Implants have been around for many years already, having a lot of advantages and high success rates, by some authors even higher than 90%. Nevertheless, throughout the years, problems and failures have occurred in practice which led to bone loss around the implants and even, in some cases, to losing the implant itself. The phenomenon behind this pathological process -peri-implantitis - is believed to be the microleakage which occurs at the implant-abutment interface.This happens due to the existence of a gap present between the implant and the prosthetic abutment. Moreover, the microleakage is amplified because of the, so called, pumo effect. The pump effect occurs when the crown-abutment complex is subjected to occlusal, vertical and oblique, forces. During these micro-movements of the abutment, the microleakage intensifies and the bacteria can easily enter inside the implant, where is impossible to reach and remove through oral hygiene, thus, creating the perfect conditions for peri-implantitis. There are two major types of implant-abutment connections widely used nowadays -internal hex and conical -which are believed to influence the phenomenon and, so, the outcome. In the present study, both types of connections are tested, using Streptococcus Mutans, a common bacteria found in the oral cavity.

The aim of this work is to assess the crystalline structure modification of an SLM Co-Cr-W dental alloy, veneered with two different ceramics, by means of X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy, coupled with energy-dispersive spectroscopy (SEM-EDS). Ten identical plates were fabricated using SLM and were subsequently subjected to ceramic veneering. Following the repeated firing of the ceramic layers, carried out at temperatures exceeding 900 °C, new crystalline phases and variations in the crystallite sizes in the SLM Co-Cr-W dental alloy used for the substructure were detected via XRD. The two veneering ceramics showed significant differences in their behavior, beginning with the first firing, accompanied by structural changes. AFM micrographs and histograms of the surface heights over the whole scanned area of the samples showed that the surface of the Co-Cr-W dental alloy is strongly affected by the repeated firings necessitated by the ceramic firing process, a finding in accordance with the XRD results. The SEM investigation revealed that the different firing parameters had an impact on the alloy, the ceramic microstructure, and the surface quality. The differences in the chemical composition of the ceramics, highlighted by EDS, are reflected in their behavior. The crystalline alloy structure is influenced by the repeated firings of the ceramic layers.