I believe Andreas is referring to a teeth meridian chart that shows energetic connections between each individual tooth with certain parts of the body. Here's a chart that might be helpful:

http://www.drwolfe.com/html/Teeth-chart.html

Find out which tooth is giving him problem and see which organs and vertebrae are connected to this tooth.

Unfortunately there may be very little to save a tooth if its already dead. root canal is definetly not a good option as it doesnt address the fact that there are miles of tubules in which bacteria can become trapped and proliferate, creating even more problems.
One viable option that can keep temporarily prevent infection from beginning is through Ozone dentistry; unfortunately this is only used in few parts of the world but it can save a tooth by ozonating the area, creating an inhabitable region for bacteria to strive in. He would most likely have to have this procedure done every few months to keep things clear.

Bear in mind that even if any procedures is able to save a dead tooth and prevent infection (almost impossible), the fact is that it still is a dead tooth and this acts as a barrier in the energy flow of that particular meridian so it will still be negatively affecting the whole system.
Mike