The comments were really interesting to read. They remind me of a lab phenomenon I call 'protocol mythology'. It starts like this: you're busy in the lab, homogenizing your samples, centrifuging your tubes, cloning your DNA fragments, running your gels, when suddenly... things go pretty much the shape of a pomaceous fruit (hint: it's not an apple). The arduous task of troubleshooting begins. You retrace your steps back to that part of the procedure when things were still working. What came next? Did you precipitate at room temperature, or on ice? What was the pH of the buffer again? Perhaps the restriction enzymes are not compatible with your extraction method. What voltage did you run the gel at? The protocol therefore gets altered, often changing many variables at once in order to save time. Big mistake. And yet, changing it up seems to have worked - the DNA fragments on your gel are of the right size. Hurrah for troubleshooting! This is how the grad lab protocol myth gets born: one student will suggest the set of in-house modifications (which they spent simply months optimizing) to the next student, who then passes it along. Newbies are often intimidated into compliance with tales woe and crying under lab benches. I know I was. Who wouldn't follow the sound advice to rather use that laminar flow cabinet instead of this one, unless you want guaranteed yet unexplained contamination of your agar plates? We can't explain why, all we know is that it works. Don't argue with us - we know what we're talking about. Or do we?
Back to the mouthwash. It seems so much like a snowballing mass hysteria thing to me. Almost everyone has at least some kind of discoloration to their teeth. This is usually in the hard-to-reach areas, like between the bottom teeth, right at the gum line. It's a spot that goes without close scrutiny for the most part - but you're bound to find it if you go looking for it specifically. And what better time to investigate your gumline than after reading a scary report that everyone who has used your new brand of mouthwash was left with stains making them look like champion tobacco chewers? As disinformation gets spread around, the whole thing takes on a mythology of its own. The staining gets rapidly attributed to various things, including the blue dye in the rinse (so why are the stains brown?) and the presence of stannous fluoride (although the Pro-Health toothpaste does contain fluoride, the mouthwash does not and besides, dental fluorosis only occurs during tooth development). Some people spit out blue gunk after using it: how strange and unexpected! Who could have guessed that the active ingredient designed to rupture microbial membranes and act as a detergent to collect cellular debris might actually do its job? We can't be having that! People have poured the contents of their bottles down the drain, or returned them and demanded refunds. The stuff of urban legend. And then there are those who have completely lost their sense of taste after using it. Now that's scary, isn't it? Truth be told, I've never used a brand of mouthwash that didn't extinguish my sense of taste for a couple of hours. Actually, I've never had a gin & tonic that didn't do pretty much the same thing.
We all react differently to different products. Some people are allergic to peanuts, others to tomatoes, some to antibiotics, some to anything that isn't cashmere, Dahlinks! That doesn't mean we should take peanuts, tomatoes or acrylic sweaters off our shelves. Well, maybe the acrylic sweaters at least... The point is that everything we consume, whether it be food or medicine (or both, in the case of nutraceuticals and dietary supplements) has side effects or is toxic to some degree. Yes, even water. The next generation of mouthwash is no exception to this. The brand in question uses cetylpyridinium chloride instead of alcohol to battle bacteria, making it an attractive, non-dehydrating alternative for children, diabetics, the aged... and recovering alcoholics, naturally. The bacterial remnants and salivary proteins disrupted this way can attract tannins from food, and form brown residues in the crevices between teeth. This is will be especially noticeable in only about 7% of people who use the product. And one person out of a million having a bad reaction to one of its ingredients doesn't imply that the product is no longer of any use to the population at large. If that were the case, we wouldn't have any antibiotics left to treat disease with. Or, indeed, food. So there you go. Since stains are not harmful, the rinse has not been slapped with a warning label. Neither are pineapples, which contain enzymes that can cause bleeding, by the way... Is the Crest Pro-Health Oral Rinse responsible for stained teeth? In some cases, probably. Does this warrant all the disinformation-based consumer hysteria? Probably not, although P&G are partly to blame for not explaining the possible side effects and their origins clearly enough. And so fear and ignorance creates a whole 21st century mythology around what is actually a marvelous advancement in human health. From chunky blue saliva to evil fluoride to burned tastebuds... to oral cancer, presumably.
All I know is that once the lab protocol fails again (as it inevitably does) reverting back to the original procedures, presented in Molecular Cloning: A Laboratory Manual by Joseph Sambrook and David W. Russell more than twenty years ago, always gives you the desired results. All that tweaking was just weaving a myth.