Lygidakis, Nikolaos; (2017) Antibacterial properties of novel dental composites for paediatric dentistry. Doctoral thesis (D.Dent), UCL (University College London).

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Abstract

Aim: To assess the antibacterial properties of novel dental composite formulations containing the antibacterial polylysine and varying type or amounts of monomer/glass/calcium phosphate. / Methods: Minimum inhibitory/bactericidal concentrations of polylysine against Streptococcus mutans UA159 were determined. The antibacterial activity of composite discs with polylysine was determined by immersing the discs into a suspension of S. mutans and carrying out bacterial counts. All the results were compared with commercial materials. Mass and volume change of the material as well as polylysine release were determined over time and compared for multiple formulations containing polylysine. Bacterial growth was visualised on the discs using LIVE/DEAD staining with confocal microscopy and using scanning electron microscopy. / Results: The addition of a minimum 1% polylysine to the novel formulations inhibited bacterial growth at low inoculum density and the addition of a minimum 2% polylysine inhibited bacterial growth at all inoculum densities in air. In an atmosphere of air enriched with 5% carbon dioxide and in the presence of sucrose there was a bacteriostatic effect with 5% polylysine addition. None of the commercial materials showed any antibacterial properties. Increasing the amount of polylysine in the novel composite formulations increased mass change over two months and increased polylysine release over three weeks. Volume was not significantly affected. Using SEM, bacterial growth was seen on composite discs after 4 days incubation in a suspension of S. mutans at 37oC in air with 5% carbon dioxide. It appeared that a biofilm was formed under these conditions for all formulations and commercial materials whereas in air, there was minimal growth. Using confocal microscopy an increase in dead bacteria was seen as the polylysine concentration increased in both air and in air with 5% CO2. / Conclusion: Novel composites with added polylysine are capable of reducing the load of Streptococcus mutans. These above experimental composites have novel characteristics that make them more suitable for minimally invasive tooth restorations. Key words: polylysine, composite, restoration, antibacterial properties

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