# Effects of Repolishing Systems on Surface Characteristics of a 3D-Printed Permanent Material
## 4 Discussion
Nevertheless, it is essential to note that there is still ongoing disagreement in the literature regarding the optimal viewing geometry for gloss measurements. Furthermore, the lack of uniformity in experimental conditions across studies precludes direct comparison of the data obtained. Only one paper reported the surface roughness and gloss of Permanent Crown Resin. [PERSON] et al., in a recent study [30], analyzed several different finishing and polishing methods and reported that all of the tested systems were able to achieve clinically acceptable results for roughness. In contrast, less acceptable results were obtained for gloss, except for a nitrogen chamber glazed system, which achieved excellent results for both roughness and gloss. A recent study focused on measuring the translucency of Permanent Crown Resin [31], and another analyzed its optical properties [32], although examining different parameters than the L\({}^{\star}\), a\({}^{\star}\), and b\({}^{\star}\) color coordinates of the CIELAB system measured in the present study. When compared to prior studies conducted on materials for prosthetic crowns using the same measurement techniques and methods applied in this study, it is shown that Permanent Crown Resin exhibited a surface roughness exceeding that of CAD-CAM feldspathic ceramic Vita Mark II [27] and similar to that of lithium disilicate ceramics such as VITA Suprinity and IPS e.max CAD [24]. Conversely, its gloss was notably lower than that of both ceramic types. Moreover, the roughness and gloss of Permanent Crown Resin were found to be lower than those of bulk composite resins for direct restorations tested under similar experimental conditions [33]. When comparing the three polishing techniques used in this study, the Opti1 Step Polisher yielded the most favorable results, supporting the manufacturer's assertions about its ability to achieve high gloss on composite resin surfaces in a single step. Conversely, the pumice particles in the Nupro prophylactic paste, designated as \"coarse\", may have exerted an abrasive impact on the material's surface, potentially diminishing its reflectivity. As a limitation of the study, even if representative of the procedures traditionally carried out during hygiene and repolishing, only three systems were used. Another limitation of the present study is that, even if representative of a \"_commonly used dental composite polishers_\" reported in the IFU of the tested materials, only one system has been selected for the initial finishing and polishing procedure, which is essential as baseline. Different strategies for achieving an initial excellent finishing and polishing degree could be the object of further studies. Likewise, it could be of interest to consider the possibility of finishing this material with glazing rather than mechanical systems. Further development of this study could involve examining how the material's printing orientation affects its optical characteristics, which appears to be a crucial factor in additive manufacturing. Additionally, other conditions in the oral cavity may influence the optical material properties, such as hydrolytic and UV aging and exposure to smoke. These aspects deserve further investigation, especially concerning the improvement of the clinical environment simulation. Conceptualization, C.G. and A.V. ; methodology, A.V. ; software, A.V. ; investigation, G.M. ; resources, A.V. ; data curation, C.G. ; writing--original draft preparation, C.G. and G.M. ; writing--review and editing, A.V., C.G., F.V., S.B. and G.P. ; visualization, C.G. and G.M. ; supervision, A.V., C.G. and G.P. ; project administration, C.G. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The data presented in this study are available upon request from the corresponding author. Due to the university's policy on access, they are not publicly available. The authors thank Formlabs GmbH, Belin, Germany, for donating the printing Materials.