16 July 2019

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Fracture of zirconia implants

Lara Figini

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Zirconia implants have been brought to the dental market as a viable alternative to titanium implants initially to fulfill a demand from patients for non-metallic materials. Although zirconia is less tough than titanium, the fracture of zirconia implants seems to be a rare event but still important to analyze, as it can provide useful information on issues related to the design of the plant, to the diameter and to the treatment of the surface. Among the most probable causes cited for zirconia implant fracture are unfavorable narrow diameters, damaging surface treatments resulting from aggressive alumina sandblasting, and patient-related overloading.           

MATERIAL AND METHODS 
In a study published on Dental Materials in February 2019, the authors performed fractographic analyzes of 15 parts of fractured zirconia implants (11 posterior and 4 anterior) with their integral ceramic crowns still cemented on them. The implants were first generations from four manufacturers (AXIS Biodental, Z-Systems, Straumann, Swiss Dental Solutions). The time-to-failure varied between 2 weeks and 9 years. The fractography was performed by identifying the origin of the failure and the characteristics of the superficial fracture. From 2D and 3D digital images of the crown-implant part, spatial coordinates anchoring the crown’s occlusal contacts with the implant’s central axis and reference plane were integrated in a mathematical model spreadsheet. Loads of 500 N in total were selectively distributed over identified occlusal contacts from wear patterns. The resulting bending and torsion moments, the corresponding shear strength, tensile strength, maximum principal stress and von Mises stress were calculated. Fractographic analyzes were performed for all samples.           

RESULTS
Implants fractured from the periphery of the smaller inner diameter between two threads at the bone-entrance level except for one implant which failed half-way within the bone. The porous coating (AXIS Biodental) and the large grit alumina sandblasting (Z-System) created surface defects directly related to the fracture origin. The model spreadsheet showed how occlusal loading with respect to the implant’s central axis affects bending moments and crack onset. Dominant loads distributed on contacts with important wear pattern provided a calculated crack onset location in good agreement with the fractographic findings of the fracture origin. 

CONCLUSIONS 
From the data of this study it can be concluded that the occlusal load influences the position of the beginning clinical fracture in zirconium implants.     

CLINICAL IMPLICATIONS
Recovered broken zirconia implant parts with their restorative crowns can provide not only information regarding the failure origin using fractography but also knowledge regarding occlusal crown loading with respect to the implant’s axis. 

For additional informations:
Translational research on clinically failed zirconia implants.