Motor coordination of articulators depends on the place of articulation

Differential articulatory movements during Japanese /s/ and /t/ as revealed by MR image sequences with tooth visualization

OBJECTIVE

To evaluate the spatio-temporal relationships between articulators in the anterior oral cavity, during the production of Japanese fricative and plosive articulation using our proposed method for tooth visualization in MR image sequences.

DESIGN

Ten healthy adults without malocclusion participated in the study. Customized maxillary and mandibular plates with space around the central incisors that was to be filled with MR-compatible contrast medium were made. During image-acquisition by a cine magnetic resonance imaging (MRI) technique, the subjects repeated vowel-consonant-vowel syllables (/asa/ and /ata/) without wearing the plates. The subjects then wore the plates for tooth imaging. All data were acquired in the midsagittal plane. Tooth boundaries were superimposed using landmarks. Several parameters and spatio-temporal changes in the centre of gravity (CoG) of the tongue were measured.

RESULTS

During /t/, the duration and amount of tongue-to-palate/incisor contact were significantly greater and the radius of the inscribed circle between the tongue-maxillary incisor-mandibular incisor was significantly shorter than those during /s/. /t/ also had a more anteriorly located CoG of the tongue than /s/ during maximum constriction. The spatio-temporal changes in the CoG of the tongue were significantly different between /asa/ and /ata/.

CONCLUSIONS

We conclude that increased tongue-to-palate/incisor contact and greater anterior closure are necessary for the production of Japanese /t/ compared to /s/. With the use of this new method for tooth visualization in MR image sequences, it should be possible to evaluate the interaction of teeth and other articulators during speech.

Application of MRI movie for observation of articulatory movement during a fricative /s/ and a plosive /t/

OBJECTIVE

To use an accurate method of tooth visualization in magnetic resonance imaging (MRI) movie for the observation of spatio-temporal relationships among articulators.

MATERIALS AND METHODS

The subjects were two volunteers. Each subject repeated a vowel-consonant-vowel syllable (ie, /asa/; /ata/), and the run was measured using a gradient echo sequence. A custom-made clear retainer filled with the jelly form of ferric ammonium citrate was then fit onto the dental arch, and a T1-weighted turbo-spin-echo sequence was taken. Landmarks were used for superimposition of the incisor boundary onto sequential images of MRI movie. Tracings were conducted to observe the spatio-temporal relationships among articulators.

RESULTS

The incisor boundary was clearly visible in the magnetic resonance images. After superimposition, the contact distance of the tongue to palate/incisor was found to be longer during /t/-articulation than during /s/-articulation. There were prominent differences in images with and without tooth superimposition in the front oral cavity.

CONCLUSIONS

The method could distinctly extract a tooth boundary in MRI. Detailed configurational relationships between the tongue and tooth were observed during the production of a fricative and a plosive in MRI movie using this method.