A posterior sulcus tooth that hurts when you bite may be suffering from chronic periapical periodontitis, which is caused by pulpitis that is not treated in a timely manner and the inflammation spreads to the inside of the alveolar bone, causing inflammation within the alveolar bone, which can stimulate the local inflammatory area causing pain when a hard object is bitten. For teeth with chronic periapical inflammation, root canal treatment is required to remove the infectious material from the pulp cavity. The pain when the posterior socket is bitten may also cause the tooth to develop a hidden fracture. When the fracture reaches deep into the dentin, the tooth will become painful after biting on a hard object, and then the fracture should be removed and treated by filling the tooth with composite resin or by wrapping the crown part of the tooth with a porcelain or all-porcelain crown. If the fracture has reached the pulp and caused pulpitis, the tooth should be treated with a root canal and then the crown part of the tooth should be restored. When periodontitis progresses to a certain level, the roots of the teeth will be exposed in the mouth and pain will occur after biting on hard objects, and then systematic periodontal treatment should be done on the teeth.