I was wondering why the teeth of cats (And dogs, as far as I know, plus possibly some other animals or even humans) get darker if they are exposed to air / light?


Animal tooth

(See the lower end of the tooth, which sticks out if the mouth is closed. No, the cat was not resisting, just slightly annoyed.)

So, my question is:

  • Why does this happen?
  • Would it happen to human teeth, if they would stick out of the mouth like the ones of cats do?

My guess is that it has something to do with the teeth reacting to air and corroding, but all my knowledge about biology comes from two years of biology in school, so I'm asking here.

  • 1
    $\begingroup$ Could you provide evidence that this is frequent or invariable? I can think of an explanation, but I'm unsure if this is common. $\endgroup$
    – CHM
    Apr 3, 2012 at 3:00
  • $\begingroup$ it probably wouldn't happen if they brushed their teeth more. Its hard to imagine human teeth are that different... :) $\endgroup$
    – shigeta
    May 26, 2012 at 6:21
  • $\begingroup$ Yeah. I think it has something to do with REDOX. $\endgroup$
    – tech
    Nov 17, 2012 at 11:09
  • 1
    $\begingroup$ As far as I know, oxygen and other oxidizing agents make the teeth whiter by bleaching it (Potassium permanganate and hydrogen peroxide solutions are used to bleach teeth). Anyways, your question isnt addressable as long as you dont support this with some more evidence. [More biological replicates!!! <Just like a sadistic reviewer> :P ] $\endgroup$
    Apr 8, 2013 at 13:04

2 Answers 2


The incisal and occlusal edges of teeth are more translucent since there is only enamel in this area and the dentin core is deeper inside. The dentin is more opaque and reflect the light back and it looks lighter whereas the enamel is translucent and allow more light to pass through and less light is reflected back so it looks darker. Many human teeth the incisal edge is translucent or darker for the same reason.


According to me animals use these teeth to chew meat particles etc. So because they don't brush these food particles get exposed to bacterial agents which in turn causes corrosion of teeth. As we see the structure of the animal teeth the food particles are trapped in between resulting into high bacterial corrosive activity. But in humans, regular maintenance and high use of water it decreases the acidity caused by the food in our mouth this prevents excessive corrosion and bacterial activity and growth. On the other hand canines have an initial use of tearing so the usually are not much affected by the food particles and also because of their protruding shape. The exposure of air and light increase the bacterial activity.

  • 4
    $\begingroup$ Do you have a reference other than yourself? $\endgroup$
    – blep
    Jun 29, 2013 at 17:40
  • $\begingroup$ This has the right idea, but the baffling (if refreshingly honest) "reference" needs to be corrected. $\endgroup$
    – Superbest
    Apr 21, 2014 at 20:54

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