**5. Conclusions**

Composites were prepared with PLS added to the filler phase at levels of 0, 4, 6, and 8 wt% and with monocalcium phosphate added simultaneously at double these levels. Upon incubating set composite discs with *S. mutans* and sucrose, a linear decline in surface biofilm mass and thickness occurred with increasing PLS level. Conversely, an abrupt increase in dead bacteria within the biofilm was observed with PLS levels above 4 wt%. Release studies sugges<sup>t</sup> this was a consequence of 24 h PLS release needing to be above a critical level to kill bacteria within the surface biofilms. Early PLS release from the composite was proportional to the square root of time, as expected for a di ffusion controlled process. Release levelled below 100%, suggesting it was from surface layers, which increased in thickness with raising PLS level. Upon damage of the composite restoration/tooth interface, either through polymerization shrinkage during placement or upon cyclic loading, a new composite surface was generated that was in contact with fluid. With rapid and su fficient PLS release from this new surface, risk of recurrent caries within the microgaps formed could potentially be reduced.

**Author Contributions:** Conceptualization, W.X., P.A., E.A., and A.M.Y.; Data curation, R.B.Y., W.X., and A.M.Y.; Formal analysis, R.B.Y. and A.M.Y.; Funding acquisition, R.B.Y., E.A., and A.M.Y.; Investigation, R.B.Y.; Methodology, W.X., E.A., and A.M.Y.; Project administration, E.A. and A.M.Y.; Resources, P.A., E.A., and A.M.Y.; Software, R.B.Y.; Supervision, P.A., E.A., and A.M.Y.; Validation, R.B.Y., W.X., P.A., E.A., and A.M.Y.; Visualization, R.B.Y.; Writing—original draft, R.B.Y.; Writing—review & editing, P.A., E.A., and A.M.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** W.X., A.Y., and P.A. were funded by National Institute for Health Research (Invention for Innovation (i4 i, http://www.nihr.ac.uk/funding/invention-for-innovation.htm)); optimisation and commercial manufacture of tooth-coloured composite dental-fillings with added poly-antimicrobial (PAM) and remineralising calcium phosphate (CaP), (II-LB-0214-20002), UK EPSRC (Engineering and Physical Sciences Research Council, https: //www.epsrc.ac.uk) (EPI/I02234/1); and Welcome Trust (Wtissf 3: Institutional Strategic Support Fund (Issf) Third Tranche, www.wellcome.ac.uk/Funding/WTP057769.htm), (ISSF/FHCE/0079, The National Institute for Health Research, University College London Hospitals, Biomedical Research Centre www.uclhospitals.brc.nihr.ac.uk. The funders had no role in study design, data collection and analysis, or interpretation, decision to publish, or preparation of the manuscript.

**Acknowledgments:** Authors would like to acknowledge Nicola J. Mordan for providing technical support.

**Conflicts of Interest:** The corresponding author Anne Young has, with Paul Ashley, had funding from NIHR and EPSRC. This funding supported the salary of Wendy Xia. In the future, the corresponding author and inventor on the above patents (Anne Young) may receive royalties if a commercial product is produced. The team is currently working with Schottlander Dental Company to aid CE marking of a similar product to those in the publication.

**Patents:** The work is covered by the following licensed patent families: Formulations and composites with reactive fillers (US8252851 B2, EP2066703B1, US20100069469, WO2008037991A1), and Formulations and materials with cationic polymers (PCT/GB2014/052349, WO2015015212 A1, EP3027164A1, US20160184190).
