Sometimes after a crown is placed on a tooth, complications can come about. If there is not an exact fit between the crown and prepared tooth, it was placed over. Symptoms of an ill-fitting crown include looseness or mobility, tooth pain or sensitivity, irregular wear to the opposing teeth, and eventually dark lines along the border of the crown due to decay. These dark lines are caused by plaque and bacteria accumulating at the border of the crown and being allowed to seep underneath it, causing the underlying tooth to deteriorate. If the ill-fitting crown is left untreated, it can result in worsening decay that can spread to the root and pulp of the tooth, requiring a root canal or potential loss of the tooth altogether. If you are concerned about possible complications with your crown placement, your doctor is the best resource to identify the issue and provide options for returning it to optimal health appearance and function.