Hidemi Itoh

Somatosensory-evoked Fields for Gingiva, Lip, and Tongue

To localize the oral primary somatosensory cortex, we measured somatosensory-evoked fields for the lip, gingiva, and tongue in six healthy subjects. The latency of the first peak of the posterior-oriented current in the contralateral hemisphere was 50.9 ± 8.3 ms for the gingiva, significantly shorter than those for the lip and tongue peaks. The equivalent current dipole was localized on the central sulcus. The gingival dipole was localized significantly inferior to the lip dipole but not different from the tongue dipole. The moment of the gingival dipole was significantly smaller than that of the lip dipole but not different from that of the tongue dipole. Differences in the above parameters were negligible between the left and right, anterior and posterior, and upper and lower locations within the same organ, except that the dipole location for the anterior upper tongue was significantly inferior to that for the lower tongue.

Influence of palate shape on lingual articulation

Abstract In this paper, the present situation in Japan regarding development and application of the electro-palatography is reviewed. Then, data on lingual articulation with respect to personal differences and child characteristics are reported. These data were obtained by combining the three-dimensional measurements of the plaster casts of the hard palates of fifteen adults, thirty children, and two children at different dental stages, with the electro-palatographic observation of the lingual contact patterns with the hard palates of the adult subjects and four children during utterances of the Japanese consonants.

Effects of L1 phonotactic constraints on L2 speech perception and production

Effects of L1 phonotactic constraints on L2 speech perception and production were analyzed during the course of audio‐visual perceptual training for Japanese adult learners of English by observing articulation of words containing /l/, /r/, and /w/. The speech identification score drastically improved during the training. The improvement in non‐native word‐initial rl distinction was clearly associated with the changes in the perceptual, articulatory, and neuronal spaces, which represent dissimilarities between the non‐native and native phonemes in each domain assessed through perceptual, palatographic, and neuromagnetic measurements. Significant difficulty in identification of consonant‐rl clusters, however, remained for some trainees even after one year of training. Analyses of palato‐lingual contact patterns during word articulation suggested that more articulatory errors tend to occur in consonant‐rl clusters than in other phonotactic contexts in such a way that both /l/ and /r/ are substituted with Japanese /r/ sometimes associated with a vowel inserted. Results suggested that the L2 phonological system can be acquired through a multimodal training, although it is strongly interfered with by L1 phonotactic constraints.

Stress Transfer Characteristics of Various Retainer Designs in Unilateral Distal Extension Mandibular Cases Abutment

Previous studies have reported on the effects of I-bar retained prostheses and splinted abutments in bilateral and unilateral distal extension cases with reduced periodontal support. Producing favorable stress redistributions in the abutments and surrounding tissues is difficult. Various retainer designs have been developed to address this issue. The purpose of this study was to investigate the stress redistribution in the abutments and surrounding tissues of three retainers device configurations based on the RPI system, Konus Krone system, and Bracing arm system using quasi three-dimensional photoelastic methods. Three composite photoelastic models were made of a mandible unilaterally edentulous distal to the right second premolars. Individual simulant materials were used for tooth structure, periodontal ligament, and alveolar bone. Three normal periodontal conditions of the right first and second premolar abutment teeth were considered, and three retainers were cast for the teeth. Unilateral partial dentures with various retainer designs, RPI system, Konus Krone system and Bracing arm system were made for the three models. Simulated vertical and lateral occlusal loads were applied to the dentures, and the stresses which developed in the supporting structures were monitored photoelastically. Under comparable loading conditions, stress redistribution patterns in the abutments and surrounding tissues differed between the three systems, and The RPI system configurations showed the most uniform redistributions across loads directed in all five directions, while Konus Crone systems showed strongly stress redistribution for vertically, posteriorly, and buccally directed loads and Bracing arms configurations showed strongly stress redistribution for anteriorly and lingually directed loads. The results of this study demonstrated that the condition of vertical axiss angle, contact position and contact area of between abutments and retainers has considerable influence on favorable stress distribution.

Biomechanical comparison of straight and staggered implant placement configurations

The effect of buccolingual staggered implant placement on stress distribution within the supporting structure was examined photoelastically. Two photoelastic models of a human mandible, edentulous distal to the canine, were fabricated. Three screw-type implants were embedded into the edentulous region of each model. The implants were placed in a straight line in one model and in a buccolingual staggered configuration in the other. Vertical and lateral loads were applied to a fixed partial denture superstructure. No clear biomechanical advantage to a staggered 1.5 mm buccal and lingual offset placement configuration was observed.

The influence of shape of palate upon lingual articulation in the speech of children

Plaster casts of the hard palates of 30 children in six kinds of dental age and those of two children in various stages of growth were made and their three‐dimensional shapes were measured. On the other hand, the patterns of lingual contact to palate in utterances of the consonants with frontal and middle tongue positions were observed in four children using the technique of electro‐palatography. By comparing the results with those of adults previously studied by the authors [H. Itoh and S. Hiki: “Observation of personal characteristics of lingual articulation by use of electro‐palatography,” J. Acoust. Soc. Am. 61, S31 (1977)], the lingual articulation characteristic of children was investigated.