Answer: D
K20.7 is the correct code for dental root caries. Alex had a history of pain while chewing and drinking that demonstrates caries and the presence below the gingiva clearly points to root caries as the root surface (below the gum line) is involved.
Option A is not correct because K02.5 is used to code for dental caries on pit and fissure surfaces.
Option B is not correct because K02.9 is used to code for dental caries that are unspecified
Option C is not correct because K02.6 codes for dental caries on a smooth surface.