A patient is missing a mandibular second molar. The first molar is present, and the opposing maxillary second molar is now unopposed. Each of the following is an appropriate way to prevent supra-eruption of the opposing tooth EXCEPT one. Which is the EXCEPTION?

Correct answer: C. Provide a night guard (occlusal appliance)

• A. This IS a legitimate measure — and the definitive one. Replacing the missing tooth restores an occlusal contact permanently, which is the most reliable way to arrest extrusion of the opposing tooth.
• B. This IS a legitimate measure. Splinting the unopposed tooth to its neighbours shares the eruptive force across several roots and physically resists continued extrusion. It is a holding measure rather than a definitive restoration, but it does address the problem.
• C. CORRECT — this is the EXCEPTION. A NIGHT GUARD does not prevent supra-eruption. It is worn intermittently, chiefly at night, and it is prescribed to manage PARAFUNCTION (bruxism, clenching) and to protect teeth and restorations from wear. It provides no continuous occlusal stop during function, so the unopposed tooth continues to erupt in the many hours the appliance is not worn.
• D. This IS a legitimate measure. A cantilevered two-unit FPD restores an occlusal stop against the opposing tooth. Once the tooth is in function again, the eruptive drive that produces supra-eruption is removed.

Note: The principle behind all of this: a tooth erupts until it meets an opposing contact. Any treatment that re-establishes that contact (prosthetic replacement) or that mechanically resists eruption (splinting) works. A night guard does neither — it is an appliance for parafunction, and it belongs to a different problem entirely.