Abstract
Objective: This study evaluated the performance of zirconia and lithium disilicate crowns supported by implants or cemented to epoxy resin dies. Methods: Eigthy zirconia and lithium disilicate crowns each were prepared and assigned in four groups according to the crown material and supporting structure combinations (implant-supported zirconia, die-supported zirconia, implant-supported lithium disilicate, and die-supported lithium disilicate). Ten crowns in each group acted as control while the rest (n=10) underwent thermocycling and fatigue with 100 N loading force for 1.5 million cycles. Specimens were then loaded to fracture in a universal testing machine. Data were analysed using one-way ANOVA and Tukey multiple comparison test with a 95% level of significance. Results: No implants or crown failure occurred during fatigue. The mean fracture load values (control, fatigued) in newton were as follows: (4054, 3344) for implant-supported zirconia, (3783, 3477) for die-supported zirconia, (2506, 2207) for implant-supported lithium disilicate, and (2159, 1806) for die-supported lithium disilicate. Comparing the control with the corresponding fatigued subgroup showed a significantly higher fracture load mean of the control group in all cases. Zirconia showed a significantly higher fracture load mean than lithium disilicate (P=0.001, P<0.001). However, comparing crowns made from the same material according to the supporting structure showed no significant difference (P=0.923, P=0.337). Conclusion: Zirconia and lithium disilicate posterior crowns have adequate fatigue and fracture resistance required for posterior crowns. However, when heavy fatigue forces are expected, zirconia material is preferable over lithium disilicate. Zirconia and lithium disilicate implant-supported crowns cemented to hybrid abutments should have satisfactory clinical performance.
Highlights
Recent developments in computer-aided design/computeraided manufacturing (CAD/CAD) have led to the introduction of all-ceramic restorative systems with increased strength, reliability, and aesthetic capabilities [1 - 3]
Zr crowns supported by implants (n=20) Zr crowns cemented to epoxy resin dies (n=20) lithium disilicate (LD) crowns supported by implants (n=20) LD crowns cemented to epoxy resin dies (n=20)
Fracture load means of LD groups were statistically significantly lower than that of the corresponding Zr groups with P = 0.001 between Zr and LD groups supported by implant and P < 0.001 between Zr and LD groups cemented to epoxy resin dies
Summary
Recent developments in computer-aided design/computeraided manufacturing (CAD/CAD) have led to the introduction of all-ceramic restorative systems with increased strength, reliability, and aesthetic capabilities [1 - 3]. The earliest introduced alternatives, such as In-Ceram or Dicor, did not achieve the expected success because of inadequate mechanical. Both LD and Zr ceramics are used to fabricate monolithic posterior restorations. A study [13] conducted in 2015 reported that monolithic Zr was the most prescribed material for posterior single crowns (32%) while LD was the top choice for anterior single crowns (54%). These preferences are obviously linked to the mechanical properties of Zr and the aesthetic properties of LD. The use of more aesthetically pleasing ceramics in the posterior region such as LD and more recently introduced zirconia reinforced lithium silicate (ZLS) restorations is expected
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