Introduction
Speech is shaped in the mouth. Air from the lungs is voiced by the vocal cords, then lips, teeth, tongue and palate turn it into sounds. A prosthesis changes several of those surfaces at once, so a patient may lisp, whistle or sound nasal if it is built wrongly.
Phonetics
Phonetics is the branch of linguistics that studies speech sounds: how they are produced (articulatory phonetics), their acoustic properties, how they are heard and their neurophysiology. For the dentist, the useful part is where in the mouth each sound is formed.
Place of articulation
Speech, teeth and occlusion
Phonetic tests in prosthetics
- "F" and "V": the edges of the upper incisors should lightly touch the wet–dry line of the lower lip. If not, the teeth are too short, too long or set too far back.
- "S": the lower incisors come very close to the upper ones without touching, the closest speaking space of about 1–1.5 mm. If the teeth touch when the patient says "sixty-six", the vertical dimension is too high.
- "M": after saying "Emma", the mandible settles into the rest position. This helps find the rest vertical dimension.
- "Th": about 3 mm of the tongue tip should show between the incisors.
- "T" and "D": a palate that is too thick behind the upper incisors makes these sounds unclear.
Common faults
Patients usually adapt to a new denture's sounds within days or a few weeks; reading aloud speeds this up. Faults that persist mean the denture needs correcting.