A 31-year-old patient complains of experiencing recurrent pain in the 48 tooth for 4 years. Objectively: right submandibular lymph nodes are enlarged, painless. Mucous membrane around the partialy erupted 48 tooth is hyperemic. On probing the subgingival pocket of the 48 tooth exudes pus mixed with blood. What additional study will be most informative for diagnosing this pathology?