Final answer:
The indicated treatment for the four mandibular incisors showing bone rarefaction is to test the pulp vitality and perform root canal therapy only on incisors with non-vital pulp, while monitoring others periodically.
Step-by-step explanation:
The four mandibular incisors of a patient that were traumatized in an automobile accident three years ago show bone rarefaction in the region of the apices of the incisors on current radiographs. The recommended course of treatment is to test the pulp vitality of the incisors and perform root canal therapy only on those teeth that do not respond to pulp testing. This approach ensures that only incisors with non-vital pulp, which may contribute to the rarefaction, are treated endodontically, potentially preserving the vitality of other teeth. This decision relies on the principle that intervening with the most conservative treatment that addresses the pathology is preferable initially. It is important to treat any teeth with necrotic pulp to prevent the potential spread of the infection. Teeth with a vital pulp should be monitored periodically instead of receiving immediate intervention like root canal therapy.