In Vivo Low Temperature Degradation of 3Y-TZP Zirconia Dental Implants

Objective: Yttria-stabilised zirconia implants have been proposed since the 2000 years, because of its tooth-like color, its high mechanical properties, its excellent biocompatibility and  osseointegration. In order to favor osseointegration of zirconia implants surface treatments are applied, but   they could also impact the stability of the tetragonal phase under humid atmosphere. This phenomenon called “Low Temperature Degradation” (LTD) or “aging”, can lead in certain cases to microcracking of the transformed zone and it could reduce the lifetime of zirconia implant. In vitro studies have recently highlighted the occurrence of LTD on zirconia dental implants but the scientific backup on the LTD in vivo, is non-existent although this phenomenon have led to series of failure of femoral heads made of  Yttria-stabilised zirconia in  the early 2000s. This paper shows that LTD could occur in vivo for a specific type of zirconia dental implants. Method: As received 3Y-TZP dental implants with porous coating (ZiUnite®, NobelBiocare) and explanted implants of the same type were assessed and characterized by Scanning Electron Microscopy (SEM), X Ray Diffraction (XRD), Focused Ion Beam (FIB) enabling 3D reconstruction. Osseointegrated area of explants was characterized by Optic Microscopy (OM), FIB and EDX (Energy Dispersive X-ray spectrometry). A Matlab® software was developed to highlight and quantify the volume of LTD on explanted implants. Result: The series of tests done show that the porous coating accelerates the LTD. Explanted implants present a residual, transformed and microcracked coating. Osseointegrated part of implant present transformed coating too. DRX quantification, FIB section and Matlab® software highlight the occurrence of accelerated LTD for this specific case of implants after artificial aging (in vitro) and after few years in vivo. Conclusion:  Surface modifications can have a large influence on the kinetic of LTD and could lead to failure of osseointegration after few years of use.