Acoustic Analysis of Voice and Speech in Men with Skeletal Class III Malocclusion: A Pilot Study

To assess the fundamental (f0) and first third formant (F1, F2, F3) frequencies of the 7 oral vowels of Brazilian Portuguese in men with skeletal class III malocclusion and to compare these measures with a control group of individuals with Angle's class I.

Sixty men aged 18-40 years, 20 with Angle's class III skeletal malocclusion and 40 with Angle's class I malocclusion were selected by speech therapists and dentists. The speech signals were obtained from sustained vowels, and the values of f0 and frequencies of F1, F2 and F3 were estimated. The differences were verified through Student's t test, and the effect size calculation was performed.

In the class III group, more acute f0 values were observed in all vowels, higher values of F1 in the vowels [a] and [ε] and in F2 in the vowels [a], [e] and [i] and lower F1 and F3 values of the vowel [u].

More acute f0 values were found in all vowels investigated in the class III group, which showed a higher laryngeal position in the production of these sounds. The frequencies of the first 3 formants showed punctual differences, with higher values of F1 in the vowels [a] and [ε] and of F2 in [a], [e] and [i], and lower values of F1 and F3 in the vowel [u] in the experimental group. Thus, it is concluded that the fundamental frequency of the voice was the main parameter that differentiated the studied group from the control.