How is a LOSS of occlusal vertical dimension best assessed?

Correct answer: D. By measuring the interocclusal rest space, using phonetics such as repeating the letter 'M' to establish rest position

• A. The 'S' sound establishes the CLOSEST SPEAKING SPACE, about 1–1.5 mm, which is used to check that the VDO is not EXCESSIVE. It is a valid technique but tests the opposite error.
• B. Condylar position on radiograph does not measure vertical dimension.
• C. Deep nasolabial folds, a reduced lower facial height and angular cheilitis are clinical CLUES that raise the suspicion, but they are subjective and cannot quantify the loss.
• D. CORRECT. The patient repeats a sound that returns the mandible to PHYSIOLOGIC REST POSITION — the classic one is the letter 'M', as in 'Emma', after which the mandible settles at rest with the lips lightly together. The vertical dimension at rest (VDR) is measured between two marked points, and the OCCLUSAL vertical dimension (VDO) is measured with the teeth in contact. The difference is the INTEROCCLUSAL REST SPACE or freeway space, normally 2–4 mm. A freeway space substantially greater than this indicates lost VDO — which is exactly this patient's picture.

Note: The two phonetic tests are worth keeping straight: 'M' → rest position → measures freeway space → detects INSUFFICIENT VDO. 'S' → closest speaking space → detects EXCESSIVE VDO (teeth click during speech). Note that this patient's THREE anticholinergic medications explain the xerostomia, which itself worsens denture retention.