Your question:Is there such a thing as over-bleaching your teeth?
Answer:Bleaching is very safe and over-bleaching cannot occur unless you are extreme and do not follow the instructions. There is little reason to attempt to over-do: Teeth will only whiten to a certain point -- at that point, they don't get any brighter -- as teeth are not meant to be truly white.
Some people report sensitive teeth after using home bleaching gels/strips. If this is a problem, you may want to increase the interval between whitening sessions and/or use a toothpaste such as Sensodyne.
Factors that affect tooth color are genetics, aging, certain medications, overfluoridated water and some colorants found in coffee, tea and carbonated drinks.
Home bleaching works by oxidizing proteins that adhere to your teeth (but note that tooth whitening treatments will not bleach artificial dental materials, such as those used for veneers, bonds or crowns.) One thing to keep in mind if you use a home whitening kit: do not drink or eat anything colored, such as colas and coffee for two hours after you take out the trays or remove the strips as this will lessen the effect of the whitening treatment.
The good news is, if you think you have over-whitened your teeth, just wait a few months and they will slightly darken to a less intense shade of white.