## 1 Introduction  
During the past few years, innovative technologies and materials have caused an increase in the use of computer-aided design/computer-aided manufacturing (CAD/CAM) restorations for structurally compromised teeth [1]. More recently, a significant development in dental materials has unfolded with the introduction of resin-matrix CAD/CAM ceramics, which can provide high aesthetics and long-term clinical survival rates of indirect restorations in one single session [2; 3; 4]. Considering that time is one of the most important factors in modern society, due to professional or other personal obligations, patients demand a shorter number of dental sessions. Modern ways of communication, combined with the use of digital technology, can also reduce anxiety and phobia for dentits, increasing, at the same time, the need for preventive dentistry. In addition, advertisements, marketing, social media, and new therapeutical protocols have also been developed over the last several years that make dental offices a friendlier environment. Various studies have also shown that the digital, compared to the analog way of dental practices, offers a higher impact and better patient compliance [1; 5]. Resin-matrix CAD/CAM ceramics (RMCs) present some advantages compared with their ceramic counterparts, including higher Weibull modulus and lower hardness and stiffness, and as a consequence, they produce less wear to the antagonistic teeth, and the milling machine can prepare the restorations easier and faster [6; 7]. Moreover, RMCs can be easily repaired, and due to the fact that they present lower brittleness than ceramics [7], they undergo chipping and crack propagation less frequently during fabrication [8] and exhibit sufficient marginal adaptation [9; 10]. They contain UDMA monomers with dispersed fillers and are fabricated with the methods of high-temperature/-pressure polymerization, providing a higher degree of conversion in comparison with resin composites for direct restorations [11; 12]. Lava Ultimate (LV) that was tested in this investigation belongs to this category of resin-based CAD/CAM materials with dispersive fillers. In particular, it contains bisphenol A diglycidylmethacrylate (Bis-GMA), urethane dimethacrylate (UDMA), ethovylated bisphenol A dimethacrylate (Bis-EMA), and triethylene glycol dimethacrylate (TEGDMA) as basic monomers and silica (SiO\({}_{2}\)) and zirconia (ZrO\({}_{2}\)) nanoclusters as dispersed filler particles. Nowadays, dental research has focused on the bonding of CAD/CAM restorations to dental tissues by applying various techniques. The bonding process can be implemented using appropriate cement materials that are able to fill the area between the surface of the restorative materials and the tooth tissues and form chemical bonds between them. Different adhesive strategies have been suggested for CAD/CAM restorations to reach adequate bond strength on the cement/material interface [13]. In particular, mechanical or chemical surface modification methods have been proposed for this reason [14]. The chemical bonding between resin cement and RMC material [15] and the application of primer (silane) for facilitating the wetting of the polymeric surface of restoratives have been reported to increase the bond strength significantly [16; 17]. Furthermore, the micromechanical modification of the material's surface by applying hydrofluoric acid (HF) [3], air abrasion with aluminum oxide (Al\({}_{2}\)O\({}_{3}\)) particles [18], or laser radiation [19; 20] can enhance the bonding as well. These surface-treatment methods induce microtentive irregularities on the material's surface [21]. Moreover, the application of a coupling agent after surface modification improves chemical adhesion prior to the application of the bonding agent [22]. In the oral environment, significant tensions can be developed at the cement/material interface during thermal changes that can result from the daily diet.