Study	Reason for exclusion
Scheinin 1975	Xylitol (plus sorbitol and 'other polyols') gum versus sucrose (plus sorbitol and 'other polyols') gum. No appropriate control group as sucrose is cariogenic (causes caries)
Kandelman 1990	Cluster randomised controlled trial but with serious problems with the randomisation procedure (some of the clusters were self selecting i.e. some schools did not allow chewing of gum in the classroom and therefore they were the controls and were not randomly assigned)
Alanen 2000	Sealants versus 2‐year use of xylitol gum versus 3‐year use of xylitol gum. No appropriate comparison of interest
Alanen 2000b	Cluster randomised controlled trial but with serious problems with the randomisation procedure (some of the clusters were selectively rather than randomly assigned)
Machiulskiene 2001	Cluster randomised controlled trial but with one cluster per arm, and therefore of inappropriate design
Kovari 2003	Children using xylitol gum but not brushing teeth during daycare hours versus children brushing their teeth with fluoride toothpaste during daycare hours (after lunch) but not using xylitol gum. No appropriate control group
Chi 2014	Cluster randomised controlled trial but with two clusters per arm, and therefore of inappropriate design
Lee 2014	The study authors kindly provided us with a prepublication copy of the study and we were able to see that the intervention was only given for 9 months. Our inclusion criterion states that the intervention must be given for at least 1 year