Marginal Adaptation and Microbial Leakage at Conometric Prosthetic Connections for Implant-Supported Single Crowns: An In Vitro Investigation

Abstract

Encouraging clinical results were reported on a novel cone-in-cone coupling for the fixation of dental implant-supported crowns (Acuris, Dentsply Sirona Implants, Mölndal, Sweden). However, the presence or absence of a microgap and a potential bacterial leakage at the conometric joint has not yet been investigated. A misfit and a resulting gap between the conometric components could potentially serve as a bacterial reservoir that promotes plaque formation, which in turn may lead to inflammation of the peri-implant tissues. Thus, a two-fold study set-up was designed in order to evaluate the bidirectional translocation of bacteria along conometrically seated single crowns. On conometric abutments filled with a culture suspension of anaerobic bacteria, the corresponding titanium nitride-coated (TiN) caps were fixed by friction. Each system was sterilized and immersed in culture medium to provide an optimal environment for microbial growth. Positive and negative controls were prepared. Specimens were stored in an anaerobic workstation, and total and viable bacterial counts were determined. Every 48 h, samples were taken from the reaction tubes to inoculate blood agar plates and to isolate bacterial DNA for quantification using qrt-PCR. In addition, one Acuris test system was subjected to scanning electron microscopy (SEM) to evaluate the precision of fit of the conometric coupling and marginal crown opening. Throughout the observational period of one week, blood agar plates of the specimens showed no viable bacterial growth. qrt-PCR, likewise, yielded a result approaching zero with an amount of about 0.53 × 10−4 µg/mL DNA. While the luting gap/marginal opening between the TiN-cap and the ceramic crown was within the clinically acceptable range, the SEM analysis failed to identify a measurable microgap at the cone-in-cone junction. Within the limits of the in-vitro study it can be concluded that the Acuris conometric interface does not allow for bacterial translocation under non-dynamic loading conditions.

Bacterial translocation and microgap formation at a novel conical indexed implant abutment system for single crowns

“…While a significant difference in qrt-PCR results was shown between the positive control and all three test groups (p < 0.0001), no difference could be detected between the negative control and the test groups the influence of the implant-abutment (I-A) microgap on marginal leakage [15][16][17][18][19][20][21][22][23][24]. This is in contrast to the limited data available on the fit and potential for microbial leakage at conometric prosthetic connections [7,10], Clinical evidence of bacterial sealing of the taper coupling at the restorative level is lacking to date. Marginal and internal fit at the abutment-prosthesis interface are critical determinants as they are directly related to bio-integrity, microbial sealing, and maintenance of peri-implant tissue health [25].…”

“…While 4 µl of mixed bacterial culture was filled directly into an Eppendorf tube as a positive control, 4 µl of pure culture medium (CDC) in one of the Acuris abutments served as a negative control. Incubation was maintained at 37 [10,[12][13][14].…”

“…The contained solution was processed with a deoxyribonucleic acid (DNA) Isolation Kit (innuPREP DNA Isolation Kit, Analytik Jena AG, Jena, Germany). In concordance to outgrowth testing, the DNA was quantified with qrt-PCR using universal and specific primers for the examined bacterial strains [10,[12][13][14] (Table 1).…”

“…Acuris Astra EV-2a A curis Xive-2b of methodology, the application of qrt-PCR has been previously proven to be an accurate screening tool with a high diagnostic sensitivity for the determination of microbial migration in a pilot study by the authors [10]. Providing consistent positive and negative controls through both directions of the assay setup rendered reliable results.…”

“…Furthermore, the interaction between metal surfaces and the oral environment may lead to the release of implant degradation products into the peri-implant sulcus, which exposes the microbiota to increased environmental stress and subsequently change immune responses to bacteria [8,9]. A recent pilot study on the microbiological sealing of the novel Acuris junction revealed no bacterial translocation at the conometric interface [10]. However, since this investigation only examined a relatively small number of specimens for a single implant system, verification of these results in a larger group of specimens for different implant abutment configurations is required.…”