## 1 Introduction  
The introduction of intraoral scanners and their combination with dental computer-aided design and computer-aided manufacturing (CAD/CAM) systems has enabled the chauside production of prostheses [1; 2; 3; 4]. As such CAD/CAM systems do not require a working model to be fabricated, prostheses are produced rapidly, which reduces the patient treatment time [1; 2; 3]. Lithium disilicate ceramics are widely used for dental prostheses because they are aesthetic materials with a short sintering time [4; 5]. Four-axial milling units are also preferred to minimize patient treatment time [4; 5; 6; 7; 8]. Crowns fabricated from lithium disilicate materials have shown a high survival rate [6]. However, lithium disilicate materials are reported to have low strength under occlusal forces [5; 7; 6]. Therefore, zirconia is used to reinforce lithium disilicate materials [8]. However, studies comparing zirconia-reinforced lithium silicate glass ceramics with zirconia-free lithium silicate glass ceramics are lacking.  
When using dental CAD/CAM systems, it is important to evaluate the consistency between the designed crown and the fabricated crown [4; 5; 9; 10]. Low consistency may affect the marginal and internal fit of a prosthesis [4; 9; 10]. Trueness indicates the similarity of the prosthesis designed first in CAD software (CAD reference model) with the fabricated prosthesis (CAD test model) [4; 9; 10]. A prosthesis exhibiting excellent trueness may offer the advantage of time for the patient to adjust to the prosthesis [4; 10]. The trueness of the fabricated crown may differ depending on the type of lithium disilicate block used due to the differences in processability [10]. However, few studies have investigated the correlation between the surface microhardness of the ceramic material and the trueness of the resulting crown.  
The marginal and internal fit of a fixed prosthesis are important predictors of successful prosthetic treatment [4; 11; 12; 13; 14]. An excellent marginal fit allows the maintenance of a healthy periodontal status and prevents the dissolution of resin cement [11; 12; 14]. An excellent internal fit increases the dropout resistance of the prosthesis [11; 14]. Therefore, many studies have focused on the marginal and internal fit parameters that affect prostheses prognosis [4; 5; 11; 12; 13; 14]. Currently, fixed prostheses produced with dental CAD/CAM systems have reported marginal fit values that are typically less than 100 \(\upmu\)m, and marginal gap values below 100-120 \(\upmu\)m have been reported to be clinically permissible in most studies [11; 14; 15].  
Although there are various methods of evaluating the marginal and internal fit, the silicone replica technique is recommended as a reliable method [5; 14]. This method involves injecting silicone to measure the rim and inner space of the prostheses by replication [5; 14]. The thickness of silicone replicas can also be measured by optical scanning [16].  
Many previous studies have evaluated the marginal and internal fit of the crowns fabricated from lithium disilicate materials and verified their stability [5; 6; 11; 15]. In addition, long-term clinical studies with these crowns have yielded promising results [6]. However, there is insufficient evidence regarding the correlation between the trueness of the crowns and their marginal and internal fit.  
This study aims to evaluate the fitness, surface microhardness, and trueness of crowns fabricated from three types of dental ceramic blocks and to analyze the correlations between them. The first null hypothesis is that there is no difference between the fitness, surface microhardness, and trueness of crowns and the type of dental ceramic block used for fabrication. The second null hypothesis is that there is no correlation between fitness, surface microhardness, and trueness.