## 4 Discussion
showed a relationship between translucency and the amount of filler content [33], different parameters can affect the translucency, such as the content, type and size of filler particles, composition of the resin matrix and its fraction, application thickness of the material, light-curing mode, photo initiators and filler coupling agents, pigment additives and opacifying agents [34; 35]. The different behaviour of \(\Delta\)TP (t0/t7) could be due to the water intake of the polymerisation initiators from both the matrix and the unpolymerised chamber, increasing the water inside the resin and modifying the refraction and diffusion index of the matrix. Monomers can also influence the translucency. For example, urethandimetheacrylate is a lesshydrophilic monomer compared with triethylene glycol dimethacrylate (TEGDMA) and bisphenol-A glycidyl dimethacrylate (BIS-GMA) [36; 37]. In fact, [PERSON] and [PERSON] reported that the water uptake in BIS-GMA-based resin materials increased from 3% to 6% as the proportion of TEGDMA increased from 0% to 1%, respectively [38]. For this reason, RLAs containing TEGDMA or BIS-GMA, such as MF and MH, were more susceptible to TP changes after storage in water. Only NX3D showed no differences between t0 and t1. This behaviour of NX3D can be explained by the colour stabilisers claimed by the manufacturer. Among the tested materials, the curing protocol affected the colour stability and the translucency of only MF and RXD. Since the knowledge of all ingredients was not available, the authors can speculate that the step luting protocol made MF and RXD instable, provoking the leakage of its ingredients, such as monomers, fillers and pigments, which are all involved in establishing the colour and translucency properties. Moreover, based on a previous study, the TPc values of healthy dentin and enamel are around 0.28 and 0.24, respectively [39]. Then, among the tested RLAs, NX3L (P1 and P2) showed the closest values to the sound dental tissue. The limitation of this study might be the use of distilled water and the evaluation of the colour and translucency of RLAs alone without considering the influence of the indirect restoration. Regarding the use of distilled water compared to saliva, while the mechanical behaviour of RBMs might be influenced by the use of one of these solutions, no difference was reported for spectrophotometric evaluations [40]. [PERSON] et al. also utilised distilled water as the control group instead of artificial saliva in a study in which they evaluated the colour of different RBMs [41]. Aside from that, [PERSON] et al. concluded that immersion in artificial saliva may cause a biased colour due to its artificial components [42]. Regarding the absence of indirect restorations during the colour measurements, although many studies tested RLAs along with veneers or overlays [43; 44; 45], the fact is that studying each RLA alone allows better understanding of its behaviour. Moreover, to the best of the authors' knowledge, no study exists regarding the analysis of RLAs alone after water sorption and using different protocols. In addition to water, in the oral cavity, other solutions can influence RLAs. For this reason, further studies will investigate the influence of the different curing protocols on the staining capability of agents such as tea, cola or coffee. For carefully translating the results of this in vitro study into clinical practice, it is possible to emphasise that all the tested RLAs changed their colour and translucency after 7 days of storage in water. Moreover, since we used RLAs that were completely cured and not immediately after the curing procedures [17], the translucency and colour changes could be even more visually perceptible in clinical practice. Hence, to establish the exact colours of these RLAs and have a preview of the exact final colour, it may be helpful to create one's own hydrated shade guide [46] using cured, hydrated RLAs, and using one's personally chosen cure protocol.