what do you mean I have 10 cavities ??? ... or why you need to floss

Believe it or not, one of the scenarios I dread most is when a new patient who hasn't been to a dentist for a year or two, does not have any dental pain, comes in for an exam, and a large number of cavities appear on the radiographs ('x-rays'). First, the patient is skeptical - who wouldn't be - here she is lying down powerless, and a total stranger, who has every incentive in making a big deal of every little dark spot in her mouth, tells her that she needs a ton of dental care. Second, it's expensive (good dental care is time consuming and relatively pricy). Third, all the patient wanted in the first place is a cleaning and maybe whiter teeth. As you can imagine, tip-toing around this is quite challenging...

Why does this happen?

First a little tooth anatomy: Teeth are composed of three layers: the outer dense 'protective' layer is the enamel (the hardest substance in the human body), then there's dentin - the softer/'shock absorbong' layer, and finally, the pulp chamber - where the blood supply and nerve structure of the tooth is.

And some basic x-rayology: Dental x-rays show gradients of density - the denser the structure in which the x-ray is passing through, the brighter it appears on the radiograph (the x-ray film), so enamel appears the brightest, then there's dentin, then the pulp chamber, which appears very dark, because it's hollow and houses blood/nerve tissue. The most commonly used type of x-rays are two-dimensional - the entire three dimensional structure of the tooth is projected on a two-dimensional film.

Back to the discussion above:

Ironically, one of the culprits is Fluoride. One of the ways in which fluoride is thought to prevent caries is by making teeth denser, hence less prone to acid attacks - this is fantastic! but... one type of 'cavity' you can have is in between teeth (we'll talk about other kinds in later posts). It starts as a small de-calcification within enamel - because the entire tooth is being projected onto a 2D film, the denser areas obliterate the less dense decalcified area in the middle, and cavities are not seen on the x-ray. This creates a false sense of comfort for the patient - "I don't floss now, and I don't have any cavities...see, I don't need to floss..." But, just because it doesn't show up on the x-ray now, doesn't mean it's not there!

By not flossing, food particles are left in the area/fluoride is prevented access to that area (will discuss caries progression in a future post) advancing caries...you have 28-32 teeth in your mouth, unless you've lost more, and this process is going on in between each one of them. They won't be detectable on an x-ray until they've progressed large enough to destroy a significant amount of dentin (the softer stuff) and are impossible to see in your mouth visually, because they're in between teeth. So unless you're flossing semi-regularly, you may find yourself at the dental office being told you've got 10 cavities!