Root Canals need to be done when the tooth pulp gets infected the main cause is usually tooth decay. When the decay is left untreated and grows towards the nerve gets infected and it needs to get removed. Another reason for root canal is external trauma from an injury or plup damage from a large filling. After root canals are done some teeth will require a crown to reinforce and protect where remains of that tooth. If you had a root cancel done schedule an appointment to see if additional reinforcements is needed.