Head movement associated with performance of mandibular tasks

summary   The present study was designed to examine the hypothesis that the motor system controlling phonation is functionally coupled with the motor system controlling posture of the head and neck, as previously suggested (U. Haddar, T.J. Steiner, E.C. Grant and F.C. Rose Human Movement Science 2: 35 and Language and Speech 26: 117). Head tilt and trunk drift in the antero-posterior and right–left directions were measured simultaneously for 20 s before and during three types of speech sounds (/pa/, /ta/ and /ka/) as well during a maximum jaw open-close task in 14 healthy young subjects. The major findings obtained in all of the four tasks were: (i) the trunk drift measured in both directions was negligible in comparison with the head tilt; (ii) the head tilt in the antero-posterior direction was much larger than in the right–left direction and (iii) the head tilt during performance of the four tasks consisted of 'initial' and 'sustained' phases. In the initial phase, the head tilted posteriorly in association with the start of individual tasks. In the sustained phase, the head tilted either anteriorly or posteriorly when the task progressed. The magnitude of the net head tilt in the sustained phase negatively correlated with that of the initial head tilt. These findings indicate that phonation, in the form of jaw open-close, accompanies head movement in two consecutive phases.     

Acid profile in carious dentin

Organic acids in carious dentin from 69 permanent teeth were analyzed by gas chromatography. Lactate, acetate, propionate, and butyrate were detected in most samples, and limited amounts of isobutyrate, valerate, isovalerate, caproate, and isocaproate were occasionally detected. Lactate, acetate, and propionate were major acids and altogether accounted for about 90% of total acid in most samples of carious dentin. However, the proportion of these three acids varied among the samples. Some samples contained over 85% lactate, while others contained mainly acetate and propionate. A high percentage of acetate was usually accompanied by an appreciable amount of propionate. All seven samples in carious dentin under fillings or restorations had little lactate, but a high percentage of acetate plus propionate. The differences in acid profiles of carious dentin may reflect differences in the microbial ecology of carious dentin, and a stage of progress of dentin caries or a type of dentin caries.