## 1 Introduction  
Implant-supported fixed partial dental prosthesis is a popular treatment option for partially edentulous patients. The mean implant failure rate of fixed partial dentures in partially edentulous patients was reported to be 6% in both the maxilla and mandible (range: 1.9-12.5%) [1, 2]. Conditions that contribute to restoration failure include cracking, chipping fracture, bulk fracture, excessive wear of the opposing tooth surface, excessive roughening of the ceramic surface, and unacceptable esthetics. [PERSON] [3] defined restoration success as intact prosthesis survival with acceptable surface quality, anatomic contour, function, and esthetic. In clinical settings, delivering an implant prosthesis is challenging when the implant tilts during implantation, which may stem from anatomic limitation, unique treatment design (such as all-on-4), or other iatrogenic factors. Delivery methods of implant crowns mainly divide into the following: Cement-retained and screw-retained implant prosthesis. The implant abutment is always milled or custom-made to fit the insertion pathway. Fixing a single implant prosthesis on a tilted implant fixture over the posterior area is often a challenging task due to limited insertion pathway, short interdental space, and difficult interproximal hygiene maintenance. After properly milling the implant abutment, one must put into consideration the ceramic materials used, prosthesis thickness, and repairing method after implant prosthesis failed in the future. The advantages of screw-retained implant prosthesis are easy retrieval, better tissue response, and capable of installing when interoclusal space is limited. On the other hand, delivering a cement-retained implant is easier than delivering a screw-retained implant. However, the clinician should evaluate the retention and resistance of the crown meticulously and clean excess cement after delivery. Based on the method of fabrication, implant abutments can be classified into prefabricated and custom-made abutments. Prefabricated abutments are often used in the esthetic zones owing to difficulty in achieving a good emergence profile, and the margin of the abutment requires milling because it remains supragingival. The milling of prefabricated implant abutment is typically performed using high-speed handpiece and diamond dental burs [4; 5]. The total occlusal convergence (TOC) [6], which is the convergence angle between two opposing axial walls, is one of the critical factors for the success of ceramic crowns. Low values of TOC [7; 8], range 2\({}^{\circ}\) to 5\({}^{\circ}\), are difficult for crown delivery and result in an increasing cement hydraulic pressure. High values of TOC [9], over 24\({}^{\circ}\), are difficult to obtain proper retention of the crown in long-term follow-up. Owing to advances in software and hardware for the open computer numerical control (CNC) system development, computer-aided design (CAD) and computer-aided manufacture (CAM) have increased interoperability and dimension control when milling the implant abutment [10]. Designing abutment using software and milling metal/zirconia material have gained great popularity in clinical dentistry. These abutments have allowed the dentists to create individual emergence profile and provide an ideal structure and crown path insertion. After manual or machine milling, the morphology of the implant abutment can be adjusted, and the prosthesis is always set on an asymmetrical convergent angle of the axial surfaces which lead to different occlusal areas. Zirconia is a crystalline form of zirconium dioxide; it has excellent mechanical properties similar to metal and with color close to natural teeth. The best properties for medical use are exhibited by zirconia stabilizing with Y\({}_{2}\)O\({}_{3}\)--also known as tetragonal zirconia polycrystal (TZP) [11]. A high flexure strength (900-1200 MPa) and compression resistance (2000 MPa) [12] render it suitable for use in clinical dentistry [13].