## 2021 Flowchart
### Tooth Color Assessment  
The initial shade values were measured using a spectrophotometer, a device that measures light absorption and is used to determine the color of a substance (VITA Easy Shade Advance 5.0, VITA Zahn fabric, Bad Sakingen, Germany). After the color measurements, the L*a*b* coordinates were recorded, and the mean values were estimated. The teeth were distributed into ten groups (n = 10) according to their colorimetric data to avoid significant variations between samples in the same experimental group. Subsequently, each tooth was measured three times by the same operator, who was blinded to group allocation to ensure procedural consistency (N.K.S.) and thus enhance reliability and minimize intra-operator variability. The experimental groups were formed with a balanced distribution of teeth having the same colorimetric references (e.g., in the same experimental group, there were three teeth colored A2, three teeth colored B1, two teeth colored B2, and two teeth colored A3) [20]. The color evaluation was conducted using CIE Lab* color space parameters. The lightness of an object is indicated by the L* coordinate, which scales from white (0) to absolute black (100). The a* coordinate signifies the chromaticity on a green (\(-\)) to red (+) axis, with values typically ranging from \(-\)70 for green to +70 for red. The b* coordinate measures chromaticity on a blue (\(-\)) to yellow (+) axis, on which values range from \(-\)80, indicating blue, up to +100, signifying yellow. The teeth were placed on a white background (a standard calibration tile following the Commission Internationale de l'Eclairage [CIE; L*: 93.84, a*: \(-\)1.48, and b*: 3.76], and the tip of the spectrophotometer was carefully positioned to be in full contact with the flattest area of the buccal surface of the tooth, specifically targeting the central region located 2 mm above the cementoenamel junction. The instrument was calibrated according to the manufacturer's guidelines before initiating measurements for each new experimental group. To ensure the precision of the color analysis, the same tooth samples were also evaluated with a DSLR camera (80D, Canon, Tokyo, Japan) equipped with a macro lens (Canon EF 100 mm; Canon, Tokyo, Japan). Digital photographs of the tooth samples were taken from the buccal aspect of the teeth at the same time intervals under laboratory conditions. A Twinflash (Godox MF12) was used as the light source with a mini-softbox. The flash heads provided daylight-balanced illumination at \(\approx\)5600 K, ensuring that each shot would have the same focal length, working distance, and flash power. The CIEDE2000 color space system (Commission Internationale de L'Eclairage, Vienna, Austria) has been used for the recording of color measurements. The change in color (\(\Delta E_{00}\)) was assessed by comparing the values obtained before endodontic treatment (baseline; T0) with those measured at (T7) 7, (T30) 30, (T90) 90, and (T180) 180 days. A \(\Delta E_{00}\) value \(\geq\) 3.5 was considered clinically perceptible. The following formula was used to calculate \(\Delta E_{00}\)[22]:  
\[\Delta E_{00}=\sqrt{\left(\frac{\Delta L^{\prime}}{k_{L}S_{L}}\right)^{2}+ \left(\frac{\Delta C^{\prime}}{k_{C}S_{C}}\right)^{2}+\left(\frac{\Delta H^{ \prime}}{k_{H}S_{H}}\right)^{2}+R_{T}\left(\frac{\Delta C^{\prime}}{k_{C}S_{C} }\right)\left(\frac{\Delta H^{\prime}}{k_{H}S_{H}}\right)}\]  
where  
\(\Delta\)L\({}^{\prime}\), \(\Delta\)C\({}^{\prime}\), and \(\Delta\)H\({}^{\prime}\) represent the differences in lightness, chroma, and hue, respectively;  
R\({}_{\rm T}\) is the rotation function used to explain the interaction between chroma and hue in the blue region;  
S\({}_{\rm L}\), S\({}_{\rm C}\), and S\({}_{\rm H}\) are the weighting functions for lightness, chroma, and hue;  
K\({}_{\rm L}\), K\({}_{\rm C}\), and K\({}_{\rm H}\) are parametric factors (all set to 1 under standard laboratory conditions.