Eight-year-old with an unerupted central incisor

Correct answer: B. Surgically remove it during the mixed dentition, once the permanent incisor roots have begun to form

• A. Waiting for symptoms is the wrong trigger. Supernumeraries are usually painless while they displace roots, cause diastemas, or seed a dentigerous cyst.
• B. CORRECT. A mesiodens that is obstructing eruption is removed. The favoured window is the MIXED DENTITION, once roots of the adjacent permanent incisors are partly formed — early enough that spontaneous eruption of #8 still occurs in the majority of cases, and late enough that the developing incisors are not damaged during surgery. Delay beyond this window means eruption will usually require orthodontic exposure and traction.
• C. Extracting a healthy, erupted permanent incisor is never the answer. The obstruction is the supernumerary, not #9.
• D. Observation is reasonable only for an asymptomatic supernumerary that is NOT obstructing anything. Here it is demonstrably preventing eruption, so watching costs the child the chance at spontaneous eruption.

Note: Mesiodens is the commonest supernumerary tooth, sits in the maxillary midline, and is often inverted and conical. Beyond failed eruption, watch for midline diastema, incisor displacement, root resorption and dentigerous cyst formation.

Correct answer: C. Nasopalatine nerve

• A. The greater palatine nerve emerges at the greater palatine foramen adjacent to the second or third molar and supplies the posterior hard palate. It is nowhere near the midline anterior region.
• B. The infraorbital nerve exits the infraorbital foramen below the orbital rim to supply the lower eyelid, lateral nose and upper lip. It is well superior to the surgical field.
• C. CORRECT. The nasopalatine nerve descends through the incisive canal and emerges at the incisive foramen just behind the central incisors, supplying the anterior palatal mucosa back to the canines. A midline supernumerary sits directly in its path, so palatal flap reflection and bone removal put it at risk. Transient numbness of the anterior palate is a recognised sequela; the territory is small and reinnervation is usually good.
• D. The anterior superior alveolar nerve, a branch of the infraorbital nerve, supplies the anterior teeth and their labial periodontium via a labial approach — relevant to a labial flap, not the palatal one described.

Correct answer: B. Coronoid process of the mandible

• A. The anterior nasal spine is a V-shaped midline radiopacity above the central incisors — a midline structure, not a corner one.
• B. CORRECT. The coronoid process appears as a triangular radiopacity in the inferior-posterior corner of maxillary molar and, with certain projections, maxillary periapical films. It is projected into the field when the patient opens wide, because opening carries the coronoid forward and upward beneath the zygomatic arch. Recognising it prevents it being read as a tuberosity lesion or retained root.
• C. The hamulus is a small hook-like projection posterior to the maxillary tuberosity, visible as a slender finger of bone rather than a broad triangle.
• D. The zygomatic process of the maxilla appears as a U- or J-shaped radiopacity superimposed over the maxillary first molar apices, not as an isolated triangle in the corner.

Note: Ask the patient to close slightly and retake if the coronoid obscures the region of interest.

Correct answer: C. Third molars > mandibular second premolars > maxillary lateral incisors

• A. Third molars, not lateral incisors, head the list.
• B. This is the commonly-chosen distractor. It ranks maxillary lateral incisors above mandibular second premolars, whereas the mandibular second premolar is the more frequently absent of the two.
• C. CORRECT. Third molars are by a wide margin the most commonly absent teeth, affecting roughly 20 to 25 percent of people. Excluding third molars, the ranking is mandibular SECOND PREMOLARS first, then MAXILLARY LATERAL INCISORS, then maxillary second premolars. The pattern makes developmental sense: the last tooth to form in each morphologic class is the most vulnerable to agenesis.
• D. This inverts the order and places lateral incisors ahead of third molars, which is not supported by prevalence data.

Note: Clinically: a missing lateral incisor should prompt you to look for an impacted or ectopic canine, since the lateral's root normally guides canine eruption.