With a complete denture in place, a patient is asked to say 'San Francisco.' This phrase is used to evaluate which specific parameter of denture fit?

Phrases containing the sibilant 'S' sound (such as 'San Francisco,' 'Mississippi,' 'sixty-six') are used to evaluate the CLOSEST SPEAKING SPACE — the minimal interocclusal distance during speech (~1 mm). When the patient produces 'S' sounds, the anterior teeth approximate to approximately 1 mm. If teeth click or contact during 'S,' the vertical dimension of occlusion (VDO) is too high. If the gap is >2 mm, the VDO may be too low. This test supplements the freeway space assessment (rest VD minus OVD = 2-4 mm). Note: The 'M' sound evaluates the rest position of the mandible. The 'F' and 'V' sounds evaluate the position and length of the maxillary incisal edges.