Phase transformation and fracture load of stock and CAD/CAM-customized zirconia abutments after 1year of clinical function.

Abstract

Functional loading and low-temperature degradation may give rise to impaired clinical long-term service of zirconia implant abutments. The aim of this study was to compare the fracture strength (primary outcome measure) and the volume percentage of monoclinic surface zirconia (m-ZrO2 ) of stock and CAD/CAM-customized zirconia implant abutments that functioned clinically for 1year with geometrically identical pristine controls in an ex vivo experiment. Twenty-three stock (ZirDesign™) and 23 CAD/CAM-customized (Atlantis™) zirconia implant abutments were retrieved after 1year of clinical service. They were compared with pristine copies with respect to the volume fraction of the monoclinic phase using Raman spectroscopy and their fracture load by means of a single load-to-fracture test. Failure analysis was performed using optical and SEM microscopy. After verification of normal distribution, paired t tests were used for comparison of fracture loads between pristine and clinically aged specimen. All statistical tests employed a level of significance of α=0.05. The fracture loads of the stock zirconia abutments were significantly (p<0.05) reduced to 78.8% (SD 29.5%) after one year of clinical function. For the CAD/CAM abutments, no reduction in fracture load was found. No m-ZrO2 volume percentages beyond the detection threshold of 5% were observed in any of the samples. After 1year of clinical service, no difference in fracture strength of the CAD/CAM-customized zirconia implant abutments could be demonstrated, whereas the stock zirconia abutments decreased considerably in fracture strength. No substantial tetragonal-to-monoclinic transformation was observed.