Final answer:
On a radiograph of the mandibular incisors, the incisive papilla, which is a soft tissue structure of the maxilla, does not appear. The lingual foramen, mental foramen, and genial tubercles are mandibular structures that can be visible on such radiographs.
Step-by-step explanation:
The anatomical structures that can be seen on a radiograph of the mandibular incisors include the lingual foramen, the mental foramen, and the genial tubercles. These are all features related to the mandible (lower jaw) and are associated with the passage of nerves or the attachment of muscles. Regarding the options provided, the incisive papilla, which is a soft tissue structure located in the oral cavity behind the maxillary incisors, does not appear on a radiograph of the mandibular incisors. Therefore, the correct answer is D) Incisive papilla.