A 48-year-old man has pain and swelling below the right side of his jaw that start whenever he eats and settle over an hour. Bimanual palpation reveals a hard, 4 mm mass in the floor of the mouth near the opening of the right submandibular duct, and an occlusal radiograph shows a radiopacity in the anterior part of the duct. The gland is not tender between meals. What is the most appropriate management?