Introduction Microbial leakage at the

Introduction Microbial leakage at the implant-abutment connection is a chief challenge for the construction of the two-stage implant systems. Gaps and cavities are formed between the implant and the abutment which lead to microbial leakage. This leakage is a major contributing factor for peri-implant inflammatory reactions [1,2]. In the two stage implant placement technique, the implant is placed at the bone crest level and, after 3–6 months, a prosthetic abutment is installed on the implant to connect the implant to future prosthetic restorations (crowns, bridges or dentures), creating a micro-gap between the implant–abutment interface that could present a risk for bacterial colonization [3,4]. The amount of bacterial colonization between the implants and abutments depends on the fit accuracy between the fixture and abutment, their tightening torque and micro-movements between the connected components during mastication [5–8]. The goal of preventing bacterial infiltration at the implant abutment interface was to minimize the inflammatory reaction and therefore maintain the bone around the implant top [9,10]. Several attempts to obtain a more secure connection between the abutment secretase signaling and the implant fixture have been studied. External and internal connections, such as hexagonal, conical (Morse taper) or a combination of both, are generally the most commonly used connections. The internal implants abutment connection is reported as being more favorable to the infiltration of fluids than other joints. The microgap in this implant design varies from 1 to 49 μm, depending on the type of abutment that is selected [11–13]. Different bacterial species with varying sizes from 1 to 10 μm were used in several in vitro studies [6,12,14–17] to detect bacterial infiltration in microgaps. However, biologically small molecules like toxins and molecular constituents of the bacterial wall are responsible for inflammatory reactions. These small molecules can penetrate much smaller gaps than whole bacteria. It is well known that endotoxin, a small molecule complex of lipopolysaccharides and proteins, is one of the most important toxins of gram-negative bacteria and plays a major role in bone destruction processes [11,18,19]. Microleakage has been confirmed to occur in both directions, from the inner parts of the implants to the external environment and vice versa. Reported measures to prevent or minimize bacterial contamination of the implant–abutment interface, such as the use of sealing materials, decontamination of the inner-implant cavity, use of shape memory alloy and different connection geometries, have been unsuccessful [15,20,21].
Material and method
Microbial sampling and detection All implant abutment assemblies were submerged in sterile tubes containing 4 mL of S. aureus broth culture and were incubated at 37 °C for 14 days. After 14 days of incubation, the specimens were removed from the test tubes using sterile pliers, immersed in 70% alcohol for 3 min to prevent external contamination, and dried with sterile gauze. The specimens were disassembled carefully. After disassembling of the specimens, the inner surfaces of the implants were sampled by sterile paper points for bacterial contamination. Then the paper points were immersed in test tubes containing sterile BHI broth. From the broth, culture was done on blood agar plates and incubated at 37 °C for 24 h. Thereafter, the resulting colonies were identified by Gram\'s stain and biochemical reactions. Figs. 2–3.
Results Data were presented as mean, median, standard deviation (SD) and range values. Mann–Whitney U test was used to compare between two groups. The significance level was set at P ≤ 0.05. Statistical analysis was performed with IBM® SPSS® Statistics Version 20 for Windows. There was a statistically significant difference between the two groups (P-value <0.001). Internal hexagon implants showed statistically significant higher mean Log10 CFU than Tri-loaded implants. Table 1.