## 1 Introduction  
This research theme was chosen due to the dynamic evolution of additive manufacturing technologies and also to the exponential development of new materials that can be processed through these technologies in comparison with subtractive techniques. The intense growth of rapid prototyping technologies in industry and their entrance in the dental field led to the necessity of new studies to investigate their behavior, proper applications, and further necessary improvements.  
Metal-ceramic restorations have long been considered the gold standard for dental restorations, and they still represent the landmark for integral ceramic crowns evaluation [1; 2; 3]. They are preferred, especially for posterior teeth, because of their higher loading forces and the possibility to produce precise structures [3; 4]. The longevity of dental restorations is dependent on numerous factors, one of the most important being their adaptability [5]. Many studies investigate the results for traditional technologies, but fewer investigated both additive and subtractive techniques, compared with traditional ones [6; 7].  
A key factor for long-term survival of fixed dental prostheses is represented by marginal gap, which is responsible for 10% of failures. A significant marginal discrepancy exposes the luting agent to saliva, promoting its dissolution in time. This permits bacterial infiltration to occur, leading to dental decay with pulp complications. The space created facilitates food retention causing periodontal suffearance, with inflammation, and gum bleeding. Cement dissolution can cause loss of retention with loosening of the restoration, ceramic chipping, and marginal discolorations. All these elements are translated into functional or aesthetic failure of dental crowns [8; 9; 10; 11; 12; 13; 14]. Previous studies propose various limits as acceptable for marginal discrepancies, [PERSON] recommended 120 \(\upmu\)m while [PERSON] recommended 100 \(\upmu\)m. Other authors suggested a range from 10 \(\upmu\)m to 160 \(\upmu\)m for marginal gap and from 81 \(\upmu\)m to 136 \(\upmu\)m for internal gap [3]. While big gaps compromise the resistance and retention of crowns, internal gap is still mandatory to provide space for the luting agent. A perfect fit will impede the proper sit of the crown due to hydrostatic pressure induced in the cement. This space is measured by tracing a perpendicular line between the inner aspect of the coping and the prepared surface of the tooth on the axial walls or incisal/oclusal surface [3]. Recently introduced technologies such as digitized technologies gained popularity due to the continuous advancements in metallurgy [15]. CAD/CAM marginal adaptability is reported between 10 and 50 \(\upmu\)m, in the range of clinical acceptance. These restorations are produced following industrial standards, so they are not subjected to variations of traditional slip-casting manufactured restorations [16].  
There are many methods to investigate restoration adaptability. One of the most used is a silicone replica technique. This is a popular method because it is non-destructive, which can be easily applied in clinical use. It consists of placing light-body silicon between coping and abutment, which is afterward removed and embedded in a heavy-body material. This complex is sectioned and analyzed. Besides the fact that the crown is intact after this procedure, it allows marginal and internal discrepancies measurements in multiple points [17].  
The purpose of this research was to assess the adaptability of ceramic-fused to metal crowns with frameworks fabricated by modern additive technologies compared to subtractive and traditional technologies. Adaptability was measured before and after ceramic veneering, to evaluate how porcelain firing is influencing ceramic fit.