Low-level Monoclinic content detection in zirconia implants using raman spectroscopy

Abstract

Stabilized zirconia is a ceramic material known for its superior mechanical properties and biocompatibility, and has been widely employed as a biomaterial (Chevalier, Biomaterials 27(4):535–543, 2006) – most recently including dental and spinal implants (Lughi and Sergo, Dent Mater Off Publ Acad Dent Mater 26(8):807–820, 2010). However, the properties of zirconia ceramic may be reduced when it contacts humid environments. Low-Temperature Degradation (LTD) – associated to a phase transformation from tetragonal to monoclinic, and thus to a loss of mechanical properties (Lughi and Sergo, Dent Mater Off Publ Acad Dent Mater 26(8):807–820, 2010; Chevalier et al. Annu Rev Mater Res 37(1):1–32, 2007) – makes detection of low levels of monoclinic a critical aspect in developing and engineering zirconia-based biomaterials. In this work, detection of extremely little amounts of monoclinic phase is demonstrated on implant prototypes by combining Raman spectroscopy and multivariate analysis. Implant prototypes made of Yttria-Stabilized Tetragonal Zirconia were subjected to pin-on-disk tests, leaving distinct wear marks on the samples surface. Arrays of Raman spectra were collected in areas across the pristine and the worn surface, using a 785 nm laser with a 50× magnification objective, 0.75NA. The spectral array was treated by means of standard univariate analysis and by multivariate analysis based on Principal Component Analysis (PCA). The results of the multivariate analysis are represented as maps. Figure 59.1 shows the scores corresponding to the loadings of the relevant component, i.e. the one that most emphasize the presence of monoclinic phase. Note that individual Raman spectrum would suggest that the sample is purely tetragonal. However, PCA results will reveal presence of traces of monoclinic phase of less than 1 vol% (Fig. 59.2). Detection of very low amounts of monoclinic phase, indicating incipient t-m transformation, was made possible by using PCA on Raman spectral arrays. This is a promising approach for early detection of LTD, a key aspect in the development of zirconia-based biomaterials.