How much toothpaste is safe to swallow for a 3 year old?

My son doesn't like to brush teeth and he is probably no exception. In order to protect his teeth, we started to use a fluoride-containing tooth paste when he was about 2 years old. However, we were always careful and didn't let him swallow the toothpaste in order to avoid overdosing. There are likely still quite a few cases of acute fluoride poisoning in small children every year (Shulman & Wells, 1997) and not surprisingly they are mostly caused by ingestion of large amounts of fluoride containing toothpaste. Just now I made the calculation and my son was probably never in danger of overdosing due to the fact that the water we get here in Helsinki from our local utility supplier Helsingin Vesi is very low in fluoride (0.1 mg/l or 0.1 ppm). He brushes his teeth twice a day and uses each time a pea-sized amount of tooth paste (equaling about 0.15 g). The toothpaste he uses (OralB Stages) contains 0.11% sodium fluoride (equaling 0.05% fluoride). This means that if he swallowed all of his toothpaste he would ingest 0.15 mg of fluoride per day. This is 30% of the daily amount of fluoride supplementation recommended by the American Dental Association for children between 3 and 6 years of age and still less than the daily amount recommended for children of ages between 6 months and 3 years (0.25 mg). I have not encouraged him to swallow the tooth paste although there seems nothing to argue against doing so apart from my parental inconsistency. Daddy probably doesn't know as he changes his mind all the time... But I guess since he is chewing very avidly his xylitol chewing gum, he should be fine even without much fluoride.