Dentists???Question about fillings???

I had two fillings in between two teeth which recently became sensitive to cold water. I went to my dentist and he replaced them for free b/c he did the original fillings, but now, less than a month later the teeth are sensitive to cold water again. What could be the problem? Does this mean I need a root canal or are the fillings just bad again?

Dentists???Question about fillings???
I have worked with dentists and thier patients have the similar problems. The thing was did he replace them with composite-resin fillings? (meaning tooth colored) or amalgam(silver fillings)? They have also said that the tooth colored fillings are more likely to cause sensitivity to cold and may last for up to 6 weeks it all depends. Has your dentist advised you to try using sensodyne???.
Reply:when a dentist drills out the decay in your tooth, he uses something to seal the tubules in the tooth. )like little water hoses in your tooth) if they aren't sealed properly, it causes sensitivity. also, i've heard it is sensitive after fillings but goes away after a few weeks. but you definatly should contact your dentist. he will probably get you to come back in to re-do it at no charge to you.