## 1 Introduction  
Computer-aided design/computer-aided manufacturing (CAD/CAM) has shown remarkable progress in recent years, and its application in dentistry is advancing annually [1, 2]. Dental milling machines and three-dimensional (3D) printers are already used in dentistry, making it possible to fabricate products in the dental laboratory in a shorter time and with higher accuracy than in the past. This aids in providing superior dental treatment quality to patients. There has been an expanding application of digital complete dentures [3, 4]. Various methods have been developed to digitize either a part or the entirety of the process. New fabrication methods, including milling complete dentures using custom disks and prefabricated artificial teeth, have been developed [5], and their vast clinical applications in university hospitals have been reported [6]. Digital complete dentures can be fabricated through two methods: subtractive manufacturing using a milling machine or additive manufacturing using a 3D printer. In milling, a prefabricated polymethyl methacrylate (PMMA) disk that has been pre-polymerized under ideal conditions is milled to a denture shape, which enables excellent mechanical properties [7, 8]. [PERSON] et al. showed that PMMA blocks had higher flexural strength and modulus, as well as lower water sorption and discoloration, than blocks fabricated using conventional denture base resins [7]. Similarly, [PERSON] et al. reported that prefabricated PMMA disks had superior flexural strength compared with self-polymerizing resin and heat-polymerizing resin [8]. Moreover, a prefabricated PMMA disk is not affected by polymerization shrinkage; [PERSON] et al. reported that it was most accurate and reproducible when compared with conventional methods such as pack and press, pour, and injection [9]. [PERSON] et al. examined changes in surface properties using artificial saliva and found that prefabricated disks were as clinically acceptable as conventional resins [10]. In addition, the fabrication of a single milled denture base and artificial teeth requires approximately 2 h individually for fabrication [11]; however, milled complete dentures can be fabricated in a lesser duration than dentures fabricated using the conventional method. [PERSON] et al. reported that when comparing the cost-effectiveness of milled complete dentures and conventional complete dentures, the cost of milled dentures was comparatively lower [6]. This could be attributed to the reduced labor cost of denture fabrication. Taken together, the use of digital technology to fabricate dentures can reduce the time spent by dental technicians on manual labor and enable more efficient denture fabrication. There are many advantages to applying digital technology for denture fabrication compared with conventional methods. However, polishing, which is an important step in the final processing of dentures, has not been digitized and is performed manually by dental technicians. Conventional denture fabrication requires complex work, including modification of the denture form after it has been retrieved from gypsum and finishing and polishing. Previous studies examining the surface quality of complete dentures have shown that milled complete dentures have better surface quality than conventional or 3D-printed complete dentures [12; 13; 14; 15]. In addition, ideally, milled complete dentures should require minimal time for fabrication and have good surface quality. However, the optimal milling conditions for achieving these parameters remain unclear. Moreover, clinically, no clear standards for selecting tools and adjusting milling conditions for the fabrication of milled complete dentures exist. They are based on the clinician's experience. The surface roughness of a composite resin block improves the bonding strength and is influenced by the milling conditions [16]. A previous study measured the milling duration; however, it did not discuss the relationship between the milling duration and the milling conditions.