## 4 Discussion
While this method may yield lower values compared to three-dimensional and non-contact methods, it is often preferred due to its cost-effectiveness and accessibility [40, 43]. While there is no universally accepted threshold value for the roughness of an ideal composite material, a limit of 0.2 Ra has been suggested to prevent microbial colonization on the dental composite surface [44]. In our study, it was observed that the group with the addition of eticol-ceramic exhibited surface roughness values lower than the control group, although not statistically significant. We attribute this result to the smaller particle size of eticol-ceramic compared to other types. In the group with the addition of etifert, which has larger particle size, higher values might be expected. However, in the etifert group, the upper surface hardness ratios were found to be at the lowest level. The addition of filler material with smaller size and rounded geometry allows for an increase in the degree of polymerization and improves polishability, resulting in smoother surfaces [45]. Color stability is a significant criterion in evaluating the clinical performance of restorative materials and can be attributed to both internal and external factors. Factors such as incomplete polymerization, the presence of surface roughness, water absorption, and the type and amount of filler can influence color stability. Spectrophotometers are the most commonly used devices for measuring color stability [46]. Such devices prevent the influence of external light conditions on measurements and allow photo-optical measurements to be converted into a numerical value in the CIE L*a*b* color space. As a consequence, it has been proven that, compared to traditional and subjective interpretations, objective and high-precision matching can be achieved in the majority of cases. For this purpose, we used an intraoral spectrophotometer device, VITA Easyshade V (VITA Zahnfabrik, Germany), in the present study [47]. According to the literature, color change values in the L*, a*, b* axes can be interpreted separately to assess color stability. However, in this study, the focus was solely on AE, and this aspect can be expressed as one of the limitations of the study. Although various threshold values have been reported in the literature, it has been suggested that the \(\Delta\)E value should be between 1 and 3. Additionally, it has been reported that color changes can be easily distinguishable clinically when values exceed 3.3 [48,49]. According to the data obtained in our study, \(\Delta\)E values for all groups except the eticol-ceramic group were found to be below the critical threshold of 3.3, indicating preserved color stability (visually observable). In the eticol-ceramic group, a dramatic color change was observed, easily noticeable to the naked eye (the discs were observed to darken towards black). Despite successful results in terms of smoothness and upper surface hardness values, the addition of eticol-ceramic significantly compromised the aesthetic properties. Despite being in a powder form and appearing white, we believe that the difference arises from factors in the structure of eticol-ceramic powder, such as a small amount of Fe\({}_{2}\)O\({}_{3}\), Al\({}_{2}\)O\({}_{3}\), SO\({}_{4}\), and moisture. While the exact chemistry causing instability is not fully known, we assume that Fe\({}_{2}\)O\({}_{3}\) can be tainted with Al\({}_{2}\)O\({}_{3}\) and traces of other elements. Under normal conditions, Fe\({}_{2}\)O\({}_{3}\) has a reddish-brown color, and sulfates can interact with metal ions, leading to color changes. Additionally, we posit that the moisture in the powder may have influenced polymerization transformation, potentially compromising color stability. By incorporating the most suitable boron derivative into the dental composite structure in the most accurate proportions, superior mechanical properties can be achieved for restorative materials. This situation can be viewed positively from an industrial and commercial perspective.