Vocal Tract Resonance and Speech Intelligibility in Combined Maxillectomy and Mandibulectomy

Abstract

Resonances characteristics are related to changes of cavity in size and configuration, Quality of oral resonance is often directly related to the opening of the mouth, achieved by mandible posturing and the relative height of the placement of the tongue within the oral cavity. Oral resonances can be perceived as the formant frequencies which are observed best during the production of vowels. Following the maxillectomy and mandibulectomy surgery for cancerous lesion, there is an observable change in size and configurations of the vocal tract resulting to changes in the resonances thus affecting the formant frequencies. Need for the study: Though there are literatures available on the speech characteristics namely articulation, resonance and speech intelligibility of maxillectomy and / or mandibulectomy patients, there is limited information documented regarding the resonance characteristics and its impact on speech intelligibility of patients who have undergone both maxillectomy and mandibulectomy with reconstruction of the mandibular defect and use of palatal prosthesis for closure of the maxillectomy defect. Aim: The present study was aimed to determine the vocal tract resonance characteristics and usefulness of palatal prosthesis in improving the resonance and speech intelligibility in subjects of combined maxillectomy and mandibulectomy. Method and Materials: Two male subjects, who had undergone maxillectomy and mandibulectomy for extensive lesion of buccal mucosa, were recruited for the study. They had undergone maxillectomy of variant type and mandibulectomy with reconstruction of the primary defect. Subject A had also received post operative radio therapy and chemotherapy for the same. The defect of the mandible was reconstructed by pectoralis major myocutaneous muscle flap. Subject B had received pre operative radiotherapy and reconstruction of the defect by radial forearm flap on right cheek and buccal fad pad on left cheek. Following maxillectomy surgery, both of the subjects been using palatal prosthesis. Objective evaluation of speech was carried out using CSL 4400 instrument to evaluate acoustic parameters of resonance such as formant frequencies of vowels and 2nd formant transition. Formant frequencies of vowels were considered for the study as they represent the resonance of the vocal tract. Since the vowels are produced orally with open vocal tract, for effective production of vowels the resonance would take place only in the oral cavity. Formant frequencies were measured with and without the prosthesis and the 2nd formant transition were also measured to evaluate objectively the placement and the movement of the tongue within the oral cavity. Analysis of formant frequencies of vowels /a/, /i/ and /u/ in isolation and in words such as /a/ in /a: ne/ , /i/ in /illi/ and /u/ in /u: ta: /, which had embedded vowels was examined spectrographically. The mouth to microphone distance was maintained at 6cms. The acoustic signals were digitized at 44100 Hz per channel with 32 bit resolution to a computer. Results and Discussion: The study revealed that both the subjects, subsequent to excision of lesion showed a varied picture of affected resonance and speech intelligibility. Oral Peripheral Mechanism Examination revealed deviated lip to left side in subject A and to right side in subject B, missing teeth on top row, with intact tongue and its movement. Velar elevation was restricted. Intra oral pressure could not be built by the subjects due to inadequate lip seal. Vocal tract resonance was observed to be altered in both subjects after surgery due to ablation of the palate, leading to impaired connection between the oral and nasal cavity. Spectrographic analysis without the palatal prosthesis revealed all formant frequencies (F1, F2 and F3) to be deviated from normal due to the presence of anti resonances due to the presence of hypernasality. Formants were not clearly visible without the prosthesis. It was noted that dampening of the energy was more without the prosthesis than with prosthesis, thus attributing to the perception of hypernasality. Assessment of second formant transition and duration of transition did not differ significantly with and without palatal prosthesis indicating that speech intelligibility is predominantly affected by the nasal air emission and rate of speech rather than imprecise placement of tongue following the surgery. Speech intelligibility was found to be better with prosthesis.