Competing interests
N.D. had an advisory role at GlaxoSmithKline (GSK) and was awarded a GSK Consumer Healthcare (GSKCH) research grant, which provided funding for this study. ND has also lectured for Oral-B. S.T. is a GSK Global Health Consultant. J.P., N.G., A.P., M.T. and M.C.M. do not report any competing interest.