In Vitro Fatigue and Fracture Load of Monolithic Ceramic Crowns Supported by Hybrid Abutment

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.

Fatigue and Fracture Behavior of Cryogenic Materials Applied to LNG Fuel Storage Tanks for Coastal Ships

The aim of this study is to investigate the applicability of automatic plasma arc welding (PAW) to cryogenic materials used in liquefied natural gas (LNG) fuel storage tanks based on experimental data. The mechanical properties of the materials were tested at room and cryogenic temperatures to investigate the fatigue and fracture performances of weld joints made by PAW. In addition, the influence of welding parameters on the welded joints such as material types and temperature were considered in this experimental study. Based on the results obtained by this experimental study, it was observed that the experimental results of all materials at room and cryogenic temperatures satisfied all the requirements of each mechanical test. Finally, we propose the experimental results of PAW that can be used in the structural design of LNG fuel storage tank applications.

Structural fatigue and fracture of shape memory alloy actuators: Current status and perspectives

Shape Memory Alloy (SMA)-actuators are efficient, simple, and robust alternatives to conventional actuators when a small volume and/or large force and stroke are required. The analysis of their failure response is critical for their design in order to achieve optimum functionality and performance. Here, (i) the existing knowledge base on the fatigue and overload fracture response of SMAs under actuation loading is reviewed regarding the failure micromechanisms, empirical relations for actuation fatigue life prediction, experimental measurements of fracture toughness and fatigue crack growth rates, and numerical investigations of toughness properties and (ii) future developments required to expand the acquired knowledge, enhance the current understanding, and ultimately enable commercial applications of SMA-actuators are discussed.

Fatigue and fracture resistance and survival of occlusal veneers of composite resin and ceramics blocks in posterior teeth with occlusal wear: A protocol for a systematic review

Review question / Objective: The aim of this systematic review is to synthesize the scientific evidence that evaluates fatigue and fracture resistance, survival, and stress distribution, of composite resin CAD/CAM and ceramic CAD/CAM occlusal veneers in posterior teeth with severe occlusal wear. Condition being studied: Currently there is an increase in cases of dental wear, due to several factors such as: excessive consumption of carbonated drinks, a diet high in acids, gastric diseases, anorexia, bulimia, dental grinding, use of highly abrasive toothpastes, or a combination of these(9) (10) (11) (12); which affect the patient in several aspects: loss of vertical dimension, sensitivity due to the exposure of dentin, esthetics, affectation of the neuromuscular system(11) (13) (14). With the advent of minimally invasive dentistry, occlusal veneers have been found to be a valid option to rehabilitate this type of cases and thus avoid greater wear of the dental structure with full coverage restorations. Sometimes when performing a tabletop it is not necessary to perform any preparation, thus preserving the maximum amount of dental tissue(3) (6) (15). Due to the masticatory load either in patients without parafunction where the maximum masticatory force is approximately 424 N for women and 630 N for men or in those who present parafunction where the maximum bite force can vary from 780 to 1120N(7), it is necessary that the occlusal veneers support that load which makes indispensable a compilation of studies investigating both fatigue and fracture resistance and the survival rate of occlusal veneers in different materials and thicknesses.