Whats your diet? I'm not trying to ignite the traditional HN flamewar about the evils of a science based paleo diet, but I have had a similar experience where not eating grains or sugar none the less results in a relatively tartar free mouth per my dentist. Even though I hate waiting and am impatient and do not visit every 3 months or whatever often its supposed to be.
Archeologically, before people started eating grains and processed "psuedo-food" we mostly died with good teeth and its a stereotypical observation that you can tell when grain agriculture sets in with a people when their teeth start rotting out at a young age.