## 4 Discussion
In fact, previous studies consistently demonstrate MTA to exhibit lower color stability when compared to alternative calcium silicate-based cements [10; 27], hypothesizing that the obtained results could arise from the incorporation of different radiopacifiers such as zirconium oxide and tantalum oxide, instead of bismuth oxide, in the more recently introduced CSCs [26]. Concerning blood contamination, the overall available scientific evidence shows blood exposure to be a factor that significantly exacerbates CSC color alteration [2]. This discoloration severity increase by blood might be related to material porosity and presence or absence of smear layer, which can reduce or increase dentin permeability, respectively. MTA has a longer setting time (2 h and 45 min) compared with all the remaining three tested materials (Biodentine, 12 min; TotalFill, 2 h; PCM, 3 min). Therefore, it seems MTA remains porous for longer which results in increased blood absorption and subsequent hemolysis, with consequently greater discoloration. On the other hand, a recent in vitro study found that contact with blood after a follow-up period of 6 months does not modify color alterations suffered by the biomaterials [24]. Our findings do not line up with the results of the previously mentioned study since, after a 6-month period of evaluation, the present study found statistically significant differences regarding the factor material, as well as regarding the treatment (blood/saline solution), meaning that blood exposure might be a critical factor in biomaterials' color variation. The contrasting results in respect to the role played by blood on color stability of CSCs, among studies with similar experimental protocols, might be related to the use of different experimental models. The study of [PERSON] et al. [24] was conducted in an acrylic model, while the present study was made under ex vivo conditions. The use of natural human teeth may have led to a discoloration enhancement in the case of blood contamination due to the penetration of blood into the dental tubules [11]. For that reason the presence of blood has become a factor that significantly influences the chromatic result in the present study, which is in agreement with the overall literature [2]. It is, therefore, crucial to ensure complete hemostasis [26] and perform adequate blood clot stabilization, as well as to clean the blood present on dentin walls as meticulously as possible, to prevent blood influx into the tooth structure prior to CSC placement [24]. Moreover, the use of natural teeth as experimental model reproduces the clinical context more faithfully, thus allowing a better forecast of the impact of blood contamination on the esthetic outcome of the treatment. According to the results of the present study concerning material/treatment interaction, regardless of the treatment, MTA was the CSC showing the highest \(\Delta\)E, which reflects that MTA presents the lowest color stability of all the tested biomaterials. Furthermore, MTA \(\Delta\)E values consistently indicate a noticeable color alteration regardless of the treatment, perceptible by the human eye \(\Delta\)E \(\geq\) 3.3), therefore impairing the esthetic outcome of the procedure. [PERSON] et al. [7] assessed the clinical and radiographic outcome of partial pulpotomy using ProRoot MTA or Biodentine and found discoloration at follow-up (average 32 months) in both groups. Teeth treated with ProRoot MTA showed grey discoloration in 80% of the total sample and only 27% of teeth treated with Biodentine were affected. This difference between materials was statistically significant and supports the findings of the present research. Nowadays, Biodentine presents a viable alternative biomaterial to MTA. In addition to having zirconium oxide within its formulation, this CSC exhibits a shorter setting time.