (F = 7.54, P < 0.005) of the initial fracture strength of the tested specimens. Zirconia showed the highest deterioration percent (34% reduction in strength) followed by IPSEmpress (32.2%), IPSe.max (27.1%) while Lava Ultimate and Vita Enamic showed the lowest percent of reduction in strength. The two types of resin infiltrated ceramics and IPSEmpress demonstrated the highest percent of fracture incidences under the influence of fatigue (35–45% splitting). None of the tested veneered zirconia restorations were fractured during testing, however, chipping of the veneer ceramics was observed in 6 crowns. The lowest percent of failure was observed for IPSe.max crowns manifested as 3 cases of minor chipping in addition to two complete fracture incidences. SEM images demonstrated the internal structure of the tested materials and detected location and size of the critical crack.ConclusionThe internal structure of the tested materials significantly influenced their fatigue behavior. Resin infiltrated ceramics were least influenced by fatigue while the characteristic strength of zirconia prevented core fracture but failure still occurred from the weaker veneer ceramic.