**5. Conclusions**

Increasing polylysine concentration from 0.5% to 2% in composite discs leads to an increase in mass but not volume change over three weeks. Whilst the PLS-release percentage was faster in the first 24 h with 2% in the filler, the final percentage release was not a ffected by increasing composite PLS level. With 2% PLS, the amount released into 1 mL of broth in 24 h was su fficient to display significantly reduced bacterial levels when the initial inoculum level was at 8 × 105, but their growth in number was only inhibited when the initial bacterial counts were raised 10-fold. With an initial inoculum of 5 × 10<sup>6</sup> bacteria, those detected on the composite surfaces after 72 h were mostly live with 1% or less PLS in the composite but dead with 2% PLS. Higher PLS may enable the greater killing of residual bacteria when composites are used for minimally invasive tooth restorations. Considering the limitations of this study and taking into account work completed in previous studies [24–26], future research should include sucrose in the experiments to allow for biofilm growth on the discs to determine the e ffectiveness of PLS against biofilms, test multispecies biofilms and assess long term polylysine release and how this may a ffect the integrity of the restoration.
