Root canal problems stem from infection and inflammation of the tooth's pulp tissue. One potential cause of infection is deep tooth decay.
Untreated dental cavities eventually allow bacteria to work their way down to the center of the tooth, where they may infect the pulp tissue. Another path by which bacteria may come into contact with pulp is via chipped or cracked teeth. Any opening in the protective enamel coating has the potential to allow bacteria access to the tooth's pulp.
Trauma to the tooth — the kind that might result from a sports injury or automobile accident, for example — is also a major cause of pulp tissue damage. In this case, it's essential to seek treatment immediately, both to try and save the tooth, and to prevent future problems.
In some cases, extensive dental work itself may cause damage to the pulp tissue that will need to be treated via a root canal. Having multiple fillings or restorations on the same tooth increases the chances of this type of injury. Occasionally, common procedures like crown preparation or orthodontics may eventually lead to root canal problems.