Why is there a myth that British people have bad teeth?

If anything wouldn't Americans have worse teeth? Since the Brits get free dental care? If someone could just tell me how this stereotype originated I'd appreciate it! :) Ta very much. xx
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Its often thought that Americans have better teeth as mentioned previously in this thread due to having the teeth shaped and veneered, this does make them look whiter and more uniform giving the quintessential American smile, however, this procedure can actually damage the teeth as the dentist has to shave off a tiny slither of the tooth so the veneer will fit flush to the correct place on the gum, this can make the tooth weak and susceptible to long term damage, as dentists in the UK will usually try to save an original tooth and this kind of potentially damaging cosmetic surgery is not carried out so often, this could indicate that whilst teeth in the UK are not so white and uniform, they are actually healthier.
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