Bacterial Microleakage and Bone Loss in Internal Connection Dental Implants Based on the Type of Abutment Used in Zirconia Partial Fixed Prosthesis: in Vivo Study

BACKGROUND

Since the discovery of osseointegration by Branemark, dental implant treatment has been growing in importance for the replacement of missing teeth until it has become the treatment of choice in most cases of partial and total tooth absences. Although in the beginning, implants were used to hold mandibular prostheses, they had a smooth surface, and the connection they presented on their platform was an external hexagon. These characteristics were established empirically in the absence of previous experience. Currently, implants are one of the most widely used dental treatments and have evolved both in their indications and in their design. Regarding their indications, they are used for the treatment of all types of edentulism, from a unitary implant to the rehabilitation of a complete arch. On the other hand, in terms of design, the modifications and variables are so numerous that it is impossible to list them all, but fundamentally, it has progressed on the surface, macroscopically and microscopically, achieving a greater proportion of tooth-implant union, and in the connection, moving from the initial external hexagon to internal connections with different designs: hexagonal, octagonal, morse cone, and hexagon, with the aim of preventing the complications that can appear in this type of prosthesis, both mechanical (the most frequent being loosening of the screw) and biological (mainly bacterial microfiltration).

The mismatch at the level of the junction between implant-abutment or implant-prosthesis in the case of a prosthesis directly screwed to the implant(s) has been and is one of the workhorses in implantology due to the influence it has on bacterial microfiltration, and this is demonstrated by the large number of studies that exist on this subject. In an ideal situation, this mismatch should not exist and should be cero, so that the bacteria existing in the oral microflora could not filter and accumulate in that implant attachment or implant prosthesis junction. In reality, it is impossible to achieve that perfection goal even in the manufacture of prefabricated machined parts and for unit implants, since a dimensional margin is necessary to allow their correct settlement, especially when connected directly to the implant (without the intermediation of a prefabricated abutment) by individualized manufacturing processes. That is why, from this point of view, it would be advisable to use prefabricated abutments in all cases of partial prostheses in order to keep the possible misalignment of the prosthesis away from the implant-attachment joint. This mismatch, however, must be understood not only as evaluated by different studies as a linear discrepancy but also from a three-dimensional point of view, since once it is accepted that the perfect fit does not exist, microfiltration will occur to a greater or lesser extent depending on the design of the connection; for example, it will not be the same in an external hexagonal connection as in an internal octagonal one.

The importance of bacterial microfiltration at the level of the implant-abutment junction from a clinical point of view is of special relevance since the accumulation of bacteria at that level, in most cases subgingival, could be directly related to the colonization of anaerobic bacteria, more aggressive, in locations that are difficult to access for sanitization by the patient. in such a way that they could favor the beginning of pathological bone destruction and the development of a peri-implant disease, complications of relative frequency, and that can be defined as infectious processes that occur in the tissues around the implants. When the inflammation around the implants presents with bone loss, bleeding, and/or suppuration on probing, it is considered peri-implantitis. It is a complication that is complicated and difficult to treat since the surface of the implant is contaminated and non-surgical treatments are usually insufficient to clean it, while surgical treatments are not only more aggressive but are also not inflatable and can also lead to aesthetic complications due to retraction of the soft tissues and even the exposure of the implant itself (metallic in most cases).

On the other hand, as for the implant prosthesis itself, its evolution since its origins with respect to its design and materials has also been very important. Among the materials used today to make fixed prostheses on implants, one of the most important is zirconia. Its use has become widespread because it has qualities that improve the materials considered until recently the gold standard, which were made with a metal structure (Titanium, Cr-Co, Cr-Ni, Cr-Ni, Cr-Ni-Pa, Pa-Co, etc.) and the aesthetic coating of porcelain, added by a brushstroke process carried out by a laboratory technician and then fired in processing ovens. Among the advantages of zirconia are: its CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) manufacturing, i.e., computer design and manufacturing by milling process (as it can be milled in a softer, pre-synthesized phase, improves metal milling, makes it cheaper, and involves much less wear); its biocompatibility; and its aesthetics, as it is a white material. This quality allows the creation of prostheses without the need for aesthetic coating, known as monolithic zirconium. This modality, monolithic zirconium, is one of the most used treatment alternatives in fixed prostheses on implants because it also manages to solve one of the most frequent mechanical complications in fixed prostheses on implants, which is the porcelain jump or chipping. The term "chipping" is defined as "the detachment of one material attached to another when subjected to a load, separating the two".