*5.3. Proposed Standard Procedure*

In the following, we suggest a standard procedure that would allow obtaining Vm values on implants which can be compared between different laboratories:


A standardization procedure of this type should be attempted and defined within a round robin study with the participation of a large number of scientific institutions worldwide. However, it should be kept in mind that such a standard procedure will have the limitation—intrinsic within both the Raman and XRD techniques—that the measurement result is the average monoclinic content at several micrometers depth and thus reveals neither the bulk composition nor the spatial distribution of the monoclinic phase. The penetration depth can be varied in Raman by changing the width of the confocal pinhole,

and in XRD by modifying the angle of incidence of X-rays. Since spectra and diffractograms will be different for each modification of those parameters (for example, with a different SNR), the standard procedure should be repeated for each penetration depth selected.

**Figure 7.** Different baseline choices on Raman spectra of Delta with (**a**,**b**) high and (**c**,**d**) low monoclinic contents. The spectrum shown in (**a**,**b**) was collected on the rear of an insert (rough surface), whereas the spectrum shown in (**c**,**d**) was collected on the apex of a head (polished surface).

A noteworthy alternative to the use of equations is the use of hyperspectral imaging and related statistical analyses (e.g., principal component analyses), as recently applied in surface-enhanced Raman spectroscopy [33].
