Fillings can crack or break for many reasons and can be sensitive, painful, or you may feel nothing at all. It is important to repair a cracked filling because if left untreated, it could lead to a root canal or worse, losing the tooth. Repairing cracked fillings maintain the longevity and strength of the tooth and adjacent teeth. It also reduces the chance of surrounding teeth from also cracking. Often old fillings can be repaired with tooth color/composite fillings that bond and support the tooth or in more severe cases, a crown.