## 4 Discussion
Considering the fact that the tested materials have different chemical compositions, and even though GR's composition is not disclosed, it differentiates from other materials with the presence of graphene, and their resistance to wear is also expected to be different from each other. There are studies on the hardness of most of the tested materials in this present study [5; 14; 23; 24; 25]; however, those studies either did not involve any aging or used thermocycling to age the specimens and were not based on direct comparisons among them. In addition, only the manufacturer of MS has disclosed theirinternal hardness data [31]. Therefore, this speculation should be supported by studies on the inherent and after-aging hardness of the tested materials. GR's and BC's volume losses being higher than PMMA may be related to their water sorption during thermomechanical aging, which might have increased the number of contact points with the indenter and caused a greater loss. However, it should be mentioned that this present study did not investigate the maximum wear depth; thus, higher volume loss of GR and BC does not necessarily mean a deeper worn area, as volume loss may have occurred on a wider surface considering the circular motion of the chewing simulator, and these differences may not lead to varying clinical effects. Despite the efforts to standardize the location of the contact point of the indenter during aging, worn areas were evident at different locations on the occlusal surfaces of the crowns (Figure 2), which supports this hypothesis. In a recent study on the volume loss of MS and BC, it was concluded that BC had lower volume loss and wear depth than MS [21]. This difference with this present study may be associated with the design of test specimens, as cement-retained molar crowns were tested in this present study, whereas screw-retained premolar crowns were tested in the previous study [21]. In addition, a laser scanner was used in [PERSON] et al. 's [21] study, and the inherent inaccuracy of the scanner might have affected the results. Nevertheless, the intraoral scanner used to scan each crown in this study has precision similar to that of laboratory scanners [32], and it has also been used in previous studies on the fabrication trueness of additively and subtractively manufactured restorations [19]. The International Organization for Standardization standard 12836 referred to the metrology-grade 3D analysis software (Geomagic Control X v.2022.1; 3D Systems, Rock Hill, SC, USA) used in this present study for digital analyses [33], and previous studies on wear analysis have also used this software [13,21]. The best-fit algorithm was deliberately preferred to avoid any operator-related error during superimpositions, given that the worn area would have been selected manually. Considering these aspects, the authors think that the methodology to analyze the volume loss is justified. None of the specimens was polished as this present study aimed to evaluate the inherent resistance of the tested materials to deviations and occlusal surface wear caused by thermomechanical aging, and it is difficult to standardize the polishing of complex geometries like crowns. However, polishing performed either at the chairside or the dental laboratory may lead to a more stable external surface and enhance the wear resistance of the tested materials due to improved surface roughness. In addition, polishing may reduce the amount of unpolymerized monomers on the external surface of tested resin-based materials, particularly those of MS, given that it was the only additively manufactured material that had to be postpolymerized. Another limitation was that the test design of this present study was based on two-body wear; however, a different design that involves three-body wear, such as brushing, may affect the results. Only one type of antagonist was used for thermomechanical aging, and the type of antagonist may affect the wear [14]. In addition, the wear of the antagonists has not been investigated in this present study.