## 1 Introduction  
Dental computer-aided design and manufacturing (CAD/CAM) systems were used to produce dental prostheses with excellent and consistent marginal and internal fit, as well as to simplify the prosthesis fabrication process [1, 2, 3]. To digitally design the complicated shapes that are required in dentistry, CAD/CAM systems use highly accurate scanners and software. These systems have enabled the development of digital dental treatments.  
Chairside CAD/CAM systems are used in dental clinics for processes that involve the formation of 3D models of abutment teeth using an intraoral scanner, the design of restorations using design software, or the fabrication of prostheses using the final processing equipment [4]. Inaccurately fabricated dental prostheses can result in clinical problems, including secondary carries, deposition of dental calculus and plaque, and restoration failure. Therefore, an excellent marginal fit of prosthesis is a critical element in successful prosthesis treatment [5]. Hence, many studies have evaluated the marginal and internal fit of fixed prostheses [6, 7, 8, 9]. These studies have used various methods, including the cross-sectional method [10], silicon replica technique [11], superimposition of 3D scan data [9], weight technique [12], and micro-computed tomography (CT) [8]. With each of these methods, the previous studies evaluated marginal and internal fit of the prosthesis with software that superimposes data and evaluates them in 3D to align the scanned data of the abutment teeth with those of the inner side of the prosthesis, assuring a best-fit. However, when using this process, errors may occur on one side while the other side is accurately superimposed [13]. If 3D modeling is overlapped without any reference data, it cannot be regarded as an accurate result because incorrect alignment is performed. The triple-scan evaluation method can compensate for such errors while carrying out 3D evaluations through data that can serve as a reference [14; 15; 16].  
The triple-scan method is performed in the following sequence: First, the abutment teeth (or a model thereof), the inner side of the prostheses, and prostheses that are appropriately located on the abutment teeth are scanned [16]. Next, the triple-scan data are superimposed using a best-fit alignment, and the space between the abutment teeth and the prostheses is measured [16]. This is a non-invasive method and it allows observation of numerous cross-sections, with no limitation on direction or numbers. This method also enables researchers to analyze the 3D space. In addition, it may improve quality control because it can verify the marginal and internal fit of prostheses prior to intraoral installation [16].  
Numerous studies have compared 3D scanners or the marginal fit of prostheses fabricated using chairside or labside CAD/CAM systems [17; 18; 19; 20; 21; 22; 23; 24]. However, few studies have compared different types of chairside CAD/CAM systems. Therefore, the purpose of this study was to evaluate the marginal and internal fit of ceramic crowns fabricated with chairside CAD/CAM systems. The null hypothesis stated that there would be no difference in the marginal and the internal fit of the three types of chairside CAD/CAM systems.