About 3 weeks ago, Lisa asked us why adding cream to your coffee (or milk to your tea for those of us with British heritage) would prevent or reduce staining to your teeth. When I first started looking into this question I thought there would be no problem finding a straight-forward, highly researched answer. After all, we live in a society that’s clearly obsessed with a whiter smile. When visiting a new dentist this past month, half the questions on the intake sheet had to do with my level of concern over how white my teeth were (turns out I was more concerned by the inability to close my jaw – but it’s good to know someone’s looking out for my aesthetics).
Yet despite all of the commercial interest in whiter teeth (most consumer reports site Americans as spending just over $1 billion on whitening products a year), scientists apparently have better things to research as there is very little in the scientific literature on the causes of tooth staining. What little research there is tends to focus on the staining of tooth composites – things like resins that are used in crowns or false teeth.
Never fear though! After an exhaustive search (more on the physical than amassing side), we have come up with some extensive great background information on exactly what causes tooth staining that is sure to bore wow you!
Before you go running off to get the newest, fastest “bleaching kit” to ensure your pearly whites* stay their brightest, you should understand that not all teeth are created equal. In colour that is. In fact, tooth colour not only varies between people, but also on individual teeth. For example, the gingival (gum) margin is usually darker than the rest of the tooth; canine’s are typically darker than the central teeth; younger people have lighter teeth; and due to differences in lighting your teeth can change colour throughout the day!
But tooth discolouration does exist, and it can be classified based on if it’s caused by intrinsic or extrinsic factors.
Intrinsic discolouration results from changes to the actual dental tissue. While ‘normal’ tooth colour is determined by the pigments of the enamel and dentin, metabolic diseases and systemic factors can affect the developing dental tissue, resulting in changes to tooth colour.
Extrinsic factors are those that cause staining to the tooth after development, from things like food or metals. Many foods contain organic chromogens which impart the natural dark pigment you see in coffee and red wine. Unfortunately, chromogens can be easily incorporated into the outer layer of the tooth (the pellicle) resulting in staining. The more often you drink, the more staining you see.
Tannins are a related group of large polyphenols found in a bunch of plant extracts – including coffee, tea, and red wine – that readily bind to proteins. In fact, binding to proteins is how tannins got their name – tree bark solutions rich in these molecules were used to tan leather back in the days of yore. The teeth in your mouth are covered in a thin layer of protein, the pellicle, which will bond to tannins in coffee and tea and cause tooth staining. Chromogens can also bind to tannins, increasing the chance of staining.
As a grad student who’s diet consists of vast quantities of coffee, tea, and red wine, this is distressing news for my smile.
So what if you add milk or cream to your coffee?
You might remember from our brief explanation of why old milk curdles in coffee that dairy proteins, such as casein, bond to tannins and other phenolic compounds in tea and coffee. In the same way that the protein-tannin bonds reduce the astringency (the “fullness” of tea, coffee, and red wine, caused by tannins binding proteins on the inside of your mouth), it also limits the number of free tannins available to bond with your tooth pellicle. I couldn’t find a study that compared the binding kinetics, how fast and tightly the binding occurs, of dairy and pellicle proteins, but considering the amount of time the tannins have to interact with the milk versus the pellicle, I’d say it’s a safe bet that few tannins that pass through your mouth release the bonded dairy proteins in favour of your teeth.
In fairness, there are some gaps in the evidence, but the logic train goes like this: tannins in coffee and tea bind to the pellicle and cause tooth staining, dairy proteins found in milk and cream readily bind to tannins, tannins bound to dairy proteins will be unavailable to bind to your teeth, so adding milk or cream to coffee and tea reduces tooth staining.
Unfortunately, because not all tannins will bind with the cream, and because the chromogens will still stain your teeth, the only way to avoid tooth discolouration is to completely forgo that cup of java. But really, who’s gonna go that far?
Thanks for the question Lisa! As always, we love getting your comments. Please take a moment to ask your own question or say what you think about this or any other article!