Introduction
Speech can be measured, not only listened to. Acoustic and graphic methods record how a patient speaks before and after a prosthesis, show which sounds have changed and point to the part of the restoration that causes the problem.
Sound in acoustics
In acoustics, sound is the vibration of a body in a medium (air) that the ear can perceive. Four properties describe it:
The speech apparatus
Lips, teeth, tongue, palate, epiglottis, nasal cavity and larynx together produce and shape speech. For uttering sounds they fall into two groups:
A prosthesis changes the passive organs: the position of the teeth, the thickness of the palate and the shape of the alveolar areas. The active organs must then learn new movements, so speech changes until they adapt.
Methods of examination
Acoustic method
The examiner listens for distorted sounds while the patient speaks, counts or reads prepared texts rich in s, f, v, t, d and th. Simple, but subjective.
Phonographic examination
Speech is recorded before treatment, with the new prosthesis and after adaptation, and the recordings are compared. This documents speech problems after prosthetic treatment and shows whether they disappear.
Sonographic (spectrographic) examination
A sound spectrograph turns speech into a picture of frequency and intensity over time. Changes in particular sounds, such as a hissing "s", show up as changes in their pattern, so they can be measured rather than guessed.
Palatography
Shows which parts of the palate the tongue touches for each sound. The palate of the denture (or a thin test plate) is dusted with powder; the patient says a sound, and the tongue wipes the powder where it touches. The print, the palatogram, is compared with the normal pattern. It is widely used to study the formation of consonants and to shape the palatal surface of a denture.