## 1 Introduction  
A marginal fit of all-ceramic crowns is considered a prerequisite for the long-term clinical success of dental restorations [1]. A complex interaction between variables related to dental restoration, luting agent and tooth structure may influence marginal misfit and microleakage [2]. A crucial factor affecting marginal discrepancy is dental cements, which act as barriers against microbial leakage, sealing the interface between the tooth and the restoration and holding them together through mechanical and/or chemical attachments [3]. Although marginal adaptation is a fundamental factor in fixed prostheses, there are limitations in analyzing its characteristics, especially with computer-aided design-computer-aided manufacturing (CAD-CAM) and all-ceramic restorations. Terminology suggested by [PERSON] et al. defined the gap between prosthetic restoration and the prepared tooth as the marginal gap [4]. When no overextension or underextension is present, the marginal gap is equal to the absolute marginal discrepancy. However, recent studies have included terminology reporting marginal gap, marginal discrepancy, marginal fit and marginal adaptation [5; 6; 7; 8]. There is no consensus on what constitutes a clinically acceptable maximum marginal gap. Numerous studies have adopted the criteria established by [PERSON] and [PERSON], who concluded that 120 \(\upmu\)m was the maximum tolerable marginal gap [9]. The most common in vitro method of evaluating the marginal discrepancy was sectioning the cemented crowns and recording marginal measurements on digital photographs using a measuring microscope. In each study, different magnifications were used, and the results ranged from 116 to 165 \(\upmu\)m [1; 5; 6; 7; 8]. On the other hand, [PERSON] et al. reported mean marginal discrepancy values of 186 to 210 \(\upmu\)m using micro-CT, without sectioning the cemented crowns. This nondestructive method allows 2D measurements of distances such as the absolute marginal discrepancy and internal gap, as well as the quantification of the cement space volume and the volume of porosities inside the luting agent. Consequently, the accuracy of the final restoration can be assessed after cementation, as well as between the stages of the working procedure [10]. Another in vitro study measured the distance between two predetermined points made on the prepared teeth and on the crowns before and after cementation using a profile projector under a torquing force. It found marginal discrepancies of 41 \(\upmu\)m for resin cement and 49 \(\upmu\)m for resin-modified glass ionomer cement. No statistical difference was found between groups [11]. An in vitro study by [PERSON] et al. on Ni-Cr alloy crowns cemented using three different agents reported marginal gap values of 75.42 to 78.49 \(\upmu\)m. Similar to the previous study, no significant difference was found between groups [1]. An in vitro study using a scanning electron microscope reported that resin cements exhibited a greater decrease in the marginal discrepancy than resin-modified glass ionomer cement following luting on an all-ceramic, complete veneer crown. The mean marginal gap after cementation was 116 \(\upmu\)m for the resin group and 165 \(\upmu\)m for the resin-modified glass ionomer group, with significant differences between groups [5]. Several in vivo studies evaluated the marginal fit of conventional cements by producing conventional impressions of the restoration before and after cementation using polyvinyl siloxane. A cast of each impression was poured using resin and was usually coated with gold. The replicas were viewed with a scanning electron microscope, and the marginal fit was examined, usually at 200\(\times\) magnification. The marginal gap discrepancies were measured directly on the screen in 100 to 200 \(\upmu\)m increments around the circumference of the tooth or by image analysis software and ranged up to 133.7 \(\pm\) 104.7 \(\upmu\)m [12; 13].