## Materials and Methods
DC\({}_{1}\) has a ratio of 20:80 and DC\({}_{2}\) is a balanced splitter, 50:50. DC\({}_{2}\) feeds a balance detection receiver from (Thorlabs, Newton, NJ, USA, model PDB460C), using two photo-detectors, PD\({}_{1}\) and PD\({}_{2}\) and a differential amplifier DA. Twenty percent from the SS power is launched towards the object arm via lens L\({}_{1}\) (focal length 15 mm), which collimates the beam towards a pair of galvoscanners XYSH, (Cambridge Technology, Bedford, MA, USA, model 6115) followed by a scanning lens, L\({}_{2}\), (25 mm focal length), which focuses the light on the sample. The optical fibers used, as well as the lenses L\({}_{1}\) and L\({}_{2}\), determine a lateral resolution of \(\sim\)10 \(\upmu\)m. The power to the object O is 2.2 mW. At the other output of DC1, 80% from the SS power is directed along the reference path via two flat mirrors, M\({}_{1}\) and M\({}_{2}\), both placed on a translation stage, TS to adjust the optical path difference (_OPD_) in the interferometer. Collimating lenses L\({}_{3}\) and L\({}_{4}\) are similar to L\({}_{1}\). The signal from the differential amplifier, DA, is sent to one of the two inputs of a dual input digitizer (Alazartech, Quebec, QC, Canada, model ATS9350, 500 MB/s). The acquired channeled spectra are manipulated via a program implemented in LabVIEW 2013 (National Instruments Corporation, Austin, TX, USA), 64 bit, deployed on a PC equipped with an Intel Xeon processing unit (Santa Clara, CA, USA), model E5646 (clock speed  
Figure 1: Aspects from the preparation of the samples: (**a**) adding the ceramic material on the copings, before sintering in blue color and larger than the (**b**) sample after its sintering in the oven (which also displays a change in color); (**c**) temperature chart displayed by the dental ceramic oven; (**d**) several samples used in this study. 2.4 GHz, 6 cores). The same program is also used to drive the two galvoscanners via a data acquisition board (model PCI 6110, National Instruments Corporation, Austin, TX, USA). Each B-scan image was built of 500 A-scans; hence, with 100 kHz sweeping speed, 10 ms were required to acquire data for a B-scan (the fast galvoscanner was driven with a triangular wave-form [35]). As a consequence, 500 \(\times\) 500 channeled spectra to build an entire 3D volume and also deliver the _en-face_ images were acquired in 5 s. Once the full dataset was acquired, _en-face_ images were produced using the MS protocol by comparing the signal delivered by the DA with the signal delivered by the DA when a mirror was used as a sample, for an optical path difference in the interferometer adjusted to \(z_{\text{en-face}}\), i.e., to 0.75 mm. All samples were subject to imaging after they have completely cooled down. For their investigations, C-scan/_en-face_ OCT images were obtained from a similar depth in all of the samples. The control of the depth was made possible by analyzing the B-scan OCT image of each sample. This depth was chosen at approximately \(z_{\text{en-face}}\) = 0.375 mm (distance measured in air) from the position corresponding to an optical path difference (_OPD_) of 0 mm considered at the top of each sample in the B-scan image. In all cases, the vestibular surface of the sample was imaged. The system was switched from either real time _en-face_ (C-scan) imaging regime to cross section (B-scan) imaging regime, based on its Master Slave procedure. The lateral size of the _en-face_ images was calibrated (size of the image versus voltage applied to the galvoscanners XY) using a high resolution test target. The scale bars in Figures 3-5 were thus \(x=y=3.25\) mm on each of the two directions considered for _en-face_ images. Along the \(z\)-axis (in-depth, perpendicular on the vestibular surface), the maximum axial range offered by the instrument employed for the study, measured in air is \(z=3.75\) mm.