This combination of cyclic loading in an alternating chemical and thermal conditions resulted in marked reduction of the mechanical properties of all-ceramic restorations.Дynamic fatigue studies represent a clinically relevant approach to investigate the failure mechanism of the tested restorations and they allow accurate calculation of their survival statistics. Restorations are loaded repeatedly in the presence of water with sub-critical masticatory loads reaching at an average of 500,000 cycle/year. Nevertheless, during clinical service, all-ceramic restorations are subjected to complex intra-oral forces. New hybrid ceramics are currently being tested as Ceria stabilized zirconium alumina titanium composite ceramics which offer much higher mechanical properties and fracture toughness. Strength of dental ceramics increased significantly over time from values lower than 100 MPa for feldspathic ceramics, to 175 MPa for leucite reinforced glass ceramic, over 400 MPa for lithium-disilicate reinforced glass ceramics, up to 687 MPa for sintered alumina, and finally 1200 MPa for zirconia polycrystalline ceramics.

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. The internal structure of the tested materials significantly influenced their fatigue behavior. SEM images demonstrated the internal structure of the tested materials and detected location and size of the critical crack. The lowest percent of failure was observed for IPS e.max crowns manifested as 3 cases of minor chipping in addition to two complete fracture incidences. None of the tested veneered zirconia restorations were fractured during testing, however, chipping of the veneer ceramics was observed in 6 crowns. The two types of resin infiltrated ceramics and IPS Empress demonstrated the highest percent of fracture incidences under the influence of fatigue (35вЂ“45% splitting). Zirconia showed the highest deterioration percent (34% reduction in strength) followed by IPS Empress (32.2%), IPS e.max (27.1%) while Lava Ultimate and Vita Enamic showed the lowest percent of reduction in strength.

ResultsДynamic fatigue resulted in significant reduction ( F = 7.54, P < 0.005) of the initial fracture strength of the tested specimens. Data were analyzed using two way analysis of variance and Bonferroni post hoc tests ( О± = 0.05). Scanning electron microscopy was performed to fractographically analyze fractured surfaces. Survival statistics were calculated and Weibull modulus was measured from fitted load-cycle-failure diagrams.

The remaining crowns were subjected to 3.7 million chewing cycles (load range 50вЂ“200 N at 3 s interval) in a custom made pneumatic fatigue tester.

Initial fracture strength of half of the specimens was calculated using one cycle load to failure in a universal testing machine. The manufactured crowns were cemented on standardized resin dies using a resin adhesive (Panavia F2.0). IPS e.max CAD and IPS Zir CAD were milled into 0.5 mm thick anatomically shaped core structure which received standardized press-on veneer ceramic. Materials and methodsД¬AD/CAM anatomically shaped crowns were manufactured using two resin infiltrated ceramics (Lava Ultimate and Vita Enamic), two reinforced glass ceramic milling blocks ( IPS Empress CAD and IPS e.max CAD) and a veneered zirconia core ( IPS Zir CAD). To evaluate influence of cyclic fatigue on two resin infiltrated ceramics and three all-ceramic crowns manufactured using CAD/CAM technology.

Reliasoft weibull crack