In Vitro Study on the Eligibility of Antibacterial Agents for Modification of Silicone in Implant-Abutment Interface Sealing



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In search of a solution to the insufficient seal of implant-abutment interfaces, with persisting bacterial penetration into the inner cavity of implants and therefore the possibility of bacterial leakage into surrounding tissues, an antibacterial modification of sealing silicone for the implant-abutment interface was investigated. One of the main reasons bacterial leakage should be avoided is an increased inflammation (peri-implantitis) with the risk of implant loss. Three agents for modification were microbiologically tested in regards to their ability to maintain their antibacterial properties and bestow them to a silicone matrix after integration. In case of microbiological success, further mechanical tests followed with the material being applied to the implant-abutment interface. The chosen agents were zinc oxide, copper naphthenate and silver 2-ethylhexanoate. Pure zinc oxide, copper and silver are known for their antibacterial properties. The microbiological experiments consisted of an agar diffusion test, biofilm assay and a measurement of bacterial growth (inhibition) in liquid medium. Zinc oxide, integrated into the silicone matrix, did not display antibacterial activity in any of the three experiments. Thus, zinc oxide was dismissed for subsequent mechanical experiments. High concentrations (> 20%) of copper naphthenate displayed great antibacterial efficiency in inhibiting bacterial growth in surrounding liquid medium. Also, there was a measured decrease in biofilm formation, but the results may rather be due to an unexpected change in colour retention, than due to less biofilm formation. Agar diffusion test did neither show inhibition zone formation around specimens, nor a reliable inhibition of bacterial growth in direct contact (underneath the specimens). Silver 2-ethylhexanoate led to formation of inhibition zones in the agar diffusion test with a positive correlation between agent concentration and inhibition zone size. The best results were achieved at 10% and 8% silver 2-ethylhexanoate. Biofilm formation was not too greatly influenced by the modification and there was no measurable bacterial growth inhibition in surrounding liquid medium, but rather more of an optical density (the method of measuring bacterial density). In the subsequent mechanical experiments the change in opening torque, as well as the change in the 3D distance between two measuring points – one on the implant, one on the abutment – were measured to evaluate whether the desired positioning was still reached after modification. Seals with 25% copper naphthenate modifications were compared to seals with 10% silver 2-ethylhexanoate and references: a pure silicone seal and empty implants. There was no significant influence of any of the tested materials on opening torque and positioning. Also, no breakage of connecting screws occurred. Within the limits of this study, silver 2-ethylhexanoate and copper naphthenate seem to be suitable for antibacterial modifications of silicone in implant abutment sealing, but further in vitro research should be conducted before in vivo application: in case of silver 2-ethylhexanoate to rule out a negative effect on bacterial counts in surrounding tissues, and in case of copper naphthenate mainly in regards to toxicology and odour.




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