I used Crest 3D white strips and now my teeth are very sensitive. Any idea how long it'll last?

You can generally expect the sensitivity to greatly decrease over the next 10 days.  I usually have my patients take two 200 mg ibuprofen tablets to decrease sensitivity caused by over-the-counter whitening agents.  I also recommend using tooth paste that is made for sensitive teeth.  For my patients, a combination of these two things reduces or eliminates the pain drastically over the next few days.  Good luck and I hope this helps. Follow me if you have more questions.Sarah Thompson, DMD

Thank you for asking a great question. Sorry to hear that your experiences pain during supposedly easy process of teeth whitening using Whitestrips.Everyone is different and we react differently to whitening products.
Usually sensetivity is transient and will go away within a short period of time like a day or two. If it does not, consdider seeing a dentist experienced in teeth whitening to rule out possible presence of caries and/or recessions of the gums, which could make your teeth very sensetive and hurting.All the best to you.

 This is a common post-op problem and can be very painful.The pain is from your teeth being stripped of some of the elements that block communication between the outside world and the inside of the tooth or "pulp chamber". The good news is that its easy to fix though. All you need is a good coating of fluoride from either a professional application or from a high strength fluoride toothpaste like Fluoridex, or Prevident 5000. Both of these are prescription only so if you are unable to get your doc to prescribe these, the next best option is Sensodyne. You should get some siginificant relief after the first 1 or 2 uses. If you continue to have sensitivity, ask your dentist about a stronger desensitizing application. There are several that work well, like CalmIt and GLUMA. Good luck!

Sensitivity is a normal side effect of teeth whitening.  Whitening products like carbamide peroxide or hydrogen peroxide work by penetrating the enamel surface to get to the discolored molecules.  Your teeth are likely to be sensitive while using any whitening products and for a time after you have stopped whitening.  To minimize sensitivity while whitening, I recommend brushing at least an hour prior to whitening and waiting at least 2 hours after whitening.  Avoid acidic foods and drinks.  Use a toothpaste for sensitive teeth or get a prescription strength topical Fluoride, i.e.- Clinpro.  If you are experiencing painful sensitivity, I would recommend taking an anti-inflammatory, i.e. Advil.  If the sensitivity persists or lingers beyond a couple weeks after stopping whitening, see your dentist.  If you have areas of active decay, the whitening products may cause increased sensitivity.  Also, if you notice that your gum tissue is red or irritated from the whitening, you may apply a thin layer of petroleum jelly to your tissue prior to whitening.