Nasalization of vowels is observed frequently in the post-palatoplasty cleft plate patients. Velopharyngeal incompetence is known as the main cause of this speech disorder. The correlation between the maxillofacial structures of cleft palate patients and the formant analysis of their nasalized vowels was investigated. The following results were obtained.Subjects were 45 cleft palate patients (23 male patients and 22 female patients) and 18 female adults as the controL Lateral cephalograms of the occlusal position and speech position of vowels were taken and measured by the cephalometric procedure. The shape of the soft palate was measured as to the thickness and the length from the cephalograms. Formant frequencies of isolated vowels were analyzed with a SH-10 speech analyzer (RION company, Japan). Subjects were classified into 6 groups by their degree of velopharyngeal incompetence and sex. All variables were compared and examined statistically.1. Skeletal class Ⅲ tendency was related to the severity of the nasalized vowel.2. Various irregularities of the spectral analysis were observed in most of the cleft palate patients’ speech;the descending of /i / 2nd formant frequency, abnormal formants, hoarseness, instability of fundamental frequency, and the probability of anti-formants.3. An inverse correlation between the upper facial height and 2nd formant frequency of /i / was observed in the female mild incompetent group.
