# Air-Polishing Powders' Effect on the Color of CAD/CAM Restorative Materials
## 2 Materials and Methods
The color parameters, L* (lightness), a* (green-red coordinates), and b* (yellow-red coordinates) of each specimen were measured on a white background (L* = 98.20, a* = \(-\)3.52, b* = 4.65) using a spectrophotometer (CM-3600d, Konica Minolta, Tokyo, Japan), with 360-740 nm wavelength interval, specular component included, standard D65 (daylight) light source, and 2\({}^{\circ}\) observer [35], double-ray UV-100% visible reflection feature with 10 nm intervals, by an experienced operator who had been trained to use the spectrophotometer. Each specimen was measured three times; the mean value was the sample's color. The device was calibrated before the measurement of each group, according to the manufacturer's instructions, using computer software (Spectra-Magic NX, Version 3.61, Konica Minolta Sensing, Inc., Tokyo, Japan). After initial color measurements, five different APPs, namely, sodium bicarbonate, aluminum trihydroxide, calcium carbonate, glycine, and erythroid, were applied to each group with an air-polishing device (Air-Flow S1, EMS, Nyon, Switzerland). The brands, manufacturers, lot numbers, particle sizes, Mohs hardness numbers, and densities of the tested APPs are presented in Table 2.  
Figure 1: Study design. The APPs were applied on the surface of the specimens with a 60\({}^{\circ}\) angle and 4-5 mm distance at a medium setting (water pressure: 3 bar, air pressure: 5.75 bar) always by the same trained operator [24; 36; 37]. In addition, the powder chamber of the device was filled to the maximum level after each application to ensure constant powder flow. A previous study reported that the application period of APP during a recall appointment should be 1-2 s for a tooth's anatomical crown, and more than 10 s would be harmful to the patient [38]. In a dental arch without any loss of interdental papilla and ideally aligned, an average upper central incisor's surface area that can be air-polished is approximately 150 mm\({}^{2}\)[39]. Therefore, if air polishing can be applied for 1 s to a 150 mm\({}^{2}\) area in a recall appointment, then it should be applied for 1/150 s to an area of 1 mm\({}^{2}\) in one recall appointment. Consequently, to simulate ten years of 3 monthly recall appointments [15; 18; 40; 41; 42], air-polishing should be applied for a period of 40 times longer, equivalent to 40/150 s for a 1 mm\({}^{2}\) area [43]. Since the surface areas of the CAD/CAM blocks were different from each other, the duration of air-polishing was calculated for the area of each CAD/CAM block separately. After surface treatment with the APPs, each specimen's L*, a*, and b* values were measured in the same way. The quantitative color difference (\(\Delta\)E\({}_{00}\)) values between the initial and final measurements of the specimens were calculated using the CIEDE2000 color difference formula [44]. \[\Delta E_{00}=\sqrt{\left(\frac{\Delta L^{\prime}}{k_{\text{L}}S_{\text{L}}} \right)^{2}+\left(\frac{\Delta C^{\prime}}{k_{\text{C}}S_{\text{c}}}\right)^ {2}+\left(\frac{\Delta H^{\prime}}{k_{\text{H}}S_{\text{H}}}\right)^{2}+R_{ \text{T}}\frac{\Delta C^{\prime}}{k_{\text{C}}S_{\text{c}}}\frac{\Delta H^{ \prime}}{k_{\text{H}}S_{\text{H}}}}\]  
In this formula, \(\Delta L^{\prime}\), \(\Delta C^{\prime}\), and \(\Delta H^{\prime}\) indicate the differences in lightness, chroma, and hue, respectively; S\({}_{\text{L}}\), S\({}_{\text{C}}\), and S\({}_{\text{H}}\) are weighting functions that provide a better correspondence with visual evaluation; and R\({}_{\text{T}}\) is the rotation function. The parametric weighting factors k\({}_{\text{L}}\), k\({}_{\text{C}}\), and k\({}_{\text{H}}\) are correction terms for experimental conditions, and they were determined as 1 [45; 46]. Microscopic morphologies and particle sizes of the APPs were analyzed under scanning electron microscopy (SEM) (Zeiss EVO LS 10, Oberkochen, Germany). The APPs were sputter-coated with gold/palladium (Quorum SC7620, West Sussex, England) and then analyzed at 10 kV, with 100\(\times\), 200\(\times\), and 15,000\(\times\) magnifications.