The other main cause of root canals are Iatrogenic meaning dentist caused. Here are some examples:
a. Decay not completely removed
b. Placing mercury - silver fillings which continue to erode the sensitive internal structure protecting the tooth's nerve system (the root canal)
c. Using undue pressure or inadequate irrigation during a tooth preparation (usually for crowns and bridges). This overheats the tooth, literally cooking the nerves and blood vessels causing necrosis (death) to these structures within the tooth.