Dentistry and fillings
At my checkup the week before the oral hygienist noted "some minor cavitation", and in the mirror I saw 2-3 dark patches on the molars. She called in the dentist and read out a long list of alphabet soup while he poked the corresponding locations with the dental explorer. Nonetheless, I was surprised on Monday to discover that there were six fillings to be done, on tooth numbers 26 OP, 27 OP, 17 OP, 16 OP, 47 O and 46 B (O=occlusal or biting surface, B=buccal or cheeck side, P=palatal or towards the palate), and the oral hygienest confirmed these were the ones. The fillings themselves were mostly-painless, and used a modern light-cured dental composite, where a bright blue light drives a polymerisation reaction, turning the filling putty into a hard tooth-coloured substance. Acid-etching beforehand gives the composite a micromechanical bond to the enamel and dentine, so the filling is pretty much one with the tooth.
After I left I wondered - how many of the fillings were really necessary? Some could have been reversible demineralised regions or incipient decay being filled preventively, rather than real cavities. Preventive dentistry isn't necessarily the best route, since fillings don't last forever (although 10+ years is usual on modern composites, even on molars), and they can go wrong rapidly if a leak occurs that allows bacteria inside. Fillings really do need the 6-month checkups they always tell you to have, because if a leak goes undetected you could find yourself needing a root canal. Seems I'm in for a lot of checkups over the rest of my life.
I read up and found that unnecessary treatment is common, but after the filling all evidence of what was there before is gone. What you are supposed to do is ask the dentist, at the checkup, to show you each site of proposed filling one at a time. If there is no visible cavity, there should be a good explanation (e.g. interproximal cavities may show only on X-rays).
If the dentist says "it is likely to be come a cavity", then you are better off taking it as a warning to modify your oral hygeine and diet rather than getting a filling. I think my problem was that October through February I got into a habit of eating chocolate on campus, at a rate of about 1 square per hour or two. Because my tooth-brushing and flossing habits were fine and I'd never had problems before, it never occured to me that adding a few squares of chocolate to my diet would cause cavities. As it turns out, prolonged sugar levels in the mouth feed acid-producing bacteria, which demineralise the tooth enamel, eventually forming cavities. Rather than brushing during the day, you're supposed to rinse your mouth with water to remove sugars and particles before they feed the bacteria: but that doesn't work with chocolate, toffee or other things which stick to your teeth.
So, don't snack on sticky sweet things between meals (fruit may be ok because fibres remove bacteria and aren't sticky), drink water after eating things, wait 10-20 minutes before brushing to soften particles stuck in your molars, brush carefully morning and evening after meals with a non-frayed toothbrush, and floss daily before brushing. That's the comprehensive diet-and-hygiene way to avoid getting (more) cavities.