During eruption of permanent premolars, what is the extent of resorption in the associated primary teeth?

• A. No resorption occurs
• B. Enamel resorption only
• C. Resorption occurs only in the root apex
• D. Extensive resorption occurs in interradicular dentin, pulp chamber, coronal dentin, and sometimes enamel

Answer: (D)

When a permanent premolar is coming in, it signals the body to begin resorbing its birth tooth to make space. The primary tooth responds to this eruption stimulus by undergoing extensive resorption of its hard tissues. The most pronounced changes happen in the root dentin, especially in the interradicular region between the roots, and the process can extend into the pulp chamber as dentin is lost. As resorption progresses, the resorptive activity can reach coronal dentin, and in advanced stages enamel resorption may occur, though enamel is more resistant and affected only if the resorption is quite extensive. This pattern—extensive dentin resorption in the roots and sometimes the crown tissues, with enamel involvement only in late stages—explains why a deciduous tooth is shed to allow the permanent premolar to erupt.