Dentist wants to pull my molar even after root canal! why is that?

Need more informtion: Although root canal treatment is a definitive treatment for a dental infection, reinfections of previously treated teeth do occur. If a reinfection occurs the dentist must determine the cause. If reinfected the root canal may require re-treatment or an apicoectomy. If the infection is caused by something else extraction may be appropriate. Get a second opinion if you have a question.

Can happen!: Root canals work very well for many years, but sometimes they do fail. At times, the failure is so severe that removing the tooth and later replacing it is much more predictable and cost effective over questionable re treatments.

Depends: You may have a more complex problem that root canal will not solve, like a cracked root.

Get explanation: My experience is that teeth are sometimes extracted unnecessarily. Not by intention but just because not all dentist may be up on new modalities. I recommend you get a second opinion, by a microscopically trained endodontist!

Many possibilities: When done properly, rct is a very successful procedure. However, there are many reasons why a dentist may recommend removing the tooth at a later point. These include- residual infection\ cyst, fracture of root, periodontal bone loss, poor long term prognosis, persistent unexplained pain, questionable use as an anchor tooth for removable or fixed prosthesis\restoration. Ask your dentist to explain.