Reading two radiographs

Correct answer: A. On the lingual aspect

• A. CORRECT. This is the SLOB rule — Same Lingual, Opposite Buccal. When two images are taken with a horizontal tube shift, an object that moves in the SAME direction as the tube lies LINGUALLY (or palatally); one that moves in the OPPOSITE direction lies BUCCALLY. It is also called the buccal object rule or Clark's tube-shift technique, and it is the standard method of recovering third-dimension information from two two-dimensional films.
• B. An occlusal restoration is superimposed centrally on the crown and, like a pulp stone, moves little relative to the tooth. Where the two need separating, the discriminators are DENSITY and MARGIN — a restoration is denser with a sharp geometric outline, a pulp stone is less dense with a rounded outline.
• C. A BUCCAL object moves in the OPPOSITE direction to the tube shift. This one moved in the same direction, so it is not buccal.
• D. A PULP STONE lies within the pulp chamber, close to the centre of the tooth and therefore close to the axis of rotation, so it does NOT shift appreciably relative to the tooth when the horizontal angulation changes. That lack of movement is exactly how a pulp stone is distinguished from an object lying on a surface. It also has a rounded outline continuous with the chamber and lower density than a restoration.

Note: Three routine uses of SLOB worth having ready: localising an impacted maxillary canine as palatal or buccal, separating the two canals of a mandibular molar root, and distinguishing a superimposed anatomical structure such as the mental foramen from a genuine periapical lesion. Where precise three-dimensional relationships genuinely matter, CBCT supersedes the technique.

Correct answer: C. Nasopalatine

• A. The GREATER PALATINE nerve emerges from the greater palatine foramen adjacent to the SECOND or THIRD MOLAR and supplies the posterior hard palate. It is far posterior to the surgical field here.
• B. The ANTERIOR SUPERIOR ALVEOLAR nerve is the tooth's own SENSORY supply, but it runs within bone in the anterior wall of the maxilla superior to the apex, and it is not crossing the surgical field. It is the nerve you ANAESTHETISE for this extraction, not the one you damage — and that distinction is the whole point of the item.
• C. CORRECT. The NASOPALATINE nerve emerges through the INCISIVE FORAMEN in the midline directly PALATAL to the central incisors, and the incisive canal runs immediately adjacent to — sometimes in contact with — the palatal aspect of the roots of #8 and #9. Luxating a central incisor palatally, and above all raising a midline palatal flap, places it directly in the surgical field. Injury produces numbness of the anterior palatal mucosa, which patients tolerate well because the territory is small and overlaps with the greater palatine supply.
• D. The MIDDLE superior alveolar nerve, present in only around 30% of people, supplies the premolars and the mesiobuccal root of the maxillary first molar. It is nowhere near tooth #8.

Note: ⚠️ The recall author marked ASA, which is the nerve that SUPPLIES the tooth rather than the one at risk from the procedure. Read the verb: ‘which nerve can be damaged’ asks about anatomical proximity to the surgical field, not about innervation. The same trap appears with the mandibular third molar — the LINGUAL nerve is the one at risk from a lingual flap or a distolingual bur, while the IAN is at risk from the roots themselves.