The Effect Of Cyclic Loading On Mechanical Properties Of Dental Ceramics

At present PFM is the most in common used clinical types of fixedprosthesis because of the aesthetics of the ceramic and strength of metal.In China the use of non-noble PFM is a broader category, includingporcelains fused to Ni-Cr alloy and Co-Cr alloy, etc.As all-ceramic restorations similar to the natural tooth color,semipermeable and biocompatibility, All-ceramic dental restorationdeveloped into one of the major trends. The all-ceramic restoration hasmore categories, such as the glass-infiltrated ceramic, castable ceramicand CAD/CAM ceramic etc.Because the oral environment is full of complex stresses,the fixedprosthesis in place will be loaded by the different stresses, which can belead to exfoliation or fracture of porcelain.The study about the change inmechanical properties of PFM and all-ceramic restorations afterlong-term using in the mouth does not fully. With a view to understandlong-term effect of different ceramic restorationg, the experiments havethe mechanical strength tests to the restorations after cyclic loading for aperiod of time in vitro. This study discusses the effect of cyclic loading on mechanicalproperties of dental ceramic materials with simulating oral environmentin vitro. This paper discusses the change of bonding strength betweenmetal and porcelain by cyclic loading with two diffierent non-noblePFM(porcelains fused to Ni-Cr alloy and Co-Cr alloy). And this paperalso discusses the change in strength of two different glass-infiltratedceramics by cyclic loading (Al₂O₃ infiltrated ceramic and ZrO₂-Al₂O₃nanocomposites infiltrated ceramic which used decorative porcelain).In experiments porcelains fused to Ni-Cr alloy and Co-Cr alloycyclic loaded 0,10³ and 10⁴ times under simulating oral environment.Then measuring the change of bonding strength between metal andporcelain with different cyclic loading times. Analysing the twomaterials bonding strength and the change of bonding strength withdifferent loading times. Al₂O₃ infiltrated ceramic and ZrO₂-Al₂O₃nanocomposites infiltrated ceramic by using decorative porcelain cyclicloaded 0 and 10⁴ times by electric-controlled cyclic loading machineunder the simulating oral environment. Then comparing the change inthe bending strength before and after cyclic loading with universaltesting machine.And also comparing the bending strengthen of the twodifferent cramics.The result as following: 1. The bonding strength between porcelainand metal of Ni-Cr alloy porcelain was higher than Co- Cr alloyporcelain(P＜0.005). After loading 10³ times,the bonding strength of two materials were all declined with no statistical significance(P＞0.1).Whencyclic loading 104 times,the bonding strength of two materials weredeclined significantly(P＜0.05).Under the same conditions,the bondingstrength of Ni-Cr alloy porcelain is higher than Co-Cr alloy(P＜0.05).2. The strength of ZrO₂-Al₂O₃ nanocomposites infiltrated ceramicwas higher than that of Al₂O₃ infiltrated ceramic(P＜0.05).After cyclicloading,the strength of vitaαdecorative porcelain was declinedsignificantly(P＜0.05). The bending strength of two core ceramics weredelined with no statistical significance(P＞0.05)Conclusions: 1.The bonding strength of Ni-Cr alloy porcelain isbetter than Co-Cr alloy.2.After cyclic loading, The bonding strength of Ni-Cr alloyporcelain and Co-Cr alloy porcelain are declining significantly. And thebonding strength also declined with the cycle times increased. Under thesame loading conditions, the bonding strength of Ni-Cr alloy porcelainis more than Co-Cr alloy.3.The bending strength of ZrO₂-Al₂O₃ nanocomposites infiltratedceramic with zirconia toughening is better than that of Al₂O₃ infiltratedceramic.4.After cyclic loading, the two-tier structure of Al₂O₃ infiltratedceramic and ZrO₂-Al₂O₃ nanocomposites infiltrated ceramic arechanging with no statistical significance in the bending strength. But thestrength of Veneering porcelain decline significantly. It show that veneeering porcelain may occur exfoliation or fracture after a period oftime using.