## 1 Introduction  
Dental lithium disilicate (LDS) ceramics are supplied either as ingots for heat pressing or as blocks and discs for computer-aided manufacturing (CAM). Some of the drawbacks of CAM fabrication techniques are the material waste and its inability to reuse the remaining parts of the milled blocks and discs. LDS ceramics are characterized by a unique crystal phase (with 70% lithium disilicate crystals), which naturally reflects light on their surfaces [1, 2]. Ceramic restorations are subject to surface degradation when exposed to aqueous solutions or changes in pH [3, 4, 5]. Additionally, this process can be intensified by temperature differences [6], which leads to undesirable outcomes for the restoration, such as microbial plaque accumulation and changes in color and appearance [7]. Many in vitro studies have shown that the color of restorative materials can be significantly changed as a result of exposure to common beverages, such as coffee [8, 9, 10]. It is possible to interpret color changes (\(\Delta\)E) based on perceptibility (PT) and acceptability (AT) thresholds. This aids in selecting dental materials, evaluating their clinical performance, and interpreting visual and instrumental observations [8, 9]. Recently, levels of color change PT and AT in dentistry were determined at \(\Delta\)E = 1.2 and \(\Delta\)E = 2.7, respectively [9]. The measurement of the color of restorative materials using digital methods eliminates human subjectivity [10, 11]. The spectrophotometer is a commonly used and accurate digital device developed to measure color changes in restorative materials. It uses a specific light that is reflected on the observed object to calculate the L, a, and b values of that object. Portable spectrophotometers have been used in the color research of dental materials; some of these devices, such as the Spectro Shade Micro, can detect the shade of the entire buccal surface of the teeth, while others, such as the Vita Easy shade device, can detect the shade of the small, rounded area of the buccal surfaces [12]. A key factor in determining the clinical success and longevity of restorative materials is their stainability over time [13]. The E-max press of Ivoclar Vivadent and Celtra press of Denstply Sirona (10% zirconia-reinforced lithium silicate, ZLS) are examples of conventional lithium disilicate glass-ceramics [14]. In newly developed lithium disilicate high-density micromization (LDS-HDM) glass-ceramics, such as Initial LiSi (GC), the entire glass matrix is filled with evenly distributed lithium disilicate microcrystals instead of larger crystals. Color stability refers to the change in color of restorative materials due to immersion in saliva. Stainability means the change in color of restorative materials due to immersion in staining solutions such as coffee. Previous studies on the color stainability of different ceramic materials have concluded that lithium-disilicate-based glass-ceramics was the most color-stable material [15; 16]. However, previous studies [2; 3; 13; 15; 17; 18; 19; 20; 21; 22] on the stainability of ceramic restorations have had several limitations. For example, the tested ceramic discs were immersed in the staining solutions so that the specimens were exposed to staining from both sides; this is not similar to clinical situations. Furthermore, the thickness of the ceramic discs used was greater than the actual thickness of ceramic restorations used clinically. Color stainability studies conducted using crown-shaped specimens may be a better representation of the clinical situation, provided that the specimens are identical and the measurement method is standardized and repeatable. The remaining part of the heat-pressed ceramic ingot is usually removed after pressing and thrown away. However, some dental laboratories repress the remaining ingot before disposing of it. It has been reported that, when heat-pressed ceramic ingots are pressed again, their flexural strength is not adversely affected [23; 24; 25].