## 1 Introduction  
Implant abutments are the chain link between dental implant and prosthetic construction. Their type, design and material have main significance for the mechanical behavior, peri-implant soft tissue support and good treatment prognosis. If the implant abutment is not appropriate, that can affect the gingival aesthetics, unfavorable crown shape and angulation and lead to implant overloading [1]. This makes the abutment selection very important step in treatment planning. There are many types of implant abutments, which makes the proper choice of implant crown supports difficult. Fatigue overloading and fractures are common prosthetic complications. They might be a result of inappropriate abutments, which could affect the implant or its suprastructure [2]. Metals and their alloys have been the most commonly used materials in dental implant treatment for decades. Titanium is established as an optimal material in fabrication of implant abutments, because of its high strength and biocompatibility. Its mechanical advantages than zirconia abutments are very well described in the literature [3; 4; 5; 6; 7; 8]. Standard titanium abutments are common treatment options, but in most cases, they cannot respond to each individual clinical need, specifically in designing a stable biologic and aesthetic emergence profile, most favorable prosthetic position of the implant crown, elimination or reduction of unfavorable implant angulation, adequate compensation for the interdental space of the defect, and optimal transfer of masticatory forces to the implant and bone-to-implant interface. Thirty years ago, [PERSON] [9] developed the setup for a customized implant abutment as an instrument for predictable management of prosthetic constructions and peri-implant soft tissues. His thesis is endorsed by the concept of prosthetic driven implant placement and number of authors who emphasize the advantages of customized abutments [9; 10; 11; 12]. Our previous laboratory and clinical studies [13; 14] proven their strengths in comparison to fabric abutments as well. One of their big values is the possibility to create personalized emergence profile, which models the implant surrounding soft tissue in healthy and stable design [15]. The introduction of CAD/CAM technologies in dental field allows the application of materials with high mechanical resistance, such as zirconium dioxide and lithium disilicate, which are widely used in implantology. Lithium disilicate possesses high optical and mechanical properties. Its flexural strength of 350-400 MPa and fracture toughness of 3.5-4.5 K (MPa/m\({}^{1/2}\)) make it a suitable material for the fabrication of highly aesthetic monolithic restorations [16; 17]. Zirconium dioxide was first introduced by [PERSON] in 1999, and later, [PERSON] and [PERSON] [18] established the thesis that yttria-stabilized zirconium dioxide exhibits high biocompatibility and excellent mechanical properties--flexural strength around 1000 MPa and fracture toughness of 10-11 K [19]. Combination between titanium abutment and monolithic crown makes the implant suprastructure very resistant to mechanical stress. A precise marginal fit reduces stress on the implant and abutment, preventing micromovements that could lead to screw loosening or fractures. However, fractures of implant suprastructures are still one of the most common complications in dental treatment [20; 21]. Contemporary approaches for marginal design of natural teeth, such as the biologically oriented preparation technique (BOPT) of [PERSON] [22], have shown durable results under mechanical loads. This concept could be applied in implant treatment, such as integration into abutment's marginal finish line. They are reliable tools for soft tissue augmentation, but its significance for the mechanical resistance of implant restorations is still not well examined. The aim of this study is to research the mechanical resistance of customized implant abutments with different types of marginal design in laboratory environment.