1. Introduction Osseointegrated implants are used safely in the rehabilitation of partially edentulous patients; however, this treatment can present long-term complications [1]. The two main implant failures are peri-implantitis and occlusal overload. These complications can act in association or independently, and both cause marginal bone loss which can lead to implant loss in advanced cases [2,3]. In the rehabilitation of partially edentulous patients, implant placement can be affected by several factors, including bone height or the anatomy of the region [4]. The implant configuration determines the load incidence pattern in that region which consequently affect the biomechanical behavior through the stress distribution between ductile materials and microstrains at the peri-implant bone [5,6]. When an implant is under functional load, the bone tissues receive a mechanical stimulus and undergo strain. This deformation is expressed with the letter ε and is defined as the relative change in bone length, often being expressed in microstrain (µε) [7]. A bone strain of 1000 means a 0.1% deformation [7], therefore bone strain in the 50–150 range allows the bone remodeling process to be kept stable, while 1500 µε tends to promote lamellar remodeling to overcome the mechanical requirement. On the other hand, 3000 µε is the physiological bone limit and when the load exceeds this limit, the implant may fail in this overloading scenario due to tissue damage [8]. To prevent peri-implant bone loss, it is important to know the masticatory system and the biomechanical behavior of all components of the implant rehabilitation, since the bone tissues are influenced by the occlusal loads transmitted to the implant [9]. Different implant systems provide many components/abutments, which can improve the prosthetic solution but also can hinder its correct selection. The correct abutment selection positively influences long-term treatment success, so it is essential to expand the knowledge on the subject and discuss new prosthetic possibilities [10]. In this context, the CMN abutment has a geometry with a height of 3.5 mm and an anti-rotational configuration, that is, it is indicated to support single prostheses screwed on the implant. However, the use of rotational copings on these abutments allows the manufacture of fixed partial dentures and, if their biomechanical behavior is compatible with this purpose, its indication can be extended to different configurations of prostheses on implants. Clinical studies observed during investigations of the biomechanical behavior of implants the magnitude of the loads applied at the prosthesis/abutment level and claimed that these same stresses cannot be found at the implant-bone interface. This limitation is due to many practical and ethical obstacles to realizing a controlled clinical trial able to evaluate occlusal overloading [11]. To improve the understanding of implant rehabilitation behavior, more studies using bioengineering can be used, such as finite element analysis (FEA) and strain gauges analysis (SG) [12,13]. The numerical method using FEA allows the simulation of the load application and provides information regarding their respective stress and strain distributions [6], while the electric linear SG is a tool with high sensitivity that allows the analysis of strain peaks [14]. The association of these two methodologies allows a correct analysis of the events evaluated and aid to understand some clinical manifestations [15]. Given the foregoing, the present study aimed to evaluate the biomechanical behavior of Morse taper implants using CMN abutment (experimental group) and miniconical abutment (control group) to support a screw-retained 3-unit fixed partial denture, under axial load, using FEA and SGs. The null hypotheses were that the stress and strain distribution would be higher for the implant rehabilitation systems using CMN abutments compared with miniconical abutments.

2. Materials and Methods 2.1. Finite Element Analysis A regular Morse taper internal connection implant (4.0 × 13 mm), a CMN prosthetic abutment (Test group), a miniconical (MC) prosthetic abutment (Control Group), and a prosthetic screw (CMN: 1.8 mm; MC: 1.2 mm) were created according to the manufacturer’s dimensions (Intraoss, Sistemas de Implantes, Itaquaquecetuba, SP, Brazil) using ComputerAided-Design (CAD) software (Rhinoceros 5.4.2, SR8, McNeel North America, Seattle, WA, USA). To simulate the 3-unit fixed partial denture, the prosthesis from the experimental model was digitized with a scanner (Sirona, InEos Blue, Beinsheim, Germany) (Figure 1) allowing the acquisition of the stereolithography (.STL) file in the dental CAD software (CEREC inLab, Sirona Dental Systems, Erlanger, Germany). Then it was exported to CAD software (Rhinoceros 5.4.2, SR8, McNeel North America, Seattle, WA, USA) (Figure 2).

Figure 1. (a) Prosthesis on Sirona InEos Blue scanner base; (b) scanning; (c) silicone-based prosthesis
with the application of Cerec Optispray (Cerec Optispray, Sirona, Bensheim, Germ